Continuous-flow LVAD proves mettle as bridge to transplantation

August 29, 2007

Boston, MA - With a design that can be traced back about 2200 years to Archimedes and his screw-based pump, a left-ventricular assist device (LVAD) that propels blood in a continuous stream successfully bridged patients to heart transplantation or sustained them at least six months while they were waiting for a donor heart in three out of four transplant candidates who received the devices, according to an observational study reported this week [1].

As the "pivotal US experience" for the HeartMate II (Thoratec, Pleasanton, CA), the findings represent a milestone of sorts for the device and an assortment of other continuous-flow LVADs in various stages of development, according to lead author Dr Leslie W Miller (Washington Hospital Center, Washington DC). Reported in the August 30, 2007 New England Journal of Medicine, the study establishes the viability of continuous axial-flow devices—which are smaller, quieter, and possibly longer-lasting than the currently available pulsatile LVADs, Miller said—for bridging patients to transplantation. "We think this is the pump design of the future," he told heart wire .

 
Proving that the continuous-flow devices get people to transplant is a good first step, but it doesn't say that this is a lifetime therapy or a durable support therapy for longer than a few months.
 

At the very least, the continuous-flow pumps can be used in a broader population than the larger models now available. "This device is much more livable than the pulsatile devices," according to Dr Lynne W Stevenson (Brigham and Women's Hospital, Boston, MA), who called the Miller et al study "very encouraging" for opening up LVAD bridge therapy to some previously excluded patients. The pulsatile devices, which include the first-generation HeartMate model used in early clinical trials, are so large that they can't fit into most women, she observed for heart wire .

The current series includes 28 women. Miller confirmed that a number of the patients had smaller body surface areas than the usual lower limit for accommodating a conventional LVAD, "and they have done well with the [continuous-flow] devices."

In fact, overall, the patients showed the kind of striking gains that are expected after LVAD implantation, including pronounced improvements in hemodynamics, six-minute-walk distance, and NYHA class.

"A good first step"

The current study from Miller et al, Stevenson said, represents a clear advance for the field of mechanical support. But she cautioned that pulsatile LVADs, used for both bridging and destination therapy, have a much longer track record. "Proving that [the continuous-flow devices] get people to transplant is a good first step, but it doesn't say that this is a lifetime therapy or a durable support therapy for longer than a few months."

Stevenson also observed that all LVADs entail a significant risk of stroke or other neurologic complications. The risk in the current data may be "slightly better" than what has been previously reported, she said, but there's no real telling without an adequately powered comparison. "It remains one of the major limitations of these devices."

The 133 patients, implanted at 26 US centers in 2005 and 2006, were in NYHA class 4 and considered high priority for heart transplantation according to United Network for Organ Sharing criteria; excluded were patients with severe renal, pulmonary, or liver dysfunction.

Of the total group, 75% reached the primary end point of transplantation (56 patients), "cardiac recovery" (one patient), or survival at 180 days with continued transplant eligibility on HeartMate II support (43 patients). Of the remaining patients, according to the authors, 25 died, five became ineligible for transplantation after clinical deterioration, and three were implanted with a different kind of LVAD.

Of the patients on LVAD support who were evaluable for NYHA class at three months, 83% had improved from class 4 to class 1 or 2. Among those who performed a six-minute-walk test, their average distance had increased seven-fold.  Significant improvements were seen on both the Minnesota Living with Heart Failure and the Kansas City Cardiomyopathy questionnaires.

Bleeding, thrombosis, and anticoagulation

Almost a third of the patients, 31%, developed bleeding that required surgery over the six-month follow-up. Respiratory failure developed in 26% and renal failure in 14%. Peripheral nonneurologic thromboembolism occurred in 7%. The rates of ischemic stroke, transient ischemic attack, and hemorrhagic stroke were 6%, 4%, and 2%, respectively; the overall rate of neurologic and psychological complications was 26%.

In the absence of a control group, Miller and his colleagues compared their complication rates with corresponding published data for pulsatile LVADs. Acknowledging the limitations of such an analysis, Miller said the incidences of stroke, bleeding, infection, and need for device-based or inotropic augmentation of right heart function were appreciably lower with the continuous-flow device. Only two of the 133 implanted devices developed thrombosis—"that's the lowest incidence, that we know of, to be reported," he said.

Patients in the study were on chronic warfarin therapy, a notable difference between treatment with the HeartMate II and the available LVADs that complicates comparisons of their bleeding and thrombotic risks. Oral anticoagulation was instituted after a spate of thrombotic complications in early tests of a continuous-flow LVAD, according to Miller. They currently anticoagulate to an INR of 1.8 to 2, "comparable to if not lower than" what is typical for patients with atrial fibrillation, he said.

The quality-of-life implications of the HeartMate's smaller size and quieter operation, compared with pulsatile LVADs, shouldn't be underestimated, according to Miller. The report notes that four of the 43 patients who remained on support at 180 days chose to take themselves off the waiting list because they preferred to continue on mechanical support. "I don't think there can be a bigger testimony to [the view] that having the device is not some horrendous ordeal."

In a Perspective that appears in the same issue as but does not discuss the report from Miller et al, Dr Kenneth L Baughman (Brigham and Women's Hospital) and New England Journal of Medicine deputy editor Dr John A Jarcho survey the range of percutaneous and totally implantable options, under investigation and approved, for patients who need mechanical circulatory support [2].

Miller reports receiving consulting fees from Astellas and lecture fees and grant support from Thoratec; disclosures for his coauthors are provided in the report. Stevenson said she has no relevant industry relationships.

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