Sleep and cardiac rhythm in healthy men

Cardiac rhythm during sleep was analysed in 168 healthy men aged 19 to 30 (mean 21.8) years using continuous nocturnal ECG recordings. Thirty five of the subjects were endurance athletes; 99 were recorded at home and 69 at a garrison during military service. The number of short term (less than one min) accelerations of heart rate of more than ten beats per minute ranged from 1.3 to 14.3 per hour; the number or accelerations (greater than one min) of more than 25 beats per minute typical of nocturnal restlessness ranged from zero to 6.1 per hour. The accelerations indicating nocturnal restlessness were more common during recordings done at the garrison than at home (2.2 per hour vs 1.3 per hour, P less than 0.01), whereas the short term accelerations were not (5.8 per hour vs 5.1 per hour, NS). Sinus pauses exceeding 2.00 sec occurred in 17 men (13 in athletes), occasional second degree atrioventricular block in 19 (eight in athletes) and ventricular premature beats in 37. Eighty-two per cent of sinus pauses, 83% of second degree atrioventricular blocks, and 81% of ventricular premature beats (when less than ten in the same subject) were associated with short term changes in heart rate. In conclusion, rapid changes in heart rate, presumably as a results of autonomic activation, are closely associated with most arrhythmias in healthy men during sleep, whereas changes in heart rate typical of nocturnal restlessness have little arrhythmogenic effect.