Effect of lidocaine on the atrial fibrillation threshold.

The effect of lidocaine on the atrial fibrillation threshold (AFT) and the ventricular fibrillation threshold (VFT) was studied in anesthetized dogs. In ten animals, injection of lidocaine 2 mg./Kg. intravenously resulted in a markded increase of the ventricular fibrillation threshold (from 11.0 +/- 1.5 to 33.3 +/- 6.2 mA., P less than 0.001). In another group of ten animals, lidocaine did not have consistent effect on the atrial fibrillation threshold. However, a dose of lidocaine of 3 mg./Kg intravenously produced a significant increase in AFT (from 14.0 +/- 0.56 to 41.1 +/- 0.32 mA., P less than 0.001). No changes in AFT or VFT were noted in control experiments. The data suggest that lidocaine possesses an antiarrhythmic effect on the atria but higher than usual doses are required.