Ventricular-Assist Devices and Total Artificial Hearts

Abstract

An estimated 5.2 million people in the United States suffer from end-stage congestive heart failure (CHF), and it is the primary cause of approximately 58,000 deaths each year.1 Cardiac transplantation is the only definitive treatment for end-stage CHF, but over the past 10 to 15 years, there has been a relatively fixed discrepancy between donor availability (approximately 2,000 to 2,500 donor hearts transplanted annually) and the need for transplant. This has led to increased waiting times for transplantation, often approaching a year or more. The discrepancy also requires transplant centers to carefully select potential recipients to optimize posttransplant survival, excluding many of the sickest patients from the opportunity to receive a transplant. Ventricular-assist devices (VADs) can bridge the gap between need for cardiac replacement and availability of transplantable organs. VADs are surgically implanted blood pumps whose purpose is to either augment or replace the function of a diseased heart. Their most common indication is as a “bridge to transplant” (BTT), allowing recovery of perfusion and stabilization of end-organ function in patients requiring heart transplantation who are too ill to be supported either medically (with oral heart failure regimens or intravenous inotropes) or with short-term mechanical assistance via an intra-aortic balloon pump (IABP) while they await a suitable donor. BTT accounts for approximately 78% of implants, according to International Society for Heart & Lung Transplantation (ISHLT) data for 2002–2004.2 In patients deemed transplant-ineligible, VADs are increasingly being used for “destination therapy” (DT), in which the device is implanted as a permanent alternative to transplant (11.9% of recipients in the ISHLT registry). Less commonly, they can be used as a short-term “bridge to recovery” (BTR), in which the expectation is to stabilize patients with acute heart failure while their native heart function recovers, subsequently allowing explantation of the device without transplantation (5.3% of implants in the ISHLT registry; 4.4% of implants were other/not specified). Although a wide variety of VADs are in use, all function by the same principle: blood is rerouted from the dysfunctional ventricle into the pump, which then mechanically propels it into circulation, doing the work the native ventricle can no longer perform. VADs may be used to augment or replace only the left ventricle (LVADs), only the right ventricle (RVADs), or both (LVAD+RVAD=BiVAD). A total artificial heart (TAH) provides complete biventricular support by replacing the native ventricles, which are excised. Blood is then transferred directly from the patient’s atria into the device. Common potential clinical problems with VADs include bleeding, thrombosis or thromboembolism, and infection. Potential mechanical problems include malfunction or failure of the device itself or of an external component, such as a controller, drive unit, monitor, or battery. Since VADs are cardiac life support systems, major mechanical failures can have devastating consequences.