Incidence and Significance of Silent MI in the ARIC Study
What is the impact of race and gender on the incidence and prognostic implication of silent myocardial infarction (MI)?
The authors assessed the implication of silent MI in 9,498 participants from the ARIC study who were free of cardiovascular disease at baseline (visit 1; 1987-1989). Incident silent MI was defined as electrocardiographic (ECG)-evidence of MI without clinically documented MI (CMI) after the baseline until ARIC (Atherosclerosis Risk in Communities) study visit 4 (1996-1998). The outcome of interest was coronary heart disease (CHD) and all-cause death until 2010.
During a median follow-up of 8.9 years, silent MI was detected in 317 (3.3%) participants, while 386 (4.1%) developed CMI. The incidence rates of both silent MI (5.08 vs. 2.93 per 1,000 person-years) and CMI (7.96 vs. 2.25 per 1,000 person-years) were higher in men than in women. There was no difference by race in the occurrence of silent MI (4.45 vs. 3.69 per 1,000 person-years; p = 0.217), but whites had a higher rate of CMI than blacks (5.04 vs. 3.24 per 1,000 person-years; p = 0.002). Silent MI and CMI (vs. no MI) were associated with increased risk of CHD death (hazard ratio [HR], 3.06; 95% confidence interval [CI], 1.88-4.99 and HR, 4.74; 95% CI, 3.26-6.90), and all-cause mortality (HR, 1.34; 95% CI, 1.09-1.65 and 1.55, 95% CI, 1.30-1.85, respectively). There was a borderline interaction with gender with both silent MI and CMI potentially imparting greater increased risk of death among women (interaction p = 0.089 and 0.051, respectively).
The authors concluded that silent MI is common and is associated with an increased risk of long-term death.
This study adds to the growing body of data that silent MIs may constitute approximately 30-40% of the MI burden in the population, and that silent MIs impart an increased long-term mortality hazard. The incidence of MI has declined in the last two decades due to better risk factor control, and it would be interesting to evaluate if this has been accompanied by a parallel decline in silent MI. Further, evidence of silent MI on ECG should be a trigger for optimizing secondary preventive measures.
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