Data from 5,280 fibrillation-defibrillation episodes in medium-size dogs, size scaled to a hypothetical 100-kg dog, and from 3,240 episodes in 100-kg calves, are used to derive families of curves showing percentage of success of unidirectional square-wave pulses in achieving defibrillation versus current amplitudes for energy levels in the range of 200 through 2,000 J. From the 3,240 episodes in the calves and 3,240 additional episodes in dogs, the incidence of post-defibrillation complete A-V block was found. In calves, the optimal 800-J curve peaks sharply at about the 93 percent success level for a current amplitude of 70 A. For the hypothetical dog, the 800-J curve has a broad peak at substantially the 100 percent success level for currents of 40 through 120 A. In general, the incidence of complete A-V block is very low in the dog and very high in the calf.

Animals↗

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Ventricular defibrillation with myocardial electrodes in the dog, calf, pony, and pig.

The defibrillation effectiveness of 4-msec rectangular wave shocks was evaluated using myocardial electrodes with 25-kg dogs and (nominally) 100-kg calves, ponies, and pigs as part of an evaluation of the suitability of these animals as models for automatic implanted defibrillator research. The percent success of defibrillation attempts in dogs ranged from 44% with 4-A, 6-J shocks to 93% with 8-A, 16-J shocks. The success achieved in calves with scaled electrodes was uniformly lower and reached a maximum of 28% with 23-A, 107-J shocks. Pigs defibrillated with scaled electrodes at a success level (43%) more comparable to dogs (54%) at the 12-A, 25-J level. Using larger electrodes in calves, only 63% success was attained with 25-A, 52-J shocks; lower (14-A, 22-J) and higher (35-A, 100-J; 47-A, 176-J) shocks were less than 30% effective. Ponies were refractory to defibrillation at up to the 25-A, 100-J level with the large electrodes; with 21-A, 43-J shocks only 42% success in pigs was achieved. In general, there were marked differences between the responses of dogs and calves that are inconsistent with the closed-chest defibrillation behavior of both animals. Failure to achieve reliable and highly successful defibrillation in the larger animals may indicate their possible unsuitability as models in implanted defibrillator research.

Animals↗