ACC 2009: Magnet-Powered LVAD Clinical, Safety Data Ready for FDA-Approval Application

March 31, 2009

March 31, 2009 (Orlando, Florida) — Patients who received the VentrAssist (Ventracor, Sydney, Australia) centrifugal-pump left ventricular assist device (LVAD) for bridge to transplantation in the device's pivotal clinical trial fared well enough, according to prespecified standards set by the FDA, for the manufacturer to go ahead with its premarket approval application to the agency, according to investigators reporting here today at the American College of Cardiology 2009 Scientific Sessions [1].

It still has hurdles to jump before it can get there, but if the magnetically driven pump is approved, it would be the second continuous-flow LVAD to become available in the US. The first was the motor-driven, axial-flow-pump HeartMate II (Thoratec, Pleasanton, CA), as reported by heartwire last April. Both devices are seen as vast improvements over the first generation of LVADs, which contain pulsatile-flow pumps that are quite a bit larger and noisier and have far more mechanical elements to potentially wear out.

At a late-breaking trials session, the trial's cardiology principal investigator, Dr Andrew J Boyle (University of Minnesota, Minneapolis), said that, at a prespecified interim analysis, the patient outcomes success rate was 79%. As defined by the FDA, success meant successful bridging to transplantation or continued support on the VentrAssist and transplant eligible (United Network for Organ Sharing status 1A or 1B) at 180 days.

Also, he said, the trial "showed a statistically and clinically significant improvement in quality of life and functional status over the duration of support, and the adverse-event profile was similar to other current LVADs and certainly was a marked improvement over what we're used to historically with pulsatile LVADs."

Formally commenting on the data after Boyle's presentation, Dr Michael A Acker (University of Pennsylvania, Philadelphia) said, "It's exciting for me--I've been in this field for a while--to see the results with the VentrAssist. . . . The survival at six months has been wonderful. It's important to note that 80% of the patients now are in NYHA class 1 or 2 vs class 4. And I think the real exciting advancement with the VentrAssist is that the morbidity of the implantation is so low [compared with pulsatile LVADs] that there is a significant decrease in bleeding, stroke, and infection, similar to what we've seen with the Heartmate II."

In contrast to the Heartmate II's axial screw-type pump mechanism, the VentrAssist features a rotor that is propelled by electrically powered magnets and doesn't actually touch the rest of the device--it's supported by the blood rushing through the device. As a result, the implant has no mechanical bearings or valves--in fact, the floating rotor is its one moving part. The pump is percutaneously connected to an external power pack and "controller" device that the patient wears.

According to Boyle, 421 patients have been implanted with a VentrAssist at some point; the longest duration of support has been 1594 days, and the mean has been 219 days.

In the current experience, he said, the average duration of support was 155 days. Of the trial's 79 patients who were successes, the 60 who went to transplantation were LVAD-supported for a mean of 134 days, and support time for the 19 still on the LVAD awaiting a donor heart at 180 days averaged 279 days.

Among those not classified as successes, five died of multiorgan system failure and two died of bleeding not associated with implantation surgery; there were two stroke deaths and one death each of heart failure, acute MI, cardiogenic shock, sepsis, and pulmonary edema. The 5% of patients who required replacement of the device were also considered treatment failures. Replacement was necessitated primarily by "failure" of the pump itself or the percutaneous leads or by thrombus within the pump.

The rate of infection, long a notorious potential LVAD complication, was low. Boyle said there was a very low rate of infection-related death, "which has not been seen historically in LVAD trials."

Overall, he said, rates of serious adverse events were similar to those published for the Heartmate II. "Bleeding-death definitions have changed over the years," Boyle observed, "which makes their results not directly comparable. But I'm comfortable saying that there's no evidence for an increased rate of bleeding with the VentrAssist compared with the Heartmate II, and perhaps a there's a suggestion of a minor improvement in that regard."

Complication Rates in the Ventrassist Pivotal Trial, Events Per Patient Year, in 138 Patients

Event Events per patient year
Confirmed pump thrombus 0.09
Infection, driveline exit site 0.04
Infection, pump pocket 0.02
Infection, sepsis 0.41
Renal dysfunction 0.26
Right-heart failure 0.24

More striking than any performance or clinical differences between the two continuous-flow devices are their differences from the older-generation pulsatile pumps, observed Boyle for heartwire . They were much larger, "and that generally discriminated, quite honestly, against women, because they tend to be of much smaller stature and you couldn't put one into a patient that size. The same was true of Asians. With all of the newer LVADs being miniaturized, women and Asians are now better candidates."

According to Boyle, durability should be similar for the two continuous-flow pumps; the VentrAssist has no physical bearings that can wear out, the Heartmate II has only two axial bearings. And durability for both models should be vastly better than that of the older pulsatile designs. "They had multiple bearings that would wear out generally at the 15- to 18-month mark," he noted.

"There's potentially no wear and tear at all with the VentrAssist, so durability will be far more dependent on the external components and the driveline itself, rather than the pump," according to Boyle. "For instance, you can slam a car door onto the lead or catch it on a railing, things like that. But the pump itself is at least theoretically indestructible."

However, Boyle said, "a variety of things will differentiate the two pumps. The external components will be different. All the companies are trying to improve lead design, the weight of the controller, and the ease of ambulating with the device," he said. "How bulky is it? How much does it weigh? For a destination therapy that a 75- or 80-year-old may have for the rest of their life, these sorts of considerations are significant."

During his prepared comments, Acker said, "Finally, with this pump likely to be approved, I hope, we're now at a phase similar to [that of] pacemakers, perhaps, or heart valves. We're going to have competing technologies. I'm not sure how you would pick one or the other of the small continuous-flow pumps, and we'll just have to wait for more data to be able to make an evidenced-based decision."

Boyle reports being scientific advisor to Ventracor without financial compensation and receiving consulting fees from Thoratec. Acker reports receiving consulting fees or honoraria from Acorn Cardiovascular.

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