Role of the compact node and its posterior extension in normal atrioventricular nodal conduction, refractory, and dual pathway properties

Introduction: The functional origin of AV nodal conduction, refractory, and dual pathway properties remains debated. The hypothesis that normal conduc tion and refractory properties of the compact node and its posterior nodal extension (PNE) play a critical role in the slow and the fast pathway, resp ectively, is tested,vith ablation lesions targeting these structures. Methods and Results: A premature atrial stimulation protocol was performed before and after PNE ablation in six isolated rabbit heart preparations. Di screte (similar to 300 mu m) histologically controlled PNE lesions amputate d the AV nodal recovery curve from its left steep portion reflecting slow p athway conduction and prevented reentry without affecting the right smooth fast pathway portion of the curve. The ablation shortened A(2)H(2)max from 159 +/- 16 ms to 123 +/- 11 msec (P < 0.01) and prolonged the effective ref ractory period from 104 +/- 6 msec to 119 +/- 11 msec (P < 0.01) without af fecting A(2)H(2)min (55 +/- 9 msec vs 55 +/- 8 msec; P = NS) and functional refractory period (174 +/- 7 msec vs 175 +/- 6 msec; P = NS), These result s did not vary with the input reference used. In six other preparations, le sions applied to the compact node after PNE ablation shifted the fast pathw ay portion of the recovery curve to longer conduction times and prolonged t he functional refractory period, suggesting a compact node involvement in t he fast pathway. Conclusion: The normal AV nodal conduction and refractory properties reflec t the net result of the interaction between a slow and a fast pathway, whic h primarily arise from the asymmetric properties of the PNE and compact nod e, respectively.