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Demonstration of presence of a sling between anterior and posterior bundle branch during tachycardia using twin atrioventricular nodes: A case of asplenia syndrome
Address reprint requests and correspondence: Dr Takahiko Kinjo, Department of Cardiology and Nephrology, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, 036-8562 Japan.
Department of Cardiology, Hirosaki University Graduate School of Medicine, Hirosaki, JapanDepartment of Advanced Management of Cardiac Arrhythmias, Hirosaki University Graduate School of Medicine, Hirosaki, JapanDepartment of Cardiac Remote Management System, Hirosaki University Graduate School of Medicine, Hirosaki, Japan
Atrioventricular (AV) reciprocating tachycardia via twin AV nodes and sling sometimes occurs in patients with asplenia syndrome.
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There are several hypotheses regarding the connection form of the sling and the cardiac conduction system.
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The electrophysiological findings in our case suggest a continuous sling, as there were 2 junctions from the cardiac conduction system to the single ventricle, both of which were considered bystanders of the tachycardia circuit.
Introduction
Atrioventricular (AV) reciprocating tachycardia via twin AV nodes and corresponding AV bundles with a connecting sling has been reported in patients with asplenia and right isomerism.
its connection form and electrophysiological properties remain to be elucidated.
Several previous reports have suggested the presence of a continuous and uninterrupted sling. For example, His bundle (HB) refractory ventricular premature depolarization (VPD) failed to reset tachycardia,
Absence of a resetting phenomenon suggests that a sling works as a part of the supraventricular tachycardia circuit involving twin atrioventricular nodes: a case of corrected transposition of the great arteries.
Furthermore, in a recent multicenter study of 59 cases, HB refractory VPD failed to advance the atrial activation in approximately two-thirds of the patients.
In contrast, a case of a patient with interventricular dyssynchrony due to unilateral AV conduction block after surgical cryoablation suggested that the sling was interrupted.
Interventricular dyssynchrony due to unilateral atrioventricular conduction block in a patient with right atrial isomerism and twin atrioventricular nodes.
This report describes a case of AV reciprocating tachycardia via twin AV nodes in a patient who underwent successful radiofrequency ablation for the posterior AV node. This case report subsequently makes a novel contribution to the literature by demonstrating the connection form of the sling and cardiac conduction system.
Case report
A 9-year-old underweight (15.4 kg) boy was diagnosed with a single right ventricle, a single atrium, L-transposition of the great arteries, a common AV valve, bilateral superior vena cava, dextrocardia, and asplenia just after birth. Glenn surgery and pulmonary artery banding were performed at 1 year and 5 months and at 1 year and 6 months of age, respectively. He developed supraventricular tachycardia during cardiac catheterization, which was terminated by intravenous administration of adenosine triphosphate. As the tachycardia was refractory to antiarrhythmic drugs, radiofrequency catheter ablation was performed during preoperative catheterization for Fontan surgery. An electrophysiological study was conducted using 3-dimensional electroanatomic mapping (CARTO 3; Biosense Webster, Irvine, CA) under deep sedation. Quadripolar catheters were placed at the common AV valve and single ventricle.
HB potentials were observed at the 11 and 8 o’clock positions of the common AV annulus, which were thought to be caused by the anterior and posterior AV nodes, respectively (Figure 1A). Pacing the atrium near the anterior AV node showed the same QRS waveform as that observed during sinus rhythm (Figure 1B), suggesting that conduction through the anterior AV node was dominant during the sinus rhythm. Pacing the atrium near the posterior AV node showed the same QRS waveform as that observed during tachycardia (Figure 1B), suggesting that the posterior AV node mediated antegrade conduction during tachycardia. Tachycardia was induced by atrial or ventricular extrastimulation. During tachycardia, the Purkinje potentials were recorded posterior to the common AV annulus (Figure 1A). The earliest atrial activation site during tachycardia was at the 11 o’clock position of the common AV annulus. The postpacing interval (PPI) after overdrive pacing from the earliest atrial activation site was equal to the TCL, suggesting that the anterior AV node mediated the retrograde conduction during tachycardia.
Figure 1His bundle (HB) potentials recording sites and QRS morphologies in the 12-lead electrocardiogram. A: HB potentials were recorded during sinus rhythm at the anterior and posterior of the common atrioventricular (AV) annulus, which are thought to be HB potentials caused by the anterior and posterior AV nodes, respectively. Anterior HB: AH 52 ms, HV 46 ms. Posterior HB: AH 102 ms, HV 42 ms. Two different QRS morphologies are recorded during sinus rhythm. During tachycardia, the Purkinje potential is recorded on the posterior side of the common AV annulus. B: Pacing of the atrium near the anterior AV node shows the same waveform as that during sinus rhythm. Pacing of the atrium near the posterior AV node shows the same QRS waveform as that observed during tachycardia. aHB = HB of the anterior AV node; AVA = AV annulus; pHB = HB of the posterior AV node.
A single VPD produced by catheter mechanical irritation during mapping failed to reset the tachycardia (Figure 2A). Catheter mechanical irritation at the Purkinje potential recording site caused the right bundle branch block (RBBB) pattern during tachycardia without changes in the TCL and AV interval (Figure 2B). Following this, overdrive pacing from the ventricular catheter, where the Purkinje potential was recorded, showed concealed entrainment, and the PPI was 32 ms longer than the TCL (Figure 2C). We did not pursue catheter ablation for that day because the RBBB pattern persisted. The next day, the QRS waveform recovered from the RBBB pattern; therefore, radiofrequency catheter ablation was performed on another day. As the anterior AV node was predominantly involved in sinus rhythm, radiofrequency catheter ablation of the posterior AV node was performed using an open-irrigated catheter (ThermoCool® SmartTouchTM Surround Flow; Biosense Webster). During radiofrequency application (25 W), an accelerated junctional rhythm was observed, which had the same waveform as conduction via the posterior AV node (Figure 2D). After ablation, any tachycardia could no longer be induced without PR prolongation, QRS waveform changes, or any complications. Fontan surgery was then performed, and 3 years passed without tachycardia recurrence.
Figure 2Intracardiac and 12-lead electrocardiograms during the electrophysiological study and catheter ablation. A: Ventricular premature depolarization (VPD) caused by catheter mechanical irritation (shown by yellow triangle) was observed during tachycardia. The Purkinje potential was recorded at the ventricular catheter. VPD preceding the Purkinje potential failed to reset the tachycardia. B: VPDs caused by catheter mechanical irritation (shown by yellow triangles) at the site of the Purkinje potential (shown by red arrows) caused the right bundle branch block (RBBB) pattern. The tachycardia cycle length (TCL) did not change after the RBBB pattern occurred. The first VPD waveform shows the inferior axis, suggesting that the mapping catheter was positioned on the anterior side of a single ventricle. The AV interval between the atrial potential recorded at the atrioventricular annulus (AVA) and the ventricular potential at the ventricular catheter was also unchanged. C: In the RBBB pattern state, overdrive pacing at the Purkinje potential recording site shows concealed entrainment. A ventricular-atrial-ventricular response was observed. Postpacing interval is 32 ms longer than the TCL. D: Radiofrequency catheter ablation of the posterior AV node. The Purkinje potential was recorded at the catheter (indicated by red triangles). A junctional rhythm was observed, the same waveform via conduction over the posterior AV node. EGM = electrogram. All other abbreviations are in Figure 1.
There are several hypotheses regarding the connection form of the sling and the cardiac conduction system. The findings in our case suggest that the sling was continuous, as there were 2 junctions from the cardiac conduction system to the single ventricle, both of which are considered bystanders of the tachycardia circuit.
Figure 3A presents a schema of the tachycardia circuit. The anterior AV bundle branch distal to the anterior AV node was thought to be a bystander of the tachycardia circuit because the TCL did not change, even after the QRS changed to the RBBB pattern (Figure 3B). An inferior axis waveform of the VPD caused by catheter mechanical irritation suggested that the catheter was positioned anterior to the ventricle, and the Purkinje potential recorded by the mapping catheter was thought to be the anterior AV bundle branch connecting to the anterior AV node. The ventricular catheter was placed on the posterior wall side, and the Purkinje potential was recorded. However, the AV interval did not change after the RBBB pattern occurred (Figure 2B), suggesting that the posterior AV bundle branch was independent of the anterior AV bundle branch.
Figure 3Schematic illustrations of the tachycardia circuit. A: A schema of the tachycardia circuit. The posterior and anterior AV nodes mediate the antegrade and retrograde conduction, respectively. B: The right bundle branch block (RBBB) pattern occurred without changes in the tachycardia cycle length (TCL) and atrioventricular (AV) intervals suggesting that the anterior AV bundle branch was a bystander of tachycardia. C: In the RBBB pattern state, overdrive pacing at the Purkinje potential recording site shows concealed entrainment. Concealed entrainment was observed as the sling is continuous, and the anterior AV bundle branch is already blocked. Therefore, the posterior AV bundle branch serves as the only breakthrough site for a single ventricle. See text for details. Abbreviations are in Figures 1 and 2.
The posterior AV bundle branch distal to the posterior AV node was thought to be a bystander of the tachycardia circuit for several reasons. The short interval between the Purkinje and local ventricular potentials indicated that this site was a junction between the posterior AV bundle branch and the ventricular myocardium. In the RBBB pattern state, concealed entrainment was observed during the overdrive pacing from this site (Figure2C). Concealed entrainment was observed as this site was the only breakthrough site for a single ventricle from the tachycardia circuit, involving an uninterrupted connecting sling in the RBBB pattern state (Figure 3C). A long PPI (>30 ms) suggested that the pacing site was a bystander of the tachycardia circuit. Although the decremental conduction property of AV nodes may misleadingly prolong PPI,
when the pacing site is included in the tachycardia circuit, a single VPD preceding the posterior Purkinje potential should readily reset the tachycardia because the ventricle is a part of the tachycardia circuit. However, the reset phenomenon was not observed in this case (Figure 2A). Alternatively, if the sling was interrupted, QRS fusion should have been present during ventricular overdrive pacing owing to excitations from both the pacing and the sling to the ventricular junction. However, it may be difficult to completely rule out that concealed entrainment was observed because the sling interruption was extremely short, and the area excited by the sling to the ventricular junction was insufficient to present QRS fusion. Although VPD or entrainment pacing from multiple ventricle sites may be helpful, we could not perform further mapping owing to concerns of intraventricular conduction block caused by catheter mechanical irritation in a small single ventricle.
Differential diagnosis from antidromic AV reciprocating tachycardia using a decremental AV/atriofascicular bypass tract may be difficult. Since the tachycardia was readily induced by atrial or ventricular pacing, the presence of retrograde conduction via the posterior AV node could not be proven by ventricular pacing. However, the lack of preexcitation during atrial stimulation and tachycardia suggested twin AV nodes rather than a decremental AV/atriofascicular bypass tract.
Conclusion
The electrophysiological findings in our case suggested a continuous sling, as there were 2 junctions from the cardiac conduction system to the single ventricle, both of which were considered bystanders of the tachycardia circuit.
Acknowledgments
The authors thank Ms Kaori Aoki and Mr Keigo Yamamoto in the Department of Clinical Engineering, Hirosaki University Hospital, for their technical assistance in the electrophysiological study. The authors also thank Drs Toru Takahashi, Katsuki Ootani, Yosuke Kitagawa, and Jun Shimada in the Department of Pediatrics, Hirosaki University Hospital, for patient care and managing the patient during the catheter ablation.
The patient and the patient’s family gave their informed consent for this report to be published.
References
Wu M.-H.
Wang J.-K.
Lin J.-L.
et al.
Supraventricular tachycardia in patients with right atrial isomerism.
Absence of a resetting phenomenon suggests that a sling works as a part of the supraventricular tachycardia circuit involving twin atrioventricular nodes: a case of corrected transposition of the great arteries.
Interventricular dyssynchrony due to unilateral atrioventricular conduction block in a patient with right atrial isomerism and twin atrioventricular nodes.
Funding Sources: This research did not receive any specific grant from funding agencies in public, commercial, or not-for-profit sectors.
Disclosures: Dr Masaomi Kimura is an associate professor and Dr Taihei Itoh is an associate professor/lecturer of the Department of Advanced Management of Cardiac Arrhythmias, which is an endowment department supported by Medtronic Japan Co, Ltd, and Fukuda Denshi Kita-Tohoku Hanbai Co, Ltd. Dr Yuji Ishida is an assistant professor of the Department of Cardiac Remote Management System, which is an endowment department supported by BIOTRONIK Japan Co, Ltd. Dr Hirofumi Tomita has received research grant support from Medtronic Japan Co, Ltd, Fukuda Denshi Kita-Tohoku Hanbai Co, Ltd, and BIOTRONIK Japan Co, Ltd, and scholarship grants from Japan Lifeline Co. Dr Takahiko Kinjo has no relevant disclosures.
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