Air versus oxygen in myocardial infarction (AVOID) trial sub-study: Time-dependent effect of oxygen administration on myocardial injury

Background: Routine oxygen therapy has been associated with increased myocardial injury following acute myocardial infarction, although the time-dependent effect of oxygen administration on myocardial infarct size has not been evaluated. Methods: This was a planned sub-study of the Australian multicentre, prospective, randomised, controlled AVOID trial, of 441 STEMI patients who were allocated to routine oxygen therapy (8L/min via facemask) or no supplemental oxygen. The primary endpoint was myocardial infarct size as assessed by cardiac enzymes, troponin (cTnI) and creatine kinase (CK). Allocated treatment was commenced by paramedics after randomisation, and continued for up to 12 hours post procedural intervention in hospital. Peak and are under the curve for cTnI and CK and were assessed using linear regression models adjusted for age, gender, pre-intervention TIMI flow, Killip class, culprit artery, and symptom-to-intervention time. Results: Pre-intervention oxygen administration was not associated with peak cTnI or peak CK release. After adjustment, when compared to no oxygen administration, longer durations of post-intervention oxygen therapy were associated with higher ratios ofmeanpeak cTnI (≤2 hours: 1.43 [95% CI: 0.99 to 2.08, p=0.059]; 2-6 hours: 1.67 [95% CI: 1.14 to 2.44, p=0.009]; 6-12 hours: 2.05 [95% CI: 1.30 to 3.24, p=0.002] and mean peak CK (≤2 hours: 1.22 [95% CI: 0.95 to 1.78, p=0.120]; 2-6 hours: 1.31 [95% CI: 1.01 to 1.71, p=0.043]; 6-12 hours: 1.62 [95% CI: 1.19 to 2.22, p=0.002]. Conclusion: In patients with STEMI, longer durations of oxygen therapy post-procedural intervention may be associated with increased myocardial injury.