According to U.S. researchers, the medical phenomenon known as the “silent” heart attacks is likely far more prevalent ““ and dangerous ““ than experts had previously suspected.
According to current estimates, some 200,000 Americans per year experience these painless heart attacks ““ known in medical terminology as unrecognized myocardial infarctions ““ often without even realizing it.
Dr. Han Kim of Duke University recently conducted a study on the subject that is set to appear in next week’s Public Library of Science Medical journal. According to him, there is reason to suspect that current figures on silent heart attacks may be far too low.
“No one has fully understood how often these heart attacks occur and what they mean, in terms of prognosis,” says Kim.
According to standard practice, when a physician wants to determine whether a patient has had a heart attack, his two standard tools are the electrocardiogram (EKG) and tests of blood-enzyme levels.
An EKG allows a cardiologist to examine the electrical signals that the heart sends out. When a patient has suffered a heart attack, there are signature changes that occur in sections of the EKG called the Q-wave and ST-segment.
In a cardiac-enzyme blood test, the physician is able to check for elevated levels of a family of enzymes known as troponins which are released from damaged myocardial cells in the heart. The levels of troponins found in a patient’s blood can remain high for as long as two weeks after a heart attack.
The problem however, according to Dr. Kim, is that with silent heart attacks you don’t always observe these telltale symptoms.
“Those are the ones we haven’t been able to count because we’ve never had a good way to document them,” said Kim.
To tackle this problem, Kim and his colleagues have begun using a new generation of magnetic resonance imaging (MRI) technology known as delayed enhancement cardiovascular magnetic resonance. This cutting-edge technology is particularly suited for locating damaged heart tissue that might have been missed by other imaging techniques.
Dr. Kim’s group examined 185 patients suffering from coronary artery disease who had no previous record of heart attacks. Of the patients they studied, some 35 percent showed signs that they had previously suffered from a heart attack according to the new imaging techniques. Among these patients, they found the silent heart attacks in which there was no change in the Q-wave, were three times more common than those that did show Q-wave changes.
Even more disturbing, the group’s follow-up study of these patients showed that after two years, patients who had suffered from a non-Q-wave heart attack were at a 17 times higher risk of dying from heart problems than patients without heart damage.
In current medical practice, patients who suffer from silent heart attacks are generally treated like patients with other heart diseases, said Kim. He hopes that his findings will lead to more specialized forms of treatment for these patients.
In the U.S. heart disease is the No.1 cause of death each year, killing on average one person every 34 seconds.
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