Bypassing Heart Transplants
By William Allstetter
They are using PET scans to identify many patients who can be saved by coronary artery bypass instead, which gives them a much better survival rate than heart transplantation. And by reducing the number of people seeking heart transplants, P&S physicians hope to give those who really do need a new heart a better chance of getting one.
"PET scans allow us to identify viable heart muscle that appears dead on standard thallium tests," says Dr. Steven R. Bergmann, professor of medicine and radiology and director of nuclear cardiology.
In a study published in the April 15, 1999, issue of the American Journal of Cardiology, Dr. Olakunle Akinboboye, assistant professor of medicine, and his colleagues at the Nuclear Cardiology Laboratory found that about half the patients whose thallium tests indicated they needed a heart transplant actually had enough viable heart muscle to be good candidates for coronary artery bypass.
In the standard thallium test, radioactive thallium is injected into the blood stream. Images taken of the heart then show where blood flows to the heart. Areas of the heart with severely restricted blood flow are considered to be dead tissue that will never be functional again. If too much of the heart muscle is dead, the patient needs a heart transplant. But some of the tissue that appears dead on thallium tests is actually alive. PET scans can identify that "hibernating tissue."
PET's advantage is that it can measure not only blood flow, but also cellular metabolism. A radioactive tracer is attached to glucose molecules, then injected into the blood stream. As with thallium tests, the resulting image shows where blood flows to the heart. But oxygen-starved cells also take up glucose, which they use as an energy source. So the radioactively labeled glucose collects in cells that are still alive but not receiving much oxygenated blood. The PET scan then shows areas of the heart muscle that would appear to be dead when judged by blood flow, but are still viable and could begin contributing to muscle contraction if they received more oxygenated blood.
"We specifically look for areas in the left ventricle where there is sluggish blood flow but good metabolism," says Dr. Bergmann. "Once a PET scan identifies such areas, we can take these patients off the transplant evaluation list and treat them successfully with bypass surgery, thus saving the scarce donor hearts for patients who really need them."
A coronary artery bypass costs around $30,000 to $40,000 and patients have excellent survival rates for 10 to 15 years. Heart transplants, on the other hand, cost on average $150,000 to $200,000 with 85 percent to 90 percent survival for one year, but only 60 percent to 75 percent survival at five years. In addition, heart transplant patients must take immunosuppressive drugs for the rest of their lives, which cost thousands of dollars every year. The drugs also increase the risk of infections and cancer.
The Nuclear Cardiology Lab does about 100 PET scans per year as part of the transplant evaluation procedure. Their use has been limited because PET scans are considerably more expensive than thallium tests and are not covered by all insurance programs, most significantly Medicare. But the potential savings are persuading more and more insurance companies to cover PET scans for transplant evaluation.
"The data are pretty compelling," says Dr. Bergmann, who believes even Medicare may soon be convinced of PET's value in saving lives, hearts, and money.