Lesion size index‐guided radiofrequency catheter ablation using an impedance‐based three‐dimensional mapping system to treat sustained atrial tachycardia in a horse

Abstract Sustained atrial tachycardia at an atrial rate of 191/min on the surface ECG was detected in a 6‐year‐old Warmblood mare. The vectorcardiogram obtained from a 12‐lead ECG suggested a caudo‐dorsal right atrial origin of the arrhythmia. Impedance‐based three‐dimensional electro‐anatomical mapping, using the EnSite™ Precision Cardiac Mapping System revealed a clockwise macro‐reentry around a line of conduction block in the caudomedial right atrium. Ten radiofrequency applications were applied to isolate the caudal vena cava myocardial sleeves at a power of 35 W and mean contact force of 14 ± 3 g until a lesion size index of 6 was reached. Sinus rhythm was restored at the first energy application. Successful isolation was confirmed by demonstrating entrance and exit block. Holter monitoring 5 days post‐ablation revealed no abnormalities. To date, 9 months after treatment, no recurrence has been observed. The use of lesion size index‐guided ablation and isolation of the arrhythmogenic substrate in the caudal vena cava may minimise the risk of recurrence.