Facilitation of macroreentry within the His-Purkinje system with abrupt changes in cycle length.

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Abstract
We have recently described the ability of abrupt short-to-long changes in atrial cycle length (CL) to prolong refractoriness of the His-Purkinje system (HPS) and increase the likelihood of aberrant ventricular conduction. We have also shown similar functional behavior in retrograde refractoriness of the HPS during changes in ventricular CL. To further assess these characteristics we evaluated the effect of abrupt short-to-long change in ventricular CL on the phenomenon of macroreentry within the HPS (Re-HPS) in 20 patients in whom Re-HPS occurred during application of a ventricular extrastimulus (V2) at a constant ventricular CL (method I) and/or with abrupt short-to-long change in CL (method II). For both methods V2 was coupled to a CL of identical duration, designated the reference CL (CLR). In method I the CLs preceding (CLP) the CLR equaled CLR, whereas in method II CLP was less than CLR. The results showed a dramatic increase in occurrence of Re-HPS with abrupt short-to-long change in CL with Re-HPS occurring in 19 patients with this method compared with in 11 patients during constant CL. In 10 patients manifesting Re-HPS with both methods the associated retrograde conduction (V2H2) delays were equal or less during abrupt short-to-long changes in CL and, remarkably, there were concomitantly shorter antegrade conduction (H2V3) delays compared with at a constant CL. Moreover, despite the resulting shorter V2V3, additional Re-HPS beats were also more likely to occur with abrupt short-to-long change in CL compared with at a constant CL.(ABSTRACT TRUNCATED AT 250 WORDS)