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

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 < .0001 for all), including smaller infarct size (5.7% vs. 12.2%), higher EF (58% vs. 53%), and lesser ischemia (SDS; 3.9% vs. 2.7%). UMI prognosis was as poor as that of RMI (annual mortality rate 4.7% vs. 4.8% with No MI rate of 2.9%; p < .001 for all comparisons), and this persisted after multivariate analysis. Infarct size quantification successfully risk-stratified ECG-UMI patients, but UMI patients continued to predict mortality even if the infarct size was 0%.

Conclusions

Although UMI patients have lesser abnormalities on nuclear scans, ECG-based UMI continues to independently predict mortality, indicating the continuing relevance of ECG in clinical practice.