Autonomic function in patients with Duchenne muscular dystrophy

Background: Assessing autonomic function is important for patients with chronic heart failure, but the way that autonomic function changes in patients with Duchenne muscular dystrophy (DMD) and correlates with other clinical parameters during their young age is not clearly known. Methods: Heart rate variability (HRV) during ambulatory electrocardiogram (ECG) was performed in 57 DMD patients (130 recordings) who were not receiving medication (mean age 15.3 ± 4.5 years). The data were compared with the serum levels of brain natriuretic peptide (BNP), the shortening fraction (SF) of the left ventricle on echocardiography, and simple parameters of heart rate from 24 h ambulatory ECG. Results: Among four parameters of HRV measurements (high frequency [HF]; percentage of adjacent normal R‐R intervals that were >50 ms different for the entire 24 h recording [%RR50]; ratio of low to high frequency [LF/HF]; and standard deviation for all normal R‐R intervals for the entire 24 h recording [SDNN]), SDNN was most frequently abnormal. Even when SF was normal, a significant percentage of patients exhibited, abnormal parasympathetic activity (HF, %RR50: 74%, 78%, respectively), sympathetic activity (LF/HF, 43%), and SDNN (96%). Similarly, even if serum BNP levels were normal, 86%, 89%, 59%, and 97% of the patients displayed abnormal autonomic function on these measurements, respectively. Mean heart rate at night most accurately predicted abnormality of SDNN. When the cut‐off point for mean heart rate at night was 71 beats/min, the sensitivity and specificity of this parameter for predicting abnormal SDNN was 94% and 85%, respectively (P < 0.0001). Conclusion: In DMD, autonomic function, especially SDNN, was frequently abnormal, although conventional clinical examinations of cardiac function (BNP levels and SF) were normal. It is proposed that mean heart rate during night could be used as a simple measurement for evaluation of autonomic function.