CHICAGO >> Almost half of all heart attacks cause no obvious symptoms, yet they can still be life-threatening, according to research on more than 9,000 middle-aged men and women.

It’s one of the biggest studies to examine so-called silent heart attacks, and to also explore them across racial and gender groups.

Researchers at Wake Forest University’s medical school led the government-funded study. Results were published online Monday in the American Heart Association’s journal, Circulation.

THE DETAILS

Middle-aged adults from four U.S. communities were enrolled: Washington County, Maryland; suburban Minneapolis; Jackson, Mississippi and Forsyth County, North Carolina. The study’s aim was to examine causes of age-related artery damage that can lead to heart disease. Whites and blacks were included.

Participants had periodic clinic exams including electrocardiograms and phone interviews with the researchers. They were followed for about 13 years.

RESULTS

Overall, 45 percent of heart attacks were the silent kind.

Silent heart attacks were discovered on EKGs in 317 participants, or about 3 percent. These patients were diagnosed based on abnormal EKG readings suggesting heart damage yet they’d had no suspicious symptoms. By contrast, 386 patients, or 4 percent, had full-blown heart attacks with symptoms. Symptoms often include chest pain, jaw and arm pain and shortness of breath. Silent heart attacks may cause mild fatigue or other vague symptoms that don’t seem serious.

THE RISKS

About 1,830 participants died during the study, 189 of them from heart disease. Those who had silent heart attacks were three times more likely to die from heart-related causes during the study than those without heart attacks. Among participants who had classic heart attacks, these deaths were five times more common than among those without heart attacks.

COMPARISONS

Both types of heart attacks were most common in men. Classic heart attacks were more common in white men; the rates were about equal in black men.

Among black women, silent heart attacks were more common than classic attacks; among white women the rates were about the same.

Previous studies on the prevalence of silent heart attacks have had varying results ranging from about 20 percent to 60 percent of all heart attacks. The authors of the current research note that many were on smaller, less diverse groups of patients.

Smoking and family history of heart disease were slightly less common among silent heart attack patients but otherwise the groups were pretty similar.

RECOMMENDATIONS

Government data show that each year more than 700,000 Americans have heart attacks and about 120,000 people die from them. The researchers say silent heart attacks should be treated as aggressively as classic heart attacks, and that includes maintaining a healthy weight, getting lots of exercise and controlling blood pressure and cholesterol.