Transthoracic ventricular defibrillation in the adult.

Since the lower the energy used, the less the possible myocardial damage, two studies of 214 patients in ventricular fibrillation (VF) were conducted, using two types of defibrillators each charged to 200 Wsec and 100Wsec. In the first study, each defibrillator was charged to 200 Wsec (150-165 Wsec delivered). Up to three 200-Wsec shocks successfully converted 222 of 233 VF episodes. In 199 episodes, a single shock successfully removed the fibrillation. In 48 episodes in patients weighing more than 80 kg, VF was removed in 43 (90 percent). In the second study, from a stored energy of 100 Wsec, 74 to 82 Wsec of energy were delivered in the initial shock to treat 161 VF episodes in 94 patients. The first shock was successful in 101 (63 percent) of the 161 episodes. Up to three 100-Wsec shocks achieved 81 percent conversion in 52 episodes. A third 100-Wsec shock seldom succeeded. Using a sequence of 100 - 200 - 400 Wsec shocks, 93 (91 percent) of 102 episodes were successfully converted. There was not a single instance of failure to remove VF among the 214 patients with a maximal delivered energy of 330 Wsec. Thus, the direction towards the production of larger instruments storing more than 400 Wsec energy seems unwarranted.