Ventricular assist devices (VADs) are increasingly being placed in patients with severe heart failure and cardiogenic shock. LVADs are essentially artificial hearts that assist the circulation and used to treat patients with advanced heart failure. These patients have deteriorating New York Heart Association class IV heart failure despite inotropic and/or intra-aortic balloon pump support, usually with end-organ dysfunction (left ventricular ejection fractions less than 25% and maximum oxygen consumption less than 15 mL/kg/min).
VADs were initially inserted as a bridge to transplantation. The decreased availability of donor hearts means that an increasing number of patients require left VAD (LVAD) support for survival when their clinical status deteriorates. LVADs are life-saving in these patients with deteriorating conditions who would otherwise die before a donor heart becomes available. These devices also improve secondary organ function for transplantation, reduce pulmonary hypertension, and allow for improved nutritional status. The evidence suggests that LVAD unloading, especially when combined with pharmacological treatment, can lead to recovery of myocardial function.
HISTORY AND VAD EVOLUTION
Cardiopulmonary bypass (CPB) paved the way for early mechanical support systems. The inability to wean some patients from CPB stimulated interest in more prolonged mechanical support. In 1971, DeBakey reported the first successful clinical application of a true VAD which was a pneumatically driven diaphragm pump. This device was first applied in a woman who could not be weaned from CPB following valve replacement and was supported for 10 days with a paracorporeal circuit from her left atrium to right axillary artery. She was then weaned successfully and subsequently discharged from the hospital. In the early 1980s, cardiac transplantation became widely utilized, but it was clear that the need for hearts was greater than donor availability. As a result, there was a strong incentive to develop better assist devices. In 1984, Portner and colleagues reported the first successful cardiac transplant following bridging with a Novacor LVAD at Stanford.
VADs can be broadly divided into first-, second-, and third-generation devices:
First-generation VAD—First-generation VADs are pulsatile volume displacement pumps (HeartMate I) that provide excellent hemodynamic support. HeartMate I has been placed in over 5000 patients. It is made of titanium with a polyurethane diaphragm and has a pusher-plate actuator. It can be powered pneumatically or electrically. A cannula is placed in the apex of the left ventricle and blood flows through a Dacron conduit in which there is a porcine valve to the pump, and returns into a Dacron outflow graft through another porcine valve to the ascending aorta. Power is supplied by two external batteries and an external controller that weighs less than 300 grams. This device can pump 4–10 L/min. Device limitations include large size, presence of a large diameter lead (higher infection risk), audible pump, and the need for a medium to large body habitus. These VADs have limited durability as they are only designed for up ...