'Unrecognized' MIs Detected by MRI Associated With Increased Risk of Mortality

September 04, 2012

September 4, 2012 (New York, NY) — New data from a Scandinavian substudy suggest that unrecognized MI is associated with an increased risk of death. Compared with ECG testing, the prevalence of unrecognized MI was higher when cardiac MRI was used, and these undiagnosed MIs detected by cardiac MRI were associated with increased mortality.

"Silent ischemia and unrecognized MI have been known about for a while," senior investigator Dr Andrew Arai (National Heart, Lung, and Blood Institute, Bethesda, MD) told heartwire . "One of the big changes is that MRI with gadolinium is so incredibly sensitive for detecting heart attacks or scarring of the heart that we knew we had a chance to find much more than people knew about, and that's what we found. There were almost one-and-a-half times more unrecognized heart attacks as recognized heart attacks."

The new data, from the ICELAND MI study, a substudy of the Age, Gene/Environment Susceptibility (AGES)--Reykjavik Study, are published in the September 5, 2012 issue of the Journal of the American Medical Association.

Cardiac MRI sensitive for detecting MI

The ICELAND MI substudy includes 936 participants who underwent ECG and cardiac MRI testing to detect unrecognized MI. Patients included in the analysis ranged in age from 67 to 93 years, and just over 28% had diabetes. Of the 936 individuals, 91 (9.7%) had a recognized MI. Using MRI and ECG, 157 (17.0%) and 46 (5.0%) of subjects had an unrecognized MI, respectively. The difference in the prevalence of undetected MI with cardiac MRI and ECG was statistically significant.

Regarding prognosis, 33% of individuals with a recognized MI and 28% of individuals with an unrecognized MI detected by cardiac MRI died over a median of 6.4 years. In contrast, just 17% of 688 subjects without MI died. Adjusted for age, sex, diabetes, and recognized MI, unrecognized MI detected with cardiac MRI was associated with a 45% increased risk of death, whereas unrecognized MI detected by ECG was not. In addition, unrecognized MI using cardiac MRI improved the classification of individuals at risk of death using the net reclassification index (NRI), but unrecognized MI detected with ECG did not alter the NRI.

"We knew right off the bat that we would have more MIs than were known about," Arai told heartwire . "What we didn't know was if they were important or not. That's why the prognosis part of the study is so critical. The fact that we now have five- to six-year follow-up on these patients, and we can say unequivocally that they die, a hard end point, at a rate that is very comparable to patients that have recognized MI. Both groups of patients are dying at a faster rate than people who have neither types of MI."

In an analysis of treatment among the patients, the researchers observed that cardiac medications were used less frequently in patients with unrecognized MRI compared with individuals who had a documented MI. Of the 157 patients with unrecognized MI, 52% were taking aspirin, 45% were taking beta blockers, 36% were taking statins, and 27% were taking ACE inhibitors or angiotensin-receptor blockers (ARBs).

Asked about the clinical implications of the findings, Arai said the study results confirm the prognostic importance of MRI-detected MIs that would be undetected by traditional screening methods. With just half of patients with unrecognized MI receiving cardiovascular medications, the study highlights an opportunity to manage these patients more aggressively with secondary prevention, the hope being that treating these patients with statins, aspirin, and ACE inhibitors, among other agents, could reduce their risk of mortality and other cardiovascular events.

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