HISTAMINE-2 RECEPTOR ANTAGONISM BY CIMETIDINE AND SINUS-NODE FUNCTION

SEVERE bradycardia has been reported with the use of cimetidine.1 2 3 Bradycardia could have been spurious, but it recurred on rechallenge.1,2 Data from animal studies4,5 and human right-atrial fibers6 indicate that histamine-enhanced automaticity is antagonized by histamine2 blockers. These observations suggest that histamine2-receptor antagonism by cimetidine could worsen sick-sinus syndrome or blunt the chronotropic response to gastrointestinal hemorrhage. Therefore, we assessed the effect of cimetidine on sinus-node function in patients undergoing electrophysiologic testing. Methods Ten unmedicated patients underwent atrial pacing by use of a quadripolar catheter positioned at the upper portion of the right atrium. Heart rate (average. © 1979, Massachusetts Medical Society. All rights reserved.