Renal Function During Cardiac Mechanical Support and Artificial Heart

Indications and Types of Mechanical Cardiac Supports

Severe cardiogenic shock that is not responsive to medical therapy is a unified indication for considering mechanical cardiac support. Based on the cause of cardiac failure and whether the expected duration of support is short term or long term, various modalities may be used. Intraaortic balloon pump (IABP) counterpulsation is a temporary form of inotropic support. Insertion of IABP is used commonly in cardiogenic shock resulting from acute myocardial infarction, in association with cardiopulmonary bypass surgery, or high-risk coronary angioplasty. Influence of IABP on renal function can be divided into two major categories. First, procedure-related complications may occur, such as renal artery occlusion, dissection, or atheroembolic and thromboembolic complications. These anatomic and embolic events may lead to a spectrum of abnormalities, including mild temporary renal dysfunction, to a more catastrophic event such as renal infarction and cortical necrosis. Second, preoperative IABP support has been demonstrated consistently to be an independent risk factor of severe postoperative acute renal failure (ARF). Whether the effect is causal, via direct interference of renal blood flow/embolic phenomenon, or IABP is a surrogate for the severity of hemodynamic state during the preoperative period remains unclear. However, it can be used as one of the key predictors to identify patients who are at a higher risk of developing postoperative kidney injury.

Over the past few decades there have been tremendous advances in other types of mechanical cardiac support such as VAD. The discussion in the following sections focuses on types of devices, selection of patients, and renal and related patient outcomes in VAD recipients.

Ventricular assist devices are “blood pumps” and can be classified in multiple ways. One of the ways to classify these devices is indicated in Table 116.1 . In terms of expected response, patients can be categorized broadly as follows: (1) BTT: patients actively listed for transplant who would not survive or would develop progressive end-organ dysfunction from low cardiac output before an organ becomes available; (2) bridge to candidacy (BTC): for patients not currently listed for transplant, but who do not have an absolute or permanent contraindication to solid-organ transplant; (3) DT: for patients who need long-term support but are not eligible for transplant because of one or more relative or absolute contraindications; (4) bridge to recovery (BTR): for patients who require temporary circulatory support, during which time the heart is expected to recover from an acute injury, and mechanical support then is removed without need for transplant; (5) bridge to bridge: many are receiving temporary percutaneous circulatory support, sometimes referred to as bridge to bridge (BTB), as a way to support circulation and triage the sickest patients for eventual durable LVAD.

Indications for ventricular assist devices include postcardiotomy shock, cardiogenic shock as a consequence of myocardial ischemia, decompensated heart failure regardless of transplant eligibility, myocarditis, and ventricular arrhythmias refractory to treatment.

Patterns of Use of Ventricular-Assist Device

The contemporary knowledge regarding the use of VAD is derived from a registry (INTERMACS: A global International Society for Heart and Lung Transplantation Registry for Mechanical Circulatory Support). Based on this data source, between 2006 and 2014, 15,745 patients who received a US Food and Drug Administration (FDA)–approved MCS device were entered into the INTERMACS database. The registry includes more than 15,000 patients from 158 participating hospitals. The predominant use of continuous flow (CF) technology is evident, with more than 90% of patients receiving an intracorporeal CF pump. During 2014, approximately twice the number of axial-flow CF pumps, as compared with centrifugal-flow CF pumps, was entered into the registry. The progressive increase in VADs implanted for destination therapy (DT) has plateaued (46% DT implants in 2014). Thirty percent of patients were listed for heart transplantation at the time of device implant (BTT), and an additional 23% were implanted with an anticipated possibility of listing (BTC).