His Bundle Parasystole: A Form of A-V Junctional Parasystole

¹ Department of Internal Medicine, Kaiser Foundation Hospital, Fontana, Ca.

A 69-year-old man demonstrated continuous A-V junctional parasystole (AVJPS) over a three-week observation period. The parasystolic cycle length, although constant during each recording, changed proportionately and in parallel with the sinus cycle length. Carotid sinus massage lengthened the cycle length. During later recordings, the parasystolic impulse became less effective and only appeared at longer coupling intervals. Parasystolic beats were slightly aberrant as compared to conducted beats. Intracardiac electrography demonstrated that the parasystolic pacemaker probably originated in the region of the His bundle. Previously reported cases of AVJPS are summarized and criticized. Unequivocal AVJPS is quite rare and His bundle parasystole even rarer. Intracardiac conduction time measurements are essential to establish the anatomic location of the ectopic pacemaker.