Magnet-driven LVADs, designed to last, establish themselves in bridge therapy
April 17, 2008 Steve Stiles
Boston, MA - The new wave of left-ventricular assist devices (LVADs), none yet approved for sale in the US but some available in Europe, go for small size and greater durability to make them more patient-friendly and, potentially, cut the need for replacement due to wear and tear, compared with the pulsatile-pump first-generation devices.
Some of these advanced, magnet-driven LVADs were able to sustain >80% of transplant-listed patients for at least six months or until transplantation if it occurred earlier, in several small observational studies presented here last week at the International Society for Heart and Lung Transplantation [ISHLT] 2008 Annual Meeting [1,2,3]. And, although the reported studies involved handfuls of patients, the risk of complications—especially the most daunting ones in LVAD therapy (stroke, infections, and bleeding)—appeared low with all the devices.
What makes these so-called "third-generation" LVADs different from the long-available pulsatile HeartMate XVE (Thoratec) and Novacor LVAS (WorldHeart) pumps is a continuous-flow propulsion system driven by electromagnets that spin an impeller—the rotor that actually moves the blood—that is levitated in position so that it doesn't actually touch the pump housing. With their impellers levitated by more magnets or the dynamic forces of the blood itself, these pumps have only the one moving part and little of the wear and tear that ages the mechanical pulsatile pumps.
In various stages of development, these new devices include:
* Centrifugal pumps with magnetically powered, hydrodynamically levitated impellers, such as the VentrAssist (Ventracor) and the HeartWare HVAD (HeartWare). * "Maglev" pumps, with magnetically powered, magnetically levitated impellers, such as the DuraHeart LVAS (Terumo Heart) centrifugal pump, the Levacor VAD (WorldHeart) centrifugal pump, and the Incor (Berlin Heart) axial-flow pump.
Dr Andrew J Boyle (University of Minnesota, Minneapolis), who presented the VentrAssist study at the ISHLT meeting, would also include in the mix mechanically driven axial-flow LVADs like the HeartMate 2 (Thoratec), which have been dubbed "second generation." That device, available in Europe for about three years, was given a unanimous vote of confidence by an FDA premarket advisory panel in December, 2007, heartwire reported at the time, and appears headed for approval. The HeartMate 2, about the same size as the VentrAssist, is probably as much of a clinical advance over pulsatile pumps as are the new magnetically driven devices, Boyle, who has participated in trials of both pumps, told heartwire.
Boyle says he avoids terms like "second generation" for the HeartMate 2 and the "third-generation" label commonly given to the magnetically driven devices. "That's just a marketing ploy. The reality is that all of them, other than the [HeartMate] XVE and the Novacor [LVAS], are the new generation," he said. "Whether they are called second or third generation, I think that's all baloney." They use different engineering approaches to address the same problems, he said, "but I think where the rubber meets the road, which is in outcomes, there will be similar results."
And, Boyle said, the new-generation devices will probably all have the same longevity. "I don't think wear and tear within the pump is going to be an issue for any of them." But whether greater durability manifests clinically has yet to be shown—that's hard to do in bridge-therapy studies, in which the time to transplantation is often less than the lifetime of even the first-generation LVADs.
The HeartMate XVE, currently the gold standard and approved for both bridge and destination therapy in the US, has a lifetime of about 15 to 18 months, Boyle said. "Then you have to replace the whole pump, usually because of bearing wear."
But, "with more and more people getting LVADs, there are more people at the top of transplant lists, so waiting times are lengthening," Boyle observed. It's increasingly possible that in some areas of the country "the waiting time for a donor to be found for a particular patient will exceed the durability of the XVE." The new-generation LVADs, he said, are expected to last five to 10 years. That's based on bench testing, since destination-therapy studies have yet to be done; Boyle has had patients live with one for up to 2.5 years, "and there are longer times at other centers."
In the prospective experience he reported at the ISHLT meeting, 28 patients awaiting a donor heart were implanted with the VentrAssist at four US centers. Of those, 23, or 82%, met the primary end point of survival to transplant or on circulatory support for at least 180 days. All were in NYHA functional class 4 at the start. At 14 weeks, >90% were in either class 1 or 2, with none in class 4. At 180 days, >78% were still in class 1 or 2, while those in class 3 had grown to 22%; but again, none were in class 4.
The 38-point mean improvement in quality-of-life score (based on the Minnesota Living with Heart Failure Questionnaire) was "statistically and clinically significant," Boyle said.
The overwhelming majority of serious adverse events occurred within the first 30 days after device implantation; adverse-event rates were comparable to what has been observed with other LVADs, according to Boyle. Adverse events associated with the VentrAssist LVAD [1]
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Similar complication rates were reported at the meeting for the magnetically driven, hydrodynamically levitated HeartWare HVAD. In a 23-patient series presented by Dr Georg Wieselthaler (Vienna General Hospital, Austria), 9% had strokes (all ischemic), 4% had transient ischemic attacks, 13% developed bleeding requiring reoperation, and 13% had infections at the percutaneous entry site over six months.
Survival at 180 days with the HeartWare device was 91%; 9% had been transplanted by that point. Both of the deaths were from sepsis. The mean LVAD-support time was 272 days.
Reporting on the maglev DuraHeart pump at the ISHLT sessions, Terumo Heart CEO Dr Chisato Nojiri said that the adverse-event rates in his 33-patient series were about 0.22 per patient year for bleeding requiring surgery, 0.40 per patient year for infections at the percutaneous site or device pocket, and 0.28 per patient year for any stroke. There were no instances of device-related thrombosis.
With the addition of 22 patients implanted with the device after European market approval based on the first 33 patients, the 180-day rate of survival for the DuraHeart was 82% (mean support time, 214 days). About one-fourth of the patients had been on the device for at least a year; among those, the mean duration of support was 568 days, according to Nojiri.
An FDA-approved bridge-to-transplant trial with a target enrollment of 140 patients is in the works for the DuraHeart pump, the company recently announced. At least 32 patients have been enrolled in the HeartWare device's corresponding trial, according to Wieselthaler. And, observed Boyle, a similar pivotal trial for the VentrAssist pump has entered 48 of a projected 140 patients for the bridge cohort and 20 out of an as-yet undetermined total number of destination-therapy patients.
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