Dependence of electrogram duration in right posteroseptal atrium and atrium-pulmonary vein junction on pacing site: Mechanism and implications regarding atrioventricular nodal reentrant tachycardia and paroxysmal atrial fibrillation

Right Posteroseptal Atrium and Atrium-PV Junction. Introduction: The fracti onated atrial electrogram, a signal helpful in identifying the target site for radiofrequency catheter ablation of the slow AV nodal pathway, is consi dered to arise from nonuniform anisotropic electrical activity. However, th e effects of pacing sites and radiofrequency ablation on these electrograms are not clear, Similarly, the nature of the fractionated atrial electrogra m in the atrium-pulmonary vein junction has yet to be determined. Methods and Results: Two experiments were performed in this study. Experime nt 1 evaluated the fractionated atrial electrogram at target sites before a nd after slow AV nodal pathway ablation during sinus rhythm or during pacin g from different sites. Group IA consisted of 16 patients with dual AV noda l pathway physiology and AV nodal reentrant tachycardia who underwent succe ssful ablation without residual slow AV nodal pathway. Group 1B consisted o f 7 patients who underwent successful elimination of AV nodal reentry but w ith residual dual AV nodal pathway physiology, Group IC consisted of 6 pati ents who still had AV nodal reentrant tachycardia after two applications of radiofrequency energy. In group 1D, there mere 16 patients with dual AV no dal pathway physiology, but without inducible AV nodal reentrant tachycardi a. In group IE, there were 15 patients without dual AV nodal pathway physio logy. Experiment 2 investigated the fractionated atrial electrogram in the ostium of the left and right superior pulmonary veins in 18 patients with p aroxysmal atrial fibrillation (2A) and in 8 patients without paroxysmal atr ial fibrillation (2B), Before radiofrequency ablation, electrogram duration in the right posteroseptal atrium during pacing from the middle coronary s inus or the right posterolateral atrium was shorter than that during pacing from the high right atrium (HRA) in all group 1 patients, After the succes sful elimination of the slow AV nodal pathway conduction in group 1A, atria l electrogram duration during HRA pacing was shorter than that before ablat ion, In experiment 2 patients, electrogram duration during pacing from the proximal or distal coronary sinus was shorter than that during pacing from HRA or sinus rhythm, Conclusion: These findings suggest that the fractionated atrial electrogram s in the right posteroseptal atrium and ostium of left or right superior pu lmonary veins are potentially consistent with nonuniform anisotropic propag ation. alternations of electrogram characteristics after successful radiofr equency ablation of the slow AV nodal pathway may arise from the changes of nonuniform anisotropic activity in the right posteroseptal atrium.