A systematic evaluation of conventional and novel transvenous pathways for defibrillation

Introduction: Conventional implantable cardioverter defibrillators employ endocardial (shock) electrodes with a lead located in the right ventricular apex (RV) and a "hot-can" electrode located subcutaneously in the left pectoral region. In the event of a high defibrillation threshold (DFT) a third electrode is frequently employed in the superior vena cava (SVC). We report the comparison of conventional and novel locations of additional electrodes with the RV/Can configuration, in a porcine model. Method: In 12 anesthetized pigs (30-45 kg), endocardial defibrillation electrodes were randomized to the following locations: RV/Can, RV/Can + SVC, RV/Can + main pulmonary artery (MPA) and RV/Can + left pulmonary artery wedge position (PAW), RV/Can + high inferior vena cava (HIVC), RV/Can + Low inferior vena cava (LIVC). Ventricular fibrillation (VF) was induced using 60 Hz alternating current. After 10 seconds VF a rectangular biphasic shock was delivered by the ARD9000 (Angeion Corp). The DFT was determined for each configuration using a modified four-reversal binary search. All configurations were compared using a repeated measures analysis of variance (ANOVA) statistical test and the five 3-electrode configurations were compared to the RV/Can position using a Dunnett test. Results: Mean DFTs: RV = 21.5 +/- 4.8 J, SVC = 16.8 +/- 4.7 J (p < 0.05 vs. RV), HIVC = 21.1 +/- 4.7 J (p > 0.05), LIVC = 19.1 +/- 5.7 J (p > 0.05 vs. RV), MPA = 16.0 +/- 5.8 J (p < 0.01), PAW = 17.5 +/- 4.6 J (p < 0.05 vs. RV). Conclusions: Relative to the RV/can configuration the addition of a third electrode in the PA, PAW or SVC significantly reduces the DFT in the pig. The addition of an electrode to the IVC did not significantly reduce the DFT in our model.