While infarct size in patients with ST-segment elevation myocardial infarction (STEMI) has been generally associated with long-term prognosis, whether a therapeutic effect on infarct size has a corresponding therapeutic effect on long-term outcomes is unknown.

Using combined patient-level data from 10 randomized trials of primary percutaneous coronary intervention (PCI) for STEMI, we created multivariable Cox proportional hazard models for one-year heart failure hospitalization and all-cause mortality, which included clinical features and a variable representing treatment effect on infarct size. The trials included 2679 participants; infarct size was measured at a median 4 days post infarction.

Mean infarct size among the control groups ranged from 16% to 35% of the left ventricle, and from 12% to 36% among treatment groups. There was a significant relationship between treatment effect on infarct size and treatment effect on 1-year heart failure hospitalization (HR 0.85, 95% CI 0.77-0.93, P=.0006), but not on one-year mortality (HR 0.97, 95% CI 0.89-1.06). The treatment effect between infarct size and heart failure hospitalization was stable in sensitivity analyses adjusting for time from STEMI onset to infarct size assessment, and when considering heart failure as the main outcome and death as a competing risk.

We conclude that early treatment-induced effects on infarct size are related in direction and magnitude to treatment effects on heart failure hospitalizations. This finding enables consideration of using infarct size as a valid surrogate outcome measure in assessing new STEMI treatments.