Chronotropic incompetence and its relation to exercise intolerance in hypertrophic cardiomyopathy (original) (raw)

2011, International Journal of Cardiology

Background: Diminished functional capacity is common in hypertrophic cardiomyopathy (HCM), although the underlying mechanisms are complicated. We studied the prevalence of chronotropic incompetence and its relation to exercise intolerance in patients with HCM. Methods: Cardiopulmonary exercise testing was performed in 68 patients with HCM (age 44.8 ± 14.6 years, 45 males). Chronotropic incompetence was defined by chronotropic index (heart rate reserve)/(220-ageresting heart rate) and exercise capacity was assessed by peak oxygen consumption (peak Vo 2 ). Results: Chronotropic incompetence was present in 50% of the patients and was associated with higher NYHA class, history of atrial fibrillation, higher fibrosis burden on cardiac MRI, and treatment with β-blockers, amiodarone and warfarin. On univariate analysis, male gender, age, NYHA class, maximal wall thickness, left atrial diameter, peak early diastolic myocardial velocity of the lateral mitral annulus, history of atrial fibrillation, presence of left ventricular outflow tract obstruction (LVOTO) at rest, and treatment with betablockers were related to peak Vo 2 . Peak heart rate during exercise, heart rate reserve, chronotropic index, and peak systolic blood pressure were also related to peak Vo 2 . On multivariate analysis male gender, atrial fibrillation, presence of LVOTO and heart rate reserve were independent predictors of exercise capacity (R 2 = 76.7%). A cutoff of 62 bpm for the heart rate reserve showed a negative predictive value of 100% in predicting patients with a peak Vo 2 b 80%. Conclusions: Blunted heart rate response to exercise is common in HCM and represents an important determinant of exercise capacity. . The diagnosis of HCM was based on the echocardiographic appearance of left ventricular maximum wall thickness greater than or equal to 15 mm, in the absence of any other cause capable of producing such hypertrophy. HCM was also considered present in patients with maximum wall thickness 13 or 14 mm in the presence of a positive family history for HCM and/or ECG changes compatible with