Low-Energy Endocardial Defibrillation Using Dual, Triple, and Quadruple Electrode Systems

Abstract

The feasibility of achieving both universal application of nonthoracotomy leads and low (≤15 J) defibrillation energy requirements by optimizing lead system configuration for use with low-output (<30 J) biphasic shock pulse generators was examined. Sixteen patients (mean age 62 ± 8 years and mean left ventricular ejection fraction of 38 ± 15%) were included in the study. All patients had either experienced syncope with induced ventricular tachycardia (n = 4) or had documented sustained ventricular tachycardia (n = 7) or ventricular fibrillation (n = 5). Defibrillation threshold testing was performed in 2 stages on different days in these patients. In the first stage, 2 defibrillation catheter electrodes were positioned in the right ventricle and superior vena cava with an axillary cutaneous patch. Fifteen-joule, 10- and 5-J biphasic shocks were delivered across 3 different electrode configurations—right ventricle to superior vena cava, right ventricle to axillary patch, right ventricle to a combination of superior vena cava and axillary patch. In the second stage, an 80-ml can electrode was added subcutaneously in a pectoral location to the previous leads. Configurations compared were the right ventricle to pectoral can, and right ventricle to an “array”-combining superior vena cava, can, and axillary patch leads. The defibrillation threshold was determined using a step-down method. In stage 1, mean defibrillation threshold for the right ventricle to axillary patch (12.7 ± 5.9 J) and right ventricle to superior vena cava plus axillary patch (9.8 ± 5.2 J) configurations was lower than the right ventricle to superior vena cava configuration (14.2 ± 6.4 J, p <0.05). In stage 2, the defibrillation was higher for the right ventricle to pectoral can (9.2 ± 5.1 J) configuration compared with the right ventricle to the array (5.6 ± 3.6 J, p ≤0.05). The right ventricle to array had the lowest defibrillation threshold, whereas the right ventricle to pectoral can was the best dual electrode system. Low-energy endocardial defibrillation (≤10 J) was feasible in 72% of tested patients with >1 electrode configuration at 10 J, whereas only 53% of successful patients could be reverted at >1 electrode configuration at 5 J (p <0.05). Reduction in maximum pulse generator output to ≤25 J using these electrode configurations with bidirectional shocks is feasible and maintains an adequate safety margin.This study examines the feasibility of achieving both universal application of nonthoracotomy leads and low (≤15 J) defibrillation energy requirements by optimizing 5 different lead system configurations. Reduction in mean defibrillation threshold to 5.6 ± 3.6 J could be observed, which allowed pulse generators with a maximum output of ≤25 J and yet maintained an adequate safety margin in all patients.