Secular variation in frequency of premature ventricular contractions in untreated individuals.

Six-hour electrocardiographic monitorings were initially recorded from 40 ambulatory adult subjects (39 male, one female) on successive days. Thirty-eight of the subjects were monitored 6 weeks to 18 months later. Studies of paired time periods, Poisson modeling, and other statistical examinations were performed. Despite an underlying consistency in the data, there was considerable variation in PVC frequency from hour to hour, day to day, and over longer periods of time.