Epicardial Conductors Can Lower the Defibrillation Threshold in Rabbit Hearts

During a defibrillation shock, epicardial conductors can introduce antistimulatory effects due to lowering of the voltage gradient in myocardial tissue under the conductor and stimulatory effects due to membrane polarization near edges. We hypothesized that increasing the area of conductors increases the defibrillation threshold (DFT), while increasing the amount of stimulatory edge of conductors decreases the DFT. To test this, we measured the DFT in excised rabbit hearts with and without sets of rectangular conductors having 250 or 500 mm(2) area and 100, 200, or 400 mm length of edges perpendicular to the line intersecting the shock electrodes. Unlike previous reports in which conductors increased or did not change DFT, present results indicate a conductor geometry having area of 250 mm (2) and edge of 200 mm decreases the DFT. This result is consistent with the hypothesis that stimulatory effects of the edge of a conductor can enhance defibrillation shock efficacy.