title: Behavior of postextrasystolic His-Purkinje system refractoriness after multiple premature beats.
abstract: Although the steady-state refractoriness of the human His-Purkinje system has been shown to be directly related to the cycle length of pacing, the effect that a varying number of premature beats would have on His-Purkinje system refractoriness of the first postextrasystolic beat has not been described. These effects were systematically investigated in 10 patients with normal intraventricular conduction. The His-Purkinje system relative refractory period (HPS-RRP) of the postextrasystolic beat and that of a comparable constant cycle length ventricular drive were measured by the ventricular extrastimulus technique. Results were as follows: the HPS-RRP of the postextrasystolic beat after one premature beat was longer than the HPS-RRP during a comparable constant ventricular drive. However, with the addition of each successive premature beat, the HPS-RRP of the postextrasystolic beat alternated between lower and higher values, in a manner dependent on whether there was an odd or even number of premature beats. In contrast, ventricular refractoriness of the postextrasystolic beats behaved in a cumulative manner, decreasing progressively with the addition of each premature beat.
mesh_terms: D002036:Bundle of His / Q000503:physiopathology*; D005117:Cardiac Complexes, Premature / Q000503:physiopathology*; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles; D006801:Humans; D009431:Neural Conduction; D011690:Purkinje Fibers / Q000503:physiopathology*; D012032:Refractory Period, Electrophysiological; D013997:Time Factors