The Effect of Caffeine on Cardiac Rate, Rhythm, and Ventricular Repolarization

To determine clinical electrophysiologic effects of a moderate dose of caffeine, we compared prevailing cardiac rhythm and rate, the prevalence and frequency of ventricular dysrhythmia, and Q-T intervals in two populations over an initial 24-hour caffeine-free period and a subsequent 24-hour period in which caffeine was ingested in a dosage of 1 mg/kg of body weight at intervals of one half-life during waking hours. Group 1 was composed of 18 clinically normal subjects; group 2 was 18 subjects with frequent ventricular ectopic beats (VEBs) and no (n = 16) or minor (n = 2) cardiac disease. Sinus rhythm was the prevailing rhythm in all subjects at all times. For group 1, the mean sinus rate during the caffeine-free period was 77 ±10 beats per minute, compared to 73 ± 9 beats per minute during the period of caffeine ingestion (not significant). Similarly, for group 2, the average sinus rate during the caffeine-free period was 76 ± 11 beats per minute, not significantly different from the average sinus rate during the test period, 76 ± 10 beats per minute. During abstention from caffeine, four of 18 subjects in group 1 had infrequent (