EFFECT OF EXERCISE-INDUCED HYPOXEMIA ON MYOCARDIAL REPOLARIZATION IN SEVERE CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Background-Exercise training is being promoted increasingly for patien ts with chronic obstructive pulmonary disease (COPD). Many of these pa tients experience exercise related arterial desaturation but the clini cal importance of these hypoxaemic episodes is not known. QTc dispersi on is a marker of myocardial repolarisation abnormalities and there ha s been much interest in its role as a non-invasive predictor of cardia c arrhythmias and sudden death. However, Little is known about the dyn amic effects that exercise and hypoxaemia have on QTc dispersion in pa tients with COPD. Methods-20 patients with severe COPD (FEV1 <40% pred icted) undertook two 15 minute treadmill tests at a speed calculated t o produce a constant workload of 50% maximum oxygen consumption (Vo(2) max) during which they were blindly given either air or 35% oxygen in random order. Physiological measurements taken throughout exercise inc luded 12 lead electrocardiograms from which QTc dispersion values were calculated according to standard criteria. Nine of the patients who d esaturated with exercise were studied further. A similar degree of hyp oxaemia was induced at rest by giving them a titrated mixture of air a nd oxygen and the changes in QTc dispersion were recorded. Results-11 of the 20 patients developed significant hypoxaemia (desaturation by g reater than or equal to 5% to <90%) with exercise breathing air. There were no significant changes in QTc dispersion with either exercise or hypoxaemia. There were no significant changes in QTc dispersion when comparing those who did and did not desaturate, and those with and wit hout a high baseline QTc dispersion values (60 ms). Induced hypoxaemia without exercise also failed to worsen QTc dispersion. Conclusions-No evidence was found to suggest that exercise, even when associated wit h hypoxaemia, causes myocardial repolarisation abnormalities in patien ts with COPD.