Integrated rate-dependent and dual pathway AV nodal functions: principles and assessment framework

Abstract

The atrioventricular (AV) node conducts slowly and has a long refractory period. These features sustain the filtering of atrial impulses and hence are often modulated to optimize ventricular rate during supraventricular tachyarrhythmias. The AV node is also the site of a clinically common reentrant arrhythmia. Its function is assessed for a variety of purposes from its responses to a premature protocol (S 1S2, test beats introduced at different cycle lengths) repeatedly performed at different basic rates and/or to an incremental pacing protocol (increasingly faster rates). Puzzlingly, resulting data and interpretation differ with protocols as well as with chosen recovery and refractory indexes, and are further complicated by the presence of built-in fast and slow pathways. This problem applies to endocavitary investigations of arrhythmias as well as to many experimental functional studies. This review supports an integrated framework of rate-dependent and dual pathway AV nodal function that can account for these puzzling characteristics. The framework was established from AV nodal responses to S 1S2S3 protocols that, compared with standard S 1S2 protocols, allow for an orderly quantitative dissociation of the different factors involved in changes in AV nodal conduction and refractory indexes under rate-dependent and dual pathway function. Although largely based on data from experimental studies, the proposed framework may well apply to the human AV node. In conclusion, the rate-dependent and dual pathway properties of the AV node can be integrated within a common functional framework the contribution of which to individual responses can be quantitatively determined with properly designed protocols and analytic tools. atrioventricular node; functional assessment; conduction; refractory period; pretest cycle length; recovery; facilitation; fatigue THE ATRIOVENTRICULAR (AV) node generates a delay between atrial and His bundle activation that helps optimize ventricular filling and blood pumping. The AV node also has rate-dependent conduction and refractory properties accounting for the filtering of atrial impulses during supraventricular tachyarrhythmias. The optimization of this filtering to control the ventricular rate constitutes a cornerstone of atrial fibrillation therapy (3). Another consistent feature of the normal AV node is its built-in fast pathway (FP) and slow pathway (SP) (29,36,45,50,60,73). In some human hearts, SP and FP interplay to result in a clinical arrhythmia known as AV nodal reentrant tachycardia, the most common form of paroxysmal supraventricular tachycardia that can now be successfully cured by ablation therapy (24,34,59,61). These properties are obviously sensitive to autonomic tone (54 -57), itself modulated by conditions such as rest, exercise, pregnancy, stress, diseases, drugs, etc. However, the basic AV nodal physiology and its assessment tools remain debated. Their understanding is the primary goal of this review.The understanding of AV nodal function remains indeed challenging. Zip...

Does Electrode Design Matter in Ablation Effect Assessments?

“…Interestingly, when applying these principles to His bundle recording, well-defined stable signals of good magnitude could be consistently recorded. 6 Despite the obviously smaller size of rabbit His bundle, these signals are typically larger and more neatly shaped than those obtained from humans with standard catheter electrodes regardless of their position. In this context, one may raise the question of whether current leakage is a limiting factor in standard large tip electrode.…”

“…Perhaps, the Teflon withdrawal could favor a current leakage to the bath liquid that could become critical when studying small sources. Interestingly, when applying these principles to His bundle recording, well‐defined stable signals of good magnitude could be consistently recorded . Despite the obviously smaller size of rabbit His bundle, these signals are typically larger and more neatly shaped than those obtained from humans with standard catheter electrodes regardless of their position.…”

“…Best signals are obtained when the sensing electrode is in direct contact with the myocardium. In our rabbit heart preparation studies, surface recordings were performed with micromanipulators‐positioned Teflon‐insulated silver wires . In these conditions, we often observed that a small withdrawal of the Teflon sheet from the electrode tip limited the quality of the recorded signals particularly from small sources such as the posterior atrioventricular nodal extension .…”

Preliminary Results from Clinical Validation Study of a Method for Non-Invasive Assessment of Atrioventricular Node Refractoriness During Atrial Fibrillation

“…The results showed that changes in AV node refractoriness, as reflected in the model parameter estimates, were in agreement with previous clinical findings. This suggests that the model parameters estimated from ECG during AF may be used as a surrogate for the AV node refractory period invasively assessed through a pacing protocol [7].…”

“…The results showed that changes in AV node refractoriness, as reflected in the model parameter estimates, were in agreement with previous clinical findings. This suggests that the model parameters estimated from ECG during AF may be used as a surrogate for the AV node refractory period invasively assessed through a pacing protocol [7].The purpose of the present study is to evaluate our model-based, non-invasive approach to assess AV node refractory periods during AF by comparing its estimates to the invasively assessed AV node refractory periods. Patients referred to the hospital for pulmonary vein isolation (PVI), being in AF upon arrival, are included in the study.…”