Role of proximal electrode position in transvenous ventricular defibrillation.

Transvenous defibrillation lead systems have been demonstrated to reduce operative morbidity and mortality associated with implantation of cardioverter-defibrillators. To determine the best position for the proximal electrode in transvenous systems, defibrillation thresholds were compared for three positions in a single-pathway, two-lead system. Two defibrillation lead electrodes were transvenously inserted into seven dogs. The distal electrode was positioned in the right ventricular apex. The proximal electrode was randomized to one of three positions: (1) the superior (cranial) vena cava (SVC) at the junction of the right atrium, (2) the left innominate vein at the junction of the SVC, or (3) the external jugular vein. Biphasic defibrillation thresholds for converting electrically induced ventricular fibrillation were determined for the three positions of the proximal electrode in each dog. The innominate vein position resulted in the lowest defibrillation threshold (555 +/- 123 V) as compared to the SVC (640 +/- 126 V; p = 0.0612) and the jugular vein (709 +/- 117 V; p = 0.0013). Lead impedance gradually increased with increasing distance between the two shocking electrodes: 58.4 +/- 11.4 omega for SVC, 76.2 +/- 13.8 omega for innominate vein, and 94.9 +/- 10.2 omega for jugular vein proximal lead electrode position (p < 0.05 for all pairwise comparisons). In two-electrode transvenous defibrillation lead systems, positioning the proximal electrode in the left innominate vein produced the lowest defibrillation threshold.