A randomised controlled trial of the effect of high concentration oxygen on myocardial ischaemia during exercise

Abstract

Background International guidelines recommend the use of oxygen for angina, based on Level C evidence. We aimed to determine whether high concentration oxygen influences the time to exercise-induced ischaemia or angina in patients with stable ischaemic heart disease (IHD). Methods 22 subjects with IHD and a positive exercise treadmill test (ETT) awaiting coronary angiography were randomised to two further ETTs according to a double-blind, crossover study design, during which they breathed oxygen or air at 15 L/min via a non-rebreather mask. Subjects in whom significant coronary artery disease was not subsequently confirmed by coronary angiography were excluded from analysis. The primary outcome was time to exercise-induced myocardial ischaemia, defined as ≥ 1 mm ST depression on contiguous electrocardiographic (ECG) leads. The secondary outcome was time to onset of angina. Results Exercise-induced myocardial ischaemia occurred in 17 of the 19 subjects with coronary artery disease, with the remaining two stopping due to shortness of breath. The mean (SD) time to inducible ischaemia was 35 (47) s longer (95% CI 11 to 59, P = 0.007) with oxygen compared to air. Exercise-induced angina occurred in 9 subjects and started a mean 19 (32) s later (95% CI - 6 to 43, P = 0.12) with oxygen compared to air. All subjects who developed myocardial ischaemia or angina did so during both of the study ETTs. Conclusion High concentration oxygen increases the time to onset of exercise-induced myocardial ischaemia in patients with stable IHD.