Silent ischemia after uncomplicated myocardial infarction: lack of incremental clinical significance

Abstract

To determine the potential utility of the detection of silent myocardial ischemia after acute myocardial infarction for clinical decision making, we investigated the hypothesis that the occurrence of silent myocardial ischemia on ambulatory electrocardiographic (EGG) monitoring after acute myocardial infarction is independently predictive of adverse outcome in patients in whom conventional clinical and investigative parameters indicate favourable prognosis on medical therapy. Among 465 consecutive patients admitted to our Coronary Care Unit with acute myocardial infarction, 42 patients (39% of those eligible) were randomly selected for study. Twenty-four hour ambulatory ECG monitoring was carried out 13 ± 10 (standard deviation) days post-acute myocardial infarction. Ninety-eight percent of patients were receiving prophylactic anti-ischemic medications and 81% on aspirin. Silent myocardial ischemia was detected in 14%. During the follow-up period of 16 ± 3 months, acute ischemic events occurred in 33% of those with silent myocardial ischemia and 19% of those without previous silent myocardial ischemia ( P = 0.59). The sensitivity of the test for prediction of future acute ischemic events was 22% (95% confidence interval: 3–60%), specificity 87% (95% confidence interval: 72–97%), positive predictive value 33% (95% confidence interval: 4–78%) and negative predictive value 81% (95% confidence interval: 64–92%). Therefore the detection of ambulatory silent myocardial ischemia after acute myocardial infarction is not of sufficient incremental value as a predictor of the occurrence of adverse cardiac events to justify its routine clinical use in this subgroup of patients.