The rate and rhythm of the human heart

24 hour ambulatory electrocardiography has become established as a routine investigation in hospital practice. The interpretation of results from any investigation depends upon a knowledge of its normal range, and in spite of the widespread use of ambulatory electrocardiography in patients with symptoms or signs of disease the normal limits for heart rate and rhythm have not been adequately defined. The aim of this research is to establish the normal pattern of heart rate and rhythm in healthy adults.Subjects aged 20 to 70 were selected at random from a general practice population and screened for evidence of disease until 250 subjects (25 in each decade/sex group) were obtained. Their apparent freedom from heart disease was established by history, clinical examination, and non-invasive investigations. The results of 24 hour ambulatory ECG monitoring were analysed in terms of heart rate, supraventricular and ventricular arrhythmias, and bradyarrhythmias. 90% of subjects had some rhythm disturbance, although the disturbance was generally of a minor nature. However, 24% of subjects had an arrhythmia usually considered to be of serious prognostic or haemodynamic significance.Most varieties of cardiac arrhythmia were observed, and their occurrence in otherwise healthy individuals makes interpretation of results from symptomatic patients difficult. It is concluded that in general a causal relationship between arrhythmias and symptoms can only be established when both occur concurrently