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Literature Review

A Fully Magnetically Levitated Circulatory Pump for Advanced Heart Failure

Mehra MR, Naka Y, Uriel N, et al. N Engl J Med. 2017;376(5): 440–450.

Reviewers: Kinjal Patel, MD1; Ahmed Awad, MD1

  1. Assistant Professor of Anesthesiology, Cooper Medical School of Rowan University, Camden, NJ
Background

Left ventricular assist systems increase survival and improve the quality of life in patients with advanced heart failure. However, these patients are known to have an increased risk of infection, bleeding, neurologic events, and pump malfunction due to pump thrombosis. Reports have linked an increased rate of thrombosis with both the HeartMate II, an axial continuous flow pump, and the HeartWare HVAD, a centrifugal continuous flow pump. The HeartMate 3, a magnetically levitated centrifugal continuous-flow device engineered to reduce shear stress on blood and avoid pump thrombosis, was evaluated in this clinical trial. This device is programmed to facilitate rapid changes in rotor speed that mimic a pulse. The authors compared outcomes in patients who received the HeartMate 3 with outcomes in patients who received the HeartMate II device.

Methods

This paper reports the results of the first prespecified analysis of the MOMENTUM 3 trial, a prospective, nonblinded, randomized trial that compared the axial flow HeartMate II device to the centrifugal flow HeartMate 3 device. This trial was sponsored by St. Jude Medical, which provided the trial devices, and was carried out at more than 69 locations in the United States. Patients had advanced heart failure unresponsive to standard medical therapy. Data were collected at baseline; 1 week after implantation; at discharge; and at 1, 3, and 6 months after implantation. Antithrombotic management in each group consisted of aspirin (81 mg to 100 mg daily) and warfarin (to achieve an international normalized ratio [INR] of 2.0 to 3.0) in each group.

The primarily evaluated end point was a composite that included survival free of disabling stroke or survival free of reoperation for device removal/replacement. Of the patients who received heart transplants prior to 6 months, the ones who were urgently transplanted for device malfunction were considered treatment failures; all other heart transplants were considered treatment successes.

Results

Two hundred ninety-four patients were enrolled in the study—152 in the centrifugal pump arm and 142 in the axial pump arm. All patients were followed for 6 months or until death. Analysis showed that the primary endpoint was reached in 131 (86.2%) of the centrifugal pump patients vs 109 (76.8%) of the axial pump patients. The study established the noninferiority of the centrifugal flow device to the axial flow device with an absolute difference of 9.4 percentage points (95% confidence interval[CI]), as well as the superiority of the centrifugal flow device (hazard ratio of 0.55 [95% CI, P=0.04]). Fourteen patients in the axial flow group had suspected or confirmed pump thrombosis while no patients in the centrifugal flow group had any such events.

Discussion

The MOMENTUM 3 trial demonstrated that the mechanical bearing-free, continuous-flow HeartMate 3 device was associated with a higher event-free survival (free of reoperation or disabling stroke at 6 months) than the axial flow HeartMate II device. The authors suggest the benefits associated with the HeartMate 3 device at 6 months were due to the absence of suspected or confirmed pump thrombosis. This was in contrast to the significant number of surgical pump exchanges or urgent transplantations needed after the HeartMate II device placement.

There were no significant differences between the two pumps in the rates of other major complications such as right heart failure, major infections, and bleeding. However, a numerical but not statistically significant trend toward an increase in the number of disabling strokes was seen in the centrifugal flow group.

The authors noted a few limitations to the study. They included the fact that investigators and patients were not blinded to the devices, and the results of patient-reported assessments might have been biased. Additionally, the decision to replace the devices for suspected or confirmed pump thrombosis was made at the discretion of the local site investigators. The authors noted that most surgeons involved were very experienced at placing the HeartMate II device, and the HeartMate 3 had not been used previously in the United States. Thus, surgical and medical outcomes may have been biased in favor of the HeartMate II.

Comments

The authors showed a significant improvement in outcomes at 6 months after placement of the HeartMate 3 device vs the HeartMate II device. These outcomes seem to be related to the interval change in design between the two iterations of the HeartMate pump. The majority of the benefit comes from a reduced rate of pump thrombosis with the newer version of the device. Thus, the HeartMate 3 seems to be a promising step forward for patients with advanced heart failure refractory to standard medical treatment. While not statistically significant, patients receiving the HeartMate 3 device did have a higher rate of disabling stroke. Further investigation into this is warranted.

Additionally, a comparison between the HeartMate 3 and the HeartWare HVAD, another centrifugal flow pump on the market, may be warranted. It will be of particular interest to see if the differential rotor speed in the HeartMate 3, which mimics a heartbeat, confers any particular advantage over the HeartWare HVAD.

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