Pexelizumab and infarct size in patients with acute myocardial infarction undergoing primary percutaneous coronary Intervention: a delayed enhancement cardiac magnetic resonance substudy from the APEX-AMI trial.

Objectives: The purpose of the study was to understand determinants of infarct size in a primary percutaneous intervention (PCI) population treated with pexelizumab compared with placebo.

Background: In the multicenter APEX-AMI (Pexelizumab in Conjunction With Angioplasty in Acute Myocardial Infarction) trial, pexelizumab did not reduce 90-day mortality. Cardiac magnetic resonance (CMR) with delayed enhancement was used in a substudy evaluating infarct size and left ventricular ejection fraction (LVEF).

Methods: Consecutive patients undergoing primary PCI for first myocardial infarction (MI) as part of the APEX-AMI trial were enrolled in this substudy at 5 centers. The CMR was completed on days 3 to 5 (n=99) and day 90 (n=83) following PCI. Central core lab-masked analyses for quantified LVEF, volumes, and infarct size by planimetry were performed.

Results: Patients were 60+/-12 years of age, male (n=83 [84%]), had similar time from symptom onset to presentation (median 2.6 h vs. 2.5 h; p=1.0), and similar baseline ST-segment deviation (13.5 mm vs. 14 mm; p=0.59) in both groups. Pexelizumab-treated patients had smaller infarct size (day 3 LV 10.5% vs. 16.2%, p=0.022; day 90 LV 5.9% vs. 12.4%, p=0.015) and higher LVEF (day 3 50.3% vs. 46.2%, p=0.073; day 90 53.9% vs. 49.3%, p=0.036) compared with placebo-treated patients. The median peak creatine kinase in the pexelizumab group was also significantly less than placebo (922 mg/dl vs. 1,973 mg/dl; p=0.03). Notably, the pexelizumab group had lower Thrombolysis In Myocardial Infarction (TIMI) flow grade pre-PCI (46.9% vs. 75.0%; p=0.018), a difference not seen in the overall APEX-AMI study. A multivariate model including baseline features and pexelizumab treatment found anterior MI location and pre-PCI TIMI flow to be significant independent predictors infarct size (p=0.001), whereas pexelizumab was not (p=0.29). No death, heart failure, or shock was noted in either substudy group at 90 days.

Conclusions: In a CMR substudy of pexelizumab in MI, baseline TIMI flow grade and anterior location were the only predictors of infarct size, with a reduction of pre-PCI TIMI flow grade 0 by 28%, leading to a 35% reduction in infarct size. (The APEX-AMI Trial; NCT00091637).