BACKGROUND: Guidelines recommend primary percutaneous coronary intervention (PCI) in patients with ST-segment-elevation myocardial infarction (STEMI) presenting ≥12 hours of symptom onset in the presence of ongoing ischemia. However, data supporting this recommendation are limited. We evaluated the effect of primary PCI on reperfusion success, using cardiac magnetic resonance, in STEMI patients with signs of ongoing ischemia presenting 12 to 72 hours after symptom onset compared with STEMI patients presenting <12 hours.

METHODS AND RESULTS: We included 865 STEMI patients who underwent cardiac magnetic resonance just after index PCI and 3 months later. Despite equal area at risk (34±12% versus 33±12%; P=0.370), patients presenting late (n=58) had larger final infarct size (13% [interquartile range, 9-24] versus 11% [interquartile range, 4-19]; P=0.037) and smaller myocardial salvage index (0.58 [interquartile range, 0.39-0.71] versus 0.65 [interquartile range, 0.49-0.84]; P=0.021) compared with patients presenting <12 hours after symptom onset (n=807). However, 65% of late-presenting patients achieved substantial myocardial salvage ≥0.50, and area under the curve for symptom onset to PCI as predictor of a myocardial salvage index ≥0.50 was poor (0.58 [95% CI, 0.53-0.63]; P<0.001). In addition, final infarct size, salvage index and left ventricular function correlated weakly with duration from symptom onset to primary PCI ( R2 values <0.05).

CONCLUSIONS: STEMI patients with signs of ongoing ischemia treated with primary PCI 12 to 72 hours after symptom onset had less myocardial salvage and developed larger infarcts. However, a large proportion achieved substantial myocardial salvage indicating a benefit from primary PCI in late-presenting patients.

CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov . Unique identifiers: NCT01435408 and NCT01960933.