[Selective increase of ventricular pacing threshold with complete exit block following DC cardioversion in a patient...

We report the case of a 78-year old patient with a dual chamber pacemaker, who was admitted for cardioversion of atrial tachycardia. Transthoracic DC shock of 160 J was followed by transient loss of ventricular capture with complete exit-block and severe nodal bradycardia. Subsequent analysis of stimulation thresholds revealed a marked rise in the ventricular threshold only, whereas atrial threshold was unchanged. The selective dysfunction of ventricular capture is most likely caused by current-induced tissue damage at the electrode-endomyocardial interface by preferential shunting of high electrical energy into the ventricular lead as compared to the atrial lead. High output pacing prior to elective DC cardioversion is recommended to ensure consistent capture, particularly in pacemaker-dependent patients, and careful evaluation of pacemaker function after shock delivery should performed.