Ambulatory electrocardiographic monitoring in 100 healthy teenage boys.

Ambulatory monitoring of the electrocardiogram in 100 healthy 14 to 16 year old boys showed heart rates ranging from 45 to 200 beats/minute during the day and from 23 to 95 beats/minute during sleep. Sinus arrhythmia was present in all cases and was the only variation noted in 17%. Sudden variations in the PP interval occurred in 41%, but a precise diagnosis of the mechanism was usually impossible; 15% had changes compatible with sinus arrest or temporary complete sinoatrial block, and one boy had a pattern compatible with type II second degree sinoatrial block. Escape rhythms were noted in 26%, first degree atrioventricular block in 12%, and second degree atrioventricular block (Mobitz type I) in 11%. Mobitz type II second degree atrioventricular block was seen on one occasion in one boy. Ventricular extrasystoles seen in 41% were of uniform morphology in 75% and multiform in 25%. Short episodes of ventricular tachycardia were recorded in 3%.