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2 Minute Medicine | July 29, 2014

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Silent myocardial infarctions more common than previously assumed

Silent myocardial infarctions more common than previously assumed
| 2 Minute Medicine
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1. The prevalence of silent myocardial infarction (MI) in patients referred for coronary artery disease (CAD) evaluation is higher than previously thought, approaching one-quarter of all patients in this study.  

2. Silent MI is 50% more common among patients with diabetes mellitus.  

Evidence Rating Level: 2 (Good)  

Study Rundown: Silent myocardial infarctions (MIs) lack unequivocal objective signs of myocardial infarction and have minimal, atypical, or no symptoms at all. Most such MIs are diagnosed with screening ECGs, though previous studies have demonstrated the low sensitivity of this method compared to myocardial perfusion single photon emission computed tomography (MPS). This study confirms that MPS improves the diagnostic capability of ECGs, as many patients with substantial infarctions lacked characteristic Q waves on ECG. It also suggests that silent MIs are more common than previously recognized, especially among diabetics. Nearly one quarter of enrolled patients had experienced a silent MI that had gone unrecognized. However, the study does not assess the prognosis of silent MIs; as such, the authors’ argument in favor of increased imaging modalities for detection and increased secondary prevention therapies cannot be backed by claims of cost-effectiveness. Future studies are required to determine optimal screening and prevention for individuals determined to be at risk for silent MIs.   

Click to read the study in The American Journal of Medicine

Relevant Reading: Silent Myocardial Ischemia in Patients With Diabetes Mellitus

In-Depth [prospective cohort study]: This study analyzes silent myocardial infarction (MI) among two cohorts of patients without a prior history of MI who were referred for stress testing. Study participants underwent stress testing (exercise, pharmacological, or combined) and myocardial perfusion single photon emission computed tomography (MPS). Silent MI was defined by myocardial scar greater than or equal to 5% of the left ventricle, based on perfusion images. In the derivation cohort of 1621 patients, prevalence of silent MI was 23.3% – 28.5% in diabetics and 21.5% in nondiabetics. Median infarct size was 10%. These findings were confirmed in a validation cohort of 338 patients, with silent MI prevalence of 26.3%. In both cohorts, diabetes was a significant independent predictor of silent MI, with silent MI prevalence 50% higher in diabetic patients. Among diabetics with silent MI, median left ventricular ejection fraction was 47%, significantly lower than among nondiabetics. Those with silent MI were more likely to be male, have a positive family history of CAD, and had a higher number of Q waves on ECG. However, classical ECG criteria missed 2 of 3 silent MIs.

By Elizabeth Kersten and Andrew Bishara

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