Mechanical pumps originally designed to supplement the pumping action of a failing heart and keep the patient alive until a transplant could be found have taken a major step toward becoming a permanent treatment, a development that could expand their use to tens of thousands of patients in the United States alone. The key to the improvement is the development of a new smaller, quieter, more reliable pump that is less likely to break down and need to be replaced -- an outcome that requires the patient to undergo a second major surgery.
The pumps are called left ventricular assist devices or LVADs. They are not meant to replace the entire heart, only to assist in the pumping action of the left ventricle, which pushes blood out through the aorta to the body. Researchers originally thought that LVADs had to mimic the action of the heart, pushing out blood in a series of pulses that were timed to coincide with pulses from the heart itself. That required complex machinery to produce the pulses and sophisticated electronics to synchronize them with the heart. Such devices had a high propensity to fail.
But more recently, researchers have concluded that a simple, continuously operating pump can work just as well, if not better. Such pumps typically have only one moving part -- the impeller -- and don't need to be synchronized with the heart, so their reliability is much greater. They are also much smaller, typically only about one-seventh the size of older models.
New results presented today at the Orlando, Fla, meeting of the American Heart Assn. show that one such device, manufactured by Thoratec Corp. of Pleasonton and called the HeartMate II, doubled the two-year survival of heart failure patients compared with the older pulsing pump. The device is currently approved by the Food and Drug Administration only as a bridge to a transplant.
"We had a sense that these smaller devices were going to have better long-term outcomes, and this trial proves it," said Dr. Alfred A. Bove, president of the American College of Cardiology, who was not involved in the research. "These devices have come a long way in five years. I expect that technology will continue to move things forward and they will be even better five years from now."
The need is great. An estimated 150,000 Americans have advanced heart failure that could be treated with a heart transplant, but there are only about 2,100 donors available in a given year. The big issue in the future may be not the availability of the devices but their cost and the strain that they will put on the healthcare system. The Thoratec pump costs about $80,000 and the surgery to implant it an additional $45,000. With thousands of patients needing the device, costs could mount quickly.
In the new trial, headed by researchers from Duke University Medical Center and the University of Louisville, researchers at 38 centers in the United States enrolled 200 heart failure patients between the ages of 26 and 81. All had failed medical therapy for their condition and were considered too sick to be candidates for a transplant. About two-thirds of the patients received the HeartMate II, and the rest received an older version that pumps in pulses.
The team reported in Orlando and in a report published online in the New England Journal of Medicine that patients receiving the new pump lived longer and had a higher quality of life than those receiving the older one. One year after the original surgery, 68% of those with the new pump were still alive, compared with 55% of those who received the older pump. But at two years, the results were much more dramatic: 58% of those who received the HeartMate II were still alive, compared with only 24% of those receiving the old pump. Similar patients receiving only medical therapy typically survive for only about six months, and fewer than 10% survive two years.
"The survival differences are compelling and provide a rationale to begin exploring use of continuous-flow LVADs earlier in the heart-failure continuum," said Dr. Joseph G. Rogers of Duke, a co-author. One reason for the better survival rate is the reliability of the new device. About one-third of the older pumps failed during the experiment and had to be replaced, compared with only 10% of the new ones.
In addition to survival, the devices also improved quality of life. "Patients with continuous-flow LVADs could walk twice as far, on average, as those with a pulsatile-flow device," said Dr. Mark Slaughter of Louisville, a co-author. "Patients with continuous-flow devices went from being unable to walk any distance at all without being short of breath to being able to walk the length of three football fields, on average. This is hugely significant for these patients."
The Thoratec device is not the only one attempting to capture this market. A similar device developed by Heartware International Inc. of Australia has been shown to keep as many as 80% of patients alive for two years in smaller clinical trials.
The bottom line of the studies: An editorial by Dr. James C. Fang of University Hospitals Case Medical Center in Cleveland in the New England Journal accompanying the new report said, "The first priority would be to make sure patients and physicians are aware that ventricular assist therapy is available, effective and safe for well-selected patients. Second, we should not delay referral until surgical morbidity and mortality become prohibitive. ... The optimal time for referral is most likley before the development of major complications from heart failure."
The new study was funded by Thoratec.
-- Thomas H. Maugh II
Photo: The HeartMate II is operated by a controller that fits on the belt. Credit: Thoratec Corp.