Sudden death of a horse with supraventricular tachycardia following oral administration of flecainide acetate

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

BACKGROUND

Atrial tachycardia (AT) can be treated by medical or electrical cardioversion but the recurrence rate is high. Three-dimensional electro-anatomical mapping, recently described in horses, might be used to map AT to identify a focal source or reentry mechanism and to guide treatment by radiofrequency ablation.

OBJECTIVES

To describe the feasibility of 3D electro-anatomical mapping and radiofrequency catheter ablation to characterize and treat sustained AT in horses.

ANIMALS

Nine horses with sustained AT.

METHODS

Records from horses with sustained AT referred for radiofrequency ablation at Ghent University were reviewed.

RESULTS

The AT was drug resistant in 4 out of 9 horses. In 8 out of 9 horses, AT originated from a localized macro-reentrant circuit (n = 5) or a focal source (n = 3) located at the transition between the right atrium and the caudal vena cava. In these 8 horses, local radiofrequency catheter ablation resulted in the termination of AT. At follow-up, 6 out of 8 horses remained free of recurrence.

CONCLUSIONS AND CLINICAL IMPORTANCE

Differentiation between focal and macro-reentrant AT in horses is possible using 3D electro-anatomical mapping. In this study, the source of right atrial AT in horses was safely treated by radiofrequency catheter ablation.

Fundamentals of arrhythmogenic mechanisms and treatment strategies for equine atrial fibrillation

Atrial fibrillation (AF) is the most common pathological arrhythmia in horses. Although it is not usually a life-threatening condition on its own, it can cause poor performance and make the horse unsafe to ride. It is a complex multifactorial disease influenced by both genetic and environmental factors including exercise training, comorbidities or ageing. The interactions between all these factors in horses are still not completely understood and the pathophysiology of AF remains poorly defined. Exciting progress has been recently made in equine cardiac electrophysiology in terms of diagnosis and documentation methods such as cardiac mapping, implantable electrocardiogram (ECG) recording devices or computer-based ECG analysis that will hopefully improve our understanding of this disease. The available pharmaceutical and electrophysiological treatments have good efficacy and lead to a good prognosis for AF, but recurrence is a frequent issue that veterinarians have to face. This review aims to summarise our current understanding of equine cardiac electrophysiology and pathophysiology of equine AF while providing an overview of the mechanism of action for currently available treatments for equine AF.

Anti-arrhythmic investigations in large animal models of atrial fibrillation

Atrial fibrillation (AF) constitutes an increasing health problem in the aging population. Animal models reflecting human phenotypes are needed to understand the mechanisms of AF, as well as to test new pharmacological interventions. In recent years, a number of large animal models, primarily pigs, goats, dog and horses have been used in AF research. These animals can to a certain extent recapitulate the human pathophysiological characteristics and serve as valuable tools in investigating new pharmacological interventions for treating AF. This review focuses on anti-arrhythmic investigations in large animals. Initially, spontaneous AF in small and large mammals is discussed. This is followed by a short presentation of frequently used methods for inducing short- and long-term AF. The major focus of the review is on anti-arrhythmic compounds either frequently used in the human clinic (ranolazine, flecainide, vernakalant and amiodarone) or being promising new AF medicine candidates (I_K,Ach , I_SK,Ca and I_K2P blockers).

Atrial fibrillation in horses Part 2: Diagnosis, treatment and prognosis

Atrial fibrillation (AF) is suspected by an irregularly irregular rhythm during auscultation at rest and should be confirmed by electrocardiography. Heart rate monitoring is potentially interesting for AF detection by horse owners, based on the disproportionally high heart rate during exercise or increased heart rate variability. Echocardiography and laboratory analysis are useful to identify underlying cardiac disease. Horses with severe cardiac disease should not undergo cardioversion due to the risk of recurrence. Cardioversion is recommended especially in horses performing high intensity exercise or showing average maximal heart rates higher than 220 beats per min or abnormal ventricular complexes during exercise or stress. Pharmacological cardioversion can be performed using quinidine sulphate administered orally, with an overall mean reported success rate around 80%. Other therapeutic drugs have been described such as flecainide, amiodarone or novel atrial specific compounds. Transvenous electrical cardioversion (TVEC) is performed by delivering a shock between two cardioversion catheters positioned in the left pulmonary artery and right atrium, with a success rate of >95%. After cardioversion, most horses return to their previous level of performance. However, the recurrence rate after pharmacological or electrical cardioversion is up to 39%. Recurrence has been related to previous unsuccessful treatment attempts, valvular regurgitation and the presence of atrial premature depolarisations or low atrial contractile function after cardioversion. Large atrial size and long AF duration have also been suggested as risk factors. Different approaches for preventing recurrence have been described such as the administration of sotalol, however, large clinical studies have not been published.

Ventricular arrhythmias in horses: Diagnosis, prognosis and treatment

Ventricular arrhythmias (VAs) are often incidental or coincidental with systemic disease. Ventricular arrhythmias are also the most likely cause of many sudden cardiac deaths in horses. This dichotomy creates challenges in the management of horses with VAs. This review presents current knowledge of diagnosis, prognosis and treatment of VAs in horses.

Treatment of recent-onset atrial fibrillation with quinidine and flecainide in Thoroughbred racehorses: 107 cases (1987-2014)

OBJECTIVE To compare the efficacy of quinidine and flecainide in treating naturally occurring, recent-onset atrial fibrillation (AF) in Thoroughbred racehorses. DESIGN Retrospective case series. ANIMALS 107 Thoroughbred racehorses. PROCEDURES Medical records of racehorses with AF that were treated with quinidine or flecainide between 1987 and 2014 were reviewed. Signalment, history, treatments, complications, and outcome data were collected. Horses were allocated to 2 groups according to the initial treatment: initial treatment with quinidine (group 1) or initial treatment with flecainide (group 2). Horses in group 2 that did not convert to sinus rhythm with flecainide were then administered quinidine (group 3). Complications, total quinidine dose, and duration of treatment were compared. Rates of conversion for horses treated with quinidine versus flecainide were also compared. RESULTS Overall rate of cardioversion was 91% (97/107). There was a significant difference in the rate of cardioversion for quinidine alone (91% [71/78]), compared with flecainide alone (41% [12/29]). In group 3, the conversion rate after the addition of quinidine treatment was 82% (14/17). Total quinidine dose and treatment duration did not differ significantly between groups 1 and 3. CONCLUSIONS AND CLINICAL RELEVANCE Overall rate of cardioversion for Thoroughbred racehorses with AF was similar to that in previous reports. Flecainide treatment was less effective than quinidine treatment, but the frequency of complications did not differ between quinidine and flecainide. Further investigation is suggested to evaluate the efficacy of flecainide for cardioversion in athletic horses.

Time-dependent antiarrhythmic effects of flecainide on induced atrial fibrillation in horses

Background

Pharmacological treatment of atrial fibrillation (AF) in horses can be challenging because of low efficacy and adverse effects. Flecainide has been tested with variable efficacy.

Objective

To test whether the efficacy of flecainide is dependent on AF duration.

Animals

Nine Standardbred mares.

Methods

Factorial study design. All horses were instrumented with a pacemaker and assigned to a control or an AF group. On day 0, all horses were in sinus rhythm and received 2 mg/kg flecainide IV. Atrial fibrillation subsequently was induced in the AF group by pacemaker stimulation. On days 3, 9, 27, and 55, flecainide was administered to all horses, regardless of heart rhythm.

Results

All horses in AF cardioverted to sinus rhythm on days 3 and 9. On day 27, 5/6 horses cardioverted, whereas only 2/6 cardioverted on day 55. The time from the start of flecainide infusion to cardioversion (range, 3–185 min, log transformed) showed linear correlation with the cumulative duration of AF (r² = .80, P < .0001). Flecainide induced abnormal QRS complexes in 4/6 AF horses and 1/3 controls. A positive correlation was found between heart rate before flecainide infusion and number of abnormal QRS complexes (0.14, P < .05). One horse suffered from cardiac arrest and died after flecainide infusion.

Conclusions and Clinical Importance

Flecainide is effective for cardioversion of short‐term induced AF, but the effect decreases with AF duration. Controlling heart rate may minimize adverse effects caused by flecainide, but the drug should be used with great caution.