Impairment of cardiac autonomic function in patients with Duchenne muscular dystrophy: Relationship to myocardial and respiratory function

Background Previous studies reported an impairment of nervous autonomic act ivity in patients with Duchenne muscular dystrophy (DMD). However, the rela tionship of the autonomic dysfunction to the impairment of cardiac mechanic al function and of respiratory failure is not completely understood. Methods We evaluated cardiac autonomic function by time- and frequency-doma in heart rate variability (HRV) analysis on 24-hour Holter recordings in 60 patients with DMD (16.8 +/- 4.8 years) and 28 healthy control patients (15 .2 +/- 4.6 years, P = not significant). The circadian rhythm of R-R interva l, low frequency, high frequency, and low-frequency/high-frequency ratio wa s also assessed. In all patients, left ventricular ejection fraction was me asured by 2D echocardiography; respiratory function was assessed by spirome try. Results All HRV parameters were lower in patients with DMD than in control subjects, with the percentage of differences between adjacent R-R intervals >50 ms (11.6% +/- 8.5% vs 27.3% +/- 14.1%, P = .00001) and high frequency (23.9 +/- 10.3 ms vs 36.1 +/- 12.2 ms, P = .0001) showing the strongest dif ferences, A significant circadian rhythm of HRV variables was present in bo th groups, but it was considerably flattened in patients with DMD. There wa s no correlation between left ventricular ejection fraction and HRV indexes except for a week correlation with high frequency (r = 0.30, P = .02) and with low-frequency to high-frequency ratio (r = -0.29, P < .03). Similarly modest correlations were found between forced vital capacity and high frequ ency (r = 0.4, P = .007) and low-frequency/high-frequancy ratio (r = -0.32, P = .026). Multiple regression analysis did not show any independent predi ctive variable For the autonomic impairment. Conclusions Our data show a marked impairment of cardiac autonomic function in patients with DMD, which appears to mainly involve the parasympathetic branch and appears to have a multifactorial origin.