Doubly unusual in double discordance: Appendage-based accessory pathway in congenitally corrected transposition

In this issue of Heart Rhythm Case Reports, Radhakrishnan et al present a case of a very unusual accessory pathway in the setting of congenitally corrected transposition of the great arteries (ccTGA, also termed L-transposition of the great arteries, L-TGA, or double discordance, referring to combined atrioventricular (AV) and ventriculoarterial discordance).1Radhakrishnan S.L. Drutel R.O. Williams C.M. Danrad R. Gajewski K.K. LeLorier P.A. Ablation of accessory pathway from right atrial appendage to anatomic left ventricle in L-Transposition of the Great Arteries.Heart Rhythm Case Rep. 2023; https://doi.org/10.1016/j.hrcr.2023.12.003Google Scholar,2Baruteau A.E. Abrams D.J. Ho S.Y. Thambo J.B. McLeod C.J. Shah M.J. Cardiac Conduction System in Congenitally Corrected Transposition of the Great Arteries and Its Clinical Relevance.J Am Heart Assoc. 2017 Dec 21; 6e007759https://doi.org/10.1161/JAHA.117.007759Google Scholar ccTGA is a complex congenital heart disease—well-known to electrophysiologists due to high rates of heart block—where the ventricles are inverted, with the left ventricle on the right side of the heart (taking deoxygenated blood from the right atrium through a mitral valve, and ejecting to the pulmonary artery), and the right ventricle on the left side of the heart (taking oxygenated blood from the left atrium through a tricuspid valve, and ejecting to the aorta). In ccTGA, the left-sided tricuspid valve often has features of Ebstein anomaly, and accessory pathways tend to be located on its annulus or in the septal/para-septal region (Table 1) 3Takeuchi D. Toyohara K. Shoda M. Hagiwara N. Electrophysiological features and radiofrequency catheter ablation of accessory pathways associated with atrioventricular discordance.J Cardiovasc Electrophysiol. 2020 Jan; 31: 89-99https://doi.org/10.1111/jce.14273Google Scholar,4Tseng W.C. Huang C.N. Chiu S.N. Lu C.W. Wang J.K. Lin M.T. Chen C.A. Wu M.H. Long-term outcomes of arrhythmia and distinct electrophysiological features in congenitally corrected transposition of the great arteries in an Asian cohort.Am Heart J. 2021 Jan; 231: 73-81https://doi.org/10.1016/j.ahj.2020.10.057Google Scholar,5Iturralde P. Rivera-Rodríguez L. Guevara-Valdivia M.E. Colín L. Márquez M.F. Calvimontes G. Radiofrequency ablation of atrioventricular accessory pathways associated with discordant atrioventricular connections.Cardiol Young. 2002 Dec; 12: 542-548https://doi.org/10.1017/s1047951102000987Google Scholar.Table 1Published series of accessory pathways in ccTGAReferencePatients, pathwaysLeft-sided pathwaysRight-sided pathwaysTakeuchi et al11, 1313/130/13Tseng et al5, 109/101/10, posteroseptalIturralde et al3, 42/42/4, posteroseptal and midseptalTotal19, 2724/273/27 Open table in a new tab In the present report, a young adult with ccTGA and Wolff-Parkinson-White syndrome presented for a fifth electrophysiology study due to intractable supraventricular tachycardia, unusually attributed to a right free wall accessory pathway. The authors ultimately identified and successfully ablated a pathway connecting the right atrial appendage and the free wall of the right-sided left ventricle. Such appendage-based pathways are rare but do occur in patients with structurally normal hearts, as reviewed in a recent issue of the journal[6Dragisic N. Backes E.R. Malloy-Walton L. Chang P.M. Atrial appendage accessory pathway ablation: tips for recognition and approach to ablation.Heart Rhythm Case Rep. 2023; https://doi.org/10.1016/j.hrcr.2023.09.007Google Scholar]. They are more commonly associated with right than with left atrial appendages, possibly due to the larger surface area of the right atrial appendage in contact with the ventricular epicardium. These pathways are challenging to identify and ablate due to their rarity, location within a relatively low-flow structure, and seemingly broad nature[7Mah D. Miyake C. Clegg R. et al.Epicardial left atrial appendage and biatrial appendage accessory pathways.Heart Rhythm. 2010 Dec; 7: 1740-1745https://doi.org/10.1016/j.hrthm.2010.08.013Google Scholar]. Some may require epicardial or surgical approaches, with extensive dissection sometimes needed to completely divide the band-like connection between the appendage and ventricle 7Mah D. Miyake C. Clegg R. et al.Epicardial left atrial appendage and biatrial appendage accessory pathways.Heart Rhythm. 2010 Dec; 7: 1740-1745https://doi.org/10.1016/j.hrthm.2010.08.013Google Scholar,8Heaven D.J. Till J.A. Ho S.Y. Sudden death in a child with an unusual accessory connection.Europace. 2000; 2: 224-227https://doi.org/10.1053/eupc.2000.0101Google Scholar. While right-sided accessory pathways are rare in ccTGA, generally this refers to traditional accessory pathways, located on the fibrous valve annulus and believed to derive embryologically from incomplete development of the valve annulus. However, appendage-based pathways have different origin and anatomy, which may explain why they seem to require more intense ablation than typical pathways. The pathway in the present case finally blocked when the power was increased to 40 watts with an irrigated tip catheter. This case serves as an excellent reminder to consider alternative substrates when a case is not proceeding as expected. Clues about the presence of an appendage-based pathway include a relatively broad area of “early” electrograms on the valve annulus in the appendage region, less early electrogram timing than would be expected, a fair-field appearance to “early” electrograms, progressively earlier activation if mapping away from the annulus, and of course difficulty achieving successful ablation. As in most congenital heart diseases, individual anatomy must be considered as the conduction system in ccTGA varies based on atrial sidedness, associated defects, and other factors. The authors note that prior operators had hesitated to attempt ablation due to uncertainty about the location of the conduction system. Indeed, in patients with ccTGA and usual atrial arrangement (situs solitus), the AV node is usually shifted superiorly to the “anterior” aspect of the right-sided mitral valve, near the region where this patient’s accessory pathway was initially mapped. As described by the authors, ablation at the anterior mitral valve annulus or right atrial appendage base may put the AV node at risk in patients with ccTGA. Cryoablation can be a valuable tool to reduce risk of AV block in patients with congenital heart disease, especially when the conduction system may be displaced due to ccTGA, ventricular septal defect, or especially atrioventricular septal defect. Cryoablation may also be useful if ablating near coronary arteries[9Stavrakis S. Jackman W.M. Nakagawa H. et al.Risk of coronary artery injury with radiofrequency ablation and cryoablation of epicardial posteroseptal accessory pathways within the coronary venous system.Circ Arrhythm Electrophysiol. 2014 Feb; 7: 113-119https://doi.org/10.1161/CIRCEP.113.000986Google Scholar], as could be the case in an atrial appendage, especially a left atrial appendage. While not a focus of the case report, the use of Stereotaxis (St. Louis, Missouri) for this case deserves mention. Robotic magnetic navigation (RMN) has been found to be as safe and effective as manual ablation and has some potential advantages[10Kim J.J. Macicek S.L. Decker J.A. Kertesz N.J. Friedman R.A. Cannon B.C. Magnetic versus manual catheter ablation of free wall accessory pathways in children.Circ Arrhythm Electrophysiol. 2012 Aug; 5: 804-808https://doi.org/10.1161/CIRCEP.1111.969485Google Scholar, 11Chun J.K. Ernst S. Matthews S. Schmidt B. Bansch D. Boczor S. Ujeyl A. Antz M. Ouyang F. Kuck K.H. Remote-controlled catheter ablation of accessory pathways: results from the magnetic laboratory.Eur Heart J. 2007 Jan; 28 (Epub 2007 Jan 11): 190-195https://doi.org/10.1093/eurheartj/ehl447Google Scholar, 12Siroky G.P. Isath A. Yacoub M. et al.Remote magnetic versus manual catheter navigation in the ablation of accessory pathways in adults.J Atr Fibrillation. 2022 May; 15: 52-56Google Scholar, 13Schwagten B. Jordaens L. Rivero-Ayerza M. Van Belle Y. Knops P. Thornton I.A. Szili-Torok T. A randomized comparison of transseptal and transaortic approaches for magnetically guided ablation of left-sided accessory pathways.Pacing Clin Electrophysiol. 2010 Nov; 33: 1298-1303https://doi.org/10.1111/j.1540-8159.2010.02810.xGoogle Scholar]. Catheters used for RMN are more flexible and atraumatic than manual catheters, which may reduce procedural risks when ablating in an appendage. In conclusion, this very interesting and thought-provoking report nicely emphasizes the importance of maintaining an appropriate index of suspicion for an atypical pathway when a case does not proceed as expected, of considering an individual patient’s anatomy and conduction system, and of thoughtfully utilizing our growing number of tools to optimize benefit and risk. This case is one the authors, and perhaps the readers, will not soon forget! Ablation of accessory pathway from right atrial appendage to anatomic left ventricle in L-Transposition of the Great ArteriesHeartRhythm Case ReportsPreviewA 24-year-old female with a history of congenitally-corrected Transposition of the Great Arteries (ccTGA), and Wolf-Parkinson-White (WPW) syndrome status-post multiple ablations presented with recurrent palpitations from a narrow complex tachycardia at 200 bpm. She was found to have a rare accessory pathway from the right atrial appendage (RAA) to the morphologic left ventricle (LV) which was successfully ablated.