CARDIAC ASSIST DEVICES

During the latter half of the twentieth century, physicians have had the capability to support the circulation with mechanical devices. Gibbon's efforts led to the first successful clinical use of cardiopulmonary bypass (CPB) in 1952. 16 This heart-lung bypass system was rapidly employed to temporarily support part or all of the circulation during cardiac operations. However, early efforts to support acute myocardial infarction shock patients with CPB were unsuccessful, 37 giving rise in the early 1960s to the concept that CPB was not well suited for the treatment of patients with cardiogenic shock who would require support for several days to weeks. It was obvious that another method of temporary mechanical circulatory support was needed to maintain patients long enough to allow myocardial recovery. Conversely, CPB in the form of extracorporeal membrane oxygenation (ECMO) was used successfully in the mid-1970s for the treatment of severe respiratory insufficiency in infants and children. For this indication, the durations of support were usually less than 10 days. More recently, peripheral CPB has been used extensively to resuscitate children and adults during episodes of cardiac arrest, but durations of support for this indication are usually less than 72 hours. Initial efforts with ventricular assist devices (VADs) were concentrated at designing integrated systems that would provide isolated left ventricular support. 6,7 In 1968 diastolic counterpulsation with an intra-aortic balloon pump (IABP) was developed, and these devices were commercially available by the early 1970s. 19,27 The introduction of the IABP reduced the need for temporary VADs, but there remained a group of critically ill patients with very low cardiac outputs in whom IABPs were ineffective. Throughout the decade of the 1970s, technologic refinements led to more elaborate and innovative devices. These systems could provide assistance to a failing ventricle for longer periods of time with less blood component damage. These second-generation systems included external and internal pneumatic VADs, pneumatic total artificial hearts (TAHs), electrical left ventricular assist devices (LVADs), percutaneous CPB, and an implantable continuous flow device. 2,3,9,15,28,31,32,34 Over the last decade, improvements in patient selection as well as clinical and device management have led to growth in the use of mechanical circulatory support. In the bridge to transplant patient population, survival rates have increased and morbidity rates are on the decline. 25,26,29,36 A small group of patients have been successfully supported for longer than 1 year with different devices, and successful perfusions of longer than 3 months are now commonplace. Patients supported with portable/wearable LVADs have been discharged from the hospital to await cardiac transplantation. Some of these patients have returned to work with the VAD in place. In some United States centers and in centers outside the United States, VADs have been used as an alternative to cardiac transplantation. 10,14,21,22 The indications for VAD support are varied, and several devices are now commercially available. Other systems are available with special exemption from the Food and Drug Administration (FDA) for investigational use. Some devices have been designed for very specific, limited circumstance, whereas others are capable of multiple applications.