Reassessing the clinical significance of electrocardiographically unrecognized myocardial infarctions: Radionuclide infarct size and its impact on long‐term prognosis

Abstract Background Silent or unrecognized myocardial infarction (UMI) diagnosed by surveillance electrocardiography (ECG) carries similarly poor prognosis as recognized MI (RMI) for poorly understood reasons. Methods This study included 5430 consecutive patients who presented to the nuclear laboratory and underwent 2‐day stress and rest Tc‐99m sestamibi and ECG studies between March 1991 and June 1999. UMI was diagnosed if ECG showed Q‐wave MI in the absence of a history of RMI. We measured infarct size (% defect size as compared with the entire left ventricular sestamibi uptake), ejection fraction (EF, %), and summed difference score (SDS, sestamibi uptake by myocardium in stress minus sestamibi uptake in rest images as a marker of ischemia). Survival was determined by follow‐up survey (median 6 years). Results We identified 346 UMIs, 628 RMIs, and 4456 subjects without MI (No MI). As compared with RMI, UMI patients had lesser abnormalities on nuclear scans (p