TRANSVENOUS-SUBCUTANEOUS DEFIBRILLATION LEADS - EFFECT OF TRANSVENOUSELECTRODE POLARITY ON DEFIBRILLATION THRESHOLD

Introduction: The defibrillation threshold (DFT) of a transvenous-subc utaneous electrode configuration is sometimes unacceptably high. To ob tain a DFT with a sufficient safety margin, the defibrillation held ca n be modified by repositioning the electrodes or more easily by a chan ge of electrode polarity. In a prospective randomized cross-over study , the effect of transvenous electrode polarity on DFT was evaluated. M ethods and Results: In 21 patients receiving transvenous-subcutaneous defibrillation leads, the DFT was determined intraoperatively for two electrode configurations. Two monophasic defibrillation pulses were de livered in sequential mode between either the right ventricular (RV) e lectrode as common cathode and the superior vena cava (SVC) and subcut aneous electrodes as anodes (configuration I) or the SVC electrode as common cathode and the RV and subcutaneous electrodes as anodes (confi guration II). In each patient, both electrode configurations were used alternately with declining energies (25, 15, 10, 5, 2 J) until failur e of defibrillation occurred. The DFT did not differ between both conf igurations (18.3 +/- 8.2 J vs 18.9 +/- 8.9 J; P = 0.72). Eleven patien ts had the same DFT with both electrode configurations, 5 patients a l ower DFT with the RV electrode as cathode, and 5 patients a lower DFT with the SVC as cathode. Four patients had a sufficiently low DFT (les s than or equal to 25 J) with only 1 of the 2 configurations. Conclusi on: A change of electrode polarity of transvenous-subcutaneous defibri llation electrodes may result in effective defibrillation if the first electrode polarity tested fails to defibrillate. In general, neither the RV electrode nor the SVC electrode is superior if used as a common cathode in combination with a subcutaneous anodal chest patch.