[Complete sub-His AV block caused by carotid sinus massage. Possible direct vagal effect on the His-Purkinje system]

A 64 year old male patient, with frequent syncopes, underwent an electro-physiologic study. A complete left bundle branch block and a first degree His-Purkinje system atrioventricular block (AH = 100 msec, HV = 60 msec) were present in basal condition. Left carotid sinus massage caused extreme sinus bradycardia (with PP intervals as long as 3000 msec), without AH and HV interval changes. Right carotid sinus massage caused a His-Purkinje atrioventricular block. Ventricular asystole of 4800 msec occurred while the sinus cycle varied between 1440 and 590 msec. Since His-Purkinje atrioventricular block is induced by the right carotid sinus massage with PP intervals even shorter than the basal cycles and since the block was not reproduced at PP intervals longer than 1440 msecs, a direct vagal effect on the His-Purkinje system may be suggested, rather than a bradycardia dependent phase 4 block.