The rhythm of the normal human heart.

The 24-hour cardiac rhythm was studied in 86 subjects (41 male, 45 female) aged 16-65 years, after exclusion of 15 additional volunteers with suspected abnormalities. The electrocardiogram was recorded continuously for two 24-hour periods. In this apparently normal population, 10 subjects (12%) had disturbances of rhythm which are widely believed to be of serious prognostic significance; they included frequent ventricular ectopic beats, R-on-T and multifocal ventricular ectopic beats, bigeminy, and ventricular tachycardia. Supraventricular tachycardia, infrequent ventricular ectopic beats, junctional rhythm, and second-degree heart block were also observed, and if these are included most of the subjects showed some disturbance of rhythm. Bradyarrhythmias and tachyarrhythmias were equally common in waking hours and during sleep. These disturbances were not confined to the older age-groups. Heart-rate but not the number of arrhythmias was significantly higher in smokers.