title: The effect of caffeine on cardiac rate, rhythm, and ventricular repolarization. Analysis of 18 normal subjects and 18 patients with primary ventricular dysrhythmia.
abstract: 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 (less than 1/hr) VEBs, compared to nine of 18 during caffeine ingestion (not significant). In group 2, some 16 of the 18 subjects had VEBs during the caffeine-free period, with the frequencies varying from less than one VEB per hour to 1,449 VEBs per hour. During the test period, 14 of the 18 subjects in group 2 increased their VEB frequency, and the group's mean frequency rose from 207 +/- 350 VEBs per hour (control period) to 307 +/- 414 VEBs per hour (test period) (p less than 0.01). The Q-T interval in group 1, measured as the corrected Q-T interval (Q-Tc), averaged 0.430 +/- 0.027 during the caffeine-free period, not significantly different from the test period (0.425 +/- 0.019). The comparable Q-Tc values for group 2 were 0.424 +/- 0.018 during the caffeine-free period and 0.433 +/- 0.025 for the period of caffeine ingestion (not significant).(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D000328:Adult; D001145:Arrhythmias, Cardiac / Q000139:chemically induced* / Q000503:physiopathology; D002110:Caffeine / Q000009:adverse effects* / Q000097:blood / Q000378:metabolism; D004562:Electrocardiography; D005260:Female; D006207:Half-Life; D006339:Heart Rate / Q000187:drug effects*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects*; D012890:Sleep / Q000187:drug effects
chemical_list: D002110:Caffeine