COMPLETE INFRAHISIAN ATRIOVENTRICULAR-BLOCK AFTER ENDOCAVITARY SHOCK DELIVERED BY AN AUTOMATIC IMPLANTABLE CARDIAC DEFIBRILLATOR

Transient reproducible complete infrahisian atrioventricular block occ urred after endocavitary cardioversion of ventricular tachycardia and ventricular fibrillation by an automatic implantable cardiac defibrill ator in a patient with left bundle branch block and baseline borderlin e H-V interval. Six months later, a permanent complete atrioventricula r block occurred after repetitive endocavitary shocks. Several hypothe tical mechanisms may explain this infrahisian atrioventricular block: a ''fatigue'' phenomenon of the HisPurkinje system, vagally mediated a trioventricular block, and/or ablation of the His conduction system. T he last seems to be the most probable, which would justify implantatio n of an automatic implantable cardiac defibrillator with backup pacing in all patients, especially in the presence of bundle branch block.