Future of VADs

Technological advancements in ventricular assist device (VAD) technology have led to significant improvement in clinical outcomes in the field (1-3). These technological advancements have significantly improved clinical outcomes to the degree that VAD therapy now competes with heart transplantation in the short term. Despite these significant advancements, there are several important hurdles that the technology must overcome for this therapy to surpass what is possible with heart transplantation. A major limitation with current devices is the risk of stroke and bleeding. Results from current clinical trials still demonstrate a risk of stroke of approximately 8 to 10% with the current generation of left ventricular assist devices (LVADs) (1-3). This risk exceeds the risk of stroke in the population of advanced heart failure (HF) patients by 2- to 3-fold (4). For LVAD therapy to be an effective therapy to expand to a less ill population with ambulatory, non-inotrope-dependent New York Heart Association class III HF, stroke risk must be reduced close to that observed in the advanced HF population.

The other significant technical hurdle to resolve is the risk of device-associated infections, particularly those associated with the percutaneous driveline (5). Elimination of the percutaneous driveline with development of a totally implantable pump using wireless energy transfer is now feasible. Although this type of technology introduces new issues with pumps, such as device reliability of implantable internal components, the elimination of the percutaneous lead is an important step in promoting greater adoption of VAD therapy.

Current pump designs operate in a fixed speed mode of operation and do not autonomously alter speeds to adapt to changes in physiological conditions of the patient. This type of pump mode of operation has significant limitations. Autonomous speed control algorithms are desperately needed to permit greater support during times of high physiological demand and decreasing support during periods of senescence (6). Autonomous speed control algorithms that permit periodic opening of the aortic valve could potentially reduce the risk of development of aortic insufficiency, which has been a serious issue for successful long-term device support. Incorporation of physiological data through use of pressure sensors in pump speed control may represent one potential method to achieve autonomous operation (6).

Although not associated with an increase in mortality, bleeding events – which affect up to 50% of patients – contribute to significant morbidity during LVAD support (7,8). Pump designs that preserve von Willebrand protein function through reduction of shear forces is desirable although the potential to achieve reduction in bleeding from a reduction in shear force is unlikely. The more practical approach would be development of pumps that are more resistant to pump thrombus formation that could permit significant reduction in the levels of anticoagulation and antiplatelet therapy needed to minimize thromboemoblic events.

Right HF is a serious and prevalent adverse event occurring during LVAD support and may manifest in up to 30% of patients (9). Right HF increases morality, adversely effects quality of life, and reduces the chance for successful heart transplantation in bridge-to-transplant applications. The survival of patients requiring biventricular support is only approximately 50% at 6 months compared to survival of almost 85% with patients requiring LVAD support alone. Technological advances are needed in the area of small implantable VAD systems that could support both right and left ventricles.  These types of systems would require pumps that operate effectively in different physiological environments with the right-sided pump exposed to a low-pressure system and the left pump exposed to a high-pressure system while autonomously maintaining appropriate flow balance.  A single control system would need to be developed to avoid the need to carry two separate control systems. Addressing stroke, bleeding, autonomous control systems, totally implantable pumps, and biventricular support systems represent the next major hurdles for device companies and scientist to overcome for VAD therapy to replace heart transplantation as a long-term circulatory support option.