Comparative Efficacy of Subcutaneous Mesh and Plate Electrodes for Nonthoracotomy Canine Defibrillation

To determine the optimal configuration for the subcutaneous placement of electrodes for the performance of ventricular defibrillation without thoracotomy, internal defibrillation using four different subcutaneous electrodes was performed in 13 anesthetized dogs (7–12 Kg, mean ± SD: 9.2 ± 1.5 Kg). An electrode (7 cm2) was positioned transvenously in the superior vena cava with the following electrodes randomly implanted subcutaneously on the left chest: small mesh electrode (14 cm2), large mesh electrode (28 cm2), small titanium plate electrode (14 cm2), and large plate electrode (28 cm2). Ventricular fibrillation was induced by applying alternating current: a monophasic defibrillation wave was administered between (he superior vena cava and the subcutaneous electrodes 10 seconds later. The energy level associated with a 50% successful defibrillation, as predicted by logistic regression analysis, was defined as the ED50. After the completion of the defibrillation protocol using the four subcutaneous electrodes, the small mesh electrode was sutured to the epicurdium and the ED50 measurements were repeated. Energy ED50s were lower when the superior vena cava electrode was used as the cathode rather than as the anode. Of the subcutaneous electrodes, the large plate electrode showed the lowest energy ED50 (3.3 ± 0.9 joules). The plate electrodes had lower energy ED50s than the mesh electrodes, and the large electrode had a lower energy ED50 than the small electrodes. Using the epicurdium electrode, transient arrhythmias and ST elevation were observed following successful defibrillation; however, no arrhythmias or ST‐T changes were observed following defibrillotion using the subcutaneous electrodes. In another eight dogs (7–12 Kg, 9.8 ± 2.0 Kg), seven subcutaneous titanium plate electrodes (surface areas 7, 14, 28, 42, 56, 70, and 98 cm2) were randomly implanted on the left chest. Increasing the surface area of the subcutaneous electrode from 14 to 70 cm2 (from 2 to 5 cm2/Kg) produced a significant reduction in the energy ED50. However, a further increase in the surface area did not further reduce the ED50. In conclusion, the subcutaneous plate electrode significantly reduced the ED50 as compared to the mesh electrodes. The optimal size of electrode for reducing the defibrillation threshold was approximately 5 cm2/Kg.