Newly available tests allow doctors to accurately diagnose mild heart attacks that might otherwise go undetected.
The tests, already being used in some emergency rooms, could save lives by making it easier to target patients for treatment and reduce the risk of death that follows a heart attack.
The tests measure two forms of cardiac troponin, a protein that is released into the bloodstream by dying heart cells. It begins to appear within about six hours after a heart attack.
Traditionally, doctors have diagnosed heart attacks with an electrocardiogram, which spots irregularities in the heartbeat, and a blood test that checks for an enzyme called creatine kinase MB that is released by dying heart cells.
However, other kinds of muscle also release creatine kinase. And in mild heart attacks, creatine kinase levels sometimes do not rise above the amounts typically seen in the bloodstreams of healthy people.
In separate studies, doctors used two competing versions of the new troponin test on patients who arrived at the hospital with chest pain. Many would have been diagnosed as having only unstable angina - severe or unusual pain that does not result in permanent heart damage.
“We are now able to diagnose heart attacks more precisely, including in those who in the past would have been described only as having unstable angina,” said Dr. Elliott Antman, director of coronary care at Brigham and Women’s Hospital in Boston.
One of the tests, which measures a variety of the protein called troponin I, is manufactured by Dade International of Deerfield, Ill., and came on the market last year. The other, which looks for troponin T, is made by Boehringer Mannheim Pharmaceuticals of Germany and was approved for U.S. use in 1994.
The two companies helped pay for the latest studies, which were published in today’s issue of the New England Journal of Medicine.
Antman and colleagues tested blood samples stored several years ago from 1,404 people seeking treatment for chest pain, most of whom were thought to have unstable angina.
The doctors found that 41 percent of them had troponin I in their blood - evidence they had suffered heart attacks. Furthermore, they found that the higher the level, the greater their risk of dying within the next six weeks.
Four percent of the patients with the protein in their bloodstream died during this period, compared with 1 percent of those who did not have it.
The other study, conducted by Dr. E. Magnus Ohman and others from Duke University, tested the use of the troponin T test on 855 patients with chest pain - most of whom were diagnosed at the time with heart attacks.
Even in those who clearly had heart attacks, the amount of troponin in the blood was an accurate indicator of the risk of death. Twelve percent of those with high troponin T died in the following month, compared with 4 percent of those with low amounts.
Ohman recommended that troponin be measured in all patients who come to the emergency room with chest pain that doctors suspect is caused by heart disease - perhaps 5 million people annually.
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