Sustained atrial tachycardia in horses and treatment by transvenous electrical cardioversion

Abstract

Summary Background Atrial tachycardia including focal atrial tachycardia and macroreentrant atrial tachycardia (atrial flutter), are occasionally found in horses. Diagnosis, treatment and follow‐up of these arrhythmias has been inadequately described. Objectives To describe the findings on surface electrocardiography (ECG), intra‐atrial electrogram recording and tissue Doppler imaging (TDI), the response to treatment by transvenous electrical cardioversion (TVEC), and TDI follow‐up, of sustained atrial tachycardia in horses. Study design Case series. Methods Records from horses with sustained atrial tachycardia treated by biphasic TVEC at Ghent University were reviewed. Horses with atrial fibrillation were not included. Results Seven horses with sustained atrial tachycardia were treated with TVEC. In six cases an exercise ECG was available and in 4 a 12‐lead ECG had been recorded. The mean bias between atrial cycle length measured from a right atrial intra‐atrial electrogram and from TDI ranged between −2 and 3 ms depending on the sampled region. All seven cases converted to sinus rhythm during the first TVEC procedure. TDI showed atrial contractile function recovery similar to cases that were treated for atrial fibrillation. One case developed atrial fibrillation 1 day after TVEC treatment, another case showed recurrence 8 years post conversion. The other five cases were still in sinus rhythm at 9 months – 5 years after TVEC. Main limitations Due to the small number of patients, data on recurrence and follow‐up of atrial recovery should be interpreted with caution. Since no invasive electrophysiology studies were performed, differentiation between focal atrial tachycardia and atrial flutter remains speculative. Conclusions Treatment of focal atrial tachycardia or atrial flutter by TVEC has a very high success rate. Tissue Doppler imaging allows noninvasive measurement of atrial cycle length and suggests reduced atrial function after cardioversion. Long‐term prognosis after cardioversion seemed similar compared to horses with atrial fibrillation, although early recurrence (<24 h) occurred in one horse.

Detection of the origin of atrial tachycardia by 3D electro‐anatomical mapping and treatment by radiofrequency catheter ablation in horses

“…In contrast to a macro‐reentrant AT, the heart rate of a focal AT might be overridden during an exercise test. However, because of the high atrial rates, an exercise test would probably have been inconclusive in our horses 2 …”

“… 12 In horses, no specific recommendations regarding AT treatment exist but the arrhythmia is treated similar to AF since RFCA was not available. 13 Current treatment options for AT in horses include biphasic TVEC, 2 administration of quinidine sulfate, 7 , 13 overdrive pacing, and administration of amiodarone. 3 , 4 Flecainide has been used for the cardioversion of AT but is potentially lethal and its issue is not advised in humans.…”

“… 1 The underlying mechanisms are still poorly understood. 2 , 3 , 4 Differentiation between a macro‐reentrant circuit (eg, atrial flutter) and a focal source is based upon characteristics of the surface ECG but remains challenging. 5 , 6 , 7 In human medicine, invasive electrophysiological studies, such as endocardial mapping, are often required to identify the underlying AT mechanism.…”

“…Until now, sustained AT in horses has been treated with medication (quinidine sulfate) or transvenous electrical cardioversion albeit with a high likelihood of recurrence. 2 , 13 …”

Science‐in‐brief: Equine Cardiology Virtual Retreat June 2020

“…Gunther van Loon (University of Ghent) proposed classifying supraventricular arrhythmias broadly (similar to what is done in human medicine). It was also emphasised that the use of a 12‐lead ECG is important to try and determine the origin of APCs (left or right atrium) which might aid in guiding any future therapeutic interventions (particularly with respect to EP mapping and ablation of arrhythmogenic foci) 4‐6 . In addition, the AF breakout group discussed the use of implantable loop recorders in horses.…”