Introduction to the Cardiac Catheterization Laboratory

Cardiac catheterization is the insertion and passage of small plastic tubes (catheters) into arteries and veins to the heart to obtain x-ray pictures (angiography) of coronary arteries and cardiac chambers and to measure pressures in the heart (hemodynamics). The cardiac catheterization laboratory performs angiography to obtain images not only of coronary arteries to diagnose coronary artery disease but also to look for abnormalities of the aorta, pulmonary, and peripheral vessels (1). In addition to providing diagnostic information, the cardiac catheterization laboratory performs catheter-based interventions (e.g., angioplasty with stent implantation, now called percutaneous coronary intervention [PCI]) or catheter-based treatments of structural heart disease (e.g., transcatheter aortic valve replacement [TAVR]) for both acute and chronic cardiovascular illness. Table 1 lists procedures that can be performed with coronary angiography while Figure 1 shows common vascular access routes for cardiac catheterization.

Table 1. Procedures Performed in the Catheterization Laboratory

Figure 1. Common Cardiac Catheterization Vascular Access Routes

Cardiac catheterization is performed in a hospital or outpatient laboratory (2). A small catheter is inserted into an artery or vein either in the leg or the arm and passed to the heart.  A 0.038” diameter safety spring guidewire facilitates the passage of this catheter through the vessels without pain or injury. The catheter is guided by fluoroscopy and positioned to inject x-ray contrast media and acquire cine x-ray pictures of the coronary arteries and the ventricular chambers, and measure pressures and oxygen content in various locations to understand the function and adequacy of blood flow through the heart muscle.

Cath lab procedures can be divided into diagnostic studies and therapeutic interventions (Table 1). The most common diagnostic studies include angiography, a term applied to the radiologic imaging of the coronary arteries (angio = vessel, graph = picture).  Ventriculography is imaging of the left ventricle (LV), the main pumping chamber of the heart.

In addition to coronary angiography, other imaging studies include aortography, peripheral vascular angiography, and pulmonary angiography. Pressures in the heart and great vessels are measured through the hollow catheter lumens, yielding hemodynamic information. For patients with varying degrees of coronary artery atherosclerotic obstructions, the pressure and flow across a specific coronary artery stenosis can be measured with exceedingly small pressure sensor 0.014” diameter guidewires.

On the therapeutic side, the most performed intervention is that of percutaneous coronary intervention (3). PCIs involve the use of a small balloon catheter, shaped like a hot dog, advanced inside an artery with a stenosis (narrowing). The balloon is inflated to expand the narrowing and the balloon catheter is then exchanged for a stent.  Stents are metal scaffolds (like a ballpoint pen spring). The stent is then positioned in the pre-dilated stenosis and expanded, holding open the narrowed artery. New tissue grows over the implanted stent over several months, creating a new conduit for blood flow.

Other catheter-based techniques are available to open heavily calcified arteries. These catheter-based interventions use small grinding burrs to enlarge calcified stenoses and are known as rotational atherectomy techniques. Thrombus or blood clots that form in vessels can be aspirated or dissolved with thrombolytic (lytic = dissolving) medications.  For patients who have a pericardial effusion, clinicians can extract the fluid from the pericardial fluid-filled space around the heart (i.e., the pericardial sac), a technique called pericardiocentesis. For patients with elevated pulmonary pressure due to heart failure, small pulmonary artery monitoring sensor chips can be implanted inside the pulmonary arteries (a method currently called CardioMEMS).

Structural heart disease interventions have expanded into a unique field of endeavor, permitting the percutaneous implantation of heart valves, shunt closures devices, and clips to narrow leaking mitral and tricuspid valves without open heart surgery. Some patients with familial hypertrophic cardiomyopathy, an excessively thick heart muscle that can obstruct the heart, can be treated without surgery by alcohol septal ablation.  Peripheral vascular disease can be treated in the same way coronary stenoses are treated with stents PCI-like

Cardiac catheterization is used to identify atherosclerotic coronary or peripheral artery disease, abnormalities of heart muscle (infarction or cardiomyopathy), and valvular or congenital heart abnormalities. In adults, the procedure is used most to diagnose coronary artery disease. Other indications depend on the history, physical examination, electrocardiogram, cardiac stress test, echocardiographic results, and chest radiograph. Indications for cardiac catheterization are summarized in Table 2.

Table 2. Indications for Cardiac Catheterization

For most patients, diagnostic cardiac catheterization is performed as an elective procedure. It should be deferred if the patient is not prepared either psychologically or physically.

If the patient’s condition is unstable because of a suspected cardiac disorder, such as acute myocardial infarction, catheterization must proceed. In the event of decompensated congestive heart failure in patients with acute unstable coronary syndromes, rapid medical management is needed. Although a patient must be able to lie flat for easy catheter passage, patients with acute cardiac decompensation may benefit more from aggressive management in the catheterization laboratory where intubation, LV mechanical support devices, and vasopressors can be instituted rapidly before angiography and a rapid decision made for revascularization.

Contraindications to cardiac catheterization include fever, anemia, electrolyte imbalance (especially hypokalemia predisposing to arrhythmias), and other systemic illnesses needing stabilization. The clinical necessity of cardiac catheterization also should be carefully considered when the diagnostic information or therapeutic intervention from the procedure would not meaningfully impact the management of a patient.

For diagnostic catheterization, an analysis of the complications in more than 200,000 patients indicated the incidences of risks: death, ~0.2%; myocardial infarction, ~0.05%; stroke, ~0.07%; serious ventricular arrhythmia, ~0.5%; and major vascular complications (thrombosis, bleeding requiring transfusion, or pseudoaneurysm), ~1% (Table 3). Vascular complications occurred more often when the brachial approach was used and least when the radial approach was used. Risks are increased in well-described subgroups such as those with diabetes mellitus, renal failure, or heart failure (4).

Table 3. Complications and Risks

• Hematoma (1% to 10%)
• Pseudoaneurysm (1% to 6%)
• Arteriovenous fistula (<1%)
• Vessel laceration (<1%)
• Free bleeding
• Intimal dissection
• Ante- or retro-grade
• Acute vessel closure (<1%)
• Thrombosis (small artery lumen)
• Retroperitoneal hemorrhage (0.2% to 0.9%)
• Nerve damage
• Infection
• Limb ischemia

New learners in the cardiac cath lab must appreciate the steps in performing procedures and often go through this list of activities to understand the procedure (Table 4). The first step is to understand the laboratory set-up and its routine in order to assist and to observe the operators before clinicians become principal operators themselves. Next, clinicians learn about vascular access from either the femoral or radial approach (5), how to insert catheters and correctly position them in the right place at the right time, how to perform angiography and ventriculography, and then learn to understand and apply hemostasis or control of the bleeding from the puncture sites that were just made. The process concludes with post procedure care, which is the administration of fluids, adjustment of medications, and scheduling of follow-up visits. The operators in the cath lab must document correctly and thoroughly to bill and be paid for this procedure.

Table 4. The Learners’  Keys to the Catheterization Lab

1. Lab set-up and routine, assist and observe
2. Vascular access
3. Catheter insertion and placement
4. Angiography
5. Ventriculography
6. Hemostasis
7. Post-procedure care
8. Documentation and billing

The cardiac cath lab (Figures 2A and 2B) uses an x-ray system mounted on a gantry, a C-shaped armature which holds the x-ray tube and the flat plate image intensifier permitting movement around the patient who lies on a platform or table between the x-ray generator and image panel (x-ray collector). The x-rays pass from below the table through the patient up to the image intensifier. The images are digitally displayed on a monitor and stored in the digital archive system for review. The image monitors show the position of the equipment, the arteries, and the structures within the chest as the x-rays pass through the patient in real time.

Figure 2. Equipment in the Catheterization Lab

The nomenclature of the angulations is important for doctors to communicate among themselves and understand what has been done as well as the importance of looking at the arteries in different projections (Figure 3). When the tube that lies under the table emits x-rays up to the image collector, which is on top of the patient, the anterior-posterior (AP) projection in the center of the screen is named. When the intensifier is moved to the right of the patient, it gets the name right anterior oblique (RAO) and when moved to the left side of the patient, it gets the name left anterior oblique or LAO. In Figure 3, the bottom two images show that when the x-ray tube and image intensifier are angled toward the head of the patient, the name given is cranial angulation and when the image intensifier is rotated down toward the foot of the patient, it is called caudal angulation.  These names are used to understand the projections and display the arteries for the best treatment of the disease.

Figure 3. Nomenclature for Radiographic Projections

An example of the biplane angiographic system is shown in Figures 4 and 5, with the image intensifiers opposing planes to one another.  Biplane imaging provides more information for the same single injection of contrast media.

Figure 4. Biplane System in the Catheterization Laboratory

Figure 5. Radial Cardiac Catheterization in Biplane Laboratory  

Good technique during cardiac catheterization reduces the radiation exposure to both the patient and the operator (6). Modern x-ray equipment now automatically sets the exposure by adjusting the kilo voltage, milliamps, and seconds of the x-ray exposure to the patient (Figure 6).

Figure 6. X-ray Equipment

Correct positioning of the image intensifier relative to the patient and the x-ray generator reduces x-ray dose. Radiation dose reduction depends on distance.  Dose decreases with the square of the distance from the x-ray source. For example, as seen in Figure 7, operator #1 receives twice as much x-ray as operator #2, and that for the different procedures such as directional coronary atherectomy, PTCA and double-vessel PTCA, the x-rays exposure is consistently higher (7).

Figure 7. Distance and Radiation Dose

Cardiac catheterization is performed from both the femoral artery and radial artery (Figure 1). Typically, the operator(s) stand on the right of the patient, the right wrist is instrumented, and a small catheter is inserted (Figure 4). Should the need arise, the operator can access the femoral artery as well having already prepared the sterile area in the groin. Note the x-ray shield limiting operator exposure has biplane C-arms that are put in a position to get the maximum amount of information for each injection.

Currently, radial artery access is preferred because it is a very safe and highly successful methodology (Figure 8). The artery is easily compressed with no major adjacent nerves, and this easy arterial compression reduces the chances of having a pseudoaneurysm or hematoma in the hand, unlike that of the femoral approach.

Figure 8. Radial Artery Anatomy 

Although a rare occurrence, the major complication of radial artery catheterization would be bleeding into the forearm producing a compartment syndrome.  The use of ultrasound guidance makes transradial access easier and reduces number of puncture attempts (Figure 9).

Figure 9. Ultrasound-guided Radial Access 

The technique for performing radial artery access (Figures 10A and 10B) begins with palpation of the radial artery (with or without ultrasound). Lidocaine is injected superficially over the artery followed by small cannula introduction. When blood is encountered, a soft spring or plastic-coated guidewire is advanced through the cannula into the artery. A sheath is then inserted over the guidewire into the artery and then flushed with a vasodilator drug to prevent spasm of the artery (8).  On occasion, the radial artery will be too small to use, and the ulnar artery may be suitable (Figure 11).

Figure 10. Radial Artery Access and Sheath Introduction

Figure 11. Ulnar Artery Insertion

The femoral artery approach was the dominant method beginning in the 1970s (Figure 12).

Figure 12. Femoral Artery Anatomy 

Not only is the femoral artery large and easy to reach, it accommodates large diameter equipment for performance of complicated percutaneous coronary intervention and for use of other vascular and left ventricular support devices such as the intra-aortic balloon pump. Angiography of the femoral artery illustrates several important features (Figure 13).

Figure 13. Femoral Angiography 

Because the common femoral artery may have anatomic variations, secure knowledge of the location is often missing. Ultrasound access has superseded reliance on physical landmarks or even use of a metal marker (Figure 14).

Figure 14. Fluoroscopy Use

The steps involved in inserting the femoral sheath (Figure 15) start with palpation and injection of lidocaine using ultrasound to guide the entrance. The needle is seen to enter the artery and then the sheath is inserted over the guidewire into the femoral puncture site much like that described for radial access.

Figure 15. Inserting the Femoral Sheath

Complications of femoral artery access range from 2% to 10% and included retroperitoneal bleeding, pseudoaneurysm, fistula, laceration, dissection, and acute clotting of the vessel.  Given the comparative safety of the radial approach, femoral access for routine diagnostic angiography should be carefully considered.

After the procedure, hemostasis for closure of the puncture site is required. For the radial approach, a plastic band with a compression balloon is enough. For femoral artery hemostasis, artery compression with manual pressure or closure with a vascular closure device applied to the artery is extraordinarily successful. However, the patient is confined to bed for at least 4 to 6 hours. Chances of bleeding with femoral puncture are higher than radial access despite closure devices.  Nonetheless, the safety of the femoral approach still is particularly good and is often used for our large vascular equipment and certainly for structural heart disease interventions.

Coronary angiography is the moving image of the coronary arteries when filled with iodine contrast media.  Multiple projections are required to visualize branches and lesions of the arteries seen in two-dimensional planes. The nomenclature of these angulations or projections was discussed earlier.

Recently, computer tomography-angiography (CTA) has been shown to  provide still frame images not only of the lumen of the coronary arteries (Figure 16) but also additional information on the structure of the arterial walls and surrounding structures. CTA is now able to provide the physiologic impact of stenoses in the coronary by applying fractional flow reserve theory and computational fluid dynamic calculations to yield valuable information for treatment decisions.

Figure 16. Coronary Artery Imaging

Cardiac catheters used in coronary angiography are shown in Figure 17.  These catheters are the most used in cardiac catheterization and designed to be positioned from the leg approach but can be used from the radial as well. These catheters would sit in the coronary artery with relative ease.

Figure 17. Angiographic Catheters

Interpretation of angiograms depends on an understanding of the cardiac anatomy (Figure 18).

Figure 18. Cardiac Arteries and Veins

The C-arm gantry is positioned to display the coronary arteries in the angulations discussed previously to permit accurate interpretation of the course, connections, and diseased segments within the artery (Figure 19). Because the branches of the coronary arteries are like roots of a tree and come rising from the aorta in a three-dimensional arrangement, the two-dimensional imaging of the angiographic picture-taking process requires rotation of the x-ray camera around the heart in different angles to improve visualization free from vessel overlap.

Figure 19. Anterior Oblique Views

Angiography can show a critical, life-threatening narrowing in the distal part of the left main segment (Figure 20). Normally, the coronary artery is smooth and tapers gradually from the aorta to the apex of the heart. When atherosclerotic obstructions appear in the vessel, a lucency or irregularity in the contrast-filled artery is present. A narrowing of the left main segment indicates critical compromise of the left anterior descending artery, the circumflex artery, and the intermediate ramus branch.  This lesion is one of the few life-threatening narrowings that people may have; it usually presents with pain at rest and requires immediate intervention with either angioplasty or bypass surgery.

Figure 20. Cineangiography of Stenosis

Another major part of a cardiac catheterization procedure is the identification of LV function based on wall motion during cineangiography (Figures 21 and 22). The left ventriculogram or picture of the left ventricle is obtained by injecting contrast into the left ventricular chamber with a pigtail catheter and observing the contraction of the anterior, anterior lateral, apical, diaphragmatic, and posterior basal segments. In the left anterior oblique projection, the lateral septal walls can be seen.

Figure 21. Wall Segments

Figure 22. Wall Segments: Cineangiography

Left ventriculography is used to support decisions on revascularization. After ventriculography, angiographers review the pressure inside the ventricle from the LV catheter as an estimate of the efficiency of LV ejection and the ability of the muscle to provide adequate cardiac output (Figure 23).

Figure 23. Left Ventriculography

Right heart catheterization involves cannulation of a vein to access pressures, oxygen saturations, and cardiac output. A specialized catheter with a balloon tip is passed up the venous system to the right atrium, right ventricle, and pulmonary arteries. The right heart catheterization is done in common with left heart catheterization. Right heart cath is a routine procedure for teaching centers and it is part of special studies and research to include as a complete hemodynamic data set as possible for these studies. Indications for right heart catheterization are listed on Table 5.

Table 5. Indications for Right Heart Catheterization

• Etiology of dyspnea
• Confirm echocardiographic findings
• Confirm new clinical findings
• Routine for teaching centers
• Special studies and research

Angina pectoris or chest pain of myocardial infarction due to obstructive coronary artery disease can be well treated by percutaneous revascularization using stents (Figure 24).

Figure 24. Percutaneous Coronary Intervention 

An example of this case is shown in Figure 25 in a patient with a right coronary artery that is 100% occluded with a thrombus or clot forming at the site of a ruptured plaque. The PCI technique employs a specialized guide catheter positioned in the opening of the coronary artery (9). A guidewire is introduced into the artery and passed through the blocked segment of the coronary artery. A balloon and stent are then inserted to expand the blockage, leaving this artery fully patent and relieving the patient’s complaints. Within 6 months, the lining of the vessel covers over the stent for a successful restoration of blood through this vessel.

Figure 25. Coronary Stenting for ST-Elevation Myocardial Infarction 

In the last decade, several advanced catheter-based techniques have been  used to imaging the coronary artery. Pressure and flow sensor 0.014” guidewires are utilized to determine the translesional hemodynamics to define flow limitations and indications to perform PCI when other objective data of ischemia is absent (Figure 26) (10-13).

Figure 26. Imaging and Hemodynamic Data

Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) imaging use ultrasound or light to produce cross sections of the vessel with reconstruction of the lengthwise view of the vessel and lumen. IVUS has a resolution of 150 µm or about half of a pencil lead in diameter, while OCT has a resolution of about 10 µm or 10x that of IVUS.  In Figure 26, the ultrasound image shows the vessel opening and the structure around it by the darker line and the eccentric plaque that sits from about 6 o’clock to 11 o’clock in distribution. Below that image can be seen the opening of the coronary artery with metal struts sending off two black rays, which are the shadows cast by these metal struts. The struts at 3 o’clock and 6 o’clock have small clots sitting on the surface that are invisible during angiography and probably of little or no consequence but are very informative as to the processes going on with some arteries, which may cause problems later.

To measure blood flow across the lesion, a pressure sensor guidewire would be inserted. Pressure distal to the stenosis (Pd) can then be compared to normal coronary artery pressure, which is the same as aortic pressure (Pa), measured in the guide catheter (14). In the absence of a blockage, Pd and Pa are the same. The percentage of normal flow across a stenosed artery is determined by the ratio of these pressures (Pd/Pa) during minimal and fixed resistance that occurs during maximal flow.  This ratio is called fractional flow reserve, and values >80% (0.80) are considered non-flow limiting (15). Similar data have been acquired with non-hyperemic pressure ratios, like instantaneous wave-free ratio.  Translesional physiology provides guidance for best practices and best long-term outcomes for patients considered needing revascularization.  These important tools are now being used daily worldwide in many cath labs.

For patients with aortic valve narrowing or stenosis, the only treatment until about 10 years ago was open heart surgery with valve replacement. Today, transaortic valve implantation is performed percutaneously and has been found equivalent to surgery in most patients (Figure 27). After appropriate assessment and artery and valve measurements, a TAVR catheter is introduced from the leg artery, taken around the aorta, and put across the aortic valve. The balloon on the catheter is inflated, expanding the stent and implanting it into the calcified native aortic valve. The balloon is then deflated, and the catheter removed, leaving behind a functioning and brand-new aortic valve providing dramatic symptomatic relief for patients with aortic stenosis and narrowed aortic valves. This methodology is now advancing into treatment of valves of different configurations and different etiologies. In addition, techniques are underway to treat the mitral valve for leakage and/or narrowing.

Figure 27. Transaortic Valve Implantation 

Finally, it is expected that cath labs of the future will integrate all imaging, pressure, and computational algorithms to detect coronary and valvular pathologies.