LAUSR

In this issue of the journal, Bayraktarova et al. compare abrupt increase in AH interval during burst pacing with the same finding during programmed atrial stimulation [1]. In line with previous studies, they find that the classically described AH jump with atrial extrastimuli was seen only in 78% of patients with a dual AV nodal physiology. However, an abrupt increase of AH interval during burst pacing was seen in another 17.8% of patients. This could, therefore, provide another method to identify dual AV nodal physiology. The identification of functionally different pathways in the atrioventricular node depends on discontinuity in the antegrade conduction characteristics seen during pacing maneuvers. While discontinuity is classically described during programmed stimulation with extrastimuli, it may also be seen with burst pacing. An abrupt increase in AH interval may be seen as a marker of dual AV nodal physiology as described in this study, typically happening because of Wenckebach block in the fast pathway with change to slow pathway conduction. Another finding that may be seen during burst pacing is extreme prolongation of the PR interval such that PR interval exceeds the RR interval. Baker et al. reported finding a PR/ RR ratio exceeding 1 in the majority of patients with AVNRT [2] and in a retrospective analysis, we noted this finding in 84% of patients with AVNRT (unpublished data). However, the authors Bayraktarova et al. report that they saw this finding only rarely in the patients in this study. The most likely reason for this difference is the method of burst pacing used. Burst pacing can be done as a single continuous series of paced beats with increase in paced rate every few beats (ramp method) or as bursts of pacing at progressively faster rates with a pause between bursts (stepwise incremental method). The ramp method is faster to perform and may be better tolerated by patients. The stepwise incremental method allows for assessment of sinus node recovery time at different cycle lengths, but may be less well tolerated by patients because of the abrupt increase in rate at the start of each burst. It has been reported that the AV conduction characteristics