IMPROVED VENTILATORY RESPONSE TO EXERCISE AFTER CARDIOVERSION OF CHRONIC ATRIAL-FIBRILLATION TO SINUS RHYTHM

The purpose of this study was to assess hemodynamic and respiratory measures of submaximal and maximal exercise performance in patients with chronic atrial fibrillation, before and one month after cardioversion to sinus rhythm. Restoration of sinus rhythm (n = 16) produced significant reductions in resting and exercise heart rates, 14 percent to 20 percent (p<0.01). Due to a proportionately larger increase in stroke volume, cardiac output increased by 9 percent during low-level exercise (p<0.01) and by 7 percent during exercise above the anaerobic threshold (p<0.05). Minute ventilation was reduced by 7 percent during low-level exercise (p<0.01) and by 9 percent above the anaerobic threshold (p<0.05). The ratio between minute ventilation and carbon dioxide elimination was significantly reduced (p<0.01). Maximum oxygen uptake (+8 percent; p<0.01) and maximal tolerated work load (+6 percent; p<0.05) increased. Hemodynamic changes during exercise were similar in patients with (n = 7) or without (n = 9) disopyramide prophylaxis. Restoration of sinus rhythm induced improvement in hemodynamics and in efficiency of ventilation, thereby reducing the ventilatory demand during submaximal exercise.