Spontaneous reperfusion (SR) in ST-elevation myocardial infarction has traditionally been assessed by coronary angiography. The frequency of SR varies widely in prior studies, and the clinical implications in the modern reperfusion era are unclear. Accordingly, using data from the ASSENT 4 PCI (ASsessment of the Safety and Efficacy of a New Treatment Strategy with Percutaneous Coronary Intervention) study, we undertook a systematic assessment of SR using both electrocardiographic (ECG) and angiographic techniques.

Five hundred eighty-five patients randomized to the primary percutaneous coronary intervention (PCI) arm of ASSENT 4 PCI were studied: all had ECG and thrombolysis in myocardial infarction flow data available approximately 60 minutes after randomization and before PCI. Electrocardiographic SR (≥70% ST-segment resolution) occurred in 14.9% (87/585) and angiographic SR (thrombolysis in myocardial infarction grade 3) in 14.7% (86/585) of patients. Thirty-day clinical outcomes of patients with ECG SR versus no ECG SR tended to have lower mortality (0% vs 3.4%, P = .091), a lower composite of death/shock/congestive heart failure (6.9% vs 12.2%, P = .148), and significant reductions in death/reinfarction (0% vs 5.6%, P = .014). By contrast, no such differences were evident in patients with angiographic SR versus no SR for death (2.3% vs 3.0%, P = 1.00), death/shock/congestive heart failure (9.3% vs 11.8%, P = .498), or death/reinfarction (2.3% vs 5.2%, P = .409).

Whereas the frequency of SR was comparable using either ECG or angiographic criteria, clinical outcomes were best aligned with ECG SR. These data support the role of the ECG in assessing reperfusion and likely reflect the overall impact of myocardial perfusion versus infarct-related artery epicardial patency alone.