ARCHIVED - New hope for heart patients
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November 05, 2009— Ottawa, Ontario
A new research study could help reduce the global shortage of donor organs for patients awaiting heart transplants. The joint NRC-UK-U.S. project aims to show that hearts that have stopped beating — which are currently not used for transplantation — could be good donor organs if they are harvested in a timely fashion and recovered appropriately.
"Heart transplantation is the only effective way to treat congestive heart failure," says Dr. Ganghong Tian, a researcher at the NRC Institute for Biodiagnostics in Winnipeg. "Each year, about 100 heart transplant surgeries are performed across Canada, but we have several hundred patients on the waiting list. That means about two-thirds of patients are not lucky enough to receive the treatment they need."
Much of this pent-up demand is due to a shortage of suitable heart donors. "The majority of heart donors are traffic accident victims whose brains have been critically injured," says Dr. Tian. "The attending physicians have pronounced them dead based on severe and irreversible brain damage, although their hearts are still beating normally." These brain-death patients are sent to the hospital and their hearts are then harvested for transplantation.
"We don't have enough brain-death, heart-beating donors, so we're seeking alternative sources," he adds. Potential heart donors may include brain-death patients whose hearts have stopped beating before being harvested. Patients on a life-support machine with severe brain damage and no hope of recovery could also be potential heart donors. Currently, hearts from these two groups are not collected for transplantation.
How brain death changed heart transplants
Until the 1970s, non-heart-beating donors were the source of all organ transplant operations. But around 1975, the medical community introduced the concept of "brain-stem death" as a criterion for pronouncing a patient dead. Once this concept was introduced, surgeons no longer used any organs harvested from non-heart-beating donors out of the belief that the organs would be damaged as soon as blood stopped flowing through the body. However, since the 1980, kidneys, livers and lungs from non-heart-beating donors have been used for transplantation.
"The rationale is that if a heart has stopped beating, no blood is circulating to supply oxygen and other nutrients to the heart, so the heart muscle must be irreversibly damaged," says Dr. Tian. With this new study, he and his collaborators want to find out whether they can safely harvest and recover the heart after it stops beating and the patient is declared dead. And if they can, what is the best way to ensure the heart can be transplanted?"
To find out, researchers at NRC-IBD and the cardiac surgery departments at St. Boniface General Hospital in Winnipeg, Cambridge University in the UK and Stanford University in the U.S. are conducting experimental pig heart transplants. The study was initiated by Cambridge researchers, who invited NRC-IBD to participate because of its experience with large animal studies, magnetic resonance imaging and spectroscopy equipment, and expertise at monitoring heart function and tissue viability. "So far, our preliminary results are very encouraging," says Dr. Tian.
"It will take time to find the optimal way to harvest these hearts," he adds. "And it will take time for health care decision-makers to accept the use of non-heart-beating donors. This procedure has to be proved before it can be used in humans. But we're confident that the lives of many heart failure patients will eventually be saved by this donor source."
Monitoring the viability of non-beating hearts
To determine whether a heart is viable after it stops beating, Dr. Tian and his colleagues use magnetic resonance (MR) spectroscopy, which monitors the energy level of heart muscle — specifically, its adenosine triphosphate and creatine phosphate levels. "In lay terms, MR spectroscopy can measure how much gas you have in your gas tank," he says. "We find that after 15 minutes of heart arrest, a pig heart is slightly damaged, but if we remove it and fill it with oxygenated blood, we can fill up the ‘gas tank' and recover the heart."
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