Ventricular defibrillation in the dog using implanted and partially implanted electrode systems

Two totally implanted and two partially implanted electrode systems were studied in 2,100 fibrillation-defibrillation episodes in large anesthetized dogs. In one of the totally implanted systems, two metal disks, 7.6 cm in diameter, were implanted between the pectoralis major muscle and the rib cage, with the right electrode high on the chest and slightly to the right of midline and the left electrode over the apex of the heart. In the other totally implanted system, a unipolar catheter electrode positioned in the right atrium and superior vena cava was used together with a 7.6 cm disk electrode over the apex of the heart. In the partially implanted systems, a unipolar catheter electrode in the right atrium and superior vena cava was used together with either a 7.6 cm disk electrode or a 6.3 by 20.3 cm rectangular sheet electrode placed on the surface of the chest over the apex of the heart. Four types of unidirectional shocks were used in evaluating the twin disk system. Nine types of shocks were used with systems involving the catheter electrode. Derived curves indicate that the 90 percent level of successful defibrillation is achieved with 38 joules on the day of implantation and 54 joules 32 weeks after implantation for the twin disk system, 12 joules on the day of implantation and 19 joules 33 weeks after implantation for the catheter-internal disk system, 15 joules for the catheter-external disk system and 24 joules for the catheter-external sheet system.