The heart-assist devices also significantly improved the cardiac function in many other heart failure patients.
"This suggests that, while the devices alone may not be sufficient to allow a meaningful number of patients to come off the heart pump instead of having a heart transplant, there may be other therapies that can be added to enhance recovery," said Simon Maybaum, M.D., lead author of the study.
In end-stage heart failure, the heart weakens, gets larger and shows other signs of deterioration. Implantable heart pumps, called left ventricular assist devices (LVADs), pump blood through the body, which lets the heart’s main pumping chamber rest. Pumps are currently approved for two purposes:
To help keep patients with end-stage heart failure alive until a donor heart becomes available for transplantation.
To serve as a long-term therapy for patients deemed unacceptable for a heart transplant.
However, for some time, transplant specialists have debated the potential for LVADs to be used as a "bridge to recovery" for the patient’s own heart. Prior small studies have yielded contrasting results. "Some centers were reporting that up to a third of their patients implanted with a heart pump were able to come off the pump without a transplant, and some centers were saying they just did not have that experience," said Maybaum, associate professor of clinical medicine and medical director of the Center for Advanced Cardiac Therapy at the Albert Einstein College of Medicine’s Montefiore Medical Center in New York City.
To resolve these inconsistent findings, researchers from seven major U.S. heart transplant centers formed the LVAD Working Group. They enrolled 67 patients with end-stage heart failure between August 2001 and October 2003 in the first prospective, multicenter study to extensively examine how LVADs affect cardiac function and exercise capacity over several months.
Patients were recruited from these centers: Baylor College of Medicine, Houston, Texas; Cleveland Clinic Foundation, Ohio; Columbia University, New York City; University of Michigan, Ann Arbor; University of Minnesota, Minneapolis; Temple University, Philadelphia, Penn.; and the Texas Heart Institute, Houston. Four different types of LVADs were used in the study. Researchers evaluated the patients every 30 days after pump implant.
"There are two contrasting, important findings in our study," Maybaum said. "One, the ability to remove an LVAD from a patient with end-stage heart failure was low. Two, there was a high degree of improvement in heart function during the use of the assist device."
Six (9 percent) of the 67 patients had their pump removed without needing a heart transplant. Six others (9 percent) had died by May 2004, when data collection ended.
Yet, after 30 days on the pump, one third of the patients had a left ventricular ejection fraction greater than 40 percent (measured when the pump flow was decreased). Ejection fraction is the percentage of blood pumped out of the left ventricle with each beat. Healthy hearts typically have an ejection fraction of 55 percent to 60 percent, Maybaum said. The proportion of patients showing this degree of improvement then waned, dropping to 27 percent of patients at 60 days, 19 percent at 90 days and 6 percent at 120 days.
Patients also showed progressive improvement in exercise capacity after LVAD implantation. From day 30 to 120 there was an increase in their peak oxygen consumption and how long they could exercise.
Tiny snips of heart tissue from 22 patients taken at implant and at the time of removal of the LVAD prior to transplantation found evidence of important improvements.
The size of the heart muscle cells, the amount of the fibrous collagen and levels of the protein TNF-alpha all decreased significantly between pump implant and heart transplant — signs of reduced heart damage.
"We now have a much more reliable description of the natural history of the changes in heart function during LVAD support," Maybaum said. "That makes us optimistic that other strategies may allow us to further improve cardiac function."
Two novel strategies will soon be tested in clinical trials for LVAD patients in the U.S. One study will utilize the muscle bulking agent clenbuterol and the second will evaluate autologous (the patient’s own) stem cells injected at the time of LVAD implantation.
Karen Astle | EurekAlert!
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