ST-elevation myocardial infarction (STEMI) patients who used supplemental oxygen therapy showed an increase in myocardial injury and major cardiac arrhythmia, compared to those who did not use oxygen, according to results of the AVOID trial presented Nov. 19 at AHA 2014.

Led by Dion Stub, MBBS, PhD, Baker IDI Heart and Diabetes Institute, Melbourne Australia, the study sought to measure the effect supplemental oxygen therapy in normoxic patients with STEMI had on myocardial infarct size. Of the 638 original study participants, 441 were diagnosed with STEMI after being randomized into supplemental oxygen (n=218) and non-supplemental (n=223) groups. Patients were excluded for oxygen saturation less than 94 percent on a pulse oximeter, oxygen administration prior to randomization, an altered conscious state and not meeting STEMI criteria. The remaining participants had similar baseline characteristics in STEMI. Primary and secondary end points for the study included the myocardial infarct size on cardiac enzymes, ST-segment resolution and survival to hospital discharge. 

Patients in both groups received a primary percutaneous coronary intervention followed by an analysis of cardiac enzymes, within 72 hours of being admitted to the hospital, to determine the extent of muscle damage from the heart attack. After six months, patients received a cardiac magnetic resonance imaging and clinical follow-up to assess for reoccurring heart attacks, abnormal heart rhythm and any further muscle damage.

Results showed that patients who received supplemental oxygen therapy had more reoccurring myocardial infarctions and abnormal heart rhythm, due to increased levels of the cardiac enzyme troponin. Furthermore, these patients also displayed more heart damage after six months than those patients who did not receive supplemental oxygen. Although oxygen therapy has been used in the initial treatment of patients with suspected myocardial infarction for over a century, the researchers conclude that supplemental oxygen therapy may not be beneficial.

Keywords: Oxygen Inhalation Therapy, Myocardial Infarction, Australia, Magnetic Resonance Imaging, Arrhythmias, Cardiac, Troponin, Percutaneous Coronary Intervention, AHA Annual Scientific Sessions

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