Chronotropic Incompetence and its Relation to Exercise Intolerance in Chronic Obstructive Pulmonary Disease

To study the relationship between chronotropic incompetence (CI) and disease severity and to assess the effect of CI on exercise capacity in patients with chronic obstructive pulmonary disease (COPD).

Arterial blood gas analysis, pulmonary function test and cardiopulmonary exercise testing were conducted in 60 patients with stable COPD and 45 healthy volunteers. CI was defined using the chronotropic response index (CRI = (peak heart rate-resting heart rate) / (220-age-resting heart rate). Based on CRI, patients with COPD were divided into the normal chronotropic group (n = 23) and CI group (n = 37).

CI was present in 61.7% of the patients with COPD. Exercise capacity (peak oxygen uptake as percentage of predicted value, peak VO₂%pred), peak heart rate and CRI were significantly lower in patients with COPD than in controls. However, resting heart rate was significantly higher than in controls. FEV₁%pred and exercise capacity were significantly decreased in the CI group when compared with those in the normotropic group. There was significant association between CRI with FEV₁%pred and peak VO₂%pred. Multivariate regression analysis showed that CRI and FEV₁%pred were independent predictors of exercise capacity in patients with COPD. A cutoff of 0.74 for the CRI showed a specificity of 94.1% in predicting patients with a peak VO₂%pred < 60%.

CRI was associated with disease severity in patients with COPD. CI may be an important parameter to reflect exercise capacity in patients with COPD.