Electrophysiological changes in the canine atrium and ventricle during progressive hyperkalaemia: electrocardiographical correlates and the in vivo validation of in vitro predictions.

The electrophysiological response to hyperkalaemia was reinvestigated in the whole dog for several reasons including: the paucity of comparative electrophysiological and electrocardiographical studies in which atrial and ventricular tissues were simultaneously investigated; the contrast between the clarity of findings in previous in vitro studies as compared with the rather conflicting results in earlier in vivo investigations; and the difficulty in validating the extrapolation from in vitro results and theory to the in vivo situation because of deficiences in the literature. Biphasic alterations in atrial and ventricular conduction times as well as excitability in response to progressively increasing hyperkalaemia were documented. The alterations in conduction times were reflected quite accurately by relevant electrocardiographical changes. Experiments in the whole animal were designed to test predictions based on membrane theory: the results offering strong support for the validity of extrapolating from the in vitro to the in vivo situation. The results of this study should help clarify and render interpretable many of the seemingly conflicting results in the literature.