Propagation through the Atrioventricular Node: A New Hypothesis for an Old Riddle

Abstract

Atrioventricular nodal cells were first impaled in 1957 by Brian Hoffman, during his fruitful sojourn at the Instituto de Biofisica. Walmor De Mello and one of us (A.P.C.) had the privilege of participating in this then remarkable achievement (Hoffman et al., 1958). During the next few years, rabbit AV node was studied both in New York and in Rio. Nodal delay was shown to be associated with a slow action potential waveform which propagated at 0.02–0.05 m/s (Hoffman et al., 1959), a conduction velocity also found in the slow action potential cells of the SA node (Paes de Carvalho et al., 1959). Slow nodal action potentials could be abolished by acetylcholine, which also affected the amplitude of transition action potentials at the atrial input of the AV node (Cranefield et al., 1959). Paes de Carvalho and Almeida (1960) introduced the classical picture of a 3-layered node (AN, N and NH zones) interposed between the atrial myocardium and His bundle. AN and NH were described as transitional zones at each side of N, the latter being the site where slow action potential shapes were observed. Due to important scatter of firing time, cells of each region were best characterized by the time course of the action potential foot during normal and retrograde activation. AN cells exhibited a sharp initial inflection in antegrade conduction but showed a slowly rising foot in retrograde beats. NH cells showed opposite behaviour.KeywordsSlow ResponseNodal CellRabbit HeartSlow ActionVersus NodeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.