An analysis of factors operating at the cellular level to cause arrhythmias

Abstract

Summary Isolated cat and rabbit heart muscle preparations were stimulated by passing current through the tissue across two compartments of a chamber. Repetitive firings in response to a single stimulus applied during the period of recovery from a preceding excitation were observed when the intensity of stimulation was proper and the tissue was comprised of a non-uniform cell population. Very weak or very strong stimulation was less effective in evoking such a response. When repetitive firing occurred, action potentials representing activities of two groups of cells alternated in their time course relations. Repetitive firing stopped when these action potentials became synchronous. Epinephrine in concentrations (W/V) ranging from 10 −6 to 2×10 −5 did not change the pattern of response, while acetylcholine in concentrations between 10 −7 and 10 −6 markedly shortened the refractory period of the tissue and increased the number and frequency of firings. Evidence supporting interactions promoting reentry of excitation in adjacent cells was discussed. The main contention supported by these observations is that arrhythmias result when excitatory impingements occur at a time when or under conditions when cells are not in a uniform state, and thus an asymmetry of action and reentry can most readily occur.