Reverse Wenckebach Block and Complete Atrioventricular Dissociation due to Potassium and Digitalis

P OTASSIUM is ani effective agent for the control of arrhythmias assoeiate(I with digitalis aiid lhvl)opotassennia and of manyA arrlhythmias of obscure etiology.1The thera)eutic effect of potassium in cardiac irregularities caused by digitalis has been ascribed to a digitalis anld )otassium "'anitagonlism." For a demonstration of this antagonism, potassium was administered intravenously to patients with atrial fibrillation after they were "fully" digitalized. The end point of digitalization was shown by a marked depression of atrioventricular (A-V) conduction and the appearance of A-V nodal escape beats, A-V uodal rhyth in, ventricular bigeininy with varyinig (colifiguration of the ectopic beats and, finally, failure to speed significantly the veiltricular rate by intravenous administration of 1.25 to 2.0 iiug. of atropine. It was assumed that in suich patients, after treatmnent with J)otassiulml, the digitalis-potassiumn anitagoniisim would be manifested by an increase of coiitliuetioti -via A-V node with disappearance of A-V imodal arrhythmias and speeding of yeniitricular rate. Surprisingly, however, inl the majority of patients the conduction in the A-V node was depressed further with the appearance of complete A-V dissociation, ventricular (eserape beats, and idioventricular rhi, tlhm. In short, the electrocardiogram looked as if the digitalis had exerted a greater (efeet alnd not leell aimtagonized by the potassium .6