'Silent' heart attacks may be far more common than previously thought, with nearly 200,000 Americans each year suffering such an attack without realizing it, according to a new study.
The unrecognized myocardial infarction, or UMI, can be hard to detect if it occurred in the distant past, and it often goes unnoticed by the victim, but it is associated with a high risk of untimely death, according to research from Duke University Medical Center.
"No one has fully understood how often these heart attacks occur and what they mean, in terms of prognosis," said Duke cardiologist Han Kim, the lead author of the study published Monday in PLoS Medicine, a peer-reviewed publication of the Public Library of Science.
"With this study, we can now say that this subset of heart attacks, known as non-Q-wave UMIs, is fairly common, at least among people with suspected coronary artery disease."
To detect heart attacks that happened in the distant past, doctors rely on specific alterations of an electrocardiogram (EKG) called a Q-wave, which signals damage of heart tissue.
But many UMIs do not result in Q-waves on an EKG, leading to a previously unknown number of silent heart attacks.
The Duke researchers employed a technique known as delayed enhancement cardiovascular magnetic resonance, or DE-CMR, to examine 185 patients suspected of having coronary artery disease but who had no record of any heart attacks.
The patients were studied for two years, and researchers found that 35 percent of them had evidence of a heart attack, and that non-Q-wave UMIs were three times more likely than Q-wave attacks.
They also found that those who suffered non-Q-wave attacks had a risk of death due to heart attacks that was 17 times higher than patients with no heart damage.
"If patients with UMIs happen to be identified, they are usually treated similarly to those patients where heart disease has already been documented," Kim said.
Heart disease is the number one killer in the United States, claiming 864,480 lives in 2005, according to the American Heart Association.