In the near future, heart attack victims may save their own lives and minimize damage to the heart by injecting themselves with a drug that unclogs coronary arteries, reported a research cardiologist at the annual meeting of the American Heart Association this week.

This prediction is based on results of the first human trials of a genetically-engineered form of tissue plasminogen activator (TPA) -- an experimental drug, said Dr. Burton Sobel, director of cardiology at the University of Washington School of Medicine in St. Louis.

In a study of 49 heart attack victims, TPA "dissolved blood clots blocking coronary arteries in about 71 percent of victims within 30 to 60 minutes without untoward responses or affects," Sobel said.

TPA is a protein found in the body in minute quantities, chiefly in endothelial cells which line the heart, blood vessels and lymphatic vessels. TPA is also found in the uterus where it keeps menstrual blood from clotting, Sobel noted, and may help explain why women have a lower risk of heart disease during their reproductive years than men.

In a pilot study published earlier this year in the New England Journal of Medicine, Sobel showed that naturally-occurring TPA is effective in dissolving clots. But because the body's TPA is so scarce, researchers turned to genetic engineering to produce enough TPA for further study.

First they extracted part of a DNA strand from a human melanoma cell -- a type of skin cancer cell that also produces high amounts of TPA. Then they spliced the DNA fragment to DNA in a bacterium, enabling the organisms to become tiny TPA manufacturing plants with limitless -- and relatively inexpensive -- production potential.

TPA joins two other drugs -- streptokinase and urokinase -- now used to dissolve blood clots during heart attacks. But unlike these drugs, TPA only affects the blood clot with little impact on the rest of the body and appears to reduce the patient's risk of general bleeding. TPA is also effective intravenously, while the other drugs are given by threading a catheter through blood vessels to the heart and injecting them near the blood clot.

Use of TPA remains experimental, pending Food and Drug Administration approval. But Sobel predicts that "we are moving towards the day when heart attacks are treated on suspicion" and damage can be minimized. "This is a first step to buy time for heart attack victims."