Influence of electrical coupling on early after depolarizations in ventricular myocytes

Computer modeling is used to study the effect of electrical coupling between a myocardial zone where early after-depolarizations (EADs) can develop and the normal neighboring tissue. The effects of such coupling on EAD development and on the likelihood of EAD propagation as an ectopic beat are studied. The influence on EAD formation is investigated by approximating two partially coupled myocardial zones modeled as two active elements coupled by a junctional resistance R. For R values lower than 800 Ω cm ², the action potentials are transmitted to the coupled element, and for R values higher than 850 Ω cm ² they are blocked. In both ranges of R, when the electrical coupling increases, the EADs appear at more negative takeoff potentials with higher amplitudes and upstrokes. The EADs are not elicited if the electrical coupling is too high. In a separate model of two one-dimensional cardiac fiber segments partially coupled by a resistance R, critical R values exist, between 42 and 54 Ω cm ² that facilitate EAD propagation. These results demonstrate that in myocardial zones favorable to the formation of EAD, the electrical coupling dramatically affects initiation of EAD and its spread to the neighboring tissue.