Dec. 19 (HealthDay News) -- When doctors in the emergency room believe that someone is having a heart attack, they are mistaken 9.2 percent of the time, a new study indicates.

Given that minutes matter with these patients and doctors have to act quickly in this setting, that percentage is tolerable, say researchers from the Minneapolis Heart Institute Foundation.

"Our conclusion is that an 8 to 10 percent false positive rate is acceptable," said study co-author Dr. Timothy Henry, who is director of the institute.

However, every effort should be taken to reduce the number of false positive diagnoses of heart attack, Henry added. The report, which is published in the Dec. 19 issue of the Journal of the American Medical Association, gives a benchmark for other institutions to meet, he said.

"The whole issue of false positive has never been presented," Henry said. "This is the first time it has been presented in a systematic way."

Henry and his colleagues studied the medical records of 1,345 people treated for suspected heart attacks in a regional system between 2003 and 2006, looking at emergency room decisions to activate the cardiac catheterization laboratory to treat for suspected heart attacks. Such decisions usually must be made in a matter of minutes, often without a record of a patient's previous cardiac history.

All the patients were suspected of having a STEMI heart attack, characterized by a specific electrocardiogram pattern. It turned out that 187 of them (14 percent) did not have obvious blockage of a coronary artery, with 127 (9.5 percent) having no significant coronary artery disease and 149 (11.2 percent) having negative results on cardiac biomarker tests. There was a significant difference in survival, with a 4.6 percent 30-day death rate for those with a blocked artery and 2.7 percent for those without blockage.

Hospitals should run a continuing check on such emergency room diagnoses and decisions, Henry said. "If they are too high, corrective action should be taken," he said.

Heart attack diagnosis has been the focus of "a number of quality improvement initiatives," said Dr. Frederick A. Masoudi, an associate professor of medicine at the Denver Health Medical Center, who wrote an accompanying editorial.

"It is well known that timing is of the essence in treating these patients," Masoudi said. "The outcome is better when the artery is opened in a timely way."

False positives are inevitable in some cases, he said. "It is really impossible to say from this one study whether there are too many or too few," Masoudi said. "Ultimately, it is important for us to evaluate the extent to which it occurs and why it occurs. We must build into the system a balance, so that only those patients who need reperfusion get it."

SOURCES: Timothy D. Henry, M.D., director, research, Minneapolis Heart Institute Foundation; Frederick A. Masoudi, M.D., associate professor, medicine, Denver Health Medical Center; Dec. 19, 2007, Journal of the American Medical Association