Influence of extracellular potassium levels on atrioventricular transmission

¹ Instituto de Biofisica, Universidade do Brasil, Rio de Janeiro, Brazil and Department of Physiology, State University of New York, Downstate Medical Center, Brooklyn, New York

Dependence of transmission of excitation along atrial and A-V pathways on extracellular K⁺ was studied in the isolated, Langendorff perfused, rabbit heart. It was found that atrial propagation velocity reaches a maximum at [K]₀ = 6 mm; slowing, presumably due to depolarization, ensues at higher [K]₀. Propagation between upper His bundle and ventricles seems to behave in a similar way. Transmission across the A-V nodal area is markedly impaired at [K]₀ below 2 mm; A-V block is often observed. Higher [K]₀ levels shorten the A-V nodal transmission time; this speeding of transmission persists in [K]₀ levels high enough to cause impairment of propagation in atria. Furthermore, A-V nodal block caused by acetylcholine was shown to be abolished when [K]₀ is raised to an appropriate level. This antagonistic action is probably not due to release of catecholamines by the increased [K]₀. A possible explanation for the [K]₀ dependence of A-V transmission is discussed in terms of the ionic hypothesis