The tests don't require surgery or other invasive methods. Instead, the patient simply gets a special EKG (electrocardiogram).
One test checks the heart's nervous system. The other test checks the heart's electrical system.
Combining the results of both tests, given 10-14 weeks after a heart attack, was the study's best predictor of heart-related death or cardiac arrest requiring resuscitation.
One of the EKG tests took about half an hour. The other test took all day, but patients didn't have to spend that time in the doctor's office; the EKG kept tabs on them for 18-24 hours.
The patients were followed for nearly four years. During that time, 30 patients died (including 22 who died of heart problems). Seven others had to be resuscitated when their hearts stopped (cardiac arrest).
Those patients tended to have poor scores on both tests 10-14 weeks after their heart attack.
At that point, one out of five patients had abnormal scores on both tests, with hearts that were still weak. Compared to other patients, they were six times more likely to suffer a heart-related death or a cardiac arrest during the study.
The researchers -- who included Dexter Exner, MD, MPH, of Canada's University of Calgary -- report their findings in the Dec. 11 edition of the Journal of the American College of Cardiology.