Systemic alkalosis and digitalis related arrhythmias

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 of 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 using metabolic alkalosis as a marker of intracellular potassium depletion. Patients with metabolic alkalosis and normokalemia with "therapeutic" concentrations of digoxin had significantly greater prevalence of arrhythmias than did patients without alkalosis. We presume this effect of alkalosis to be mediated by effects on extra- to intracellular ratios of potassium.