Circadian rhythm of heart rate in myotonic dystrophy

Journal of Clinical and Basic Cardiology 2000; 3 (3): 181-186

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Keywords: Chronobiologie,  Elektrokardiographie,  Herzfrequenz,  Myotonische Dystrophie,  zirkadianer Rhythmus,  chronobiology,  circadian rhythm,  electrocardiography,  heart rate,  myotonic dystrophy

This study investigates the heart rate circadian rhythm (CR) in patients affected by myotonic dystrophy. The purpose was to detect whether or not the heart rate CR is preserved until the last stage of the disease. The study was performed in 53 myotonic dystrophy patients (29 men and 24 women, age: 14-62 yrs) without apparent signs of cardiac involvement, subdivided into four groups according to the severity of their neuromuscular impairment. The control group was constituted by 10 sedentary clinically healthy subjects (5 men and 5 women, age: 23-30 yrs). Each participant underwent a 24-hour Holter electrocardiogram. Heart rate was measured for each minute using the sinusal R-R intervals. The heart rate in beats per minute was averaged for each hour of the day-night span. The Cosinor method was applied to verify and quantify the heart rate CR. A diurnal sinusal tachycardia was detected in myotonic dystrophy patients at the initial stage of their disease. No evident sinusal bradycardia was observed in that the day-night variability of heart rate was seen to decrease during the process of the disease. The heart rate CR was seen to be preserved in all the stages of the disease. Myotonic dystrophy, that evolves without the involvement of the cardiac apparatus, allows the heart rate to maintain its CR even in advanced cases. The preservation of the heart rate CR suggests that the disease may leave intact the pacemakers which control the heart rate rhythmicity such as the sine node as well as the suprachiasmatic nuclei. J Clin Basic Cardiol 2000; 3: 181-186.