Calculation of transmembrane current from extracellular potential

A mathematical/computer model of cardiac tissue was used to study the estimation of transmembrane current (EI_m) from extracellular potential recordings. Simulated EI_m measurements from normal propagation and for conduction block were compared against EI_m measurements obtained during ventricular fibrillation in dogs. Just as in the animal experiments the authors observed three types of EI_m curves. The first type, charge balanced EI_m curves, were associated with normal propagation. The second type “transitional forms” had a larger outward component than inward component, the third type “electrotonic forms” had no inward component at all