Sustained atrial tachycardia in horses and treatment by transvenous electrical cardioversion.

Abstract

BACKGROUND\nAtrial 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.\n\n\nOBJECTIVES\nTo 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.\n\n\nSTUDY DESIGN\nCase series.\n\n\nMETHODS\nRecords from horses with sustained atrial tachycardia treated by biphasic TVEC at Ghent University were reviewed. Horses with atrial fibrillation were not included.\n\n\nRESULTS\nSeven 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\xa0ms 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\xa0day after TVEC treatment, another case showed recurrence 8\xa0years post conversion. The other five cases were still in sinus rhythm at 9\xa0months - 5\xa0years after TVEC.\n\n\nMAIN LIMITATIONS\nDue 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.\n\n\nCONCLUSIONS\nTreatment 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\xa0h) occurred in one horse.