Accurate estimation of coronary epicardial flow in patients with ST-elevation myocardial infarction (STEMI) is crucial to evaluating the effect of therapy and predicting outcome. Whether operator bias exists in visual estimation of TIMI flow grade among patients with STEMI undergoing primary percutaneous coronary intervention (PCI) remains uncertain. Hence, we examined this issue in the angiographic substudy of the Assessment of Pexelizumab in Acute Myocardial Infarction (APEX-AMI) trial.

TIMI flow grade of the infarct-related artery was assessed before and after PCI by visual estimation of local investigators (LI) and by an independent core laboratory (CL). We evaluated agreement between the CL and LI and the relationship between post-PCI TIMI flow grade and 90-day outcomes (mortality; death/congestive heart failure/shock).

Of 922 patients with independent CL estimation of TIMI flow grade, there was moderate agreement in the pre-PCI assessment (κ = 0.56) and poor agreement post-PCI (κ = 0.36); moreover, these disparities were directionally different before versus after PCI. Disagreement between LI and CL occurred in 167 patients pre-PCI (19%) and in 123 (14%) patients post-PCI. LI TIMI grades consistently underestimated flow pre-PCI in 63% and overestimated flow post-PCI in 78% of patients relative to the CL. Core laboratory estimation of post-PCI TIMI flow grade provided better prediction of 90-day mortality and death/congestive heart failure/shock than that of LI.

Significant quantitative and directional variation existed in TIMI flow grades assessed by LI versus a CL in nearly a fifth of the patients. Core laboratory interpretation post-PCI provides better prediction of clinical outcomes. These data deserve consideration when interpreting angiographic data from STEMI patients without CL estimation.