The Magnetically Levitated Centrifugal Continuous-Flow Circulatory Pump and Pump Thrombosis: New Momentum, or Inertia?

A scarcity of effective therapeutic options for advanced heart failure (HF) has led to the emergence of durable mechanical circulatory support devices which improve survival and quality of life in patients with advanced HF. However, the clinical benefits of left ventricular assist devices (LVAD) come at a cost of an increased risk of infection, bleeding, neurologic events, and pump malfunction due principally to pump thrombosis. Pump thrombosis with both axial (HeartMateII, St. Jude Medical) and centrifugal (HVAD, Medtronic) continuous-flow pumps can necessitate surgical pump exchange with the associated complications and increased cost of care.

The HeartMate 3 is a centrifugal continuous-flow pump like the HVAD, but differs in significant ways: it is fully magnetically levitated with wide blood-flow passages and no mechanical bearings, is frictionless, and rapid changes in rotor speed create an intrinsic artificial pulse. This fixed pulse, which is asynchronous with the native heartbeat, reduces stasis in the pump. The purpose of the MOMENTUM-3 (Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Therapy with HeartMate 3) trial was to compare clinical outcomes with the HeartMate 3 with outcomes with the HeartMate II in patients with advanced HF refractory to standard medical therapy.

The results of the first prespecified analysis of the MOMENTUM-3 trial were recently published in the New England Journal of Medicine.1 The primary endpoint was a composite of survival free of disabling stroke or survival free of reoperation to replace or remove the device at 6 months after implantation.

The majority of patients were Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) Profile 3 (stable on inotropic support) at study entry. Roughly half of the devices were implanted as destination therapy while the rest were either bridge to candidacy or bridge to transplant. The primary endpoint of the study was reached by more patients in the HeartMate 3 arm (86.2% vs 76.8%, HR 0.55; 95% confidence interval [CI], 0.32 to 0.95 [two-tailed P = 0.04 for superiority]. This outcome was primarily driven by the significantly lower rate of reoperation for pump malfunction in the HeartMate 3 group versus the HeartMate II group. Only one patient (0.7%) in the HeartMate 3 group underwent pump replacement (because of a drive-line communication fault), whereas 11 patients (7.7%) in the HeartMate II group underwent either a device exchange (9 patients) or device removal with urgent transplantation (two patients) (P=0.002).

Regarding other important endpoints, there were no significant differences between the two groups in the rates of death, disabling stroke, or right heart failure at 6 months. Subgroup analyses showed no significant interaction between treatment group and age, sex, race, intended goal of pump support (bridge to transplantation or destination therapy), INTERMACS profile, or the surgeon's learning curve (outcomes of the first two HeartMate 3 implants compared with later recipients). However, in both groups, an age of 70 years or older was associated with lower all-cause survival than an age of younger than 70 years.

The most important question facing advanced HF and transplant cardiologists is how this study impacts patient management. Certainly, the results are important, in that a reduction in the need for surgical pump exchange due to pump thrombosis is a significant finding that impacts patient care. However, it is important to note that the decision to remove or replace a pump for suspected or confirmed pump thrombosis was informed by the lactate dehydrogenase level or evidence of pump dysfunction but was at the discretion of the local site investigators. Nonetheless, it is difficult to write off this difference in outcomes between the HeartMate 3 and HeartMate II to the fact that the study was nonblinded as surgical pump exchange is not a decision lightly undertaken. Furthermore, a rate of surgical pump exchange of 7% at 6 months is consistent with prior reports with the HeartMate II pump and thus the results appear valid.2,3

While it may be unsatisfying that a reduction in the risk of pump thrombosis meriting pump exchange with the HeartMate 3 was not matched by similar reductions in the rate of death, disabling stroke, right heart failure, or gastrointestinal bleeding in this 6-month analysis, one can hope that a reduction in these important endpoints will be observed in longer-term analysis. For now, the HeartMate 3 appears to be gathering momentum, and further analyses will determine if this grows stronger with time.

References

  1. Mehra MR, Naka Y, Uriel N, et al. A fully magnetically levitated circulatory pump for advanced heart failure. N Engl J Med 2016. [Epub ahead of print]
  2. Starling RC, Moazami N, Silvestry SC, et al. Unexpected abrupt increase in left ventricular assist device thrombosis. N Engl J Med 2014;370:33-40.
  3. Kirklin JK Naftel DC, Kormos RL, et al. Interagency registry for mechanically assisted circulatory support (INTERMACS) analysis of pump thrombosis in the HeartMate II left ventricular assit device. J Heart Lung Transplant 2014;33:12-22.

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