CHICAGO (AP) - Heart attack patients with normal EKGs may be in more danger than doctors realized.

Unexpectedly high death rates were found in a study of hospitalized heart attack patients whose initial electrocardiogram readings were normal.

The findings suggest such patients may need more aggressive treatment than previously thought, researchers said.

The study looked at six years of data involving 391,208 heart attack patients. The patients' initial hospital work-ups included EKGs, which look for abnormal electrical patterns in heart activity.

The researchers had expected that patients with normal test results would have better short-term survival rates than those with abnormal results.

And, indeed, the 30,759 normal-EKG patients were 41 percent less likely to die while hospitalized than the 222,875 with abnormal EKGs.

Still, 1,752 in the normal-EKG group died, nearly 6 percent. That is about triple the rate researchers had expected given previous studies.

Heart attack patients with abnormal EKGS are often given such treatments as angioplasty, blood-thinning drugs and surgery to open narrowed arteries. Those treatments often are considered unnecessary for patients whose initial EKGs are normal.

The latest findings suggest that that attitude should probably be reconsidered, said Dr. Robert Welch, an emergency medicine specialist at Wayne State University in Detroit who led the study. The death rate found in such patients "is not trivial," he said.

The study appears in Wednesday's Journal of the American Medical Association.

The study does not indicate whether normal-EKG patients who received aggressive treatment had better outcomes. It does show that a normal EKG "does not always indicate a favorable hospital course," the researchers said.

"We probably need to be fairly proactive toward patients with normal or minimally abnormal EKGs to try to find out what's really going on," said Dr. Lynn Smaha, a Sayre, Pa., cardiologist and spokesman for the American Heart Association.

EKGs are one tool used by doctors to determine if a person has had a heart attack. Blood tests are another. These detect enzymes that leak into the bloodstream when the heart muscle has been damaged. This was the diagnostic method used in most of the normal EKG patients studied.

The patients in the study were about 68 on average, 84 percent were white and 59 percent were men.

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