Delineation of AV Conduction Pathways by Selective Surgical Transection: Effects on Antegrade and Retrograde Transmission

Wenckebach cycle length: A novel predictor for AV block in AVNRT patients treated with ablation

BACKGROUND

Radiofrequency catheter ablation remains the most effective management option for atrioventricular nodal reentry tachycardia (AVNRT). The risk of atrioventricular (AV) block requiring permanent pacemaker is substantial, but, currently, a reliable method to predict this complication is lacking.

METHODS

The electrophysiologic studies (EPS) and baseline characteristics of patients who underwent catheter ablation for the treatment of AVNRT were retrospectively analyzed to investigate predisposing factors for AV block after treatment. Patients were followed for AV block at one month and one year after hospital discharge.

RESULTS

Among 784 patients treated with catheter ablation for AVNRT between 1999 to 2019, 15 developed AV block. Patients with AV block were older (p = .001). Among the recorded EPS parameters, patients with AV block had significantly higher Atrial His interval (120 vs. 110 ms, p = .049), Wenckebach cycle length (WCL) (400 vs. 353 ms, p < .001) and tachycardia CL (400 vs. 387 ms, P = .01) during the ablation compared to their peers without AV block. Additionally, only WCL (OR = 1.1, 95% CI 1.02-1.19, p = .017) remained significant after adjustment for age, gender, ERP, AH interval, and HR. This association was confirmed by comparing patients with (n = 15) and without (n = 15) AV block using propensity score-matching. A WCL≥400ms was associated with a 4-fold higher incidence of AV block (4.79% vs. 1.25%).

CONCLUSION

Increased pre-procedural WCL was associated with a high risk for AV block after catheter ablation treatment for AVNRT. These findings suggest that this readily available EPS-derived parameter may be a novel marker of risk for severe complications in these patients.

Atrioventricular junctional ablation: The good, the bad, the better

Background

The management of patients with atrial fibrillation and an abnormally fast ventricular response has been through the use of pharmacologic agents. In those cases where rate control cannot be achieved pharmacologically, a standard approach has been atrioventricular (AV) junctional ablation and ventricular pacemaker implantation to achieve a stable ventricular rate. Long-term ventricular pacing has been shown to result in diminished ventricular function that can lead to heart failure.

Objective

To describe an experimental and clinical study demonstrating a modified form of AV junction ablation.

Methods

Ablation of the slow and fast AV nodal input does not produce AV block. Ablation of the connection between the two induces AV block, leaving the AV node and His bundle intact.

Results

Subsequently the escape heart rate is close to normal and responds well to exercise.

Conclusion

In a clinical study with a 42 month follow-up, the modified procedure resulted in significantly reduced pacemaker dependence and mortality compared to the standard AV ablation procedure.

Localization of the sinoatrial and atrioventricular nodal region in neonatal and juvenile ovine hearts

Localization of the components of the cardiac conduction system (CCS) is essential for many therapeutic procedures in cardiac surgery and interventional cardiology. While histological studies provided fundamental insights into CCS localization, this information is incomplete and difficult to translate to aid in intraprocedural localization. To advance our understanding of CCS localization, we set out to establish a framework for quantifying nodal region morphology. Using this framework, we quantitatively analyzed the sinoatrial node (SAN) and atrioventricular node (AVN) in ovine with postmenstrual age ranging from 4.4 to 58.3 months. In particular, we studied the SAN and AVN in relation to the epicardial and endocardial surfaces, respectively. Using anatomical landmarks, we excised the nodes and adjacent tissues, sectioned those at a thickness of 4 μm at 100 μm intervals, and applied Masson's trichrome stain to the sections. These sections were then imaged, segmented to identify nodal tissue, and analyzed to quantify nodal depth and superficial tissue composition. The minimal SAN depth ranged between 20 and 926 μm. AVN minimal depth ranged between 59 and 1192 μm in the AVN extension region, 49 and 980 μm for the compact node, and 148 and 888 μm for the transition to His Bundle region. Using a logarithmic regression model, we found that minimal depth increased logarithmically with age for the AVN (R2 = 0.818, P = 0.002). Also, the myocardial overlay of the AVN was heterogeneous within different regions and decreased with increasing age. Age associated alterations of SAN minimal depth were insignificant. Our study presents examples of characteristic tissue patterns superficial to the AVN and within the SAN. We suggest that the presented framework provides quantitative information for CCS localization. Our studies indicate that procedural methods and localization approaches in regions near the AVN should account for the age of patients in cardiac surgery and interventional cardiology.

Stable patterns of AH block arising from longitudinal dissociation and reentry within the superfused rabbit AV junction

INTRODUCTION

Multiple forms of antegrade AH Wenckebach block (WB) observed in 14 of 221 superfused rabbit AV junctions.

METHODS

Bipolar and microelectrode recordings were used to examine the mechanism of multiple forms of AH WB.

RESULTS

Each of the 14 preparations demonstrated typical 3:2 and 2:1 AV block, but also demonstrated longitudinal dissociation within the slow pathway input (N = 11) or compact AV node (N = 3). A 3:2 WB in one pathway and 1:1 conduction in a parallel pathway summated to provide antegrade conduction of the third atrial beat. Retrograde conduction (reentry) blocked conduction of the fourth impulse (4:3 block). A 5:4 block was similarly observed, with summation providing for antegrade AH activation of the third and fourth atrial beats. Retrograde activation observed with the fourth beat, terminated antegrade conduction of the fifth beat.

CONCLUSIONS

The studies demonstrate multiple AH WB patterns consistent with rate-dependent longitudinal dissociation, summation of dissociated AV conduction pathways, and retrograde conduction block within the AV junction.