Recognizing heart attacks in time.

Every year, U.S. hospitals admit more than 4 million people with chest pain, but fewer than one-third of them prove to have heart attacks. When patients with chest pain have inconclusive electrocardiograms and no prior history of cardiac problems, physician face a dilemma. If the pain is a heart attack, quick administration of clot-dissolving drugs could help prevent serious injury to heart tissue, perhaps even saving the patient's life. But these drugs also carry serious complications such as bleeding, and physicians hesitate to use them without a definite diagnosis. Yet confirming a heart attack through further testing takes longer than the six-hour "window" available for effective clot-business therapy.

New research may soon resolve that dilemma. At a meeting of the American Association for Clinical Chemistry, held late last month in Washington, D.C., scientists described two blood tests that could allow physicians to diagnose heart attacks in time to begin treatment with potentially lifesaving drugs. These tests -- modified versions of assays already in use -- may become available within the next two years, they say.

Both tests detect substances released by damaged hearts. One measures creatine kinase (CK), an enzyme normally used by the heart to pump blood. During a heart attack, the enzyme leaks into the blood and gets converted to a different form of CK -- the same form normally used by other muscle tissues. Therein lies the difficulty. Current tests do not distinguish between CK leaked from the heart and CK leaked from other damaged tissue. For an accurate diagnosis, physicians must monitor CK blood levels over a period of eight hours or more.

Alan H.B. Wu, a pathologist at the University of Texas Medical School in Houston, now reports that small quantities of the still-unconverted cardia enzyme can be detected in the blood as early as two hours after a heart attack. Specific assays for this CK "isoform" already exist, he says, but scientists need to confirm the diagnostic reliability of those tests.

Hemant Vaidya, a biochemist with the Du Pont Co. in Wilmington, Del., points out that physicians in Europe have long used myoglobin -- an oxygen-carrying molecule in muscle tissue -- as a marker for heart attack. As in the case of CK, the heart and other muscle tissues all release myoglobin when damaged. However, Vaidya says, Finnish researchers have found that carbonic anhydrase -- which helps muscle cells metabolize carbon dioxide -- is released only by damaged tissues other than the heart. By monitoring the ratio of myoglobin to carbonic anhydrase, doctors could distinguish between a heart attack and other muscle injuries, obtaining an accurate diagnosis within a few hours of the attack, he says.