Digoxin toxicity in patients with normokalemic potassium depletion

Reviews of large series of patients with digitalis-induced arrhythmias create a seeming paradox: Hypokalemia is infrequently associated with digitalis-induced arrhythmias but the clinical benefit of supplementation of potassium for most digitalis-induced arrhythmias is obvious. Examination of the electrophysiologic abnormalities induced by digitalis coupled with the electrophysiologic effects dependent on the ratio intracellular to extracellular concentrations of potassium clarifies the issue. We present evidence that supports additive effects of the toxicity of digitalis and abnormal ratios of concentrations of potassium inside and outside the cardiac cell. We provide guidelines for assessing this crucial ratio of intracellular to extracellular concentrations of potassium to aid the clinician in the diagnosis and effective treatment of digitalis-induced arrhythmias.