Pump thrombosis has been such a well-established shortcoming of left ventricular assist devices (LVADs), that one heart surgeon went so far as to borrow Winston Churchill's phraseology to describe it as "a riddle, wrapped in a mystery, inside an enigma" for the title of his September 2014 article in the Annals of Cardiothoracic Surgery. But St. Jude Medical Inc. may have unraveled that riddle with its Heartmate 3 LVAD system.

According to short-term results of the company's U.S. pivotal study, MOMENTUM 3, there were no cases of pump thrombosis in patients implanted with the Heartmate 3 system at six months compared to 14 cases (10 percent) of pump thrombosis in patient's implanted with the St. Paul, Minn.-based company's earlier Heartmate 2 system.

The investigational device exemption trial is designed to compare the two LVAD systems with a short-term endpoint of six months and a long-term endpoint of two years. The current data, presented at the American Heart Association Scientific Session in New Orleans, includes the six-month results in the first 294 patients enrolled. Overall, more than 1,000 patients are participating in the randomized, unblinded, multi-center study.

In Europe, the Heartmate 3 is approved for advanced heart failure patients who are awaiting transplantation or are not candidates for transplantation. St. Jude said the new MOMENTUM 3 data confirm the results observed in its CE mark study of the device, which were reported in April.

The Heartmate 3 is designed with St. Jude's Full Maglev technology, which allows the pump's rotor to be suspended by magnetic forces. St. Jude said the device was designed that way to reduce trauma to blood passing through the pump and improve outcomes for patients.

Investigators in the MOMENTUM 3 study also noted an 86.2 percent survival rate with freedom from disabling stroke and re-operation to repair or replace the device in the Heartmate 3 arm, which met the study's primary endpoint and was statistically superior to the 77 percent survival rate reported in the Heartmate 2 arm.

Mandeep Mehra, medical director of Brigham and Women's Hospital Heart and Vascular Center and chair of the publication and presentation committee for the study, noted that it was especially important that the clinical gains achieved with the Heartmate 3 system occurred without an increase in other adverse events, "providing important therapeutic progress for our advanced heart failure patients." ADDING STROKE TO THE MIX

While the pump thrombosis results were probably the biggest takeaway for Larry Biegelsen, of Wells Fargo Securities LLC, the analyst noted in a report that the 8 percent all-cause stroke in the Heartmate 3 arm of the study at six months was also encouraging because it represents an improvement over the CE mark study results, which were 12 percent at six months and 18 percent at one year.

Biegelsen cautioned, however, that while investors may want to compare the six-month survival rate of the U.S. pivotal study against the CE mark study results, the definition of "survival" does not appear to be consistent across studies.

The analyst also noted that disabling stroke in MOMENTUM 3 was numerically higher at six months for Heartmate 3 compared to Heartmate 2, which "was somewhat disappointing." He said patient outcomes for both arms would likely have been more favorable if the study enrolled a greater proportion of bridge-to-transplant (BTT) versus destination therapy (DT) patients as DT patients are generally sicker.

EXPECTED SHARE GAIN

Overall, Biegelsen said the MOMENTUM 3 data should lead to FDA approval and help St. Jude take share from Dublin-based Medtronic plc in the U.S. LVAD market, but he said Medtronic should still remain competitive in the space given Heartware's strong physician relationships and HVAD's ability to be implanted via thoractomy.

"While we view the [Heartmate 3] data to be mostly positive, we believe the study was somewhat negatively impacted by enrolling sicker patients than we are accustomed to seeing in BTT studies," Biegelsen said.

Medtronic inherited the HVAD earlier this year through its nearly $1.1 billion cash acquisition of Heartware International Inc. The HVAD is touted as the smallest full-support VAD on the market and is designed to reduce surgical invasiveness. The deal also included multiple technologies in development that are designed to offer progressively less-invasive mechanical circulatory support options for patients with end-stage heart failure. (See Medical Device Daily, June 28, 2016.)

St. Jude has not provided any recent update on its expected U.S. timing for Heartmate 3 though, Biegelsen said, but previously the company said it planned to file for FDA approval in the second half of this year. Given that information, the analyst said he expects FDA approval of the new LVAD in the second half of 2017 and forecasts St. Jude gaining 630bps of U.S. share next year, exiting 2017 with about 79 percent of the market share.