[Resistance and facilitation gradient in synchronized cardiac stimulation in the dog]

Electrical stimulation synchronized on spontaneous or paced cardiac rhythms demonstrates, in dogs : 1) phenomena of intermittent capture (I.C.), and intermittent loss (I.L.) of control, at all moments in the idastole ; 2) constant lowering of Excitability Threshold (E.T.) and Pacing Threshold (P.T.). These experiments confirm the existence of Resistance Gradients (including I.C. and I.L. phenomena) and Facilitation Gradients (measuring E.T. and P.T. lowerings). These gradients -- that we previously described in human pacing -- are parameters of the cardiac excitability.