Repolarization in Rabbit Myocardium Implications for Reentry Induction

We have investigated the effects of electric field stimulation on membrane repolarization in rabbit papillary muscles and assessed the consequences of these effects for the dispersion of intracellular potentials and the production of a propagation wave front or unidirectional block in relatively refractory tissue. The stimuli studied had electric field strength of 0.25-14 V/cm, duration of 2 msec, and field orientation along or across the myocardial fibers. The field strengths to excite the muscles in diastole were 0.68 or 1.23 V/cm for stimuli oriented along or across the fibers, respectively (p<0.01, along versus across). A 2.5-V/cm stimulus given near the end of the action potential (AP) produced either no response or, after increasing the stimulus delay only 2-3 msec, a full response with almost no AP durations that