[Effects of several anti-arrhythmia agents on excitability and conduction depressed by digitalis agents]

Digitalis intoxication is characterized by the appearance of most of the types of severe arrhythmias described and also by important disturbances of cardiac excitability and impulse propagation. Most of the antiarrhythmic agents that are used in the treatment of these conditions also depress excitability and impulse propagation. These characteristics are frequently responsible of severe complications. The purpose of this paper is to determine the type of interactions that exist between digitalis and some antiarrhythmic agents, and compare them with the effects of magnesium. The experiments were done in several groups, of dogs anesthetized with pentobarbital and with the chest open. Excitability, conduction time and functional refractory period were determined using the classical methods. The protocol used consisted in the comparison of the actions of toxic doses of digitalis on excitability and conduction times of the atrial and ventricular tissues, under control conditions and in the presence of therapeutic doses of procainamide, lidocaine and magnesium. The results showed that procainamide worsened the depression of excitability and conduction produced by digitalis intoxication, while lidocaine does not add to the digitalis effects and in some cases it produces a partial improvement of these parameters. Magnesium completely reverts the effects on excitability and conduction. These results provide us with rational pharmacological bases for the treatment of digitalis intoxication and suggest that magnesium could be very useful in the management of patients with severe digitalis intoxication.