The role of myocardial membrane leakage channels in the production of fibrillation: studies with an analog computer model.
The conditions under which automatic activity and fibrillation can occur were studied through the use of an analog model. Parameters (transmembrane active and passive properties) were established from biological data of mammalian myocardial fibers. The definition of instability of membrane potential can be given by the following functions of inward and outward steady state current (I) to voltage relationships of the membrane. 1) With decreasing angle between the tangent of the slope of the Iout and (-1) Iin, instability increases at constant potential. 2) Instability is also a function of the membrane potential as related to peak inward current (nonsteady state) at a given angle. 3) Maximum peak inward current and minimum angle produced such instability as to cause fibrillation. The most likely explanation is that automaticity and/or fibrillation is induced by leakage currents which change the normal current/voltage relatiosnhip in the described manner. The membrane leakage currents could be specific to sodium or unspecific.