Impulse propagation in the Purkinje system and myocardium of intact dogs

To characterize Purkinje activation (PA) patterns, we studied 15 alpha-chloralose-anesthetized dogs. During left ventricular basal or apical pacing, PA was mapped with a row of four to eight multipolar electrodes placed in the left ventricular wall to record Purkinje and muscle potentials. PA times increased linearly with distance from the pacing site (r = 0.8, slope 1.8 +/- 0.15 mm/ms, P < 0.05). With a single premature stimulus (S2) delivered from the apical or basal site, delay of PA times was first evident at remote sites (> or = 50 mm) with S1-S2 = 185 +/- 5 (SD) ms, while at peripacing sites (< or = 10 mm), delay was first evident when S1-S2 = 176 +/- 6 ms (Purkinje relative refractory period; P < 0.05). With S2,...S5 such that S1-S2 = S2-S3, and so on, an alternating mode of conduction, both temporally and spatially, occurred. The alternation was due to refractoriness and conduction interactions. With short premature intervals, remote coupling intervals were 30 ms less than the premature intervals. Conduction delay in Purkinje fibers with premature stimuli allowed remote epicardium to be activated by alternate routes. Conduction of constant-rate stimuli in the Purkinje system is relatively uniform. With single premature stimuli, conduction is delayed first remotely from the pacing site, whether apical or basal stimulation was employed. When S1-S2 is less than Purkinje relative refractory period, the usual endocardial-to-epicardial activation sequence is altered. Multiple premature stimuli cause remote coupling intervals to alternate.