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

Background 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. Objectives To report the use of three‐dimensional electro‐anatomical mapping (3D EAM) to identify a concealed AP and treatment by RFCA in a horse. Study Design Retrospective case report. Case Description 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. Main Limitations 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.