Contrary to general belief among doctors, clot-busting drugs -- the main emergency treatment for heart attack victims -- fail to benefit patients over the age of 75 and may actually increase their risk of death, according to results of a Johns Hopkins-led study.

Older heart attack patients who received intravenous thrombolytics -- medications that dissolve clots in the blood vessels supplying the heart -- were nearly 40% more likely to die within 30 days of treatment than their counterparts not given the medications, according to the study.

Results were published in the May 16 issue of Circulation, an American Heart Association journal.

"There has been a widespread belief that clot-busting drugs help older patients just as they do younger ones, but the evidence always has been equivocal and the question had never been directly tested until now," said David R. Thiemann, M.D., lead author of the study and assistant professor of medicine at Hopkins.

"We found that in actual clinical practice the effectiveness of these drugs varies markedly with age. Younger patients clearly benefit from thrombolytics, but the one-third of heart attack patients who are older than 75 are unlikely to have any benefit and may be at higher risk of death."

The study used data on 7,864 Medicare patients aged 65 to 86, who arrived at hospitals with an acute heart attack and who were candidates for clot-dissolving therapy. There were 5,191 patients aged 65 to 75 and 2,673 patients aged 76 to 86.

Patients aged 65 to 75 who received thrombolytic therapy had a 30-day death rate of 6.8%, compared with 9.8% for patients who did not get the medications.

Among patients aged 76 to 86 years, the pattern was reversed. The death rate for patients treated with thrombolytics was 18%, compared with 15.4% for patients who did not get the medications.