Background: Previous studies reported an impairment of nervous autonomic activity in patients with Duchenne muscular dystrophy (DMD). However, the relationship of the autonomic dysfunction to the impairment of cardiac mechanical function and of respiratory failure is not completely understood.
Methods: We evaluated cardiac autonomic function by time- and frequency-domain 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 interval, low frequency, high frequency, and low-frequency/high-frequency ratio was also assessed. In all patients, left ventricular ejection fraction was measured by 2D echocardiography; respiratory function was assessed by spirometry.
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 differences. A significant circadian rhythm of HRV variables was present in both groups, but it was considerably flattened in patients with DMD. There was no correlation between left ventricular ejection fraction and HRV indexes except for a weak 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 frequency (r = 0.4, P =.007) and low-frequency/high-frequency ratio (r = -0.32, P =.026). Multiple regression analysis did not show any independent predictive 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.