THE INHIBITION OF ACETYLCHOLINE-INDUCED ATRIOVENTRICULAR BLOCK BY POTASSIUM*

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Abstract
In 11 experiments performed in dogs, an amount of acetylcholine found consistently to induce similar degrees of atrioventricular block and alteration of P wave and Ta segment was injected at the base of the aorta. Elevation of the plasma K from a control mean of 3.4 (range 2.7 to 4.2) mEq per L to a mean of 6.1 (range 5.0 to 7.2) mEq per L inhibited the acetylcholine-induced block and prevented changes of the P wave and Ta segment. The observed anti-acetylcholine effect of moderate hyperkalemia is discussed as a possible explanation of the paradoxical behavior of atrioventricular conduction in patients with atrial fibrillation treated with digitalis and with K.