I.7	Echocardiography in Translational Research

A. Introduction

Echocardiography is the the most commonly used imaging test in daily clinical cardiology practice and has been the reference method for cardiac morphological and functional assessment for several decades. Echocardiography is perfomed from a trans-thoracic or trans-oesophageal approach, and is characterized by its low cost, its high availability and its portability allowing to easily perform complete examinations in the laboratory or at the bedside. It allows real time imaging with a high temporal and spatial resolution in a time-efficient manner. From the initial M-modes linear measurements, echocardiography rapidly evolved into 2D imaging, which is now the standard modality of imaging for morphology and function. Doppler echocardiography followed and rapidly became the reference method for valvular assessment; it also provided the possibility of a non-invasive haemodynamic assessment of the patients, including the measurement of the cardiac output, the characterization of the left ventricular diastolic function or the measurement of the pulmonary artery pressure. More recent developments allowed the assessment of the regional myocardial deformation using tissue-Doppler derived techniques or speckle tracking algorithms from standard 2D images, and provided new quantitative measurements of regional myocardial contraction and relaxation. 3D echocardiography was another major recent development, which permitted a more accurate and reproducible assessment of the volume of the cardiac chambers with no limitations related to geometric assumptions or to image orientation. 3D echocardiography greatly improved the morphological assessment of the cardiac valves and it is increasingly used to guide structural interventions in the catheterisation laboratory or the electrophysiology suite.

Despite tremendous technological improvements, some important limitations of human echocardiography are still unresolved. First, the image quality will depend on the position of the heart in the thorax and of the habitus of the patient. The ultrasound beam is completely reflected from bone or lung structures and cardiac images can only be obtain from specific windows –typically parasternal, apical and subcostal, where the heart is in direct contact with the chest wall. Optimal positioning of the patient and –if needed- breathing instructions to the patient allow to obtain the standard images with adequate orientation in the majority of patients. However, in about 5-10% of patients (1,2) image quality remains unsatisfactory with insufficient delineation of the endocardial border or apical foreshortening, preventing a complete quantitative assessment of the cardiac structures. Second, if the left ventricle and left atrium are well characterized with echocardiography, the right cardiac structures are difficult to image because of their position behind the sternum. Imaging of the right ventricle improved with 3D techniques but clear imaging of the right ventricular outflow tract remains difficult for a significant subset of patients. Third, echocardiography is an operator-dependent method and the accuracy and reproducibility of all the measurements performed will depend on the experience of the operator.

These limitations are somewhat counterbalanced by the versatility of echocardiography and by the ease to combine this technique with physical exercise or pharmacological stress, or with invasive or non-invasive simultaneous pressure measurement to derive pressure-volume or pressure-strain loops. The use of LV opacification is safe (3) and can improve endocardial border detection and LV volume quantification, and it can be used to assess myocardial perfusion during rest and pharmacological stress (4).

This chapter will describe the currently available technique for clinical echocardiography in humans, and how they can be applied to translational research in small animal models. Murine echocardiography has specific requirements including the use of a higher frequency linear array probe ( >8 MHz, but up to 70 Mhz) to achieve temporal and spatial resolutions that are adapted to the small size of the animal and to the high heart rate, and a careful sedation of the animal to avoid bradycardia and myocardial depression during image acquisition. Importantly, morphologic images are essentially obtained from the parasternal windows as it is difficult to display non-forshortened views form the apical window, and interpretable images can be expected in >95% of cases with commercially available equipments (5,6).

B. Echocardiographic Measures of Structure and Global Function for Intermediate End-Points

Left ventricular volume, ejection fraction and mass all have important prognostic value and represent important end-points in clinical research (7,8).

Linear measurement is the simplest way to assess left ventricular structure by measuring end-diastolic and end-systolic diameters as well as septal and posterior wall thickness using M-mode (Figure 1), or 2D echocardiography from a parasternal window. M-mode diameters slightly overestimate 2D measurements because of the difficulty to obtain a perfect alignment of the interrogation line to the left ventricle, and M-mode is therefore being progressively abandonned (9). Although the measures are reproducible (10,11), they should not be used to calculate left ventricular volumes because of major inaccuracies related to geometric assumptions (12). Estimation of left ventricular mass is still largely based on calculations from linear measurements (13) but, despite a good reproducibility, the method has a limited accuracy with a systematic underestimation of mass and wide limits of agreement when compared to cardiac magnetic resonance (CMR) (14).

Left ventricular volumes and ejection fraction are most commonly calculated from two apical 2D images (Video 1) after manual tracing of the endocardial border (modified biplane Simpson method, Figure 2). These measurements may be inaccurate in case of LV remodelling because they also rely on geometrical assumptions, and their inter-observer reproducibility is only moderate (15,16). When compared to CMR, 2D echocardiography systematically underestimates the LV volumes and to a lesser extent ejection fraction. The use of LV opacification (Video 2) significantly reduces this under-estimation and improves agreement between both methods (17,18). Recommendations for image acquisition and normal values for linar and 2D measurements are described in detail in the current clinical guidelines (19).

The development of 3D imaging allowed to obtain a volume acquisition of the left ventricle (Video 3) and to directly measure the LV volumes and function without geometrical assumption using a semi-automated algorithm of endocardial border detection (Video 4). This resulted in higher accuracy in the measurement of volumes and ejection fraction using CMR as a reference: comparison between both techniques showed a good agreement with a significantly lower underestimation of volumes with 3D echocardiography as compared with 2D techniques (20,21) and a good intra-observer, inter-observer and inter-study reproducibility (22). The combination of 3D acquisition and LV opacification provided the best agreement with CMR in one study of 50 patients (mean difference of -6 ±14 ml for end-diastolic volume and 0±3% for LVEF) (23). LV mass can be calculated with 3D echocardiography after tracing the endocardial and epicardial border, and this method again showed a very good agreement with CMR and a high inter-observer reproducibility (24). 3D echocardiography is at the present time the echographic method of choice for the assessment of left ventricular structure and function and its high reproducibility is attractive for clincal study, allowing a significant reduction in study sample size as compared with 2D echocardiography. Limitations of 3D echocardiography include the dependence on good image quality, a more limited availability and a low temporal resolution with real-time imaging. To increase image resolution, multi-beat imaging can be performed, but this mandates the collaboration of the patient for breath-holding, and a regular heart rate to avoid stitching artefacts. At last, LV segmentation is performed offline and the post-processing time has to be taken into account in the clinical or research workflow.

Achieving a high temporal resolution is crucial for murine echocardiography as the heart rate is frequently >500/min. A frame rate of 150-200 frames/s will be needed to obtain 15-20 frames per heart cycle and correctly identify systole and diastole. Linear measurements using 2D-guided M-mode represent the current standard due to the very high temporal resolution of this technique ( >1000 frames/s), and they have shown an adequate reproducibility in intra-observer and inter-observer analysis (25). 2D-imaging using a high-frequency probe is technically more demanding but can improve the accuracy of measurement in case of irregular geometry of the ventricle (26) by direct measurement of the LV volume using the monoplane Simpson method or the area-length method from parasternal long axis and short axis views. 3D reconstruction of LV volume from a series of 2D short-axis acquisitions avoids geometric assumptions and showed a high concordance with CMR for LV volumes measurement (27). It is however time-consuming and mandates a good image quality and a regular heart rate. Real-time 3D imaging is not available for small animal models.

C. Echocardiographic Measures of Regional LV Function and Myocardial Deformation

LV myocardium has a a 3-layered structure of obliquely and circumferentially oriented fibers and its deformation during systole is complex in 3 spatial directions (28). LV ejection fraction, as a global marker of systolic function, is limited in describing myocardial deformation at the level of myocardial wall or segment. Newer techniques allowing to measure myocardial deformation (strain) and rate of deformation (strain rate, SR) in longitudinal, circumferential and radial direction, segment by segment, improved our understanding of myocardial function (29). Strain is defined as a change in length of the myocardium from its original length (Lagrangian strain) or as a change in length relative to the length at a previous time instance (natural strain), whereas strain rate is the change of strain over time (30). Strain and strain rate can be measured in longitudinal direction from apical views, and in radial and circumferential direction from parasternal views. Longitudinal and circumferential strains are negative as they describe myocardial shortening, whereas radial strain is positive, corresponding to myocardial thickening in systole. From experimental studies using closed-chest dog and pig models, strain rate has been shown to to be closely related to the regional contractility, while strain better corresponded to regional change in stroke volume (31,32).

Tissue Doppler imaging (TDI) was the first developed echocardiographic technique to assess myocardial deformation. By measuring instantaneous myocardial velocities (Figure 3) at different locations in the myocardium, regional strain rate (Figure 4) can be derived (33). Strain can then be calculated by integrating SR over time (Figure 5). As Doppler-derived technique, myocardial velocities are measured according to the position of the probe and an optimal alignment of the myocardal region of interest to the ultrasound beam is mandatory (34). As a consequence, TDI strain and strain rate can only be measured in longitudinal direction from apical views or in radial direction (anteroseptal and inferolateral segments) from parasternal views. TDI strain and strain rate have been validated against sonomicrometry in an open-chest dog model (35) and against tagged magnetic resonance in humans (36), and normal values in humans have been published (37). TDI strain and strain rate imaging remains technically demanding because of a high susceptibility to noise from movement in the blood pool, to aliasing and to reverberation artefact, resulting in substantial variability even in a normal population (37). An advantage of this technique is its high temporal resolution, allowing for a precise measurement of timing events during myocardial contraction and relaxation.

Speckle tracking technique is a more recent development of 2D echocardiography allowing to measure strain (Video 5, Figure 6) and calculate strain rate (Video 6, Figure 7) from a standard B-mode image. Speckle tracking echocardiography analyses the displacement of individual acoustic markers (speckles) within the myocardial wall during the cardiac cycle and the semi-automated tracking algorithm allows for a frame-by-frame calculation of strain (38). Unlike TDI strain, 2D strain measurement is not performed relative to the adjacent myocardial region, making this technique angle-independent. Furthermore, it allows to assess myocardial deformation in all direction for all myocardial segments (39) (Video 7) as well as myocardial rotation (40). The technique has been validated against sonomicrometry in an open-chest pig model (41) and tagged magnetic resonance imaging in humans (42), and normal values have been published (43). A high correlation has been shown between 2D strain and TDI strain (44) but 2D strain techniques showed a higher reproducibility (45,46). However, high quality 2D images with an adequate frame-rate (50-100 frames per second) is required for an optimal tracking of the acoustic signals (47). Rotation analysis using 2D speckle tracking also has been validated against tagging MRI (48) but its reproducibility is limited by the difficulty to standardize the acquisition of the basal and apical short-axis planes (49). Rotation analysis provides new measurement endpoints like twisting, torsion, untwisting and untwisting rate, that can refine the characterization of myocardial mechanics (50).

Part of the variability in the strain measurement using 2D speckle tracking is related to out-of-plane motion of the myocardium during the cardiac cycle, mainly affecting strain measurement in the basal short axis view, and the recent development of 3D speckle tracking imaging should overcome this important limitation (50,51). 3D speckle tracking (Video 8) has been validated against sonomicrometry in an open-chest sheep model (53) and it has been proposed as a more adequate tool to assess myocardial rotation (54). 3D speckle tracking has been reported to have a better reproducibility for radial strain assessment (55) and normal values have been proposed (56,57). However, a significant variability between vendors and between post-processing softwares has been highlighted (58,59) and more validation is needed before a widespread use of this promising technique.

Strain and strain rate analysis provide several new quantitative measures of myocardial function, including peak strain (maximal deformation), systolic strain (maximal deformation occurring before aortic valve closure), post-systolic index (ratio of post-systolic strain to global strain), systolic, early diastolic and late diastolic strain rate, twisting, and untwisting rate (60). Global longitudinal strain has been validated as an index of global left ventricular systolic function (61) with a superior reproducibility as compared with LV ejection fraction (measured by 2D biplan Simpson) (62) and a high prognostic value (63,64,65). In case of ischemic heart disease, strain analysis offers a quantitative assessment of regional function (66). Furthermore, even in case of normal ejection fraction, longitudinal strain analysis is able to detect early systolic dysfunction in the context of hypertension and diabetes (67), heart muscle disease (68,69), inflitrative heart disease (70,71), heart failure with normal ejection fraction (72), valvular heart disease (73,74), of after anti-cancer chemotherapy (75,76).

Strain measurement using TDI or speckle tracking technique has been used in large animal models (35,41,42,77): closed-chest models only allowed to acquire parasternal views for radial or circumferential strain assessment while open-chest models using epicardial echocardiography from the apex were needed for longitudinal strain assessment. Using high-frequency probes achieving frame rates between 225 and 350 frames/s, both TDI and speckle tracking strain could be obtained from parasternal images in mice. While TDI assessment is restricted to radial strain of the posterior wall and circumferential strain of the lateral wall, speckle tracking allows to calculate strain from both short-axis and long-axis parasternal views. Both methods showed a good agreement with invasive measures of systolic function at rest but TDI strain performed better during dobutamine challenge (heart rate >600/min) due to a higher temporal resolution (78,79). TDI strain and speckle tracking strain were able to detect subtle changes in systolic function with more sensitivity than conventional measures of systolic function (80,81).

D. Echocardiographic Measures of LV Systolic Dyssynchrony

Dyssynchrony of the myocardial contraction is an important component in the pathogenesis of systolic heart failure and cardiac resynchronisation therapy (CRT) using bi-ventricular pacing greatly improved the outcome of the patients (82). Due to its high temporal resolution, echocardiography is as an ideal tool to measure the timing of mechanical events during the cardiac cycle and several single-center studies proposed echocardiographic parameters to characterize mechanical ventricular dyssynchrony and predict a favourable response to CRT. Techniques for echocardiographic assessment of myocardial dyssynchrony have been described in detail in the 2008 guidelines of the American Society of Echocardiography (83).

M-mode echocardiography of the LV from a parasternal window has been used to measure the time difference between peak septal displacement and peak posterior wall displacement (septal to posterior wall motion delay) (84). The feasability of this simple parameter is limited in case of ischemic cardiomyopathy when either the septum or the posterior wall is akinetic and its reproducibility was low in a multicentre setting (85).

Global makers of delayed mechanical action of the left ventricle have been proposed, based on pulse-wave Doppler flow measurements across the aortic and the mitral valve. Left ventricular pre-ejection interval (LPEI) is measured as the time interval between the onset of the QRS and the onset of ejection across the aortic valve and is prolonged in case of significant mechanical dysynchrony. Myocardial performance index (MPI) is the ratio of isovolumic times (isovolumic contraction + isovolumic relaxation times) to the duration of systolic ejection and this parameter increases with increasing dyssynchrony (86). Despite being simple parameters, their reproducibility was only moderate in a multicentre trial setting (85), and their ability to predict response to CRT was low.

High expectations were placed into tissue Doppler imaging to assess dyssynchrony. Using this high temporal resolution technique, longitudinal velocities of the basal and midventricular myocardial segments can be assessed with a high precision in all 6 myocardial walls from the apical window. The most frequently used measurement was time-to-peak systolic velocity, the time interval between the onset of the QRS and the maximal myocardial velocity occurring before aortic valve closure. The differences in time-to-peak systolic or maximal velocity between facing walls (Figure 8)(87,88) or the standard deviation of the time to peak systolic velocity measured in 12 different sites (basal and midventricular segments in each of the 6 myocardial walls) (89) have been proposed as criteria to detect LV dyssynchrony and predict response to CRT. Tissue Doppler is however an angle-dependent technique, and the recording of myocardial velocities cannot differentiate between an active muscle contraction and a passive movement of the myocardial wall. These limitations were partly responsible for its low reproducibility in a multi-centre setting (85) and its limited value in predicting the clinical response to CRT.

2D speckle-tracking strain analysis is able to differentiate active contraction from passive translational movement and could overcome some limitations of TDI velocity assessment despite its lower temporal resolution. Delay in peak radial strain ( >130 ms) between opposing walls (Video 9) was suggested to be a predictor of EF improvement after CRT (90,91) but these results could not be reproduced in another large study (92). More recently, the calculation of the strain delay index (defined as the sum of the differences between peak global longitudinal strain and peak systolic longitudinal strain in 16 myocardial segments), a marker of the amount of mechanical energy wasted by dyssynchrony (Video 10), has been proposed a promising marker of reverse remodelling of the LV after resynchronization in a multicentre study (93). In this study, the variability of measurement was low, but the feasability of the measurement was only 80%, which may be a practical limitation. Finally 2D strain has also been used to guide the positioning of the LV pacemaker lead by detecting the last activated myocardial segment, and resulted in improvement in outcome after CRT in a randomized controlled (94) study.

3D imaging is appealing for the assessment of LV dyssynchrony because it can assess the contraction of all myocardial segments simultaneously. Using the same semi-automated border detection algorithm used for the assessment of EF, postprocessing of the volume data provides individual time-volume curves corresponding to the 16 myocardial segments. The standard deviation of the time to minimal segmental volume expressed as a percentage of the cycle duration (systolic dyssynchrony index, (Video 11) SDI) has been proposed as a quantitative index of LV dyssynchrony (95,96,97). Normal values for SDI have been reported in the normal population (98), but there is no widely accepted cut-off value to predict clinical response to CRT. Apart from the general limitations of 3D imaging including the need for high-quality images, this assessment can be difficult to perform in case of very low systolic function as segmental volume will only minimally change during the cardiac cycle, rendering the definition of the timepoint of minimal segmental volume unprecise (99). 3D SDI has been compared to tissue Doppler velocity techniques and a low agreement was found between both techniques, indicating that significant differences exist when dyssynchrony is assessed using markers of radial or longitudinal mechanics (100,101) and the combination of both techniques could increase the prediction of response to CRT (102).

The most suitable animal model for LV dyssynchrony is a canine model with left bundle branch block as it is charcterized by an electrical dyssynchrony comparable to human LBBB (103). Dysynchrony assessment in experimental studies was reported using speckle tracking strain in an open-chest dog model (104) and using M-mode from parasternal views in a closed-chest dog model (105). The use of time to peak strain has also been proposed in mice models of ischemia using speckle tracking longitudinal strain measurement from a parasternal long axis image (5).

E. Echocardiographic Assessment of Myocardial Viability in Ischemic Heart Disease

Standard 2D echocardiography has been used as a simple method to assess myocardial viability in ischemic heart disease by simply measuring wall thickness. Transmural fibrous scars are often associated with wall thinning and a wall thickness < 6mm was predictive of absence of function recovery after revascularization (106,107). Despite a high sensitivity, its specificity of this parameter is low, limiting its utility in practice.

Left ventricular opacification using myocardial contrast echocardiography allows to easily assess myocadial perfusion at rest. Myocardial contrast agents are ideally designed for perfusion assessment as they have a pure intravascular distribution. The grading of the myocardial perfusion of each individual segment can be performed semi-quantitatively by visual assessment or quantitatively using using intermittent triggered high mechanical impulse imaging to derive myocardial contrast intensity replenishment curves. The absence of myocardial opacification early after myocardial infarction is highly predictive of an absence of functional recovery (108,109); in chronic ischemic heart disease, preserved myocardial perfusion allows to predict function recovery after revascularization with a sensitivity comparable to that of dobutamine stress echocardiography and 201-thallium scintigraphy (110). The diagnostic performance of contrast echocardiography was reproduced in another study in comparison with 18-FDG-positron emission tomography (111) and its prognostic value demontrated (112).

As ischemic lesions progress from the endocardial muscle layers toward the epicardium, longitudinal myocardial function is expected to be reduced first as the longitudinally oriented myocardial fibers are located sub-endocardially. In comparison with delayed-enhancement CMR, 2D strain and strain rate analysis using speckle tracking technique showed a reduction in longitudinal contraction (Figure 9) in both subendocardial and transmural infarctions wheras a reduction in circumferential contraction was only seen in case of transmural infarctions (113). Early after reperfused acute myocardial infarction, resting global longitudinal strain correlated with the final infarct size and transmural extent (114) and a global strain value < -13.7% predicted functional recovery (115). Although promising and simple, these new techniques need further validation.

The standard echocardiographic method for viability detection is low-dose dobutamine echocardiography to detect contractile reserve in viable but hibernating myocardial segments. The set-up for this examination is more complicated as it requires the presence of a nurse for drug infusion during the dynamic examination, a continuous cardiac monitoring and the availability of rescuscitation facilities in case of an arrhythmic or ischemic complication of dobutamine infusion. The procedure of dobutamine stress echocardiography is described in details in the dedicated guidelines (2,116). Hypokinetic or akinetic segments at rest, which improve their contraction during low-dose (2.5 to 10 mcg/kg/min) dobutamine have been shown to improve their function after revascularisation. The probability of functional recovery after revascularization is considered maximal when the patient show a biphasic response, with an improvement of contraction with low-dose and a reduction in contraction with high-dose dobutamine, indicating viable but ischemic myocardium (117). The assessment of regional wall motion is classically performed with visual assessment and, as a consquence, high image quality is required. Despite improvements in global image quality, the inter-institution reproducibility of this technique is still not optimal (118). Even with these limitations, this technique has been largely validated in clinical practice (119) although the prognostic value of viability assessment has been recently challenged (120). The use of LV opacification can be used to improve endocardial border detection and confidence in visual interpretation (121). The use of deformation imaging using tissue Doppler or speckle-tracking strain and strain rate in combination with dobutamine stress echocardiography allow to obtain a quantitative assessment of changes in segmental contraction. In a pig model, the assessment of TDI-derived myocardial strain and strain rate during dobutamine stress was able to detect myocardial infarction and differentiate between subendocardial and transmural necrosis (122). In a clinical setting, an increase in longitudinal strain rate >0.23 s^-1 by tissue Doppler was proposed as a cut-off value to predict viability using 18-FDG PET as a reference (123). However, in comparison with standard visual assessment, the use of deformation imaging during DSE only slightly improves the accuracy for viability detection, and tissue Doppler techniques appear more accurate than speckle tracking in this context (124,125).

In a murine model of infarction, resting TDI radial strain rate was superior to wall thickening to identify transmural myocardial infarction (126), and to differentiate between transmural and non-transmural infarction in the acute and chronic phase (127). Resting LV opacification using intravenous contrast accurately detects area at risk or myocardial infarction following coronary artery ligation (128).

F. Echocardiographic Detection of Myocardial Ischemia

Dobutamine stress (or exercise) echocardiography is the standard method for ischemia detection using echocardiography. Detailed procedure of the test is described in the dedicated guidelines (2,116). Briefly the segmental contraction of the myocardium is assessed at rest, during low-dose (5-10 mcg/kg/min) dobutamine, peak-dose dobutamine (40 mcg/kg/min ± atropine to reach 85% of the maximal predicted heart rate) and during recovery. An ischemic myocardial segment presents normal contraction and becomes hypokinetic during stress, or presents the typical biphasic response described in the previous section. As described for the viability assessment, ischemia detection using DSE is usually performed with visual assessment only. The use of LV opacification improves wall segment visualization (121) (Plana) and the use of deformation imaging could provides a quantitative assessment of segmental myocardial contraction at rest and during peak stress. Animal studies using tissue-Doppler (129,130), described a reduction of longitudinal systolic strain and an increase in post-systolic strain during acute ischemia. This pattern has been confirmed in patients during DSE where a reduction in systolic strain and the presence of a post-systolic index (the ratio of post-sytolic to maximal peak strain) >20% were predictive of ischemia (131,132). Reduction of systolic strain rate was also found to be predictive of ischemia (133). Similarly, speckle-tracking longitudinal strain reduction with DSE was associated with ischemia in an animal model (41) and in patients (134) altough the quality of tracking may be reduced at high heart rate during peak stress (135). Diagnostic accuracy and prognostic value of DSE have been largely validated in clinical studies (136,137).

Myocardial contrast echocardiography is performed for ischemia detection by assessing myocardial perfusion, and uses a purely intravascular contrast medium. The principle is the comparison of myocardial opacification at rest and during maximal coronary hyperemia induced by adenosine or dipyridamole. Intermittent triggered high mechanical impulse imaging is used for myocardial perfusion assessment during contrast infusion and consists in delivering a brief high mechanical flash of ultrasound to destroy the micro-bubbles of and observe the replenishment of the myocardium. Qualitatively, normal perfusion is characterized by a complete opacification of the myocardium within 5 heart beats at rest and within 2 heart beats at peak stress. Quantitative assessement of the replenishment curves allows to measure myocardial blood volume and blood velocity (β) and to calculate myocardial blood flow (138,139). The ratio of myocardial blood flow (or blood velocity as a surrogate) during stress and at rest allows in turn to calculate coronary flow reserve (140). This method has been validated against SPECT (141) scintigraphy and in a head to head comparison of the two methods, MCE showed a superior sensitivity but a lower specificity (142). However, the method of image acquisition and the post-processing of the data are technically demanding and associated with a significant learning curve.

A last method of ischemia detection with echocardiography is the direct measurement of flow in the epicardial coronary arteries using pulse wave Doppler at rest and during adenosine or dipyridamole coronary hyperaemia (143,144). Image acquisition is technically more challenging (145) but in experienced hands and with the use of myocardial contrast, the mid to distal left anterior descending artery can be visualized in almost 100% of cases. The distal circumflex and right coronary arteries are more difficult to assess but the success rate was 92% and 88% for the RCA and LCx respectively in a recent study (146). The Doppler spectum of coronary flow at rest shows a predominantly diastolic flow and the flow increases with coronary hyperaemia during adenosine infusion. Since adenosine is not associated with a significant dilation of the epicardial coronary arteries, the ratio of the coronary mean velocity flow at peak hyperemia and at rest allows to estimate coronary flow reserve (CFR) of the dependent myocardial territory with good reproducibility (147,148). This method has been validated against invasive coronary flow measurement, SPECT (149) and PET (150).

In murine models, coronary flow Doppler of the left coronary artery at rest and during adenosine vasodilation was used to calculate coronary flow reserve. CFR was significantly reduced in case of coronary artery stenosis and in case of pressure overload hypertrophy (151,152). A quantitative assessment of myocardial blood flow using LV contrast opacification at rest and during pharmacological vasodilation was reported to be feasible in 98% of mice and showed a close correlation with a reference myocardial blood flow measurement using microspheres (153).

G. Echocardiographic Assessment of Right Ventricular Volume and Function

A precise assessment of right ventricular size and function is of great importance as these parameters provide independent prognostic informations in right-sided (154) and left-sided heart diseases (155,156).

The right ventricle is more difficult to assess with echocardiography due to its retro-sternal position. Its complex structure with a crescentic basal shape and a separated outflow tract does not allow a complete visualisation of its morphology in one single 2D imaging plane. RV size is classically assessed separately from an apical “RV-focused” 4-chamber view (with no visualization of the RV outflow tract, (Video 12)) and a parasteral view (to visualize the RVOT and the pulmonary arteries), which will provide complimentary informations. Several standard linear or area measurements to assess RV size from these views have been recommended in the recent guidelines and normal ranges have been defined (157). However, the ideal apical imaging plane for RV is difficult to standardize and the proposed normal values are not adjusted to age or body size, limiting the accuracy of these methods.

RV function can be estimated with the fractional area change (FAC), a surrogate of RVEF calculated from the RV area in diastole and in systole from a RV-focused apical 4-chamber view. FAC correlates with the RVEF measured with cardiac MRI (158) but overestimations of RV function are expected to occur if the RVOT is dilated or hypokinetic. Other commonly used indices of RV function are based on the longitudinal displacement of the tricupsid annulus using M-mode (tricuspid annulus plane systolic excursion, TAPSE) or its systolic velocity using tissue Doppler (Figure 10). Altough TAPSE showed a prognostic value in pulmonary hypertension (159), it is angle-dependent and it estimates the whole RV function from the motion of one single wall, limiting its reliability is case of regional dysfunction (160). Deformation imaging of the RV free wall using tissue Doppler or speckle tracking have been used to characterize RV function. Despite their feasability, the normal values derived from different studies were inconsistent and these methods are not recommended for clinical use until further validation (157). RV strain studies allowed however to better understand the the complexity of the RV contraction and its tight dependency on loading conditions (161).

3D echocardiography recently offered a tool to globally assess the RV morphology without any geometrical assumptions (Video 13). With this technique, RV diastolic and systolic volumes can be obtained to calculate a true RV ejection fraction using dedicated post-processing softwares (Video 14). As for 2D imaging, the retro-sternal postion of the RV may be seen as a limitation and significant image drop-outs can be observed in the RVOT region. Despite this limitations, 3D volume measurement is feasible in 81-94% of patients and correlates well with CMR (162,163,164). Normal values adjusted to age and gender have recenly been made available (165).

Right ventricle cannot be clearly visualized from trans-thoracic echocardiography in mice due to interference of the sternum. Transoesophageal echocardiography using an intravascular ultrasound probe has been proposed to overcome this limitation despite the lower frame rate of the probe (166).

H. Non-Invasive Hemodynamic Assessment

Basic haemodynamic assessment can be performed by combining simple linear and pulse wave Doppler measurements. Trans-aortic stroke volume is calculated from the measurements of the LVOT diameter (to calculate LVOT cross-sectional area) and the pulse wave Doppler of LVOT flow. This technique is limited by a significant variability as it relies on several measurements from different orientations. Stroke volume can also be measured at mitral or pulmonary level using the same technique, and the comparison of the stroke volumes at different locations can be used to quantify valvular regurgitant volumes or intra-cardiac shunts. Technique for standard Doppler measurements is presented in detail in the dedicated clinical guidelines (167).

Diastolic function and LV filling pressures estimation is an important but difficult challenge of Doppler echocardiography. While echocardiography can accurately measure pressure gradient, its ability to accurately assess filling pressures is controversial (168). The mitral inflow pattern using pulse-wave Doppler (E and A waves, (Figure 11)) was the first described parameter to assess diastolic function. Although easy to acquire (169) and predictive of outcome (170) it is highly load-dependent and cannot be used as a single parameter. Tissue-Doppler measurement of mitral annular early diastolic velocities (E’) is a less load-dependent parameter of LV relaxation (Figure 12) correlated with invasive measures of LV relaxation (171) and provide strong prognostic informations (172). The combination of both parameters, the E/E’ ratio, provides a robust semi-quantitative estimate of LV filling pressures (173), which has been validated against invasive pressure measurement in stable (174) and decompensated patients (175). In case of inconclusive results, the multi-parametric approach of diastolic function assessment has to be completed with additional parameters including pulse wave Doppler recording of pulmonary venous flow (176), mitral flow during Valsalva manœuvre, timing measurements of E and E’ waves (177,178), systolic pulmonary artery pressure estimation and left atrial volume measurement. Guidelines for diastolic function assessment describe in detail these parameters and how to interpret them in combination to grade diastolic dysfunction and estimate LV filling pressures (179). Deformation imaging is a new but promising tool for assessment of LV relaxation. Using speckle-tracking echocardiography, longitudinal strain rate during isovolumic relaxation has shown to correlate with invasive parameters of LV relaxation and the ratio E/(SRIVR) has been suggested to more accurately predict LV filling pressures compared to E/E’ ratio (180). Finally, LV torsion is increased with early diastolic dysfunction (181) and LV untwisting rate is correlated with invasive parameters of LV relaxation. However, as untwisting rate also depends on LV systolic function (182), more data are needed before rotation parameters can be recommended to assess diastolic function.

Left atrial (LA) size is part of the hemodynamic assessment as LA enlargement is a marker of chronically elevated LV filling pressures (183). It is also a powerful prognostic marker of adverse cardiac events including atrial fibrillation, heart failure, stroke and death (184). LA volume (Figure 13) is a better prognostic marker than LA area or diameter and is the recommended parameter to acquire (185). 3D echocardiography allows to measure LA volume without geometric assumptions (Video 15) and is more accurate than 2D measurements; it showed an excellent agreement with CMR and a good reproducibility (186). By measuring the LA volume at different time instances (minimal, maximal and pre-A volume), different markers of LA function can be calculated for LA reservoir, conduit and contractile function (187). 2D speckle tracking echocardiography recently offered new quantitative parameters of LA deformation by measuring atrial longitudinal strain (Video 16) and strain rate (188). Reduced longitudinal LA strain during systole can be seen as an early marker of reduced LA compliance and is associated with diastolic dysfunction and reduced exercise capacity (189). In combination with the mitral E/E’ ratio, atrial strain during systole allow to estimate LA stiffness, suggested as an accurate marker to identify diastolic heart failure (190).

Pulmonary artery pressure (PAP) is a major prognostic marker (191) and an important diagnostic parameter for diastolic dysfunction as most cases of elevated PAP are secondary to elevated LV filling pressure. Systolic PAP is measured from the maximal velocity of the tricuspid regurgitation jet, corresponding to the pressure gradient between right ventricle and right atrium during systole (192). Careful alignment to the jet orientation is mandatory to avoid underestimations and no RVOT outflow obstruction should be present. Right atrial pressure, estimated from inferior vena cava diameter and its collapse during inspiration, is added to the RV-RA gradient to obtain sPAP (193). This calculation showed linear correlation with invasive sPAP although the strength of the correlation was moderate, resulting in an imperfect diagnostic accuracy (194). Other parameters have been proposed for the estimation of mean PAP, including tricuspid regurgitant jet time velocity integral (195), pulmonary flow acceleration time (196) and early-diastolic velocity of the pulmonary regurgitant jet (197), and can be used as additional markers of pulmonary hypertension. Pulmonary vascular resistance PVR) can be assessed as the ratio of tricuspid regurgitant flow maximal velocity and pulmonary forward flow time-velocity integral (198). A good correlation was reported for moderately elevated PVR, but this index becomes inaccurate when PVR increases to >8 Wood units (199). Further indexes of pulmonary haemodynamics have been summarized in a recent review (200).

Pulse-wave and color Doppler can be used in murine echocardiography from parasteranal and apical 4 chamber views to measure trans-mitral, trans-aortic or trans-pulmonary flow velocity. Diastolic function in mice can be characterized using transmitral flow pattern (E and A waves, isovolumic relaxation time) (201), but mitral annular velocities measured with tissue Doppler imaging (E’ and A’ waves) are more sensitive makers of early diastolic dysfunction (202,203). As in human, the E/E’ ratio is correlated with LV end-diastolic pressures in mice (204).

I. Echocardiographic Measures of Cardiac Valves Morphology and Function

The high temporal resolution imaging combined with Doppler techniques for flow measurement make echocardiography an ideal technique for the assessment of valve morphology and quantification of valvular stenosis or regurgitation. Two-dimensional echocardiographic assessment of valve disease is clinically validated and represents a key examination in the management of valvular heart disease (205), but some important limitations are too keep in mind. Metrics to characterize valve stenosis include trans-valvular gradient measurement, direct valve planimetry, or calculation of aortic orifice area using continuity equation (206). The accuracy of these techniques depends on an optimal alignment of the probe with the structure of interest, which is not achievable in all patients. Furthermore, continuity equation is a calculation based on three different parameters and potential measurement errors at several levels can increase the variability. 2D color Doppler is used to quantify valvular regurgitations by measuring the vena contracta width of the regurgitant jet or by calculating the effective regurgitant orifice area (EROA) using the proximal isovelocity surface area (PISA) method. Regurgitant volumes can in turn be calculated by multiplying EROA by the time velocity integral of the regurgitant jet but this calculation will also rely on multiple measurements, increasing its variability. More importantly, vena contracta width and PISA methods assume that the regurgitant orifice is circular and the valve insufficiency can be underestimated in case of an oval or irregular orifice, as it is typically seen in functional mitral regurgitation (207).

3D echocardiography provides a more comprehensive assessment of valve morphology and can overcome some limitations of 2D imaging by avoiding geometric assumptions. Morphologic assessment of the mitral valve dramatically improved with 3D echocardiography (most commonly performed from a trans-oesophageal route) as it provided a direct en face visualisation of the leaflets allowing an accurate description of localized prolapses (Video 17). Post-processing of the volume datasets using commercially available quantification softwares provides several metrics of the valve morphology including size and shape of the mitral annulus, coaptation area, leaflet area, tenting volumes or billowing height (Figure 14)(208). These parameters can help to better characterize the mechanism of regurgitation and estimate the chances of a successful surgical repair. In case of mitral stenosis, the 3D approach garantees that the planimetry of the valve orifice will be measured in the right imaging plan, independently from the alignment of the probe, resulting in a better accuracy than 2D techniques and a high reproducibility (209). In mitral regurgitation, color Doppler 3D echocardiography is used to directly measure the cross-sectional area of vena contracta of the jet without geometric assumptions. This technique has been validated against CMR and showed a high reproducibility and a better accuracy than 2D methods (210,211), but it still needs further clinical validation. Other 3D methods for quantification of mitral regurgitation are based on 3D stroke volumes measurement and on the 3D PISA method, but their validation is less well established than for vena contracta area (21). Finally 3D echocardiography is an important tool to plan and to monitor several percutaneous valve interventions including transcatheter aortic valve implantations, balloon mitral valvuloplasty, mitral clipping, or paravalvular leak plugging (213).

Conclusions

Echocardiography is the first-line imaging modality for morphologic and functional assessment of the heart in clinical cardiology. The technique has been largely validated and new modalities including myocardial deformation imaging, 3D echocardiography and myocardial contrast echocardiography provide new promising quantitative endpoints for translational and clinical research. However, a high-level training in image acquisition and post-processing is to emphasize to reduce the variability in measurement as echocardiography is an operator-dependent technique. Despite that and some other well-known limitations including poor image quality in a subset of patients or angle-dependency of Doppler measurements, echocardiography remains an attractive research modality because of its high temporal and spatial resolution, its versatility, and the rapidity of image acquisition. Echocardiography could be successfully used in human and animal research, with almost all modalities (except real-time 3D due to its insufficient temporal resolution) being applicable to even small animal models, highlighting its central role for translational research in cardiology. Finally, the portability, the wide availabilty and lower cost of the technique could represent further important advantages in the research setting.

References

1. Thanigaraj S, Nease RF, Schechtman KB et al. Use of contrast for image enhancement during stress echocardiography is cost-effective and reduces additional diagnostic testing. Am J Cardiol 2001; 87:1430-2
2. Sicari R, Nihoyannopoulos P, Evangelista A et al. Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registrered branch of the ESC). Eur J Echocardiogr 2008; 9:415-37
3. Weiss RJ, Ahmad M, Villanueva F et al. CaRES (Contrast Echocardiography Registry for Safety Surveillance): a prospective multicenter study to evaluate the safety of the ultrasound contrast agent definity in clinical practice. J Am Soc Echocardiogr 2012; 25:790-5
4. Senior R, Becher H, Monaghan M et al. Contrast echocardiography: evidence-based recommendations by European Association of Echocardiography. Eur J Echocardiogr 2009; 10:194-212
5. Ram R, Mickelsen DM, Theodoropoulos C, Blaxall BC. New approaches in small animal echocardiography: imaging the sounds of silence. Am J Physiol Heart Circ Physiol 2011; 301:H1765-80
6. Syed F, Diwan A, Hahn HS. Murine echocatdiography: a practical approach for phenotyping genetically manipulated and surgically modelled mice. J Am Soc Echocardiogr 2005; 18:982-990
7. Burns RJ, Gibbons RJ, Yi Q, et al. The relationship of left ventricular ejection fraction, end-systolic volume index and infarct size to six-month mortality after hospital discharge following myocardial infarction treated by thrombolysis. J Am Coll Cardiol 2002; 39:30-6.
8. Verma A, Meris A, Skali H et al. Prognostic implications of left ventricular mass and geometry following myocardial infarction. The VALIANT (Valsartan in acute myocardial infarction) echocardiographic study. J Am Coll Cardiol Cardiovasc Img 2008; 1:582-91
   Feigenbaum H. Role of M-mode technique in today’s echocardiography. J Am Soc Echocardiogr 2010; 23:240-57
9. Ilercil A, O’Grady MJ, Roman MJ et al. Reference values for echocardiographic measurements in urban and rural populations of differing ethnicity: the Strong Heart Study. J Am Soc Echocardiogr 2001; 14:601-11
10. Palmieri V, Dahlof B, DeQuattro V et al. Reliability of echocardiographic assessment of left ventricular structure and function: the Preserve Study: Prospective Randomized Study Evaluating Regression of Ventricular Enlargement. J Am Coll Cardiol 1999; 34:1625-32
11. Lang RM, Bierig M, Devereux RB et al. Recommendations for chamber quantification. Eur J Echocardiography 2006; 7:79-108
12. Devereux RB, Alonso DR, Lutas EM et al. Echocardiographic assessment of left ventricular hypertrophy: comparison to necropsy findings. A m J Cardiol 1986; 57:450-8
13. Myerson SG, Montgomery HE, World MJ, Pennell DJ. Left ventricular mass. Reliability of M-mode end 2-dimensional echocardiographic formulas. Hypertension 2002; 40:673-8
14. Gordon EP, Schnittger I, Fitzgerald PJ et al. Reproducibility of left ventricular volumes by two-dimensional echocardiography. J Am Coll Cardiol 1983; 2:506
    Himelman RB, Cassidy MM, Landzberg JS et al. Reproducibility of quantitative two-dimensional echocardiography. Am Heart J 1988; 115:425-31
15. Malm S, Frigstad S, Sagberg E, et al. Accurate and reproducible measurement of left ventricular volume and ejection fraction by contrast echocardiography. J Am Coll Cardiol 2004; 44:1030-5
16. Hoffmann R, von Bardeleben S, Kasprzak JD et al. Analysis of regional left ventricular function by cineventriculography, cardiac magnetic resonance imaging, and unenhanced and contrast-enhanced echocardiography: a multicenter ceomparison of methods. J Am Coll Cardiol 2006; 47:121-8
17. Lang RM, Bierig M, Devereux RB et al. Recommendations for chamber quantification: a report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branche of the European Society of Cardiology. J Am Soc Echocardiography 2005; 18:1440-63
18. Chuang ML, Hibberd MG, Salton CJ et al. Importance of imaging method over imaging modality in noninvasive determination of left ventricular volumes and ejection fraction: assessment by two- and three-dimensional echocardiography and magnetic resonance imaging. J Am Coll Cardiol 2000; 35:477-84
19. Mor-Avi V, Jeankins C, Kuhl HP et al. Real-time 3-dimensional echocardiographic quantification of left ventricular volumes: multicenter study for validation with magnetic resonance imaging and investigation of sources of error. JACC Cardiovasc Imaging 2008; 1:413-23
20. Jenkins C, Bricknell K, Hanekom L, et al. Reproducibility and accuracy of echocardiographic measurements of left ventricular parameters using real-time three dimensional echocardiography. J Am Coll Cardiol 2004; 44:878-86
21. Jenkins C, Moir S, Chan J et al. Left ventricular volume measurement with echocardiography: a comparison of left ventricular opacification, three-dimensional echocardiography, or both with magnetic resonance imaging. Eur Heart J 2009; 30:98-106
22. Pouleur AC, le Polain de Waroux JB, Pasquet A et al. Assessment of left ventricular mass and volumes by three-dimensional echocardiography in patients with or without wall motion abnormalities: comparison against cine magnetic resonance imaging. Heart 2008; 94:1050
23. Yang XP, Liu YH, Rhaleb NE et al. Echocardiographic assessment of cardiac function in conscious and anesthetized mice. Am J Physiol 1999; 277:H1967-74
24. Youn HJ, Rokosh G, Lester SJ et al. Two-dimensional echocardiography with a 15-MHz transducer is a promising alternative for in vivo measurement of left ventricular mass in mice. J Am Soc Echocardiogr 1999; 12:70-5
25. Dawson D, Lygate CA, Saunders J et al. Quantitative 3-dimensional echocardiography for accurate and rapid cardiac phenotype characterization in mice. Circulation 2004; 110:1632-7
26. Buckberg G, Hoffman JI, Mahajan A et al. Cardiac mechanics revisited: the relationship of cardiac architecture to ventricular function. Circulation 2008; 118:2571-87
27. Sengupta PP, Krishnamoorthy VK, Korinek J et al. Left ventricular form and function revisited: applied translational science to cardiovascular imaging. J Am Soc Echocardiogr 2007; 20:539-51
28. Hoit BD. Strain and strain rate echocardiography and coronary artery disease. Circ Cardiovasc Imaging 2011; 4:179-90
29. Weidemann F, Jamal F, Sutherland GR, et al. Myocardial function defined by strain rate and strain during alterations in inotropic states and heart rate. Am J Physiol Heart Circ Physiol 2002; 283:H792-9
30. Greenberg NL, Firstenberg MS, Castro PL et al. Doppler-derived myocardial systolic strain rate is a strong index of left ventricular contractility. Circulation 2002; 105:99-105
31. Heimdal A, Stoylen A, Torp H et al. Real time strain rate imaging of the left ventricle by ultrasound. J Am Soc Echocardiogr 1998; 11:1013-9
32. Storaa C, Aberg P, Lind B et al. Effects of angular error on tissue Doppler velocities and strain. Echocardiography 2003; 20:581-7
33. Urheim S, Edvardsen T, Torp H et al. Validation of a new method to quantify regional myocardial function. Circulation 2000; 102:1158-64
34. Edvardsen T, Gerber BL, Garot J et al. Quantitative assessment of intrinsic regional myocardial deformation by Doppler strain rate echocardiography in humans: validation against three-dimensional tagged magnetic resonance imaging. Circulation 2002; 106:50-6
35. Sun JP, Popovic ZB, Greenberg NL et al. Doppler-derived velocity, displacement, strain rate and strain in healthy volunteers: effects of aging. J Am Soc Echocardiogr 2004; 17:132-8
36. Leitman M, Lysyansky P, Sidenko S et al. Two-dimensional strain – a novel software for real-time quantitative echocardiographic assessment of myocardial function. J Am Soc Echocardiogr 2004; 17:1021-9
37. Geyer H, Caracciolo G, Abe H et al. Assessment of myocardial mechanics using speckle tracking echocardiography: fundamentals and clinical applications. J Am Soc Echocardiogr 2010; 23:351-69
38. Helle-Valle T, Crosby J, Edvardsen T et al. New nonivasive method for assessment of left ventricular rotation: speckle tracking echocardiography. Circulation 2005; 112:149-56
39. Reant P, Labrousse L, Lafitte S et al. Experimental validation of circumferential, longitudinal and radial 2-dimensional strain during dobutamine stress echocardiography in ischemic conditions. J Am Coll Cardiol 2008; 51:149-57
40. Amundsen BH, Helle-Valle T, Edvardsen T et al. Noninvasive myocardial strainmeasurement by speckle tracking echocardiography: validation against sonomicrometry and tagged magnetic resonance imaging. J Am Coll Cardiol 2006; 47:789-93
41. Yingchoncharoen T, Agarwal S, Popovic Z et al. Normal ranges of left ventricular strain: a meta-analysis. J Am Soc Echocardiogr 2013; 26:185-91
42. Modesto KM, Cauduro S, Dispenzieri A et al. Two-dimensional acoustic pattern derived strain parameters closely correlate with one-dimensional tissue Doppler derived strain meaasurements. Eur J echocardiogr 2006; 7:315-21
43. Amundsen B, Crosby J, Steen P et al. Regional myocardial long-axis strain and strain rate measured by different tissue Doppler and speckle tracking echocardiography methods: a comparison with tagged magnetic resonance imaging. Eur J Echocardiogr 2009; 10:229-37
44. Sjoli B, Orn S, Grenne B et al. Diagnostic capability and reproducibility of strain by Doppler and by speckle tracking in patients with acute myocardial infarction. JACC Cardiovasc Imaging 2009; 2:24-33
45. Mondillo S, Galderisi M, Mele D et al. Speckle tracking echocardiography. A new technique for assessing myocardial function. J Ultrasound Med 2011; 30:71-83
46. Notomi Y, Lysyansky P, Setser RM et al. Measurement of ventricular torsion by two-dimensional ultrasound speckle traking imaging. J Am COll Cardiol 2005; 45:2034-41
47. Parisi V, Losi MA, Contaldi C et al. Speckle-tracking analysis based on 2D echocardiography does not reliably measure left ventricular torsion. Clin Physiol Funct Imaging 2013; 33:117-21
48. Russel I, Gotte MJW, Bronzwaer JG et al. Left ventricular torsion. An expanding role in the analysis of myocardial dysfunction. J Am Coll Cardiol Img 2009; 2:648-55
49. Wu VC, Takeuchi M, Otani K et al. Effect of through-plane and twisting motion on left ventricular strain calculation:direct comparison between two-dimensional and three-dimensional speckle tracking echocardiography. J Am Soc Echocardiogr 2013; 26:1274-81
50. Saito K, Okura H, Watanabe N et al. Comprehensive evaluation of left ventricular strain using speckle tracking echocardiography in normal adults:comparison of three-dimensional and two-dimensional approaches. J Am Soc Echocardiogr 2009; 22:1025-30
51. Seo Y, Ishizu T, Enomoto Y et al. Validation of 3-dimensional speckle tracking imaging to quantify regional myocardial deformation. Circ Cardiovasc Img 2009; 2:451-9
52. Andrade J, Cortez LD, Campos O. Left ventricular twist:comparison between two- and three-dimensional speckle-tracking echocardiography in healthy volunteers. Eur J Echocardiogr 2011; 12:76-9
53. Altman M Bergerot C, Aussoleil A et al. Assessment of left ventricular systolic function by deformation imaging derived from speckle tracking:a comparison between 2D and 3D echo modalities. Eur Heart J Cardiovasc Imaging 2013 sept 18 (Epub ahead of print)
54. Kleijn SA, Aly MF, Terwee CB et al. Three-dimensional speckle tracking echocardiography for automatic assessment of global and regional left ventricular function based on area strain. J Am Soc Echocardiogr 2011; 24:314-21
55. Kaku, K, Takeuchi M, Tsang W et al. Age-related normal range of left ventricular strain and torsion using three-dimensional speckle-tracking echocardiography. J Am Soc Echocardiogr 2013 Nov 13. doi:pii:S0894-7317(13)00801-8. 10.1016/j.echo.2013.10.002 (epub ahead of print)
56. Badano LP, Cucchini U, Muratu D et al. Use of three-dimensional speckle tracking to assess left ventricular myocardial mechanics:inter-vendor consistency and reproducibility of strain measurements. Eur Heart J Cardiovasc Imaging 2013; 14:285-93
57. Park CM, March K, Williams S et al. Feasability and reproducibility of left ventricular rotation by speckle tracking echocardiography in elderly individuals and the impact of different software. PLoS One 2013; 8:e75098. Doi:10.1371/journal.pone.0075098
58. Mor-Avi V, Lang RM, Badano LP et al. Current and evolving echocardiographic techniques for the quantitative evaluation of cardiac mechanics:ASE/EAE consesnus statement on methodology and indications. Endorsed by the Japanese Society of Echocardiography. J Am Soc Echocardiogr 2011; 24:277-313
59. Brown J, Jenkins C, Marwick T. Use of myocardial strain to assess global left ventricular function:a comparison with cardiac magnetic resonance and 3-dimensional echocardiography. Am Heart J 2009; 157:102e1-102e5
60. Sjoli B, Orn S, Grenne B et al. Comparison of left ventricular ejection fraction and left ventricular global strain as determinants of infarct size in patients with acute myocardial infarction. J Am Soc Echocardiogr 2009; 22:1232-8
61. Cho GY, Marwick TH, Kim HS et al. Global 2-dimensional strain as a new prognosticator in patients with heart failure. J Am Coll Cardiol 2009; 54:618-24
62. Nahum J, Bensaid A, Dussault C et al. Impact of longitudinal myocardial deformation on the prognosis of chronic heart failure. Circ Cardiovasc Imaging 2010; 3:249-56
63. Stanton T, Leano R, Marwick TH. Prediction of all-cause mortality from global longitudinal speckle strain:comparison with ejection fraction and wall motion scoring. Circ Cardiovasc Imaging 2009; 2:356-64
64. Blondheim DS, Friedman Z, Lysyansky P et al. Use of an automated application for wall motion classification based on longitudinal strain: is it affected by operator expertise in echocardiography? A multicentre sudy by the Israeli Echocardiography Research Group. Eur Heart J Cardiovasc Imaging 2012; 13:257-62
65. Muranaka A, Yuda S, Tsuchihashi K, et al. Quantitative assessment of left ventricular and left atrial functions by strain rate imaging in diabetic patients with and without hypertension. Echocardiography 2009; 26:262-71
66. Kato TS, Noda A, Izawa H et al. Discrimination of nonobstructive hypertrophic cardiomyopathy from hypertensive left ventricular hypertrophy on the basis of strain rate imaging by tissue Doppler ultrasonography. Circulation 2004; 110:3808-14
67. Prakasa KR, Wang J, Tandri H et al. Utility of tissue Doppler and strain echocardiography in arrhythmogenic right ventricular dysplasia/cardiomyopathy. Am J Cardiol 2007; 100:507-12
68. Koyama J, Ray-sequin PA, Falk RH. Longitudinal myocardial function assessed by tissue velocity, strain and strain rate tissue Doppler echocardiography in patients with AL (primary) cardiac amyloidosis. Circulation 2003; 107:2446-52
69. Phelan D, Collier P, Thavendiranathan P et al. Relative apical sparing of longitudinal strain using two-dimensional speckle tracking echocardiography is both sensitive and specific for the diagnosis of cardiac amyloidosis. Heart 2012; 98:1442-8
70. Edvardsen T, Helle-Valle T, Smiseth OA. Systolic dysfunction in heart failure with normal ejection fraction:speckle-tracking echocardiography. Prog Cardiovasc Dis 2006; 49:207-14
71. Delgado V, Tops LF, van Bommel RJ et al. Strain analysis in patients with severe aortic stenosis and preserved left ventricular ejection fraction undergoing surgical valve replacement. Eur Heart J 2009; 30:3037-47
72. Onishi T, Kawai H, Tatsumi K et al. Preoperative systolic strain rate predicts postoperative left ventricular dysfunction in patients with chronic regurgitation. Circ Cardiovasc Imaging 2010; 3:134-41
73. Ho E, Brown A, Barrett P et al. Subclnical anthracycline- and trastuzumab-induced cardiotoxicity in the long-term follow-up of asymptomatic breast cancer survivors:a speckle tracking echocardiographic study. Heart 2010; 96 :701-7
74. Hare JL, Brown JK, Leano R et al. Use of myocardial deformation imaging to detect preclinical myocardial dysfunction before conventional measures in patients undergoing breast cancer treatment with trastuzumab. Am Heart J 2009; 158:294-301
75. Jamal F, Strotmann J, Weidemann F et al. Noninvasive quantification of the contractile reserve of stunned myocardium by ultrasonic strain rate and strain. Circulation 2001; 104:1059-65
76. Sebag IA, Handschumacher MD, Ichinose F et al. Quantitative assessment of regional myocardial function in mice by tissue Doppler imaging:comparison with hemodynamics and sonomicrometry. Circulation 2005; 111:2611-6
77. Ferferieva V, van den Bergh A, Claus P. et al. Assessment of strain and strain rate by two-dimensional speckle tracking in mice: comparison with tissue Doppler echocardiography and conductance catheter measurements. Eur Heart J Cardiovasc Imaging 2013; 14:765-73
78. Neilan TG, Jassal DS, Perez-Sanz TM et al. Tissue Doppler imaging predicts left ventricular dysfunction and mortality in a murine model of cardiac injury. Eur Heart J 2006; 27:1868-75
79. Bauer M, Cheng S, Jain M et al. Echocardiographic speckle tracking based strain imaging for rapid cardiovacular phenotyping in mice. Circ Res 2011; 108:908-16
80. Cleland JG, Daubert JC, Erdmann E et al. The effect of cardiac resynchronization on mobidity and mortality in heart failure. N Engl J Med 2005; 352:1539-49
81. Gorcsan J III, Abraham T, Agler DA et al. Echocardiography for cardiac resynchronization therapy:recommendations for performance and reporting – a report from the American Society of Echocardiography Dyssynchrony Writing Group endorsed by the Heart Rhythm Society. J Am Soc Echocardiogr 2008; 21:191-213
82. Pitzalis MV, Iacoviello M, Romito R et al. Cardiac resynchronization therapy tailored by echocardiographic evaluation of ventricular asynchrony. J Am Coll Cardiol 2002; 40:1615-22
83. Chung ES, Leon AR, Tavazzi L et al. Results of the predictors of response to CRT (PROSPECT) trial. Circulation 2008; 117:1608-16
84. Stockburger M, Fateh-Moghadam S, Nitardy A et al. Baseline Doppler parameters are useful predictors of chronic left ventricular reduction in size by cardiac resynchronization therapy. Europace 2008; 10:69-74
85. Bax JJ, Bleeker GB, Marwick TH et al. Left ventricular dyssynchrony predicts response and prognosis after cardiac resynchronization therapy. J Am Coll Cardiol 2004; 44:1834-40
86. Notabartolo D, Merlino JD, Smith AL et al. Usefulness of the peak velocity difference by tissue Doppler imaging technique as an effective predictor of response to cardiac resynchronization therapy. Am J Cardiol 2004; 94:817-20
87. Yu CM, Fung WH, Lin H et al. Predictors of left ventricular reverse remodeling after cardiac resynchronization therapy for heart failure secondary to idiopathic dilated or ischemic cardiomyopathy. Am J Cardiol 2003; 91:684-8
88. Tanaka H, Nesser HJ, Buck T et al. Dyssynchrony by speckle-tracking echocardiography and response to cardiac resynchronization therapy:results of the Speckle Tracking and Resynchronization (STAR) study. Eur Heart J 2010; 31:1690-700
89. Delgado V, Ypenburg C, van Bommel RJ et al. Assessment of left ventricular dysynchrony by speckle tracking strain imaging comparison between longitudinal, circumferential and radial strain in cardiac resynchronization therapy. J Am Coll Cardiol 2008; 51:1944-52
90. Miyazaki C, Redfield MM, Powell BD et al. Dyssynchrony indices to predict response to cardiac resynchronization therapy:a comprehensive prospective single-center study. Circ Heart Fail 2010; 3:565-73
91. Lim P, Donal E, Lafitte S, et al. Multicentre study using strain delay index for predicting response to cardiac resynchronization therapy (MUSIC study). Eur J Heart Fail 2011; 13:984-91
92. Khan FZ, Virdee MS, Palmer CR et al. Targeted left ventriculr lead placement to guide cardiac resynchronization therapy:the TARGET study:a randomized, controlled trial. J Am Coll Cardiol 2012; 59:1509-18
93. Kapetanakis S, Kearney MT, Siva A et al. Real-time three-dimensional echocardiography:a novel technique to quantify global left ventricular mechanical dyssynchrony. Circulation 2005; 112:992-1000
94. Marsan NA, Bleeker GB, Ypenburg C et al. Real-time three-dimensional echocardiography as a novel approach to assess left ventricular and left atrium reverse remodelling and to predict response to cardiac resynchronisation therapy. Heart rhythm 2008; 5:1257-64
95. Soliman OI, Geleijnse ML, Theuns DA et al. Usefulness of left ventricular systolic dysynchrony by real-time three-dimensional echocardiography to predict long-term response to cardiac resynchronization therapy. Am J Cardiol 2009; 103:1586-91
96. Gimenes VM, Vieira ML, Andrade MM et al. Standard values for real-time transthoracic three-dimensional echocardiographic dyssynchrony indexes in a normal population. J Am Soc Echocardiogr 2008; 21:1229-35
97. Sonne C, Sugeng L, Takeuchi M et al. Real-time 3-dimensional echocardiographic assessment of left ventricular dyssynchrony:pitfalls in patients with dilated cardiomyopathy. J Am Coll Cardiol Img 2009; 2:802-12
98. Kleijn SA, van Dijk J, de Cock CC et al. Assessment of intraventricular mechanical dyssynchrony and prediction of response to cardiac resynchronization therapy:comparison between tissue Doppler imaging and real-time three-dimensional echocardiography. J Am Soc Echocardiogr 2009; 22:1047-54
99. Burgess MI, Jenkins C, Chan J, Marwick TH. Measurement of left ventricular dysynchrony in patients with ischaemic cardiomyopathy: a comparison of real-time three-dimensional and tissue Doppler echocardiography. Heart 2007; 93:1191-6
100. Auger D, Bertini M, Marsan NA et al. Prediction of response to cardiac resynchronization therapy combining two different three-dimensional analyses of left ventricular dyssynchrony. Am J Cardiol 2011; 108:711-7
101. Strik M, van Middendorp LB, Vernooy K. Animal Models of dyssynchrony. J Cardiovasc Trans Res 2012; 5:135-45
102. Russel K, Eriksen M, Aaberge L, et al. A novel clinical method for quantification of regional left ventricular pressure-strain loop area:a non-invasive index of myocardial work. Eur Heart J 2012; 33:724-33
103. Vernooy K, Cornelussen RN, Verbeek XA et al. Cardiac resynchronisation therapy cures dyssynchronopathy in canine left bundle-branch block hearts. Eur Heart J 2007; 28:2148-55
104. Cwajg JM, Cwajg E, Nagueh SF et al. End-diastolic wall thickness as a predictor of recovery of function in myocardial hibernation:relation to rest-redistribution Tl-201 tomography and dobutamine stress echocardiography. J Am Coll Cardiol 2000; 35:1152-61
105. Schinkel AF, Bax JJ, Boersma E et al. Assessment of residual myocardial viability in regions with chronic electrocardiographic Q-wave infarction. Am Heart J 2002; 144:865-9
106. Janardhanan R, Swinburn JM, Greaves K, Senior R. Usefulness of myocardial contrast echocardiography using low-power continuous imaging early after acute myocardial infarction to predict late functional left ventricular recovery. Am J Cardiol 2003; 92:493-7
107. Balcells E, Powers ER, Lepper W et al. Detection of myocardial viability by contrast echocardiography in acute infarction predicts recovery of resting function and contractile reserve. J Am Coll Cardiol 2003; 41:827-33
108. Shimoni S, Frangogiannis NG, Aggeli CJ et al. Identification of hibernating myocardium with quantitative intravenous myocardial contrast echocardiography. Comparison with dobutamine echocardiography and thallium-201 scintigraphy. Circulation 2003; 107:538-44
109. Korosoglou G, Hansen A, Hoffend J et al. Comparison of real-time myocardial contrast echocardiography for the assessment of myocardial viability with fluorodeoyglucose-18 positron emission tomography and dobutamine stress echocardiography. Am J Cardiol 2004; 94:570-6
110. Dwivedi G, Janardhanan R, Hayar S et al. Prognostic value of myocardial viability detected by myocardial contrast echocardiography early after acute myocardial infarction. J Am Coll Cardiol 2007; 50:327-34
111. Chan J, Hanekom L, Wong C et al. Differentiation of subendocardial and transmural infarction using two-dimensional strain rate imaging to assess short-axis and long-axis myocardial function. J Am Coll Cardiol 2006; 48:2026-33
112. Vartdal T, Brunvand H, Pettersen E et al. Early prediction of infarct size by strain Doppler echocardiography after coronary reperfusion. J Am Coll Cardiol 2007; 49:1715-21
113. Mollema SA, Delgado V, Bertini M et al. Viability assessment with global left ventricular longitudinal strain predicts recovery of the left ventricular function after acute myocardial infarction. Circ Cardiovasc Imaging 2010; 3:15-23
114. Pellika PA, Nagueh SF, Elhendy AA et al. American society of echocardiography recommendations for performance, interpretation and application of stress echocardiography. J Am Soc Echocardiogr 2007; 20:1021-41
115. Afridi I, Kleiman NS, Raizner AE et al. Dobutamine echocardiography in myocardial hibernation. Optimal dose and accuracy in predicting recovery of ventricular function after coronary angioplasty. Circulation 1995; 91:663-70
116. Hoffmann R, Marwick TH, Poldermans D et al. Refinements in stress echocardiographic techniques improve inter-institutional agreement in interpretation of dobutamine stress echocardiograms. Eur Heart J 2002; 23:821-9
117. Allman KC, Shaw LJ, Hachamovitch R, Udelson JE. Myocardial viability testing and impact of revascularization on prognosis in patients with coronary artery disease and left ventricular dysfunction:a meta-analysis. J Am Coll Cardiol 2002; 39:1151-8
118. Bonow RO, Maurer G, Lee KL et al. Myocardial viability and survival in ischemic left ventricular dysfunction. New Engl J Med 2011; 364:1617-25
119. Plana JC, Mikati IA, Dokainish H et al. A randomized cross-over study for evaluation of the effect of image optimization with contrast on the diagnostic accuracy of dobutamine echocardiography in coronary disease. The Optimize trial. JACC Cardiovasc Imaging 2008; 1:145-52
120. Weidemann F, Dommke C, Bijnens B et al. Defining the transmurality of a chronic myocardial infarction by ultrasonic strain-rate imaging:implications for identifying intramural viability: an experimental study. Circulation 2003; 107:883-8
121. Hoffmann R, Altiok E, Nowak B et al. Strain measurement by Doppler echocardiography allows improved assessment of myocardial viability in patients with depressed left ventricular function. J Am Coll Cardiol 2002; 39:443-9
122. Hanekom L, Jenkins C, Jeffries L et al. Incremental value of strain rate analysis as an adjunct to wall-motion scoring for assessment of myocardial viability by dobutamine echocardiography:a follow-up study after revascularization. Circulation 2005; 112:3892-900
123. Bansal M, Jeffries L, Leano R, et al. Assessment of myocardial viability at dobutamine echocardiography by deformation analysis using tissue velocity and speckle tracking. JACC Cardiovasc Imaging 2010; 3:121-31
124. Thibault H, Gomez L, Donal E et al. Acute myocardial infarction in mice:assessment of transmurality by strain rate imaging. Am J Physiol Heart Circ Physiol 2007; 293:H496-502
125. Thibault H, Gomez L, Donal E et al. Regional myocardial function after myocardial infarction in mice:a follow-up study by strain rate imaging. J Am Soc Echocardiogr 2009; 22:198-205
126. Scherrer-Crosby M, Steudel W, Ullrich R et al. Echocardiographic determination of risk area size in a murine model of myocardial ischemia. Am J Physiol Heart Circ Physiol 1999; 277:H986-992
127. Skulstad H, Edvardsen T, Urheim S et al. Postsystolic shortening in ischemic myocardium. Active contraction or passive recoil? Circulation 2002; 106:718-24
128. Skulstad H, Urheim S, Edvardsen T et al. Grading of myocardial dysfunction by tissue Doppler echocardiography: a comparison between velocity, displacement, and strain imaging in acute ischemia. J Am Coll Cardiol 2006; 47:1672-82
129. Voigt JU, Exner B, Schmiedehausen K et al. Strain-rate imaging during dobutamine stress echocardiography provides objective evidence of inducible ischemia. Circulation 2003; 107:2120-6
130. Voigt JU, Lindenmeier G, Exner B et al. Incidence and characteristics of segmental postsystolic longitudinal shortening in normal, acutely ischemic and scarred myocardium. J Am Soc Echocardiogr 2003; 16:415-23
131. Weidemann F, Jung P, Hoyer C et al. Assessment oft he contractile reserve in patients with intermediate coronary lesions: a strain rate imaging study validated by invasive myocardial fractional flow reserve. Eur Heart J 2007; 28:1425-32
132. Ng ACT, Sitges M, Pham PN et al. Incremental value of 2-dimensional speckle tracking strain imaging to wall motion analysis for detection of coronary artery disease i patients undergoing dobutamine stress echocardiography. Am Heart J 2009; 158:836-44
133. Hanekom L, Cho GY, Leano R et al. Comparison of two-dimensional speckle and tissue Doppler strain measurement during dobutamine stress echocardiography: an angiographic correlation. Eur Heart J 2007; 28:1765-72
134. Schinkel AF, Bax JJ, Geleijnse ML et al. Noninvasive evaluation of ischaemic heart disease: myocardial perfusion imaging or stress echocardiography? Eur Heart J 2003; 24:789-800
135. Schuijf JD, Poldermans D, Shaw LJ et al. Diagnostic and prognostic value of non-invasive imaging in known or suspected coronary y artery disease. Eur J Nucl Med Mol Imaging 2006; 33:93-104
136. Wei, Jayaweera AR, Firoozan S et al. Quantification of myocardial blood flow with ultrasound-induced destruction of microbubbles administered as a constant venous infusion. Circulation 1998; 97:473-83
137. Vogel R, Indermuhle A, Reinhardt J, et al. The quantification of absolute myocardial perfusion in humans by contrast echocardiography:algorithm and validation. J Am Coll Cardiol 2005; 45:754-62
138. Wei K, Ragosta M, Thorpe J et al. Noninvasive quantification of coronary blood flow reserve in humans using myocardial contrast echocardiography. Circulation 2001; 103:2560
139. Dijkmans PA, Senior R, Becher H et al. Myocardial contrast echocardiography evolving as a clinically feasible technique for accurate, rapid, and safe assessment of myocardial perfusion:the evidence so far. J Am Coll Cardiol 2006; 48:2168-77
140. Senior R, Moreo A, Gaibazzi N et al. Comparison of sulfur hexafluoride microbubble (SonoVue)-enhanced myocardial contrast echocardiography with gated singl-photon emission computed tomography for detection of significant coronary artery disease. A large European multicenter study. J Am Coll Cardiol 2013; 62:1353-61
141. Meimoun P, Tribouilloy C. Non-invasive assessment of coronary flow and coronary flow reserve by transthoracic Doppler echocardiography:a magnic tool for the real world. Eur J Echocardiography 2008; 9:449-57
142. Kiviniemi T. Assessment of coronary blood flow and the reactivity of the microcirculation non-invasively with transthoracic echocardiography. Clin Physiol Funct Imaging 2008; 28:141-55
143. Rigo F, Murer B, Ossena G et al. Transthoracic echocadiographic imaging of coronary arteries:tips, traps and pitfalls. Cardiovasc Ultrasound 2008; 6:7.
144. Wada T, Hirata K, Shiono Y et al. Coronary flow velocity reserve in three major coronary arteries by transthoracic echocardiography for functional assessment of coronary artery disease:a comparison with fractional flow reserve. Eur Heart J Cardiovasc Imaging 2013 dec 3. Doi :10.1093/ehjci/jet168 (epub ahead of print)
145. Hozumi T, Yoshida K, Akasaka T et al. Noninvasive assessment of coronary flow velocity and coronary flow velocity reserve in the left anterior descending coronary artery by Doppler exhocadiography:comparison with invasive technique. J Am Coll Cardiol 1998; 32:1251-9
146. Caiati C, Montaldo C, Zedda N et al. Validation of a new noninvasive method (contrast-enhanced transthoracic second harmonic echo Doppler) for the evaluation of coronary flow reserve:comparison with intracoronary Doppler flow wire. J Am Coll Cardiol 1999; 34:1193
147. Daimon M, Watanabe H, Yamagishi H et al. Physiologic assessment of coronary artery stenosis by coronary flow reserve measurement with transthoracic Doppler echocardiography: comparison with exercise thallium-201 single photon emission computed tomography
148. Saraste M, Koskenvuo J, Knuuti J et al. Coronary flow reserve:measurement with transthoracic Doppler echocardiography is reproducible and comparable with positron emission tomography. Clin Physiol 2001; 21:114-22
149. Wikstrom J, Gronros J, Bergstrom G Gan L. Functional an morphologic imaging of coronary atherosclerosis in living mice using high-resolution color Doppler echocardiography and ultrasound biomicroscopy. J Am Coll Cardiol 2005; 46:720-7
150. Hartley CJ, Reddy AK, Madala S et al. Doppler estimation of reduced coronary flow reserve in mice with pressure overloead cardiac hypertrophy. Ultrasound Med Biol 2008; 34:892-901
151. Raher MJ, Thibault H, Poh KK et al. In vivo characterization of murine myocardial perfusion with myocardial contrast echocardiography. Validation and application in nitric oxide synthase 3 deficient mice. Circulation 2007; 116:1250-7
152. van Wolferen SA, Marcus JT, Boonstra A et al. Prognostic value of right ventricular mass, volume, and function in idiopathic pulmonary arterial hypertension. Eur Heart J 2007; 28:1250-7
153. Gulati A, Ismail TF, Jabbour A et al. The prevalence and prognostic significance of right ventricular systolic dysfunction in nonischemic dilated cardiomyopathy. Circulation 2013; 128:1623-33
154. Larose E, Ganz P, Reynolds HG et al. Right ventricular dysfunction assesed by cardiovascular magnetic resonance imaging predicts poor prognosis late after myocardial infarction. J Am Coll Cardiol 2007; 49:855-62
155. Rudski LG, Lai WW, Afilalo J et al. Guidelines for the echocardiographic asessment of the right heart in adults:a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. J Am Soc Echocardiogr 2010; 23:685-713
156. Anavekar NS, Gerson D, Skali H et al. Two-dimensional assesment of right ventricular function:an echocardiographic-MRI correlative study. Echocardiography 2007; 24:452-6
157. Forfia PR, Fisher MR, Mathai SC et al. Tricuspid annular displacement predicts survival in pulmonary hypertension. Am J Respir Crit Care Med 2006; 174:1034-41
158. Morcos P, Vick GW 3rd, Sahn DJ et al. Correlation of right ventricular ejection fraction and tricuspide annular plane systolic excursion in tetralogy of Fallot by magnetic resonance imaging. Int J Cardiovasc Imaging 2009; 25:163-70
159. La Gerche A, Jurcut R, Voigt JU. Right ventricular function by strain echocardiography. Curr Opin Cardiol 2010; 25:430-6
160. Leibundgut G, Rohner A, Grize L et al. Dynamic assessment of right ventricular volumes and function by real-time three-dimensional echocardiography:a comparison study with magnetic resonance imaging in 100 adult patients. J Am Soc Echocardiogr 2010; 23:116-26
161. van der Zwaan HB, Helbing WA, McGhieJS et al. Clinical value of real-time three-dimensional echocardiography for right ventricular quantification in congenital heart disease:validation with cardiac magnetic resonance imaging. J Am Soc Echocardiogr 2010; 134-40
162. Grewal J, Majdalany D, Syed I et al. Three-dimensional echocardiographic assessment of right ventricular volume and function in adult patients with congenital heart disease:comparison with magnetic resonance imaging. J Am Soc Echocardiogr 2010; 127-33
163. Maffessanti F, Muraru D, Esposito R et al. Age-, body size-, and sex-specific reference values for right ventricular volumes and ejection fraction by three-dimensional echocardiography. Circ Cardiovasc Imaging 2013:6:700-10
164. Scherrer-Crosbie M, Thibault H. Echocardiography in translational research:of mice and men. J Am Soc Echocardiogr 2008; 21:1083-92
165. Quinones MA, Otto CM, Stoddard M et al. Recommendations for quantification of Doppler echocardiography:a report from the Doppler Quantification Task Force of the Nomenclature and Standards Committee of the American Society of Echocardiography. J Am Soc Echocardiogr 2002; 15:167-84
166. Tschope C, Paulus WJ. Is echocardiographic evaluation of diastolic function useful in determining clinical care ? Doppler echocardiography yields dubious estimates of left ventricular pressures. Circulation 2009; 120:810-20
167. Bess RL, Khan S, Rosman HS et al. Technical aspects of diastology:why mitral inflow and tissue Doppler imaging are the preferred parameters ? Echocardiography 2006; 23:332-9
168. Bella JN, Palmieri V, Roman MJ et al. Mitralratio of peak early to late diastolic filling velocity as a predictor of mortality in middle-aged and elderly adults:the Strong Heart Study. Circulation 2002; 105:1928-33
169. Opdahl A, Remme EW, Helle-Valle T et al. Determinants of left ventricular early-diastolic lengthening velocity:independent contributions from left ventricular relaxation, restoring forces, and lengthening load. Circulation 2009; 119:2578-86
170. Mogelvang R, Sogaard P, Pedersen SA et al. Cardiac dysfunction assessed by echocardiographic tissue Doppler imaging is an independent predictor of mortality in the general population. Circulation 2009; 119:2679-85
171. Nagueh AF, Middleton KJ, Kopelen HA et al. Doppler tissue imaging:a noninvasive technique for evaluation of left ventricular relaxation and estimation of filling pressures. J Am Coll Cardiol 1997; 30:1527-33
172. Ommen SR, Nishimura RA, Appleton CP et al. Clinical utility of Doppler echocardiography and tissue Doppler imaging in the estimation of left ventricular filling pressures:A comparative simultaneous Doppler-catheterization study. Circulation 2000; 102:1788-94
173. Nagueh SF, Bhatt R, Vivo RP et al. Echocardiographic evaluation of hemodynamics in patients with decompensated systolic heart failure. Circ Cardiovasc Imaging 2011; 4:220-7
174. Rossvoll O, Hatle LK. Pulmonary flow velocities recorded by transthoracic Doppler ultrasound:relation to left ventricular diastolic pressures. J Am Coll Cardiol 1993; 21:1687-96
175. Rivas-Gotz C, Khoury DS, Manolios M et al. Time interval between onset of mitral inflow and onset of early diastolic velocity by tissue Doppler:a novel index of left ventricular relaxation. J Am Coll Cardiol 2003; 42:1463-70
176. Diwan A, McCUlloch M, Lawrie GM et al. Doppler estimation of left ventricular filling pressures in patients with mitral valve disease. Circulation 2005; 111:3281-9
177. Nagueh SF, Appleton CP, Gillebert TC et al. Recommendations for the evaluation of left ventricular diastolic function by echocardiography. J Am Soc Echocardiogr 2009; 22:107-33
178. Wang J, Khoury DS, Thohan V et al. Global diastolic strain rate for the assessment of left ventricular relaxation and filling pressures. Circulation 2007; 115:1376-83
179. Park S, Miyazaki C, Bruce C et al. Left ventricular torsion by two-dimensional speckle tracking echocardiography in patients with diastolic dysfunction and normal ejection fraction. J Am Soc Echocardiogr 2008; 21:1129-37
180. Wang J, Khouri DS, Yue Y et al. Left ventricular untwisting rate by speckle tracking echocardiography. Circulation 2007; 116:2580-6
181. Tsang TS, Barnes ME, Gersh BJ et al. Left atrial volume as a morphophysiologic expression of left ventricular diastolic dysfunction and relation to cardiovascular risk burden. Am J Cardiol 2002; 90:1284-9
182. Abhayaratna WP, Seward JB, Appleton CP et al. Left atrial size. Physiologic determinants and clinical applications. J Am Coll Cardiol 2006; 47:2357-63
183. Tsang TS, Abhayaratna WP, Barnes ME et al. Prediction of cardiovascular outcomes with left atrial size. Is volume superior to area or diameter ? J Am Coll Cardiol 2006; 47:1018-23
184. Mor-Avi V, Yodwut C, Jenkins C et al. Real-time 3D echocardiographic quantification of left atrial volume:multicenter study for validation with CMR. JACC Cardiovasc Imaging 2012; 5:769-77
185. Anwar AM, Soliman OII, Geleijnse ML et al. Assessment of left atrial volume and function by real-time three-dimensional echocardiography. Int J Cardiol 2008; 155-61
186. Todaro MC, Choudhuri I, Belohlavek et al. New echocardiographic techniquews for evaluation of left atrial mechanics. Eur Heart J Cardiovasc Imaging 2012; 13:973-84
187. Morris DA, Gailani M, Vaz Perez A et al. Left atrial systolic and diastolic dysfunction in heart failure with normal left ventricular ejection fraction. J Am Soc Echocardiogr 2011; 24:651-62
188. Kurt M, Wang J, Torre-Amione G et al. Left atrial function in diastolic heart failure. Circ Cardiovasc Imaging 2009; 2:10-5
189. Lam CS, Borlaug BA, Kane GC, et al. Age-associated increases in pulmonary artery systolic pressure in the general population. Circulation 2009; 119:2663-70
190. Yock PG, Popp RL. Noninvasive estimation of right ventricular systolic pressure by Doppler ultrasound in patients with tricuspid regurgitation. Circulation 1984; 70:657-62
191. Brennan JM, Blair JE, Goonewardena S et al. Reappraisal of the use of inferior vena cava for estimating right atrial pressure. J Am Soc Echocardiogr 2007; 20:857-61
192. Fisher MR, Forfia PR, Chamera E, et al. Accuracy of Doppler echocardiography in the hemodynamic assessment of pulmonary hypertension. Am J Respir Crit Care Med 2009; 179:615-21
193. Aduen JF, Castello R, Lozano MM et al. An alternative echocardiographic method to estimate mean pulmonary artery pressure:diagnostic and clinical implications. J Am Soc Echocardiogr 2009; 22:814-9
194. Yared K, Noseworthy P, Weymanj AE et al. Pulmonary artery acceleration time provides an accurate estimate of systolic pulmonary arterial pressure during transthoracic echocardiography. J Am Soc Echocardiogr 2011; 24:687-92
195. Abbas AE, Fortuin FD, Schiller NB et al. Echocardiographic determination of mean pulmonary artery pressure. AM J Cardiol 2003; 92:1373-6
196. Abbas AE, Fortuin FD, Schiller NB et al. A simple method for noninvasive estimation of pulmonary vascular resistance. J Am Coll Cardiol 2003; 41:1021-7
197. Rajagopalan N, Simon MA, Suffoletto MS et al. Noninvasive estimation of pulmonary vascular resistance in pulmonary hypertension. Echocardiography 2009; 26:489-94
198. Milan A, Magnino C, Veglio F. Echocardiographic indexes for the non-invasive evaluation of pulmonary hemodynamics. J Am Soc Echocardiogr 2010; 23:225-39
199. Schmidt AG, Gerst M, Zhai J et al. Evaluation of left ventricular diastolic function from spectral and color M-mode Doppler in genetically altered mice. J Am Soc Echocardiogr 2002; 15:1065
200. Schaefer A, Klein G, Brand B et al. Evaluation of left ventricular diastolic function by pulsed Doppler tissue imaging in mice. J Am Soc Echocardiogr 2003; 16:1144-9
201. Slama M, Ahn J, Peltier M et al. Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats. Am J Physiol Heart Circ Physiol 2005; 289:H1131-6
202. Prunier F, Gaertner R, Louedec L et al. Doppler echocardiographic estimation of left ventricular end-diastolic pressure after MI in rats. Am J Physiol Heart Circ Physiol 2002; 283:H346-52
203. Vahanian A, Alfieri O, Andreotti F et al. Guidelines on the management of valvular heart disease (version 2012). The joint Task Force on the management of valvular heart disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS). Eur Heart J 2012; 33:2451-96
204. Baumgartner H, Hung J, Bermejo J et al. Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice. J Am Soc Echocardiogr 2009; 22:1-23
205. Lancellotti P, Tribouilloy C, Hagendorff A et al. Recommendations for the echocardiographic assessment of native valvular regurgitation:an executive summary from the European Association of Cardiovascular Imaging. Eur Heart J Cardiovasc Imaging 2013; 14:611-44
206. Maffessanti F, Marsan NA, Tamborini G et al. Quantitative analysis of mitral valve apparatus in mitral valve prolapse before and after annuloplasty: three-dimensional intraoperative transesophageal study. J Am Soc Echocardiogr 2011; 24:405-13
207. Zamorano J, Cordeiro P, Sugeng L et al. Real time three dimensional echocardiography for rheumatic mitral valve stenosis evluation. An Accurate and Novel approach. J Am Coll Cardiol 2004; 43:2091-6
208. Marsan MA, Westenberg JJ, Ypenburg C et al. Quantification of functional mitral regurgitation by real-time 3D-echocardiography:comparison with 3D-veelocity-encoded cardiac magnetic resonance. JACC Cardiovasc Imaging 2009; 2:1245-52
209. Shanks M, Siebelink HM, Delgado V et al. Quantitative assessment of mitral regurgitation:comparison between three-dimensional transesophageal echocardiography and magnetic resonance imaging. Circ Cardiovasc Imaging 2010; 3:694-700
210. Thavendiranathan P, Phelan D, Thomas JD et al. Quantitative assessment of mitral regurgitation. Validation of new methods. J Am Coll Cardiol 2012; 60:1470-83
211. Zamorano JL, Badano LP, Bruce C et al. EAE/ASE recommendations for the use of echocardiography in new transcatheter interventions for valvular heart disease. J Am Soc Echocadiogr 2011; 24:937-65