Effects of lidocaine on defibrillation threshold in the pig: evidence of anesthesia related increase.

Some antiarrhythmic drugs may influence the ability of a shock to defibrillate a patient but the effect of lidocaine on defibrillation efficacy has been controversial, suggesting multiple influencing factors. We determined the effects of three doses of lidocaine on defibrillation thresholds, using single and sequential shocks, in 36 open chest halothane-anesthetized pigs. An additional eight pigs were anesthetized with barbiturate and received the highest infusion regime of lidocaine. Shocks were delivered through three mesh electrodes sutured over the anterior right ventricle, posterior right ventricle, and lateral left ventricle for sequential pulse shocks and between a lateral right to a lateral left ventricular mesh electrode for single pulse shocks. Triplicate defibrillation thresholds (DFTs) were obtained before and after lidocaine (n = 32) or saline (n = 12) administration, either with halothane or barbiturate anesthesia. Lidocaine did not alter DFT at any dose with either the single pulse (control 17.4 +/- 3.7 joules [J], highest dose of lidocaine 13.5 +/- 1.7 J, P = NS) or sequential pulse shocks (control 7.6 +/- 0.8 J, highest dose lidocaine 6.6 +/- 0.7 J, P = NS), when halothane anesthesia was used. Similar results were obtained with lower doses. In contrast, lidocaine in pentobarbital anesthetized pigs produced a significant increase of the DFT with single (control 13.7 +/- 1.9, during lidocaine 16.6 +/- 3.1, P less than 0.01) and sequential shocks (control 11.1 +/- 2.2, during lidocaine 14.5 +/- 3.4, P less than 0.01). Interaction between barbiturates and lidocaine, and/or pH may account for the inconsistency in previous studies and must be considered for animal and clinical experiments.