Fig. 14.1
(a) Survival curves for patients who had normal albumin levels (≥3.5 g/dL), moderate hypoalbuminemia (2.5–3.5 g/dL), and severe hypoalbuminemia (<2.5 g/dL) before undergoing implantation of a continuous-flow left ventricular assist device. (b) Survival curves for patients who had preoperative prealbumin levels ≥17 or <17 after implantation of a continuous-flow left ventricular assist device. (c) Survival curves for patients who had preoperative MELD score ≥17 or <17 after implantation of a continuous-flow left ventricular assist device
Contraindications for LVAD implantation include irreversible end-organ failure, particularly renal, hepatic, and respiratory, which are uniformly independent predictors of poor outcome [5–7]. Severe, unrecoverable neurological dysfunction is also a contraindication for LVAD implantation. Systemic sepsis poses a significant risk to patients who undergo LVAD implantation because it can cause a profound, refractory, vasodilatory state and an increased incidence of infections such as device-related endocarditis [8, 9]. Patients who have had sepsis should have two negative blood cultures over a 1-week period before LVAD implantation to indicate that the infection has been cleared from the bloodstream. Another contraindication for LVAD implantation is the presence of a malignancy leading to a life expectancy of less than 2 years. Each of these cases requires individual attention and evaluation for appropriate decision-making. A patient with human immunodeficiency virus (HIV) infection who is compliant with medical therapy and who has a normal CD4 count and undetectable viral levels should be considered for LVAD implantation .
Types of Devices
Using Short-Term MCS
Data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) patient profiles indicate that mortality and morbidity rates are worst in profile 1 patients (critical cardiogenic shock). Because INTERMACS profile 1 patients have a poor survival (ranging from 65 to 76% at 1 year), the patient population undergoing LVAD implantation is shifting from INTERMACS profile 1 toward those with less severe illnesses such as INTERMACS profiles 2 or 3. In 2008, 30% of LVAD implantations in the INTERMACS registry were performed in profile 1 patients, whereas that percentage decreased to 15% in 2013. Therefore, short-term MCS has become a necessary component of the therapeutic strategy for patients in cardiogenic shock, and implanting a short-term MCS device as a bridge to decision has gained popularity. This approach is used to stabilize the patient’s hemodynamic status and improve end-organ function , thereby reducing the surgical risk associated with implanting an LVAD [10, 11]. Ideal strategy with short-term MCS would reduce surgical risk before LVAD implant with stabilizing hemodynamics and improving end-organ function. The most commonly used short-term MCS device is the intra-aortic balloon pump (IABP); other forms of MCS include the TandemHeart (CardiacAssist Inc., Pittsburgh, PA), Impella (Abiomed, Danvers, Massachusetts, MA), venoarterial extracorporeal membranous oxygenation (VA-ECMO ) , and CentriMag (Thoratec Corporation, Pleasanton, CA) devices.
Appropriate patient selection is the central tenet of the current paradigm of MCS. Indeed, compared with more stable patients on medical therapy , inotrope-dependent patients with rapid deterioration and end-organ dysfunction have unacceptable outcomes, including a 1-year mortality rate of nearly 50% among those who survive to discharge while receiving long-term LVAD support [12, 13]. Patients who receive short-term MCS before LVAD implantation are sicker at baseline than LVAD-only patients, and short MCS is used to optimize patients’ condition before LVAD placement and to increase their suitability as long-term MCS candidates. Despite their poorer condition at baseline, MCS-supported patients had similar outcomes to LVAD-only patients, suggesting that short-term MCS decreases preoperative risk and achieves outcomes similar to those using LVAD support only. In a meta-analysis of data from patients with cardiogenic shock who were randomly assigned to receive a percutaneous ventricular assist device (p-VAD, including TandemHeart and Impella) or IABP support, outcomes were similar between the groups, although p-VAD support appeared to improve hemodynamics [13, 14]. Clinical criteria for using MCS are difficult to determine, but in our center, short-term MCS is initiated when patients show signs of significant hemodynamic instability or end-organ dysfunction, such as renal or respiratory failure, despite maximum medical support. Previous studies suggest that VA-ECMO is as safe and effective as a p-VAD to bridge patients to more advanced therapies such as heart transplantation or long-term LVAD support [15–18]. However, patients with VA-ECMO had only a 40–50% rate of survival to recovery or next therapy. One potential advantage of p-VADs over ECMO is that their design and mechanism of action allow direct ventricular unloading, thereby reducing the myocardial oxygen demand and the workload of the failing heart [19]. In contrast, a sizable proportion of patients supported with ECMO may develop refractory pulmonary edema , necessitating ventricular decompression secondary to increased afterload [20].
Using Long-Term MCS
Axial Flow Pump for Long-Term Mechanical Support: Thoratec HeartMate II
The most commonly used pump at our institution is the Thoratec HeartMate II LVAD (HM II; Thoratec Corp.), which is an axial flow rotary pump constructed of titanium. Smaller than the Thoratec HeartMate XVE (XVE; Thoratec Corp.), the HM II pump housing is implanted in the peritoneal space and requires a less invasive operative approach. It can provide flow up to 10 L/min at pump speed of 6000–15,000 RPM, with inflow via the left ventricular apex or diaphragm and outflow via the ascending aorta. A small percutaneous driveline exits the skin in the right upper abdomen. Patients are placed on systemic anticoagulation with warfarin and antiplatelet therapy with aspirin to prevent thromboembolic events. The Food and Drug Administration (FDA) has approved the HM II for BTT and DT.
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