Cardiac autonomic function in patients with myasthenia gravis: analysis of the heart-rate variability in the time-domain

Aim: Myasthenia gravis (MG) is a neuromuscular transmission disorder caused by acetylcholine receptor autoantibodies. Cardiac autonomic dysfunctions were rarely reported in patients with MG. Functional cardiac abnormalities were variable and reported in patients at severe stages of the disease and with thymoma. We investigated cardiac functions in patients with MG using Ambulatory 24-h electrocardiographic Holter-Monitoring.Methods: This study included 20 patients with MG with a mean age of 28.45 ± 8.89 years and duration of illness of 3.52 ± 1.15 years. The standard Holter reports include data for heart-rate, ventricular ectopies (VEs), supraventricular ectopies (SVEs), heart-rate variability (HRV), ST, QT, atrial fibrillation and T-wave alternans.Results: VEs, SVEs and ST-T changes were reported in 55%, 40% and 20% of patients respectively. Compared with healthy subjects (n = 20), HRV components including SDNN, SDANN, SDNN Index, RMS-SD and pNN50 (P = 0.001 for all) were reduced in patients indicating sympathetic and parasympathetic autonomic dysfunctions. HRV abnormalities were reported in 30-60% of patients. No significant correlations were identified between SDNN, RMS-SD, pNN50, and duration of illness.Conclusion: Depressed HRV may be an early manifestation of autonomic neuropathy in patients with MG even in milder stages of the disease. This information is useful in rating disease progression and the efficacy of therapeutic interventions