Equine veterinary journal2026; doi: 10.1002/evj.70361

Treatment of a concealed accessory pathway by radiofrequency catheter ablation in a horse.

Buschmann, E
·
Van Steenkiste, G
·
Verhaeghe, LM
·
Heirman, L
·
Schauvliege, S
·
Decloedt, A
·
van Loon, G

Abstract: Accessory pathways (APs) are myocardial bundles directly connecting the atria and the ventricles, bypassing the atrioventricular node-His-Purkinje system. Retrograde AP conduction in horses can result in orthodromic atrioventricular re-entry tachycardia or bradycardia. Radiofrequency catheter ablation (RFCA) can provide a permanent treatment by eliminating the retrograde conducting AP, but was previously unsuccessful in one case. Objective: To report the use of three-dimensional electro-anatomical mapping (3D EAM) to identify a concealed AP and treatment by RFCA in a horse. Methods: Retrospective case report. Methods: An irregular heart rhythm was detected in a 4-year-old, 518 kg Paint mare as an incidental finding. Frequent atrial depolarisations were identified in the ST segment with a fixed coupling interval to the preceding QRS complex on the ECG. A differential diagnosis of frequent premature atrial complexes displayed as bigeminy or a retrograde conduction along an AP was made. The presence of a retrograde conducting AP was confirmed by ventricular pacing, which resulted in 1:1 ventriculo-atrial activation. Three-dimensional EAM revealed the earliest atrial activation and thereby the atrial insertion of the AP in the caudal left atrium. Subsequent RFCA at 40 W eliminated AP conduction. Conclusions: Single case report. Conclusions: This case report describes the identification of an AP by 3D EAM and the first successful permanent treatment of a retrograde conducting AP by RFCA in an adult horse.

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Publication Date: 2026-11-05 PubMed ID: 42987806DOI: 10.1002/evj.70361Google Scholar: Lookup

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Summary

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Overview

This study reports the successful use of three-dimensional electro-anatomical mapping (3D EAM) and radiofrequency catheter ablation (RFCA) to identify and treat a concealed accessory pathway (AP) causing irregular heart rhythm in a horse.

Introduction to Accessory Pathways and Their Clinical Significance

Accessory pathways (APs) are abnormal myocardial bundles that directly connect the atria and ventricles, bypassing the normal atrioventricular (AV) conduction system.
In horses, APs can conduct impulses retrogradely (from ventricles back to atria), potentially causing arrhythmias such as orthodromic atrioventricular re-entry tachycardia or bradycardia.
These arrhythmias can lead to irregular heart rhythms, which may affect the horse’s health and performance.
Previously, attempts to treat such pathways in horses using radiofrequency catheter ablation (RFCA) have been reported but were unsuccessful in at least one case.

Objective of the Study

The study aimed to demonstrate the use of three-dimensional electro-anatomical mapping (3D EAM) to accurately locate a concealed accessory pathway in a horse.
It also aimed to document the first successful application of RFCA to permanently eliminate the retrograde conducting AP in an adult horse.

Case Presentation and Diagnostic Procedures

The subject was a 4-year-old Paint mare weighing 518 kg with an irregular heart rhythm that was incidentally discovered.
Electrocardiogram (ECG) analysis showed frequent atrial depolarizations occurring during the ST segment, with a fixed timing relationship (coupling interval) to the preceding QRS complex.
The differential diagnosis included either:
- Frequent premature atrial complexes displayed in a bigeminy pattern (premature beats occurring after each normal beat), or
- Retrograde conduction along an accessory pathway causing the observed abnormal rhythm.
To confirm the diagnosis, ventricular pacing was performed, which demonstrated 1:1 ventriculo-atrial conduction—indicating a retrograde conduction pathway consistent with a concealed AP.

Use of Three-Dimensional Electro-Anatomical Mapping (3D EAM)

3D EAM technology was employed to pinpoint the precise location of the AP’s atrial insertion.
The mapping revealed that the earliest atrial activation during retrograde conduction originated in the caudal left atrium.
This precise localization was key for targeting the ablation procedure effectively.

Radiofrequency Catheter Ablation (RFCA) Procedure

Following identification of the accessory pathway location, RFCA was performed at the atrial insertion site within the caudal left atrium.
Ablation was conducted with energy delivery at 40 watts.
This procedure successfully eliminated the retrograde conduction capability of the AP, thereby resolving the arrhythmia.

Conclusions and Clinical Implications

This is the first reported successful permanent elimination of a retrograde conducting concealed AP in an adult horse using RFCA guided by 3D EAM.
The study demonstrates that advanced mapping techniques can identify challenging arrhythmogenic substrates in large animals like horses.
RFCA offers a promising, minimally invasive treatment option for arrhythmias caused by accessory pathways in equine patients.
The report encourages further investigation and application of these technologies in veterinary cardiology for horses.

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APA

Buschmann E, Van Steenkiste G, Verhaeghe LM, Heirman L, Schauvliege S, Decloedt A, van Loon G. (2026). Treatment of a concealed accessory pathway by radiofrequency catheter ablation in a horse. Equine Vet J. https://doi.org/10.1002/evj.70361

Publication

Equine veterinary journal

ISSN: 2042-3306

NlmUniqueID: 0173320

Country: United States

Language: English

Researcher Affiliations

Buschmann, Eva

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Van Steenkiste, Glenn

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Verhaeghe, Lize-Maria

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Heirman, Lennert

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Schauvliege, Stijn

Department of Large Animal Surgery, Anaesthesia and Orthopaedics, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Decloedt, Annelies

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

van Loon, Gunther

Equine Cardioteam Ghent, Department of Internal Medicine, Reproduction and Population Medicine, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium.

Grant Funding

01B05818 / Bijzonder Onderzoeksfonds UGent
1SE9122N / Fonds Wetenschappelijk Onderzoek

References

This article includes 28 references

Anderson RH, Ho SY, Gillette PC, Becker AE. Mahaim, Kent and abnormal atrioventricular conduction.. Cardiovasc Res 1996;31:480–491.
Issa ZM, Miller JM, Zipes DP. Typical atrioventricular bypass tracts.. Clinical arrhythmology and electrophysiology 3th ed. Philadelphia, PA: Elsevier; 2019. p. 599–676.
Wright KN, Connor CE, Irvin HM, Knilans TK, Webber D, Kass PH. Atrioventricular accessory pathways in 89 dogs: clinical features and outcome after radiofrequency catheter ablation.. J Vet Intern Med 2018;32:1517–1529.
Santilli RA, Pañero MM, Vázquez DMP, Perini A, Perego M. Radiofrequency catheter ablation of accessory pathways in the dog: the Italian experience (2008–2016).. J Vet Cardiol 2018;20:384–397.
Centurión OA, Shimizu A, Isomoto S, Konoe A. Mechanisms for the genesis of paroxysmal atrial fibrillation in the Wolff—Parkinson—White syndrome: intrinsic atrial muscle vulnerability vs. electrophysiological properties of the accessory pathway.. Europace 2008;10:294–302.
Brugada J, Katritsis DG, Arbelo E, Arribas F, Bax JJ, Blomström‐Lundqvist C. 2019 ESC guidelines for the management of patients with supraventricular tachycardia.. Eur Heart J 2020;41:655–720.
Buschmann E, Van Steenkiste G, Boussy T, Vernemmen I, Schauvliege S, Decloedt A. Three‐dimensional electro‐anatomical mapping and radiofrequency ablation as a novel treatment for atrioventricular accessory pathway in a horse: a case report.. J Vet Intern Med 2023;7:728–734.
Muir WW, Mcguirk SM. Ventricular preexcitation in 2 horses.. J Am Vet Med Assoc 1983;183:573–576.
Viu J, Armengou L, Decloedt A, Jose‐Cunilleras E. Investigation of ventricular pre‐excitation electrocardiographic pattern in two horses: clinical presentation and potential causes.. J Vet Cardiol 2018;20:213–221.
Jesty SA, Kraus MS, Johnson AL, Gelzer AR, Bartol J. An accessory bypass tract masked by the presence of atrial fibrillation in a horse.. J Vet Cardiol 2011;13:79–83.
Santilli RA, Spadacini G, Moretti P, Perego M, Perini A, Tarducci A. Radiofrequency catheter ablation of concealed accessory pathways in two dogs with symptomatic atrioventricular reciprocating tachycardia.. J Vet Cardiol 2006;8:157–165.
Pelliccia A, Sharma S, Gati S, Bäck M, Börjesson M, Caselli S. 2020 ESC guidelines on sports cardiology and exercise in patients with cardiovascular disease.. Eur Heart J 2021;42:17–96.
Buschmann E, Easton‐Jones C, Van Steenkiste G, De Wilde H, Roberts V, Durando M. Orthodromic atrioventricular reentry bradycardia and tachycardia caused by an accessory pathway in horses.. J Vet Intern Med 2025;39:e70175.
Leung LWM, Gallagher MM. Review paper on WPW and athletes: let sleeping dogs lie?. Clin Cardiol 2020;43:897–905.
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A. Lesion size index‐guided radiofrequency catheter ablation using an impedance‐based three‐dimensional mapping system to treat sustained atrial tachycardia in a horse.. Equine Vet J 2025;57(4):1009–1016.
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A. Caudal vena cava isolation using ablation index‐guided radiofrequency catheter ablation (CARTO™ 3) to treat sustained atrial tachycardia in horses. J Vet Intern Med 2025;39:e17251.
Buschmann E, Van Steenkiste G, Bulckens H, Schauvliege S, Decloedt A, van Loon G. Three‐dimensional electro‐anatomical mapping of premature atrial complexes originating from the right atrial free wall and treatment by radiofrequency ablation in three horses. Equine Vet J 2026;58(4):1032–1040.
doi: 10.1111/evj.70095google scholar: lookup
Paulussen E, Van Steenkiste G, Hermans BM, Decloedt A, van Loon G, Delhaas T. Einthoven's triangle adapted for horses: proposal for the Delta configuration. J Vet Intern Med 2024;38:2698–2706.
van Loon G, Decloedt A. Arrhythmias and abnormalities of the cardiac conduction system in athletic horses. In: Hinchcliff K, Kaneps A, Geor R, van Erck‐Westergren E, editors. Equine sports medicine and surgery. 3rd ed. Missouri: Elsevier; 2024. p. 831–865.
Van Steenkiste G, Delhaas T, Hermans B, Vera L, Decloedt A, van Loon G. An exploratory study on vectorcardiographic identification of the site of origin of focally induced premature depolarizations in horses, part I: the atria. Animals 2022;12:549.
Vernemmen I, Buschmann E, Van Steenkiste G, Demeyere M, Verhaeghe L, De Somer F. Intracardiac ultrasound‐guided transseptal puncture in horses: outcome, follow‐up and peri‐operative anticogulant treatment. J Vet Intern Med 2024;38:2707–2717.
Vernemmen I, Van Steenkiste G, Buschmann E, Cornelis K, Schauvliege S, Ibrahim L. Development of an atrial transseptal puncture procedure in horses to access the left heart: an ultrasound‐guided jugular vein and transhepatic approach. Equine Vet J 2025;57:243–255.
Buschmann E, Van Steenkiste G, Duytschaever M, Boussy T, Vernemmen I, Ibrahim L. Successful caudal vena cava and pulmonary vein isolation in healthy horses using 3D electro‐anatomical mapping and a contact force‐guided ablation system. Equine Vet J 2023;56:1068–1076.
Santilli RA, Spadacini G, Moretti P, Perego M, Perini A, Crosara S. Anatomic distribution and electrophysiologic properties of accessory atrioventricular pathways in dogs. J Am Vet Med Assoc 2007;231:393–398.
Gavic EA, Stauthammer CD, Masters AK, Morgan KRS, Rendahl A, Ciccozzi M. Clinical, electrocardiographic, and diagnostic imaging features and outcomes in cats with electrocardiographic diagnosis of ventricular pre‐excitation: a retrospective study of 23 cases (2010–2022). J Vet Cardiol 2024;56:97–109.
Holmes DR, Hartzler GO, Maloney JD. Concealed retrograde bypass tracts and enhanced atrioventricular nodal conduction—an unusual subset of patients with refractory paroxysmal supraventricular tachycardia. Am J Cardiol 1980;45:1053–1060.
Maffei A, Perego M, Cavallini D, Santilli R. Atrial depolarization electrocardiographic features during orthodromic atrioventricular reciprocating tachycardia mediated by right‐sided accessory pathway in the dog. J Vet Cardiol 2025;61:10–19.
Buschmann E, Van Steenkiste G, Vernemmen I, Demeyere M, Schauvliege S, Decloedt A. Multiple catheter recording in horses to investigate atrial depolarization pattern during sinus rhythm and induced premature atrial complexes. J Vet Intern Med 2025;39(5):e70218.