New ST-depression: An under-recognized high-risk category of ‘complete’ ST-resolution after reperfusion therapy

It is not known if there is an association between resolution of ST-elevation to ST-depression following fibrinolysis and 30-day mortality. In an ECG substudy of HERO-2, which compared bivalirudin to unfractionated heparin following streptokinase in 12,556 patients with ST-elevation myocardial infarction ECGs were recorded at baseline and at 60 minutes after commencing fibrinolysis. The main outcome measure was 30-day mortality. Using summed ST-segment elevation and five categories of changes in the infarct leads, further ST-elevation, 0–30% ST-resolution, >30–70% (partial) ST-resolution, >70% (complete) ST-resolution, and new ST-depression occurred in 21.7, 24.9, 36.8, 14.8, and 1.8% of patients, with 30-day mortality of 12.3, 11.7, 8.0, 4.2, and 8.1%, respectively. For the comparison of new ST-depression with complete ST-resolution and no ST-depression, p<0.01 with 24-hour mortality 4.5 vs. 1.3%, respectively (p=0.0003). Patients with new ST-depression had similar peak cardiac enzyme elevations as patients with complete ST-resolution without ST-depression. On multivariate analysis including summed ST-elevation at baseline, age, sex, and infarct location, new ST-depression was a significant predictor of 30-day mortality (OR 1.82, 95% CI 1.42–4.29). In patients with complete ST-resolution following fibrinolysis, new ST-depression at 60 minutes developed in 10.8% of patients. These patients had higher mortality than patients with complete ST-resolution without ST-depression and represent a high-risk group which could benefit from rapid triage to early angiography and revascularization as appropriate.