Key result
Posterior extension ablation prolonged anterograde effective refractory period from 91 to 141 ms (P<0.01), indicating normal AV nodes have bidirectional dual pathways.
Why the study?
Does ablation of the posterior extension or compact node alter direction-dependent AV nodal conduction properties in rabbit hearts?
Does ablation of the posterior extension or compact node alter direction-dependent AV nodal conduction properties in rabbit hearts?
Direction-dependent properties of the AV node arise from the compact node-based fast pathway and posterior extension-based slow pathway, demonstrating bidirectional dual pathways in the normal AV node.
Answers are grounded in this paper and cite their sources.
Animal data support bidirectional dual AV nodal pathways; leaves open translation to human ablation decisions.
INTRODUCTION: AV nodal conduction properties differ in the anterograde versus the retrograde direction. The underlying substrate remains unclear. We propose that direction-dependent changes in AV nodal function are the net result of those occurring in the slow and fast pathways. METHODS AND RESULTS: Anterograde and retrograde AV nodal properties were determined with a premature protocol before and after posterior extension (slow pathway) ablation, and before and after upper compact node (fast pathway) ablation. Each ablation was performed in a different group of six rabbit heart preparations. In control, nodal minimum conduction time (NCTmin) and effective refractory period (ERPN) typically were longer, and maximum conduction time (NCTmax) was shorter in the retrograde compared to the anterograde direction. Posterior extension ablation prolonged anterograde ERPN from 91 +/- 10 ms to 141 +/- 15 ms (P < 0.01) and shortened NCTmax from 150 +/- 13 ms to 82 +/- 7 ms (P < 0.01) but did not affect retrograde conduction. Thus, the posterior extension normally contributes to the anterograde but not retrograde recovery curve. Compact node ablation prolonged anterograde conduction (NCTmin increased from 57 +/- 2 ms to 73 +/- 7 ms, P < 0.01) but did not alter ERPN and NCTmax. This ablation abolished retrograde conduction in two preparations and resulted in retrograde slow pathway conduction in four, the latter being interrupted by posterior extension ablation. Thus, the compact node accounts for the baseline of the recovery curve in both directions. Ablation of the compact node results in anterograde slow pathway conduction over the entire cycle length range and may result in retrograde slow pathway conduction. CONCLUSION: Direction-dependent properties of the AV node arise from those of the compact node-based fast pathway and posterior extension-based slow pathway. Normal AV node has bidirectional dual pathways.
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REID et al. (2003) studied AV nodal conduction (n=12). Posterior extension and upper compact node ablation vs. Baseline (before ablation) was evaluated on Anterograde and retrograde AV nodal properties (ERPN, NCTmin, NCTmax) (p=<0.01). Posterior extension ablation prolonged anterograde effective refractory period from 91 to 141 ms (P<0.01), indicating normal AV nodes have bidirectional dual pathways.
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