ACUTE EFFECTS OF CAFFEINE INGESTION ON SIGNAL-AVERAGED ELECTROCARDIOGRAMS

Background Although moderate caffeine ingestion has not been shown to be arrhythmogenic, caffeine toxicity can cause severe cardiac arrhythm ias, including atrial fibrillation and ventricular tachycardia. Atrial fibrillation and ventricular tachycardia have been associated with pr olongation of P-wave and QRS complex durations on signal-averaged elec trocardiograms. This study investigated acute effects of caffeine inge stion on signal-averaged P-wave and QRS complexes. Methods and Results Signal-averaged electrocardiograms were obtained from 12 normal subje cts (6 men, 6 women; ages 21 to 26 years) before and after ingestion o f caffeine (5 mg/kg body weight) or placebo in a randomized, double-bl ind, crossover fashion. Electrocardiograms for signal averaging were r ecorded from electrodes left in a constant location, After bandpass fi ltering (30 to 300 Hz) and amplification, signals were sampled over 7. 2 minutes at 2000 Hz. Signal-averaged P-wave and QRS complex durations did not significantly change after placebo ingestion, After caffeine ingestion QRS duration prolonged in 9 of 11 subjects at 90 minutes (me an +/- SEM = 0.8 +/- 0.3 ms, P < .02) and in 8 of 9 after 3 hours (1.1 +/- 0.2 ms, P < .001), No significant change in P-wave duration or he art rate was found after caffeine ingestion at any test interval. Aver age caffeine level in saliva 90 minutes after ingestion was 6.6 +/- 1. 6 (SD) mu g/dl. Conclusions Although probably not arrhythmogenic in no rmal subjects, moderate caffeine ingestion does produce a smell but st atistically significant prolongation of signal-averaged QRS complexes. Further prolongation caused by excessive caffeine intake may be a fac tor in the genesis of arrhythmias associated with caffeine toxicity.