medwireNews: The prevalence of unrecognized myocardial infarction (MI) by cardiac magnetic resonance (CMRI) in elderly patients is higher than that of recognized MI and is associated with increased mortality, say researchers.
By contrast, the prevalence of unrecognized MI by ECG was lower than that of recognized MI and was not associated with increased mortality, report Andrew Arai (National Heart, Lung, and Blood Institute, Bethesda, Maryland, USA) and colleagues in JAMA.
In their study of 936 diabetic and nondiabetic participants aged 67-93 years, 91 (9.7%) had recognized MI and 157 (17%) had unrecognized MI according to CMRI, which was more than the 46 unrecognized MIs detected by ECG.
Individuals with diabetes (n=337) had more unrecognized MIs detected by CMRI than ECG, at 21% versus 4%. Unrecognized MI by CMRI was significantly associated with atherosclerosis risk factors, coronary calcium, coronary revascularization, and peripheral vascular disease.
Over a median follow-up period of 6.4 years, 30 (33%) of 91 participants with recognized MI died and 44 (28%) of the 157 participants with unrecognized MI died; both were higher rates than the 119 (17%) of the 688 individuals with no MI who died.
Unrecognized MI by CMRI improved risk stratification for mortality over recognized MI, at a net reclassification index of 0.34. After adjusting for age, gender, diabetes, and recognized MI, unrecognized MI by CMRI remained significantly associated with a 45% increase in mortality and improved risk stratification for mortality, at a net reclassification index of 0.16.
However, unrecognized MI by ECG was not significantly associated with mortality.
Compared with individuals with recognized MI, those with unrecognized MI by CMRI used cardiac medications less often.
Arai et al explain that ascertaining the prevalence and prognosis of unrecognized MI in older patients with and without diabetes is important as age and diabetes increase the risk for coronary heart disease.
They suggest that several factors may contribute to the high prevalence of unrecognized MI in this population. "First, subclinical coronary plaque rupture occurs frequently, particularly in diabetic individuals. CMR [imaging] may detect the myocardial sequelae of coronary plaque rupture or coronary plaque erosion that either spontaneously reperfused or were nonocclusive. Second, symptom variation in acute MI may lead patients or their clinicians to attribute MI symptoms to noncardiac causes.
"Third, given their propensity to be clinically detected, recognized MI may be more severe than unrecognized MI and impart greater lethality."
Arai and team conclude that detection of unrecognized MI by CMRI may provide an opportunity to optimize treatment for the vulnerable individuals highlighted in their study, but add that further research is needed.
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