Digitalis toxicity.

The principal causes of digitalis toxicity are overdose, reduced volume of distribution, reduced renal elimination, and increased myocardial sensitivity. The metabolic mechanism of digitalis toxicity is intense inhibition of sarcolemma Na-K ATPase, which leads to increases of intracellular Na+ and Ca2+ and arrhythmogenic membrane ionic currents. A variety of cellular electrophysiologic effects and effects on the nervous system are responsible for the array of clinical arrhythmias seen during digitalis toxicity, i.e., sinus bradycardia, atrioventricular block, nonparoxysmal atrioventricular junctional tachycardia, and ventricular tachycardia.