Mechanical circulatory support in acute heart failure.

Acute heart failure (AHF) consists of a varied set of clinical syndromes characterized by sudden decrease in cardiac function and systemic hypoperfusion. The most serious manifestation of AHF is severe refractory cardiogenic shock (SRCS), which carries a mortality rate in the range of 50% to 80%.1,2 The immediate goal of therapy for SRCS is to restore systemic perfusion to levels that will avoid the development of secondary organ failure. Initial treatment of SRCS includes inotropic agents, vasodilators, diuretics, anticoagulants, volume management, and intra-aortic balloon pump (IABP) support; and for ischemic heart failure, prompt interventional or surgical revascularization is the standard of care. Despite aggressive treatment approaches for this challenging population, the long-term prognosis is poor and more advanced treatment options are necessary.3–5 Mechanical circulatory support technology that can restore normal levels of cardiac output with improved systemic perfusion helps to avoid end-organ damage and can have an important impact on survival for the AHF population. Ventricular assist devices (VADs) vary from large extracorporeal systems to small devices that can be inserted percutaneously. Surgically placed devices have the advantage of providing total cardiac output support; however, they require reoperation for left VAD (LVAD) removal. Continuous anticoagulative therapy is necessary for both surgically and percutaneously placed VADs; however, for surgically placed devices, there is usually a delay before starting the anticoagulation, due to risk of postoperative bleeding. This can result in thrombosis of the device, cardiac chambers, or aorta. The surgically placed VAD systems might be preferable for postcardiotomy shock, because these devices can provide uni- or biventricular support and enable an easy transition from cardiopulmonary bypass. For resuscitation before surgical intervention, percutaneous VAD systems can be inserted rapidly in the cardiac catheterization laboratory, yielding prompt restoration of end-organ perfusion. The percutaneous VADs are designed primarily for LVAD support and are best used in patients with SRCS after acute myocardial infarction, or for those with acute cardiac decompensation from other causes. The surgically placed VAD systems in use today include the Thoratec Paracorporeal Ventricular Assist Device (PVAD™) (Thoratec Corporation; Pleasanton, Calif), the CentriMag® blood pump (Thoratec), and the AB5000™ Circulatory Support System (Abiomed, Inc.; Danvers, Mass). The Thoratec PVAD and the AB5000 are pulsatile devices, whereas the CentriMag pump provides continuous blood flow by means of a rotating, magnetically levitated impeller. Direct cannulation of the vena cava, atria, aorta, or ventricles is necessary. These devices can provide 6 to 10 L/min of cardiac output, and, because they are located externally, they can be used in patients of various sizes. Cannulation methods are versatile, but the cannulas must be externalized through the chest wall. Because surgery for implantation and continuous anticoagulation are required, bleeding is a major complication during the use of these devices. They are not well suited for ambulatory use; therefore, these devices are ordinarily used for hours to weeks in duration. Percutaneously inserted VADs are less invasive, and support can be provided within a relatively short time. The IABP has been the most widely used circulatory assist device because of its ease and rapidity of use. The IABP has been used for treating all forms of AHF since the late 1960s and continues to be the first device used for AHF at most centers worldwide.6,7 Although clinical trials that show the IABP's efficacy have not been performed, more than 40,000 IABPs are used annually in the United States.7 The IABP is suitable only for patients who need low levels of support, because this device can provide no more than 1.5 L/min of cardiac output support. Cardiopulmonary support (CPS) with extracorporeal oxygenation has been used for about 4 decades, with varying success.8,9 Once used primarily in neonates and in a few adults for severe respiratory distress, CPS has become more widely used as improvements in oxygenator technology have been made. Although CPS can be used for SRCS, the level of complexity is high; this method is usually reserved for patients with the severe pulmonary failure that accompanies SRCS. The Impella® Recover 2.5 device (Abiomed) is used for temporary support and can provide a maximum blood flow of 2.5 L/min. The device is inserted via the femoral artery and is passed retrograde through the aorta and across the aortic valve. The axial-flow pump is positioned in the ascending aorta and aspirates blood from the left ventricle through the cannula. This device has been used for short-term support of patients with AHF and for high-risk percutaneous coronary intervention (PCI). Contraindications for Impella Recover 2.5 use are the presence of a mechanical aortic valve, peripheral vascular disease, and a severely calcified aorta. Clinical studies comparing support from the Impella device and the IABP in patients with cardiogenic shock showed that the Impella device could produce better hemodynamics, but there was no survival advantage over the IABP.10 The TandemHeart® LVAD (CardiacAssist, Inc.; Pittsburgh) consists of a small centrifugal-flow pump, a transseptal inflow cannula, and a standard arterial outflow cannula. When implanted, the device pumps blood from the left atrium to the femoral artery at a rate up to 5 L/min. Insertion requires expertise in transseptal cannulation but can be achieved in less than 20 minutes after the arrival of a patient in the catheterization laboratory. The TandemHeart device is used to stabilize patients in SRCS and provide brief LVAD support during high-risk PCI.11 Stabilization of patients in SRCS provides the opportunity for more complete diagnostics and precise therapeutic planning. Patients have been successfully bridged to myocardial recovery, heart transplantation, implantation of long-term LVADs, and corrective surgery. When the TandemHeart LVAD has been used to support patients in cardiac arrest, the survival rate has been 43% at 30 days and 37% at 6 months.12 In summary, the current use of percutaneously inserted VADs is leading to a paradigm shift in the treatment of SRCS. Supportive medical therapy, along with rapidly applied circulatory assistance, can help to avoid the development of multisystem failure and death. Unfortunately, due to the severity of illness with SRCS, randomized controlled clinical trials are not feasible. As a consequence of the availability of new blood-pump technology and well-trained teams, the restoration of adequate circulation in a short time might have an important impact on long-term survival in patients with SRCS.