AIMS: We aimed to evaluate the impact of delay from diagnostic pre-hospital electrocardiogram (ECG) to wiring of the infarct-related vessel (ECG-to-wire) >120 minutes on cardiovascular magnetic resonance (CMR) markers of reperfusion success and clinical outcome in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS AND RESULTS: We included 1,492 patients in the analyses of clinical outcome. CMR was performed in 748 patients to evaluate infarct size and myocardial salvage. In total, 304 patients (20%) had ECG-to-wire >120 minutes, which was associated with larger acute infarct size (18% [interquartile range (IQR), 10-28] vs. 15% [8-24]; p=0.022) and smaller myocardial salvage (0.42 [IQR 0.28-0.57] vs. 0.50 [IQR 0.34-0.70]; p=0.002). However, 33% of the patients with ECG-to-wire >120 minutes still had a substantial myocardial salvage ≥0.50. In a multivariable analysis, ECG-to-wire >120 minutes was associated with an increased risk of all-cause mortality and heart failure (hazard ratio 1.61, 95% confidence interval [CI] 1.14-2.26, p=0.007).

CONCLUSIONS: ECG-to-wire >120 minutes was associated with larger infarct size, smaller myocardial salvage and a poorer clinical outcome in STEMI patients transferred for primary percutaneous coronary intervention. However, myocardial salvage was still substantial in one third of patients treated beyond 120 minutes of delay.