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Perfusion of isolated rabbit hearts with high potassium, low potassium, and quinidine solutions caused a diffuse widening of the QRS complex with no change in shape. These QRS changes were correlated with the magnitude and upstroke velocity of the ventricular transmembrane potential. An increase of QRS duration by 132% produced by high K was accompanied by a decrease of the action potential, resting potential, and upstroke velocity. A similar increase in QRS duration produced by quinidine was accompanied by a slow upstroke velocity but no change in magnitude of the action potential or resting potential. An increase of QRS duration by 49% produced by low K was accompanied by an increased action and resting potential, and upstroke velocity. We attributed the QRS changes produced by high K and quinidine, at least partly, to a slow conduction in the ventricle, caused by a slow upstroke velocity of the action potential. The QRS changes produced by low K could be explained by hyperpolarization. Early arrhythmias caused by low K were due to atrioventricular conduction disturbances.
Gettes et al. (Sat,) studied this question.