Objective: The aim of this study was to evaluate cardiac autonomic nervous system function using Holter-derived and standard electrocardiographic parameters in patients with myotonic dystrophy (dystrophia myotonica, DM) and no clinically overt heart involvement.
Methods: Eighty-four DM patients without conditions potentially influencing cardiac autonomic function were enrolled in the study: 44 with DM type 1 and 40 with DM type 2 (mean age 34.9 ± 11.5 and 47.8 ± 13.5 years, respectively). Two corresponding control groups of aged-matched healthy subjects were selected for DM1 (n = 35) and for DM2 (n = 30). Standard electrocardiography for QT interval dispersion and 24-h Holter monitoring with time-domain heart rate variability and heart rate turbulence were performed.
Results: No significant differences in time-domain heart rate variability parameters between DM1 or DM2 subjects and controls were observed. However, heart rate turbulence parameters were significantly impaired in DM1 patients as compared to their controls: turbulence onset (p = 0.025), and turbulence slope (p = 0.018). Moreover, turbulence slope was also impaired in DM2 patients (p = 0.042). As compared to controls, we observed an increased QT dispersion, both in DM1 (p = 0.003) and also in DM2 patients (p < 0.0001). No relationship between disease duration or neurological status and time-domain heart rate variability, heart rate turbulence, and QT dispersion was observed.
Interpretation: Despite normal time-domain heart rate parameters, impaired heart rate turbulence and increased QT dispersion may suggest cardiac autonomic nervous system dysfunction in DM patients. The present study is the first one in which heart rate turbulence and QT dispersion assessment were examined both in DM1 and DM2 patients.
Keywords: Heart rate turbulence; Heart rate variability; Myotonic dystrophy type 1; Myotonic dystrophy type 2; QT dispersion.