Chest, Vol 87, 319-324, Copyright © 1985 by American College of Chest Physicians

ARTICLES

The effect of caffeine on cardiac rate, rhythm, and ventricular repolarization. Analysis of 18 normal subjects and 18 patients with primary ventricular dysrhythmia

DJ Sutherland, DD McPherson, KW Renton, CA Spencer and TJ Montague

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)

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