Complete His-Purkinje Block Produced by Carotid Sinus Massage

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Abstract
A case of complete heart block (CHB), localized in the His-Purkinje system, induced by carotid sinus massage (CSM) is presented. A 63-year-old male with right bundle branch block and left anterior hemiblock was evaluated for recurrent syncope. Right or left CSM produced brief periods of CHB with presyncopal symptoms. His bundle (HB) studies during normal sinus rhythm revealed normal conduction times (A-H interval = 80 msec; H-V interval = 48 msec). Carotid sinus massage produced progressive slowing of the sinus rate, and complete heart block below the HB occurred whenever the sinus rate fell below 42 beats/min. During atrial pacing at 70 beats/min, CSM produced 2:1 block above the HB with an effective rate to the HB of 35 and complete block below the HB. Atrial pacing at rates above 93 beats/min resulted in 2:1 block below the HB. Administration of intravenous atropine produced an apparent junctional tachycardia with 2:1 block below the HB. Thus, complete heart block related to both bradyCardia (phase 4) and tachycardia (phase 3) was demonstrated. The complete heart block induced by CSM was thought to be secondary to bradycardia-induced left posterior fascicular or intra-His block. However, the possibility of a direct vagal effect on ventricular conduction could not be ruled out.