Selective dysfunction of ventricular electrode-endocardial junction following DC cardioversion in a patient with a dual chamber pacemaker.

A patient with a dual chamber pacemaker received two transthoracic (anterior-anterior paddle position) shocks for VF. Subsequent analysis of stimulation thresholds revealed a marked rise in the ventricular threshold only. Later, she received three additional shocks (anterior-posterior paddle position) during electrophysiological study to terminate episodes of induced VT. Following these, the ventricular stimulation threshold was > 10 V at 2.0 ms. The selective damage at the ventricular site in this patient led us to carry out in vitro studies that revealed a preferential shunting of high electrical energy into the ventricular lead, as compared to the atrial lead, following a DC shock. These observations may explain the selective pacing malfunction observed in out patient.