Factors Contributing to Exercise Intolerance in Patients With Atrial Fibrillation

Reduced exercise capacity and exercise intolerance are commonly reported by individuals with atrial fibrillation (AF). Our objectives were to evaluate the contributing factors to reduced exercise capacity and describe the association between subjective measures of exercise intolerance versus objective measures of exercise capacity.

Two hundred and three (203) patients with non-permanent AF and preserved ejection fraction undergoing cardiopulmonary exercise testing (CPET) were recruited. Clinical characteristics, AF-symptom evaluation, and transthoracic echocardiography measures were collected. Peak oxygen consumption (VO_2peak) was calculated during CPET as an objective measure of exercise capacity. We assessed the impact of 16 pre-defined clinical features, comorbidities and cardiac functional parameters on VO_2peak.

Across this cohort (Age 66±11 years, 40.4% female and 32% in AF), the mean VO_2peak was 20.3±6.3 mL/kg/min. 24.9% of patients had a VO_2peak considered low (<16 mL/kg/min). In multivariable analysis, echocardiography-derived estimates of elevated left ventricular (LV) filling pressure (E/E') and reduced chronotropic index were significantly associated with lower VO_2peak. The presence of AF at the time of testing was not significantly associated with VO_2peak but was associated with elevated minute ventilation to carbon dioxide production indicating impaired ventilatory efficiency. There was a poor association between VO_2peak and subjectively reported exercise intolerance and exertional dyspnoea.

Reduced exercise capacity in AF patients is associated with elevated LV filling pressure and reduced chronotropic response rather than rhythm status. Subjectively reported exercise intolerance is not a sensitive assessment of reduced exercise capacity. These findings have important implications for understanding reduced exercise capacity amongst AF patients and the approach to management in this cohort. (ACTRN12619001343190).