Air Versus Oxygen in ST-Segment Elevation in Myocardial Infarction
The Article: Air Versus Oxygen in ST-Segment Elevation in Myocardial Infarction (aka AVOID). Stub et al. (2015) Circulation. 2143-2150
The Idea: Is supplemental oxygen beneficial or harmful in normoxic patients who have a STEMI, and what are the effects on infarct size compared to no oxygen supplemental
The Study: A multicenter, prospective, open-label randomized trial conducted at 9 hospitals with 24-hr PCI availability in Australia. Paramedics initially screened chest pain patients; exclusion criteria included O2 sats less than 94%, bronchospasm, oxygen supplementation prior to randomization, AMS, transport to non-participating hospital, no STEMI as per ED physician. Patients were split into two arms, the oxygen arm (N=218) received 8 L/min via face mask and the no oxygen arm (N=223) did not receive supplemental O2 unless their sats fell below 94%. Baseline and periodic CTNI and CK levels were measured. Patients were followed up with at 6 months to assess cardiac infarct size by MRI. Primary endpoints was myocardial injury measured by CTNI and CK levels. Secondary endpoints were mortality due to cardiac event, arrhythmias, recurrent MI, repeat revascularization, infarct size.
The Findings: No statistical difference found between the two groups in regards to peak CTNI levels (both mean and AUC at 72 hours). However, there was a statistically significant difference between CK levels with a 20% increase in the oxygen group. The oxygen group also had larger infarct size when assessed at 6 months, which was statistically significant. However, when the infarct size was normalized for LV mass, this become statistically insignificant (however, approaching clinical significance).
The Takeaway: Oxygen supplemental is not associated with improvement of symptoms and can actually be harmful in normoxic patients who have a STEMI due to reperfusion injury. Study was powered only to detect initial myocardial injury, so larger studies with greater power need to be performed before making changes to guidelines. Keeping this in mind, could this be the beginning of the end of MONA?