The Nomenclature of MCS
A ventricular assist device (VAD) is a MCS device that is used to partially or completely support the function of a failing heart. Left ventricular assist devices (LVAD) pump blood from the left ventricle and transfer it to the ascending aorta. LVADs may be used as a bridge to transplant (BTT) for candidates awaiting heart transplantation; as destination therapy (DT) for patients who are not candidates for transplantation; as a bridge to decision for patients too sick to survive the transplant evaluation (so that their suitability for transplantation has not been determined at the time of VAD implantation) and as a bridge to recovery for selected patients who might recover their cardiac function. The latter patients are mostly those with acute cardiomyopathies (ie. fulminant lymphocytic myocarditis, peripartum cardiomyopathy, etc).11 Interestingly, according to the Sixth annual report of the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) the proportion of patients treated with LVAD as DT in the United Sates has increased from 14.7 % in 2006–7 to 41.6 % in 2011–13.14
The first-generation VADs had pulsatile flow, designed to mimic the normal function of the heart. These devices were shown to increase survival and quality of life (QoL) of patients with end-stage HF compared to optimal medical therapy (OMT).16 The second and third generation devices currently in use (primarily HeartMate II, Thoratec Corp. and HVAD, HeartWare Ltd., see Figure 1), have continuous flow patterns, and can generate up to 10 litres/minute. Although these devices generate continuous flow, pulsatility may still be present in some patients since the flow delivered by the device is modified by native left ventricular (LV) contractility. Nevertheless, some studies suggest that pulsatile flow is not necessary for adequate perfusion of the end organs.17
In the ‘HeartMate II’ trial, treatment with continuous-flow HeartMate II devices as DT was associated with improved survival compared to pulsatile-flow devices.18 In addition, patients treated with continuous flow-devices as DT had a significant reduction in the rate of adverse events and hospitalisations and had improved QoL and functional capacity compared to patients treated with pulsatile-flow devices.18. To evaluate whether ‘real life’ outcomes are similar to those observed in the clinical trials, Jorde et al.19 followed the first 247 patients treated with HeartMate II devices as DT who were not in a clinical trial and compared their outcome with those achieved
in the clinical trials. Survival in the later group trended to be better than in the initial clinical trial, with an absolute difference of 74 % versus 68 % at 1 year and 61 % versus 58 % at 2 years (p=0.2). Moreover, the rate of survival free of stroke (both haemorrhagic and ischaemic), device-related infection, or pump replacement was significantly higher in patients treated in the later group.19 These results are consistent with the outcomes summarised in the
Sixth INTERMCAS annual report of 80 % 1-year survival and 70 % 2-year survival.14
Treatment with the HeartWare HVAD device as a bridge to transplantation (BTT) was evaluated in the ADVANCE (HeartWare Ventricular Assist Device Bridge to Transplant) trial.20 In this study, the HeartWare HVAD device was compared to ‘commercially available devices’, mainly HeartMate II, in patients awaiting heart transplantation. The HVAD device was non-inferior to the HeartMate device with 1-year survival of 86 % and enhanced QoL and functional capacity similar to what was seen with the HeartMate II.20 The safety and effectiveness of HeartWare HVAD as DT is being evaluated in the ENDURANCE trial, yet to be published.