Take heart: there's a new way to detect whether someone has suffered a so-called silent heart attack, one in which vessels to the ticker become blocked but there are few of the typical telltale signs such as chest pain. The bad news: it appears that more people than previously believed are suffering from these unrecognized myocardial infarctions, according to a new study

Silent heart attacks cause vague symptoms such as shortness of breath or heartburn-like sensations that usually fade with time, often leading victims – and even physicians – to assume they were nothing serious. The potential danger: the victims are more likely to die from future heart attacks, irregular heart rhythms, and other heart-related ailments but may take no additional precautions.

Every year, about 1,460,000 Americans suffer from heart attacks, and 195,000 (or 13 percent) of those attacks go unnoticed, according to a 2009 report by the American Heart Association. But study coauthor Han Kim, a cardiologist at Duke University Medical Center in Durham, N.C., suspects there are probably twice as many silent heart attacks as the stats suggest. The reason, he says: the method currently used to detect heart damage wrought by them – the electrocardiogram (EKG), which measures the electrical activity of the heart – is not a surefire test.

But Kim and his colleagues at Duke and Northwestern Memorial Hospital in Chicago discovered that another technology often used to assess damage after obvious heart attacks called delayed enhancement cardiovascular resonance (DE-CMR) can pick up damage that EKGs may miss. DE-CMR uses magnets and radio waves to generate images of the heart. 

The researchers report in next week's PLoS Medicine that they studied the heart health of 185 patients ages 25 to 86 who had no known history of heart trouble but had been flagged by their doctors as being at risk because of factors such as high cholesterol and blood pressure. After giving all the patients both EKG and DE-CMR tests, the researchers found that 65 of them (35 percent) had suffered silent heart attacks some time in the past; only 15 of those cases were picked up by the old EKG method, whereas 50 were detected by the new DE-CMR method.

What's more, patients who had suffered silent heart attacks detected with DE-CMR were more likely to die than those whose attacks were detected by EKG. Over an average two-year follow-up, only one out of 15 patients (7 percent) with EKG-detectable silent heart attacks died, whereas 15 out of 50 (30 percent) with DE-CMR-detectable cases died.

The next step, Kim says, is figuring out how common silent heart attacks are in the general population (not just those at risk for heart disease). Then, he says, "we can determine whether screening these patients and treating them early helps avoid deaths."

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