Nov 28 2005
Pumps implanted into the chest to maintain circulation can significantly extend the lives of the sickest patients in end-stage heart failure who are not candidates for heart transplantation, according to the results of a clinical trial led by Duke University Medical Center cardiologists.
The pumps, known as left ventricular assistant devices (LVADs), are employed when the heart's left ventricle – the chamber of the heart that pumps blood throughout the body – is too weak to pump enough blood to nourish the body's tissues. LVADs have been used as successful short-term "bridges to heart transplant" and are increasingly being considered as a long-term heart failure destination therapy, said the researchers.
In the current trial, the researchers found that patients who received LVADs had an average survival time of 10.3 months, compared to 3.1 months for those who did not receive the device. In this group of end-stage heart failure patients, 78 percent died within six months and 90 percent within a year.
"The patients who received the devices not only had a lengthened quantity of life, but they appeared to have an improved quality of life," said Duke cardiologist Joseph Rogers, M.D., who presented the results of the trial Nov. 14, 2005, at the annual scientific session of the American Heart Association meeting in Dallas. "We had patients who were doing the normal activities of life, such driving cars, fishing and golfing."
Patients who were on the LVADs scored significantly higher on standard measures of quality of life than patients in the control group, Rogers said.
"This is a remarkably ill group of patients," Rogers continued. "When you look at the control group, which was receiving the best care medicine has to offer, we can only keep ten percent of them alive after one year. We need to focus on this as a group of patients, since most are still in the prime of life and can still be quite productive."
To be considered for the trial, patients had to be taking powerful intravenous drugs in the hospital just to keep their hearts pumping, and they were also too sick to be considered for a heart transplants. Most were in intensive care units.
"Despite the shortcomings of the device, the results of this trial speak to our ability to improve the functionality for a very sick group of patients," Rogers said. The major complications of LVADs, said the researchers, include stroke, bleeding episodes and infections, especially at the site in the side of the body where the pump is connected to an external power source and computer.
"We already had a lot of data on the device when it was being used as bridge to transplantation," he continued. "We knew it could go for extended periods without problems, and that was the most compelling argument to use for implanting the device in patients who have no other options."
For the trial, researchers enrolled 55 patients from 2000 to 2003. Thirty-seven patients received the device and 18 did not. Patients were on average of 59 years old and as a group their hearts beat at only 14 percent of normal strength. The pump tested in the trial was the Novacor device, which is produced by WorldHeart, Oakland, Calif.
"While the survival time for those patients receiving LVADs was more than three times longer, we even had two patients who are both four years out from implantation," said Rogers. "Furthermore, unlike some earlier studies, there were no catastrophic mechanical failures."
According to Rogers, there are a number of challenges to be addressed before the use of LVADs can be considered as a widespread destination therapy.
The first challenge is selecting appropriate patients, which is crucial, since the patients most likely to survive would be those who are quite sick, but not too sick to be beyond help. This fine line in determining which patients are optimal will need to be defined by future clinical trials, he said. The other challenges pertain to the limitations of LVAD technology.
"Like most new technologies, we're limited by our power supply," Rogers said, "We need to develop a battery that is not only small enough and powerful enough to be safely implanted into the human body, but one that could be recharged through the skin without burning the skin. That way there would be no external parts, which would greatly reduce the incidence of infection."
Another technological challenge involves the pump itself, Rogers said. The Novacor device is a pulsatile pump which contains blood in a polyurethane sack. The blood is then propelled out of the pump between two pusher plates. However, because of its size, it cannot be used in children or comfortably in small women. Rogers said that numerous pump designs are being tested that are smaller and lighter. Durability will also be an issue, he said, since replacing an LVAD entails just as substantial and involved a surgical procedure as the initial placement.
Duke is currently participating in a number of different trials testing different device models and pumps designs.
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