Carotid sinus massage during evaluation for transient loss of consciousness: Just a positive test?

An electrocardiographic recording obtained during diagnostic evaluation of recurrent transient loss of consciousness in a 53-year-old man is presented. Carotid sinus massage (CSM), having elicited a ventricular asystole of >5 s duration was deemed to have provided a possible diagnostic basis for syncope. However, apart from the pause and somewhat unexpectedly, CSM also suppressed preexisting frequent ventricular ectopy. Explanations for this unexpected finding can only be considered speculative, but include direct CSM-induced parasympathetic suppression of ectopic activity at intra-ventricular pacemaker sites, concomitant diminution of sympathetic neural activity at ectopic sites, or interruption of 'linking' of normal ventricular activation to initiation of premature ventricular contractions.