PLoS: DE-MRI reveals commonality of 'silent' heart attacks
Delayed enhancement cardiovascular MR (DE-CMR) has revealed that "silent" heart attacks may be much more common than previously believed, according to research published online April 21 in PLoS Medicine.

Studies have shown that each year, nearly 200,000 people in the U.S. suffer a heart attack but may not realize it. "Silent" heart attacks are not noted because they do not cause pain, or at least any pain that patients believe is related to their heart, and they do not leave behind any telltale irregularities on electrocardiograms (ECGs).

New imaging research from Duke University Medical Center in Durham, N.C., suggests that these heart attacks--unrecognized myocardial infarctions (UMIs)--may be happening much more frequently than physicians had suspected. Duke investigators also found that the attacks were associated with a surprisingly high risk of untimely death.

"No one has fully understood how often these heart attacks occur and what they mean, in terms of prognosis," said the author's lead author Han Kim, MD, a cardiologist at Duke. "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."

Physicians can usually tell when a heart attack has recently occurred by signature changes on ECGs and in certain blood enzyme levels. But if a heart attack happened in the distant past, physicians rely on the appearance of a specific alteration on an ECG called a Q-wave, which signals the presence of damaged tissue.

"The problem is not all UMIs result in Q-waves on the electrocardiogram. Those that don't are called non-Q-wave MIs. Those are the ones we haven't been able to count because we've never had a good way to document them," Kim said.

Kim and colleagues used DE-CMR to examine 185 patients suspected of having coronary artery disease but who had no record of a heart attack. All of them were scheduled to undergo angiography to find out if excess plaque had narrowed or blocked any of their arteries. Investigators followed the patients for two years to see if the presence of any unrecognized non-Q-wave heart attacks were associated with a higher risk of death.

The investigators found that 35 percent of the patients had evidence of a heart attack and that non-Q-wave attacks were three times more common than Q-wave UMIs. Non-Q-wave attacks were also more common among those with more severe coronary artery disease.

In addition, researchers discovered that those who suffered non-Q-wave UMIs 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.

"Right now, there are no specific guidelines about how patients with UMIs should be treated," Kim said. "If patients with UMIs happen to be identified, they are usually treated similarly to those patients where heart disease has already been documented. Future studies will likely examine how common unrecognized non-Q-wave heart attacks are in other patient groups and how these UMIs should be treated."

The National Institutes of Health (NIH) supported the study.