Factors Affecting Platelet Reactivity 2 Hours After P2Y12 Receptor Antagonist Loading in Primary Percutaneous Coronary Intervention for ST-Elevation Myocardial Infarction – Impact of Pain-to-Loading Time –

BACKGROUND Delay in the onset of antiplatelet action occurs in patients with ST-elevation myocardial infarction (STEMI) and is likely due to disturbed absorption. We hypothesized that patients presenting relatively late after the onset of symptoms would have faster antiplatelet action. METHODS AND RESULTS We analyzed patient-level data from 5 studies of 207 P2Y12 receptor antagonist-naive patients with STEMI undergoing primary percutaneous coronary intervention (PCI). All patients had available platelet reactivity (PR) assessment with the VerifyNow assay (in P2Y12 reaction units; PRU) prior to and 2 h after loading. High PR (HPR) was defined as ≥ 208 PRU. Pain-to-antiplatelet loading time independently predicted PR at 2 h after loading: every 1-h increase in pain-to-antiplatelet loading time produced a 7% decrease in PR (P=0.001). Pretreatment PR, body mass index, morphine and novel P2Y12 receptor antagonist also affected PR 2 h after loading. Novel P2Y12 receptor antagonist use and per hour increase in pain-to-antiplatelet loading time were independently associated with lower probability for HPR with an OR (95% CI) of 0.145 (0.095-0.220) and 0.776 (0.689-0.873), P