A 2ND DEFIBRILLATOR CHEST PATCH ELECTRODE WILL INCREASE IMPLANTATION RATES FOR NONTHORACOTOMY DEFIBRILLATORS

Nonthoracotomy defibrillator systems can be implanted with a lower mor bidity and mortality, compared to epicardial systems. However, implant ation may be unsuccessful in up to 15% of patients, using a monophasic waveform. It was the purpose of this study to prospectively examine t he efficacy of a second chest patch electrode in a nonthoracotomy defi brillator system. Fourteen patients (mean age 62 +/- 11 years, ejectio n fraction = 0.29 +/- 0.12) with elevated defibrillation thresholds, d efined as greater than or equal to 24 J, were studied. The initial lea d system consisted of a right ventricular electrode (cathode), a left innominate vein, and subscapular chest patch electrode (anodes). If th e initial defibrillation threshold was greater than or equal to 24 J, a second chest patch electrode was added. This was placed subcutaneous ly in the anterior chest (8 cases), or submuscularly in the subscapula r space (6 cases). This resulted in a decrease in the system impedance at the defibrillation threshold, from 72.3 +/- 13.3 Omega to 52.2 +/- 8.6 Omega. Additionally, the defibrillation threshold decreased from greater than or equal to 24 J, with a single patch, to 16.6 +/- 2.8 J with two patches. These changes were associated with successful implan tation of a nonthoracotomy defibrillator system in all cases. In concl usion, the addition of a second chest patch electrode (using a subscap ular approach) will result in lower defibrillation thresholds in patie nts with high defibrillation thresholds, and will subsequently increas e implantation rates for nonthoracotomy defibrillators.