The aim of this study was to evaluate the relative impact of spontaneously occurring and periprocedural myocardial infarction (MI) on survival after percutaneous coronary intervention (PCI).

The clinical significance of periprocedural MI after PCI remains uncertain.

Outcomes during a 1-year follow-up were evaluated among 7,773 patients enrolled in the ACUITY (Acute Catheterization and Urgent Intervention Triage Strategy) trial with a non–ST-segment elevation acute coronary syndrome in whom PCI was performed.

Periprocedural MI developed in 466 patients (6.0%), and spontaneous MI unrelated to PCI subsequently developed in 200 patients (2.6%). Patients developing spontaneous and periprocedural MI compared with those patients without MI had significantly greater unadjusted rates of mortality at 30 days (5.0% vs. 3.2% vs. 0.8%, respectively, p < 0.0001) and at 1 year (16.0% vs. 6.0% vs. 2.6%, respectively, p < 0.0001). In a time-updated multivariable analysis, after adjusting for differences in baseline and procedural characteristics between the groups, we found that spontaneous MI was a powerful independent predictor of subsequent mortality (hazard ratio: 7.49, 95% confidence interval: 4.95 to 11.33, p < 0.0001), whereas periprocedural MI was not a significant predictor of mortality (hazard ratio: 1.30, 95% confidence interval: 0.85 to 1.98, p = 0.22).

Among patients with acute coronary syndrome undergoing PCI, the spontaneous development of an MI unrelated to PCI is a powerful predictor of subsequent mortality. In contrast, periprocedural MI is a marker of baseline risk, atherosclerosis burden, and procedural complexity but in most cases does not have independent prognostic significance. (Comparison of Angiomax Versus Heparin in Acute Coronary Syndromes [ACS]; NCT00093158)