US researchers, in a study using new imaging technology reported that silent heart attacks may be far more common, and more deadly. By looking for signature changes on a test of the heart's electrical activity called an electrocardiogram and by checking for certain enzymes in the blood, it is possible for doctor to identify whether a patient has had a recent heart attack. Changes on an electrocardiogram called a Q-wave, a marker for damaged tissue gives a clue to doctors to find that a heart attack might have occurred in the past. But Q-waves may not predict all silent heart attacks. To identify these attacks, Dr. Han Kim of Duke University in North Carolina and team used a new type of magnetic resonance imaging technology called delayed enhancement cardiovascular magnetic resonance, which is especially adept at finding damaged heart tissue. The study involved 185 patients with coronary artery disease but no record of heart attacks who were scheduled to have a test to look for possible blockages in their heart arteries. They found that 35 percent of the patients had evidence of a prior heart attack. And they found that these so-called non-Q-wave heart attacks were three times more common than silent heart attacks with Q-waves. They also found that after two years of follow up, people who had suffered a silent, non-Q-wave heart attack had an 11-fold higher risk of death from any cause and a 17-fold higher risk of death due to heart problems, when compared to patients who did not have any heart damage.