The antiarrhythmic action of lidocaine has been attributed solely to its direct electrophysiological effects on the heart. However, lidocaine is particularly effective in treating ventricular arrhythmias associated with increased sympathetic activity, e.g., in myocardial infarction and digitalis toxicity. We tested the hypothesis that lidocaine administered intravenously depressed cardiac sympathetic nerve activity (CSNA). We measured CSNA in six dogs in control state and after lidocaine in doses of 0.625, 1.25, and 2.5 mg/kg i.v. over 2 min. These doses of lidocaine produced graded decreases of CSNA of -8 +/- 2, -18 +/- 1, and -41 +/- 5%, respectively (P less than 0.05, mean +/- SE). In six additional experiments the bolus of lidocaine was followed by an infusion for 20 min (1.25 mg/kg followed by 100 micrograms/kg per min and 2.5 mg/kg followed by 200 micrograms/kg per min). Infusion of lidocaine maintained depression of CSNA at a level that was 23 +/- 3 and 35 +/- 5% less than control (P less than 0.05), respectively, at plasma lidocaine levels of 5.2 +/- 0.6 and 7.5 +/- 1.4 micrograms/ml, respectively. CSNA returned to control during recovery periods. CSNA did not decrease with the passage of time or administration of vehicle. In five dogs with vagi intact, carotid sinuses isolated and held at a pressure of 100 mmHg, and aortic baroreceptors denervated, administration of lidocaine (2.5 mg/kg followed by 200 micrograms/kg per min) decreased renal nerve activity to 71 +/- 8% of control. Increases in left ventricular systolic pressure and maximum derivative of pressure with respect to time (dP/dtmax) resulting from electrical stimulation of preganglionic sympathetic nerves were not significantly altered by lidocaine, but were markedly attenuated by hexamethonium, a ganglionic blocker. In conclusion, lidocaine administered intravenously produces dose-dependent and sustained decreases in cardiac sympathetic nerve activity. These decreases can occur with therapeutic plasma levels. We speculate that this effect is due to central nervous system effects of the drug and that this effect may contribute to the antiarrhythmic actions of lidocaine.
B D Miller, M D Thames, A L Mark