Prevalence and prognostic significance of silent myocardial ischaemia detected by exercise test and continuous ECG monitoring after acute myocardial infarction

The incidence and prognostic significance of silent myocardial ischaemia in 165 patients who survived a first acute myocardial infarction were assessed by means of maximal exercise stress test and 24 h continuous ECG monitoring performed before discharge. During the 1 year follow-up period 10 cardiac deaths occurred; moreover seven patients suffered a fatal myocardial re-infarction and 14 developed unstable angina. Cardiac death occurred in five of 40 patients (12.5%) with ST segment depression on stress test by in only three of 117 (2.6%) without ST segment changes (P<0.01). One-hundred-and-three of 117 patients (88.0%) without angina or ST segment depression on stress testing survived 1 year without cardiac events, compared with 24 of 40 patients (60.0%) with ST segment depression whether or not associated with angina (P<0.001). Cardiac death occurred in five of 25 patients (20.0%) with ST segment depression on continuous ECG monitoring, compared with five of 140 (3.6%) without (P<0.01). One-hundred-and-seventeen out of 140 patients (83.6%) without angina or ST segment depression survived 1 year follow-up without cardiac events, compared with 13 of 25 (52.0%) with ST segment depression with or without angina (P<0.01). Classifying patients in a 2 x 5 contingency table according to the occurrence of ST segment depression on exercise testing and/or ECG ambulatory monitoring, the Yates corrected chi-square test showed a significant pattern when cardiac deaths and cardiac events were considered together (P<0.01). However, in patients with exercise ST segment depression, the incidence of cardiac deaths and cardiac events was not influenced by the occurrence of ST segment changes during continuous ECG monitoring. All eight patients who stopped exercising before reaching the target heart rate because of dyspnoea (five patients), arrhythmias (two patients), or hypertension (one patient) had ST segment depression during ECG monitoring: two of them died during follow-up and three suffered from unstable angina. Thus, ST segment analysis of ambulatory ECG yields prognostic information in patients with a doubtful stress test result and is a useful technique after acute myocardial infarction. However, caution is needed when evaluating patients without ischaemia during ECG monitoring if a stress test is not available.