Effect of transthoracic impedance on defibrillation efficacy and safety in a porcine model

Abstract

Objective Two different transthoracic impedances were made with an adjustable impedance instrument to compare the success rate of defibrillation, heart and skin damage in a porcine model. Methods A total of sixteen pigs were randomly(random number) divided into two groups: low impedance group (about 50 Ω, n=8) and high impedance group (about 100 Ω, n=8). Defibrillation (recommended 150 J) was first attempted at 15 s after induction of ventricular fibrillation(VF). If spontaneous circulation was not recovered, 2-minute chest compression and subsequent defibrillation attempts (maximum 200 J) were attempted. Model animal kept stabilization for 30 min after return of spontaneous circulation before induction of the next episode of VF, which was induced five episodes in each pig. Results In the low impedance group, VF was induced 39 times, 39 of 43 attempted defibrillations were successful. In the high impedance group, VF was induced 40 times, 40 of 70 attempted defibrillations were successful. The current and success rate of the first defibrillation were (34.9±3.2)A and 94.9% respectively in the low impedance group, while those of the high impedance group were (19.1±2.1)A and 50% respectively(both P<0.05). There were no significant differences in skin damage between two groups, but myocardial injury was lighter in the high impedance group. Conclusions Success rate of the first defibrillation with recommend 150 J obviously decreases with the increase of transthoracic impedance. The main factor of myocardial injury is current instead of the numbers of defibrillation. Key words: Defibrillation; Transthoracic impedance; Current; Myocardial injury; Pig