Postextrasystolic alterations in refractoriness of the His-Purkinje system and ventricular myocardium in man.

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Abstract
The changes in refractoriness of the His-Purkinje system (HPS) and ventricular myocardium (VM) that are associated with the occurrence of postextrasystolic beats in man are unknown. Accordingly, using a pacing model of the cycle length changes created by a ventricular extrasystole-postextrasystole sequence, we measured retrograde HPS and VM relative and effective refractory periods (RRP and ERP) in 15 patients with the use of ventricular test extrastimuli during preextrasystolic basic control drive (method I) and after programmed extrasystolic (method II) and postextrasystolic (method III) beats. The basic cycle length (same for all three methods) ranged from 500 to 700 msec (mean 613 +/- 74 msec) and the extrasystolic coupling interval (identical for methods II and III) comprised 68 +/- 4% of the basic cycle length. In method III the postextrasystolic pause was programmed to equal the basic cycle length (i.e., noncompensatory) so that method I could serve as control for method III. RRP-HPS decreased from 331 +/- 37 msec in method I to 245 +/- 37 msec or less during the extrasystolic beat (p less than .001). A less dramatic corresponding shortening of ERP-VM and RRP-VM was observed, i.e., from 245 +/- 21 and 264 +/- 23 msec (method I) to 233 +/- 23 and 251 +/- 22 msec (method II), respectively (p less than .001). With the postextrasystolic beat, however, RRP-HPS increased to exceed the control value of method I by 23 +/- 11 msec (p less than .001). This greater-than-expected RP prolongation was also associated with significantly increased retrograde HPS conduction times (in method III vs method I) at both long and short test stimulus coupling intervals.(ABSTRACT TRUNCATED AT 250 WORDS)