Risk of death with unrecognised myocardial infarction equal to that with recognised myocardial infarction by 10 years

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Tushar Acharya (National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, USA) and others report in JAMA Cardiology that within 10 years, the risk of all-cause mortality among patients who have had an unrecognised myocardial infarction is not significantly different from those who have had a recognised myocardial infarction.

According to the authors, unrecognised myocardial infarction—as identified via cardiac MR—is associated with poor survival but the long-term prognosis is unknown. “We investigated the long-term prognosis of unrecognised myocardial infarction would have higher risk of long-term mortality, non-fatal myocardial infarction, and heart failure than those without myocardial infarction,” they write.

Using data from the AGES (Age, gene/environment susceptibility) Reykjavik prospective cohort, Acharya et al reviewed long-term outcomes of patients who did not have myocardial infarction, a history of myocardial infarction (recognised myocardial infarction), and unrecognised myocardial infarction as identified with cardiac MR (all patients underwent cardiac MR at baseline). Of 925 patients overall, 156 (17%) had unrecognised myocardial infarction and 91 (10%) had recognised myocardial infarction (the remaining 686 patients had no myocardial infarction)

At three years, there were no significant differences in rate of mortality between those who had unrecognised myocardial infarction and those who had no myocardial infarction; furthermore, the rate of all-cause mortality was significantly lower among unrecognised myocardial infarction patients than those with recognised myocardial infarction. The authors comment: “By five years, unrecognised myocardial infarction mortality rates (13%) were intermediate between no myocardial infarction rates (8%) and recognised myocardial infarction (19%). However, at 10 years, unrecognised myocardial infarction and recognised myocardial infarction rates were not statistically different (49% and 51%, respectively; p=0.99) and were significantly higher than no myocardial infarction rates (30%; p<0.001).” After adjustment for cofounding risk factors, the risk of mortality with unrecognised mortality was similar to that with recognised mortality.

Two possible mechanisms, Acharya et al report, may explain why the mortality rates of unrecognised and recognised myocardial infarction progressively started to converge after years. The first being that unrecognised myocardial infraction may represent a different coronary disease phenotype with more small vessel involvement and atrial fibrillation than recognised myocardial infarction, and second preventative therapy for secondary events in patients with recognised myocardial infarction may have attenuated mortality rates. The authors add: “The recognition of a myocardial infarction may have changed risky behaviours, as individuals with recognised myocardial infarction were less likely to continue smoking. High mortality rates in the unrecognised myocardial infarction might be explained by fewer prescriptions of preventative treatments.”

Concluding, the authors note: “Being more prevalent than recognised myocardial infarction, unrecognised myocardial infarction constitutes an underappreciated public health problem. Whether early detection of unrecognised myocardial infarction by cardiac MR could allow for the institution of risk factor management and thus reduce the associated long-term risks merits further investigation.”

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