An 83-year-old man was referred for evaluation of a single episode of syncope. Electrocardiogram showed sinus rhythm with first degree atrioventricular (AV) block. On left carotid sinus massage, he developed complete AV block, with only minor slowing of the sinus rate (Fig. 1). During right carotid sinus massage, he developed sudden, marked sinus brady-cardia, without any significant change in the PR interval. Both maneuvers elicited symptoms, and a pacemaker was implanted. He remains well at follow-up, without further episodes of syncope.While it has been proposed that carotid sinus massage may have differential effects depending on the side, this finding has not been confirmed. Our patient shows preferential effects of the right carotid sinus on the sinoatrial node and left carotid sinus on the AV node.
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