Behavior of postextrasystolic His-Purkinje system refractoriness after multiple premature beats

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.