Background: Silent events with newly developed Q waves in electrocardiogram (ECG) [silent myocardial infarction (MI)] in diabetic patients is reported to be independently associated with an increased risk of fatal MI. However, the incidence rate of silent MI in diabetic patients has yet to be clarified. We sought to determine the incidence rate of first symptomatic MI and silent MI in diabetic patients.
Methods: We conducted a prospective cohort study on patients enrolled in the Japanese primary prevention of atherosclerosis with aspirin for diabetes (JPAD) trial which was started in 2002. It is a randomized controlled trial to examine the efficacy of low-dose aspirin therapy for the primary prevention of atherosclerotic events in type 2 diabetic patients. No patients had Q waves in their ECG before entry to the JPAD trial. We followed-up 1825 patients until July 2015 after completion of the JPAD trial in 2008. The median follow-up period was 10.3 years. We collected 1648 patients' ECGs to identify patients with silent MI.
Results: Symptomatic MI occurred in 65 patients and silent MI occurred in 22 patients. The incidence rate of symptomatic MI was 4.26 per 1000 patient-years and 1.44 for silent MI in diabetic patients. Thus, 25% of total MIs were silent. Cause-specific Cox proportional hazard model indicated that age (hazard ratio 1.06, 95% confidence interval; 1.03-1.10, p=0.0004) and long history of diabetes (1.00, 1.01-1.07, p=0.01) were independently associated with symptomatic MI, but these were not associated with silent MI.
Conclusions: We demonstrated that incidence rate of first silent MI and that proportion of silent MI to all MIs was 25% in diabetic patients without a history of atherosclerotic events. Diabetic patients frequently need ECG screening for detection of silent MI.
Keywords: Cohort study; Electrocardiogram; Myocardial infarction; Primary prevention; Type 2 diabetes mellitus.
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