OBJECTIVES: We sought to examine whether intracoronary electrocardiogram (IC-ECG) assessment in patients with non-ST-segment elevation myocardial infarction (NSTEMI) can predict cardiac outcomes. BACKGROUND: There has been no data correlating myocardial damage and cardiac events with an IC-ECG ST-segment change after percutaneous coronary intervention (PCI) in NSTEMI patients. METHODS: We examined 111 NSTEMI patients undergoing PCI with an IC-ECG recording. IC-ECG ST-segment elevation (STE) was defined as >0.1 mV in the risk area, located by placing the guidewire distal to the culprit lesion. Clinical characteristics and in-hospital and long-term follow-up adverse cardiac event rates were compared between IC-ECG STE and non-IC-ECG STE groups at the completion of PCI. RESULTS: IC-ECG STE was observed in 36 patients (32.4%) immediately after PCI. Peak cardiac biomarkers were significantly elevated in patients with IC-ECG STE versus those without (cardiac troponin I 31.9 ng/mL (18.0-104.5) vs. 8.2 ng/mL (1.8-21.4); P < 0.001). At a median follow-up of 35 months, the cardiac event free rate was significantly worse in patients with IC-ECG STE than in those without (long-rank test χ(2) = 10.9; P = 0.001). Cox proportional hazards analysis showed IC-ECG STE (hazard ratio, 2.54; 95% confidence interval [CI], 1.38-4.70; P = 0.003) was an independent predictors of cardiac events. CONCLUSIONS: The present study suggests that presence of IC-ECG STE might help identify high-risk NSTEMI patients with greater myocardial injury leading to adverse cardiac events.