The elusive extracellular AV nodal potential: studies from the canine heart, ex vivo

Anatomical Ablation of the Atrioventricular Node

Background

Atrioventricular (AV) conduction ablation has been achieved by targeting the area of penetration of the conduction axis as defined by recording a His bundle potential. Ablation of the His bundle may reduce the possibility of a robust junctional escape rhythm. It was hypothesised that specific AV nodal ablation is feasible and safe.

Methods

The anatomical position of the AV node in relation to the site of penetration of the conduction axis was identified as described in dissections and histological sections of human hearts. Radiofrequency (RF) ablation was accomplished based on the anatomical criteria.

Results

Specific anatomical ablation of the AV node was attempted in 72 patients. Successful AV nodal ablation was accomplished in 63 patients (87.5%), following 60 minutes (IQR 50-70 minutes) of procedure time, 3.4 minutes (IQR 2.4-5.5 minutes) of fluoroscopy time, and delivery of 4 (IQR 3-6) RF lesions. An escape rhythm was present in 45 patients (71%), and the QRS complex was similar to that before ablation in all 45 patients. Atropine was administered in six patients after the 10-min waiting period and did not result in restoration of conduction. In nine patients, AV conduction could not be interrupted, and AV block was achieved with ablation of the His after delivery of 12 (IQR 8-15) RF lesions. No cases of sudden death were encountered, and all patients had persistent AV block during a median 10.5 months (IQR 5-14 months) of follow-up.

Conclusion

Anatomical ablation of the AV node is feasible and safe, and results in an escape rhythm similar to that before ablation.

High-density mapping of Koch's triangle during sinus rhythm and typical atrioventricular nodal re-entrant tachycardia, integrated with direct recording of atrio-ventricular node structure potential

BACKGROUND

The mechanism of typical slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) and its anatomical and electrophysiological circuit inside the right atrium (RA) and Koch's Triangle (KT) are not well known.

OBJECTIVE

To identify the potentials of the compact AV node and inferior extensions and to perform accurate mapping of the RA and KT in sinus rhythm (SR) and during AVNRT, to define the tachycardia circuit.

METHODS

Consecutive patients with typical AVNRT were enrolled in 12 Italian centers and underwent mapping and ablation by means of a basket catheter with small electrode spacing for ultrahigh-density mapping and a modified signal-filtering toolset to record the potentials of the AV nodal structures.

RESULTS

Forty-five consecutive cases of successful ablation of typical slow-fast AVNRT were included. The mean SR cycle length (CL) was 784.1 ± 6 ms and the mean tachycardia CL was 361.2 ± 54 ms. The AV node potential had a significantly shorter duration and higher amplitude in sinus rhythm than during tachycardia (60 ± 40 ms vs. 160 ± 40 ms, p < .001 and 0.3 ± 0.2 mV vs. 0.09 ± 0.12 mV, p < .001, respectively). The nodal potential duration extension was 169.4 ± 31 ms, resulting in a time-window coverage of 47.6 ± 9%. The recording of AV nodal structure potentials enabled us to obtain 100% coverage of the tachycardia CL during slow-fast AVNRT.

CONCLUSION

Detailed recording of the potentials of nodal structures is possible by means of multipolar catheters for ultrahigh-density mapping, allowing 100% of the AVNRT CL to be covered. These results also have clinical implications for the ablation of right-septal and para-septal arrhythmias.

New insights into atrioventricular nodal anatomy, physiology, and immunochemistry: A comprehensive review and a proposed model of the slow-fast atrioventricular nodal reentrant tachycardia circuit in agreement with direct potential recordings in the Koch's triangle area

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most frequent regular tachycardia in humans. In this review, we describe the most recent discoveries regarding the anatomical, physiological, and molecular biological features of the atrioventricular junction that could underlie the typical slow-fast AVNRT mechanisms, as these insights could lead to the proposal of a new theory concerning the circuit of this arrhythmia. Despite several models have been proposed over the years, the precise anatomical site of the reentrant circuit and the pathway involved in the slow-fast AVNRT have not been conclusively defined. One possible way to evaluate all the hypotheses regarding the nodal tachycardia circuit in humans is to map this circuit. Thus, we tried to identify the slow potential of nodal and inferior extension structures by using automated mapping of atrial activation during both sinus rhythm and typical slow-fast AVNRT. This constitutes a first step toward the definition of nodal area activation in sinus rhythm and during slow-fast AVNRT. Further studies and technical improvements in recording the potentials of the atrioventricular node structures are necessary to confirm our initial results.

Variability of AV nodal potentials recorded, in vivo: direct demonstration of dual AV nodal physiology

OBJECTIVES OF STUDY

We developed a method to record extracellular A-V nodal potentials in the beating dog heart, in vivo.

METHODS

In eleven Na-pentobarbital anesthetized, open-chest dogs, an octapolar electrode catheter (2 mm rings, 2 mm spacing) was inserted through a purse-string suture in the coronary sinus (CS) distal to the ostium and positioned electrographically so that the tip electrode recorded a His bundle (Hb) potential.

RESULTS

Stable recordings of A-V nodal potentials (amplitude, 178 +/- 94 microV; duration 78 +/- 26 msec) were consistently made during sinus rhythm from the second and/or third bipolar pairs of electrodes. Programmed atrial stimulation and vagal stimulation resulted in loss of amplitude and increased duration of the A-V nodal potentials associated with A-H prolongation. In another series of experiments, crushing the sinus node in 6 dogs resulted in AV nodal rhythms with AV nodal potentials of varying amplitudes (132 to 840 microV) and durations (range 25 to 71 msec) as the earliest activation which preceded the Hb, atrial and ventricular deflections. One dog, showing dual AV nodal physiology as documented from the AV nodal function curve, had two distinctly different AV nodal potentials. The low-level, longer duration potentials were associated with longer (slow pathway) A-H intervals; whereas the shorter higher amplitude potentials (fast pathway) showed shorter A-H intervals, each occurring at a critical paced cycle length.

CONCLUSION

We conclude that consistent extracellular AV nodal electrograms can be recorded in vivo although the configuration of these potentials varies depending on heart rate, autonomic stimulation and different arrhythmic conditions such as AV nodal escape rhythms and dual AV nodal physiology.