Twenty-four-hour ambulatory ECG monitoring relevancy in myotonic dystrophy type 1 follow-up: Prognostic value and heart rate variability evolution

Background Patient prognosis in type 1 myotonic dystrophy (DM1) is very poor. Annual 24-hour holter ECG monitoring is recommended but its relevance is debated. Main objective was to determine whether holter ECG parameters could predict global death in DM1 patients and secondarily to assess whether they could predict cardiovascular events and sudden cardiac death, to compare DM1 patients and healthy controls, and to assess their evolution in DM1 over a 5-year period. Methods This retrospective study included genetically confirmed DM1. Primary endpoint was global death. Secondary endpoints were labeled "sudden cardiac death" which was a composite of sudden cardiac death, aborted sudden cardiac death, implantable cardioverter defibrillator therapy, sustained ventricular tachycardia, atrioventricular block grade 3, pause >3 s; and "cardiovascular events" which was a composite of all-cause mortality, pacemaker or cardioverter defibrillator implantation, sustained ventricular tachycardia, supraventricular tachycardia, hospitalization for acute cardiac cause and heart failure. Results Forty-seven patients (22 women, 40 +/- 13 years old) were included. Three (7%) DM1 patients died, 9 (19%) experienced "sudden cardiac death" endpoint and 21 (45%) experienced "cardiovascular event" endpoint during mean follow-up of 95 +/- 22 months. None of holter ECG parameters were discriminant to predict death or secondary endpoints. Compared to healthy controls, DM1 patients had higher SDNN and LF/HF ratio. Finally, heart rate variability parameters remained stable over a mean interval of 61 +/- 15 months excepting pNN50 which decreased significantly. Conclusion Results suggest that annually-repeated holter ECG in DM1 is not useful for stratifying risk of sudden death and cardiovascular outcomes.