UMMC cardiac surgeons have now performed the first two U.S. implants of the VentrAssist heart pump.
Cardiac surgeons at the University of Maryland Medical Center are the first in the United States to implant a new, third generation heart pump as part of a five-center, 10-patient pilot study. The pump, which assists the heart’s main pumping chamber, the left ventricle, is called the VentrAssist. It was developed by Ventracor, an Australian company. The first U.S. patient to receive the pump, a 40-year-old Baltimore man with end-stage heart failure, had the device implanted on July 14, 2005. The experimental VentrAssist has been implanted in more than 30 patients in Australia, New Zealand and Europe.
“The University of Maryland’s leadership in this study exemplifies the innovative, lifesaving care we offer to heart failure patients,” says principal investigator Bartley P. Griffith, M.D., chief of the Division of Cardiac Surgery at the University of Maryland Medical Center and a professor of surgery at the University of Maryland School of Medicine. “Heart pump technology has evolved as has our experience with these devices,” says Dr. Griffith, who is a pioneer in the evaluation and development of a variety of mechanical support devices for the heart.
Co-principal investigator, Erika D. Feller, M.D., says the need for new generations of heart pumps is driven by the increasing need to help patients with heart failure. “End-stage heart failure is a growing problem, especially among patients who don’t qualify for a heart transplant,” says Dr. Feller, an assistant professor of medicine at the University of Maryland School of Medicine and a cardiologist at the University of Maryland Medical Center. “Also, the shortage of donated hearts has limited the number of transplants that can be performed,” she adds.
Cardiologist Erika Feller and chief of cardiac surgery Bartley Griffith.
Heart failure is a condition in which the heart cannot pump enough blood to the body’s other organs. According to the American Heart Association, nearly five million Americans have heart failure; about 550,000 new cases are diagnosed each year. For many on the transplant waiting list, a heart pump is a “bridge” to transplant, a means to keep them alive and improve their quality of life until a donor heart is available. Some heart pumps have also been approved as “destination therapy,” permanent treatment for severely ill heart failure patients who are not candidates for heart transplants.
Each new generation of heart pumps has brought operational improvements and reduced risks. First generation heart pumps are large devices that mimic the pulsating action of the natural heart with moving parts that potentially could wear out. Cardiac surgeons at the University of Maryland Heart Center have implanted several models of these pumps, which have been refined after many years of use and are approved by the Food and Drug Administration (FDA).
A second generation pump, the Jarvik 2000, is offered at the University of Maryland Heart Center as part of an investigational study overseen by the FDA. The thumb-sized Jarvik supplements the heart’s natural pumping action by means of a rotary, turbine motor that provides continuous blood flow without creating a pulse. The Jarvik 2000 is designed to last at least ten years. Dr. Griffith says more years of testing will be required to determine whether it meets or exceeds that goal, but that the Heart Center has had a good track record with the Jarvik. Dr. Griffith led a team in September 2002 that implanted the Jarvik in the first patient in the U.S. to go home with the pump to await a transplant as part of a special FDA protocol.
The VentrAssist, a third generation pump, uses centrifugal force to provide blood flow. The VentrAssist was primarily designed as a permanent alternative to heart transplants, but for this U.S. pilot study, it is being tested only as a bridge to transplant, so it is offered to patients who are listed for a heart transplant.
The VentrAssist weighs ten ounces and measures 2.5 inches in diameter. “The VentrAssist pumps the same volume of blood as larger pumps, but its small size takes up very little space in the abdomen, potentially making it useful for smaller adults, and even children,” says Dr. Griffith.
Surgeons attach a tube or cannula from the left ventricle to deliver blood from the failing heart to the VentrAssist. A second tube carries the pumped blood to the ascending aorta, the body’s main artery. The pump is implanted in a small pocket created on the left side of the body, behind the abdominal wall muscles just below the rib cage. A thin cord from the pump exits the body below the ribs and is connected to a speed controller and rechargeable batteries worn on an external belt or backpack.
The VentrAssist has one moving part, an impeller, which is a component made of small blades that rotate. The impeller blades, which are embedded with permanent magnets, spin when an electrical current is sent to six copper coils within the pump’s titanium housing. The rotation draws blood from the heart and pushes it out to the aorta.
The impeller is suspended by a thin sheen of blood, which forms a liquid cushion to hold it steady. Dr. Griffith says this so-called hydrodynamic suspension lifts the spinning impeller so that it doesn’t touch any part of the pump’s housing. “This is a very clever way to suspend the impeller. It results in unobstructed blood flow and reduces the risk of anything wearing out,” says Dr. Griffith. Further, the inside of the device is smooth with no nooks or crannies where blood could stop and clot.
The VentrAssist runs at two-to-three thousand revolutions per minute (RPM), slower than the Jarvik’s 12,000 RPM. Dr. Feller says that U.S. researchers are studying whether this pump causes less damage to blood cells compared to other pumps. “Faster impeller speeds may cause blood cells to break apart as they come in contact with the device,” says Dr. Feller. The researchers are also looking at another potential benefit of the slower speed, reduced heat build up, which can also damage cells and lead to clotting.
An interesting aspect is the VentrAssist’s quiet sound. “You can’t hear the pump without a stethoscope. The first generation of pumps make a loud clunking sound, the Jarvik is more like a soft whir, while the VentrAssist is somewhere in between,” says Dr. Feller.
The other sites for the U.S. pilot study are the Cleveland Clinic, Columbia University, the University of Minnesota, and the University of Pittsburgh Medical Center.
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