Exercise-Induced ST Depression as a Prognostic Indicator of Cardiac Morbidity in Thrombolytic-Treated Post-Myocardial Infarction Patients with Silent Ischemia

Background: The significance of silent ischemia after acute myocardial infarction (MI) has been questioned. Objective: The aim of this study was to assess the risk for cardiac events in patients with silent ischemia after thrombolytic-treated first acute MI. Methods and Results: The Danish Trial in Acute Myocardial Infarction randomized 505 patients to conservative treatment after thrombolytic-treated first acute MI. For this analysis, patients were included if they demonstrated silent ischemia, i.e. ST deviations during exercise but without angina, during a symptom-limited bicycle exercise test. A total of 287 patients had silent postinfarct inducible ischemia. The 1-year incidence rate of combined cardiac endpoints, defined as death, reinfarction, need for revascularization or admission with unstable angina, was 22%. The level of maximum ST change during a stress test was used to categorize patients into three groups: group A: ST elevation (n = 54, 1-year event rate 15%); group B: >1 to 2 mm of ST depression during a stress test (n = 147, 1-year event rate 29%). Using a Cox proportional hazards model, the predictor of cardiovascular endpoints was the level of ST depression during a stress test (relative risk 2.4, 95% confidence limits 1.1–5.0, group C versus group A). Conclusion: This study identifies ST depression of more than 2 mm during a stress test as a significant risk factor for cardiac morbidity.