Heart Rate Variability Declines with Increasing Age and CTG Repeat Length in Patients with Myotonic Dystrophy Type 1

Background: Cardiac myopathy manifesting as arrhythmias is common in the neurological disease, myotonic dystrophy type 1 (DM1). The purpose of the present study was to evaluate heart rate variability (HRV) in patients with DM1. Methods: In a multicenter study, history, ECG, and genetic testing were performed in DM1 patients. Results: In 289 patients in whom the diagnosis of DM1 was confirmed by a prolonged cytosine‐thymine‐guanine (CTG) repeat length the most common ambulatory ECG abnormality was frequent ventricular ectopy (16.3%). The 24‐hour time domain parameters of SDNN (SD of the NN interval) and SDANN (SD of the mean NN, 5‐minute interval) declined as age and CTG repeat length increased (SDNN: −8.5 ms per decade, 95% confidence intervals [CI]−12.9, −4.2, −8.7 ms per 500 CTG repeats, CI −15.7, −1.8, r = 0.24, P < 0.001 ; SDANN: −8.1 ms per decade, CI −12.4, −3.8, −8.8 ms per 500 CTG repeats, CI −15.7, −1.9, r = 0.23, P < 0.001 ). Short‐term frequency domain parameters declined with age only (total power: −658 ms 2 per decade, CI: −984, −331, r = 0.23, P < 0.001 ; low frequency (LF) power −287 ms 2 per decade, CI: −397, −178, r = 0.30, P < 0.001 ; high frequency (HF) power: −267 ms 2 per decade, CI: −386, −144, r = 0.25, P < 0.001 ). The LF/HF ratio increased as the patient aged (0.5 per decade, CI: 0.1, 0.9, r = 0.13, P = 0.03 ). Conclusions: In DM1 patients a decline in HRV is observed as the patient ages and CTG repeat length increases. A.N.E. 2003; 8(3):227‐232