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JAMA. 1963;186(3):256. doi:10.1001/jama.1963.03710030096018.
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Clinicians have been puzzled by paradoxical myocardial responses to potassium. This electrolyte administered to patients who have been treated with digitalis sometimes results in improvement of atrioventricular conduction, but at other times progression of atrioventricular block occurs. An understanding of the mechanisms responsible for these variable reactions may provide guidance in clinical situations which require simultaneous administration of these agents. Is potassium a vagotonic drug or does it, on the contrary, inhibit vagal impulses? Is the response to potassium dependent upon whether the digitalis-induced atrioventricular block is secondary to the vagal or to the direct effect of the glycoside on conduction tissue? These questions have recently been studied by Fisch, Feigenbaum, and Bowers1 in an investigation designed to test the hypothesis that hyperpotassemia acts by inhibiting the effect of acetylcholine on atrioventricular conduction. Acetylcholine was used to produce atrioventricular block in dogs. Infusion of potassium resulted in inhibition of


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