Unrecognized myocardial infarction (MI) is common in asymptomatic patients with diabetes without a history of cardiac disease. In this population, unrecognized MI is associated with a markedly increased risk for clinical MI and mortality independent of traditional risk factors, according to study results published in Diabetes Care.

Recent advances in cardiovascular imaging that have made it possible to identify unrecognized MI, such as delayed-enhancement magnetic resonance imaging (MRI), may assist in predicting future risk for clinical events. It is well known that in symptomatic patients with diabetes, evidence for MI by delayed-enhancement MRI is associated with increased cardiovascular risk. However, limited data are available regarding the prognostic significance of unrecognized MI by delayed-enhancement MRI in asymptomatic patients with diabetes.

The researchers conducted a prospective study focusing on asymptomatic patients with diabetes and without a history of heart disease to investigate the prevalence and prognostic significance of unrecognized MI by delayed-enhancement MRI.

The study population included 2 cohorts that underwent delayed-enhancement MRI: a high-risk group of 50 patients with type 1 diabetes and advanced renal insufficiency and an average-risk group of 70 patients with type 2 diabetes without renal insufficiency. In addition, the study included a control group of 24 healthy volunteers. The primary study end point was the composite of all-cause mortality and clinical MI. A secondary end point was the composite of cardiac mortality and MI.

During up to 5 years of follow-up, the overall prevalence of unrecognized MI by delayed-enhancement MRI was 19% (n = 23), with higher prevalence in the high-risk compared with the average-risk patients with diabetes (28% vs 13%; P =.038). The prevalence of unrecognized MI by electrocardiography was much lower (5%).

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Among the 23 patients with unrecognized MI, there were 6 deaths (4 were secondary to cardiac causes) and 4 nonfatal MIs, representing a total event rate of 16% per year and a cardiac event rate of 12.8% per year. In the 97 patients without unrecognized MI, there were 6 deaths (all were secondary to noncardiac causes) and 1 nonfatal MI, representing a total event rate of 1.8% per year and a cardiac event rate of 0.3% per year.

After adjusting for Framingham risk score, left ventricular ejection fraction, and type of diabetes, unrecognized MI by delayed-enhancement MRI predicted an 8-fold increased risk for death and clinical MI (95% CI, 3.0-21.1; P <.0001). Furthermore, delayed-enhancement MRI provided a high level of risk discrimination, as 90% of all patients who experience a cardiac event (8 of 9 patients) were individuals with unrecognized MI identified with delayed-enhancement MRI.

The researchers acknowledged the most notable limitation of this study was that not all patients with diabetes are candidates for risk stratification by delayed-enhancement MRI. Small sample size, low rate of statin use, and lack of data regarding additional variables that might influence prognosis were also limiting factors in this study.

“[V]igorous efforts to target these vulnerable patients with diabetes and unrecognized MI with intensive medical therapy and adjunctive coronary revascularization is a strategy worthy of prospective testing,” wrote the researchers.

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Reference

Elliott MD, Heitner JF, Kim H, et al. Prevalence and prognosis of unrecognized myocardial infarction in asymptomatic patients with diabetes: a two-center study with up to 5 years of follow-up [published online, April 22, 2019]. Diabetes Care. doi:10.2337/dc18-2266