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The extracardiac Fontan (EC-Fontan) has recently become the most commonly used approach in the Fontan operation. In such patients, catheter ablation (CA) is difficult to perform because the venous access to the heart is limited. A transcaval cardiac puncture (TCP) technique for gaining access to the heart chamber has previously been suggested for EC-Fontan patients.
We report a case of VT from the outlet septum in a double-outlet right ventricle (DORV) after an EC-Fontan, wherein CA was performed via a TCP. Multiple PVCs were completely eliminated by ablating the site of distinct prepotentials on the aortic side of the outlet septum.
The patient had a left atrial isomerism, DORV, subaortic ventricular septal defect, common atrioventricular valve, and aorta originating from the right ventricle with subvalvular stenosis. She underwent pulmonary artery banding at 2 months, a Damus–Kaye–Stansel operation (DKS), bidirectional Glenn operation, and central shunt surgery at 1 year of age and an EC-Fontan operation at 3 years of age (Figure 1, Supplemental Figure 1). She had recurrent syncope and headaches since she was 13 years old. A 12-lead electrocardiogram (ECG) showed 2 types of PVCs and 24-hour Holter monitoring documented an episode of nonsustained VT (NSVT), which was not related to the syncope. Her neurological evaluation was normal. She underwent an electrophysiological study and no arrhythmias were induced by the electrophysiological study. An implantable loop recorder was implanted; however, she did not have any further episodes of syncope, and the device was removed owing to battery depletion 3 years postimplantation. After the removal, she had further syncopal episodes, and 24-hour Holter monitoring showed a significant burden of PVCs (12%) with NSVT. She underwent a CA at 18 years of age owing to recurrent syncope and high PVC burden.
The resting ECG (Figure 2A ) exhibited a right upper axis in the frontal plane, qR in V1, and R/S ratio <1 in V5 and V6 during sinus rhythm, suggesting that the atrioventricular node could be in a posterior position of the common atrioventricular canal. There were 2 types of PVCs with a left bundle branch block pattern and inferior axis. Each PVC morphology slightly differed in leads I and V1: R in I and rS in V1 (PVC1) and RS in I and small rS in V1 (PVC2). Those PVCs were thought to originate from the outflow tract with slightly different exit sites. Cardiac magnetic resonance imaging did not show any significant late gadolinium enhancement. A computed tomography scan (Figure 1) was performed to plan for the transcaval puncture and ablation strategy. We prepared for both a retrograde approach via the DKS anastomosis and antegrade approach via a transcaval puncture because of the possibilities of failure to access the target.
CA was performed under general anesthesia with propofol, remifentanil, and rocuronium. After an inferior vena cava angiography, we performed a TCP under intracardiac echocardiography guidance using a radiofrequency (RF) needle (NRG Transseptal Needle; Baylis Medical, Montreal, Canada) and Swartz introducer (SL-0, Fast-cath; St. Jude Medical, St. Paul, MN). A deflectable long sheath (Agilis NxT sheath; Abbott Medical) was inserted into the atrium after balloon dilatation of the puncture hole (Sterling 4-mm-diameter balloon; Boston Scientific, Tokyo, Japan). Diagnostic catheters were placed in the conduit via the internal jugular vein and right ventricle from the femoral artery in a retrograde manner. At baseline, there were frequent PVCs with 3 different morphologies, all with a left bundle branch block and inferior axis QRS morphology (Figure 2B). An NSVT with the PVC1 morphology was induced with an isoproterenol infusion. The PVCs were reproducibly elicited by programmed stimuli. The His bundle electrogram was confirmed inferior to the common atrioventricular valve and far from the outflow septum. Catheter manipulation was performed with an Agilis sheath via the TCP, because the catheter manipulation was challenging via the retrograde approach owing to the aortic stenosis and DKS anastomosis.
A PVC activation map using CARTO III mapping and a NAVISTAR catheter (Biosense Webster, Irvine, CA) revealed the earliest activation in the outlet septum. The PVC1 activation map on the subpulmonary side of the outlet septum revealed the earliest site of the ventricular activation, which was 32 ms earlier than the QRS complex on the surface ECG (Figure 1E and 1H and Figure 3B ). The prepotential was recorded at that site, which preceded the QRS complex by 61 ms. Pace mapping nearly matched the QRS morphology of PVC1 (Figure 2C). The PVC transiently disappeared after delivering RF energy for 60 seconds at a temperature below 55°C with a power limit of 40 W. The earliest ventricular activation during PVC2 was on the subaortic side of the outlet septum, which was 28 ms earlier than the QRS complex on the surface ECG. However, its discrete prepotential, which was 106 ms earlier than the QRS complex, was recorded (Figure 1F and 1I and Figure 3A), and its pace mapping coincided with the PVC2 morphology (Figure 2C).
All PVCs were eliminated by delivering RF energy on the subaortic side of the outlet septum (Figure 3A). At 3 months postablation, she has not had any syncopal episodes and Holter monitoring revealed a PVC burden of 2% with no VT.
To the best of our knowledge, this is the first report of a successful CA of NSVT originating from the outlet septum in a patient with a DORV after an EC-Fontan operation via a transcaval puncture. Three PVC morphologies were simultaneously eliminated by an RF application at the site of the distinct prepotential electrograms during the PVC on the subaortic side of the outlet septum (not at the earliest ventricular activation site during the PVC). Three studies have discussed percutaneous VT ablation in patients that underwent a Fontan operation, which were ablated via a retrograde approach.
The approach to the heart is restricted after an EC-Fontan operation: retrograde approach and transbaffle or transcaval approaches. Catheter manipulation can be quite challenging via a retrograde approach in the setting of subaortic stenosis. However, a transbaffle and transcaval approach could be useful for CA or the creation of a fenestration. In this case, the subaortic stenosis made the retrograde approach difficult. The transcaval approach using a TCP and deflectable sheath made it easier to manipulate the ablation catheter. Thus, when a PVC/VT originating from the outlet septum in Fontan patients is suspected, the operators should be prepared to attempt multiple approaches to accomplish a successful ablation.
Idiopathic ventricular arrhythmias commonly originate from the right (RVOT) and left ventricular outflow tracts. The adult RVOT forms from the embryonic outflow tract, which is primarily composed of myocardium and exhibits slow conduction and spontaneous activity. During development, the embryonic outflow tract acquires a working myocardial phenotype (eg, fast conduction) and transforms into the RVOT. A small ring of primary myocardium, however, remains just below the pulmonary valve, and this may give rise to automaticity, as seen in patients with idiopathic RVOT tachycardia.
On the other hand, the “dead-end tract” has been linked to the occurrence of ventricular arrhythmias. This is a remnant of the developing conduction system and is seen in addition to the right and left bundle branch, fading out on the crest of the muscular ventricular septum.
In this case, the multiple PVCs were completely eliminated by delivering RF on the aortic side of the outlet septum, rather than on the pulmonary artery side, which was the earliest ventricular site during the PVCs. This suggested the existence of preferential conduction (Supplemental Figure 2). Although there is a secondary interventricular foramen (ie, a defect between the muscular ventricular septum and conus septum [outlet septum]), the outlet septum inserts into the ventriculo-infundibular fold and continues to the muscular ventricular septum, wherein a preferential pathway can exist. When it is difficult to ablate outflow PVCs/VTs in complex congenital heart diseases, the existence of preferential conduction should be considered.
To the best of our knowledge, this is the first reported case of the successful ablation of NSVT originating from the outlet septum via the transcaval approach in a patient with a DORV after an EC-Fontan operation. Multiple PVCs were completely eliminated by ablating the site of distinct prepotentials on the aortic side of the outlet septum, suggesting the existence of preferential conduction. Thus, in such cases, it is important to study the patient’s anatomy, conduction system, mechanism of the arrhythmia, and strategic approach, as well as prepare the required equipment.
Key Teaching Points
The outlet septum could be one of the origins of the ventricular arrhythmias in Fontan patient.
Look for the early discrete potentials in outflow ventricular arrhythmias in tough cases.
A transconduit approach is effective in extracardiac Fontan patients.
We are grateful to Hiroko Asakai for carefully proofreading the manuscript. We would like to thank enago (www.enago.jp) for the English-language editing.
Appendix. Supplementary data
Factors associated with long-term mortality after Fontan procedures: a systematic review.
In this issue of Heart Rhythm Case Reports, Mori and colleagues1 present a case in which multiform ventricular ectopy was successfully ablated from the remnant of outflow tract septum in an adolescent with complex congenital heart disease. As the authors demonstrate with multimodality imaging and hand illustration, the ectopic focus was within the bar of muscle above a large ventricular septal defect and between the paired outflows in this patient with heterotaxy syndrome, double-outlet right ventricle, and prior single-ventricle palliation including surgical amalgamation of the proximal aorta and pulmonary artery (the Damus-Kaye-Stansel operation) and total cavopulmonary connection (the extracardiac conduit Fontan operation).