Electrophysiologic Characteristics and Topographic Distribution of Focal Atrial Tachycardias in Dogs

Spontaneous pre-excited supraventricular tachycardias in a Labrador Retriever

A four-year-old Labrador Retriever was presented for intermittent tachycardia. The electrocardiogram showed sinus rhythm conducted with ventricular pre-excitation and short runs of orthodromic atrioventricular reciprocating tachycardia. Four months later, the rhythm degenerated into a symptomatic sustained tachycardia, suspected to be pre-excited atrial fibrillation, a potentially life-threatening rhythm in the presence of an accessory pathway with a short refractory period. Two days after initiating oral diltiazem, the dog deteriorated and represented with sustained orthodromic atrioventricular reciprocating tachycardia, which was terminated by a precordial chest thump. It proceeded to sinus rhythm with ventricular pre-excitation followed by an episode of pre-excited focal atrial tachycardia. A bolus of lidocaine IV successfully restored sinus rhythm and sotalol treatment was started. The dog clinically recovered but died spontaneously 24 h later. This is the first case report that describes spontaneous pre-excited focal atrial tachycardia.

Localization and characterization of atrial depolarization waves on the surface electrocardiogram in dogs with rapid supraventricular tachycardia

BACKGROUND

Supraventricular tachycardias (SVTs), despite having various anatomical substrates and pathophysiological mechanisms, frequently show similar electrocardiographic presentations.

OBJECTIVES

To locate and characterize atrial deflections (ADs) on 12-lead electrocardiograms in dogs with sustained rapid SVT and assess the utility of different electrocardiographic variables in differentiating types of tachycardia.

ANIMALS

Ninety-two dogs with orthodromic atrioventricular reciprocating tachycardia, 17 with atrial flutter, 33 with focal atrial tachycardia recorded and confirmed by electrophysiological study, and 40 dogs with sinus tachycardia.

METHODS

Atrial deflection position on the 12-lead surface electrocardiogram was assessed according to the sequence of intracardiac activation. Its features were evaluated together with the relationship between AD and QRS complex interval (AD-R) and QRS complex and AD interval (R-AD).

RESULTS

Orthodromic atrioventricular reciprocating tachycardia was characterized by an AD-AD interval of 213 ± 30 ms, mean electrical axis (MEA) of AD of -90 (-90/-78)°, R-AD interval of 75 (65-80) ms, and R-AD/AD-R of 0.54 (0.45-0.64). Atrial flutter was characterized by an AD-AD interval of 199 ± 57 ms, MEA of 76° (72/81), R-AD of 120 (72-144) ms, and R-AD/AD-R of 0.81 (0.63-1.13). Focal atrial tachycardia was characterized by an AD-AD interval of 270 ± 38 ms, MEA of 49 (-72/76)°, R-AD of 160 (120-200) ms, and R-AD/AD-R of 1.45 (0.92-1.67). Sinus tachycardia was characterized by an AD-AD interval of 292 ± 31 ms, MEA of 66° (52/73), R-AD of 215 (192-222) ms, and R-AD/AD-R of 2.68 (2.25-3.08).

CONCLUSIONS AND CLINICAL IMPORTANCE

Analyzing AD on 12-lead electrocardiogram is helpful in differentiating the most common SVTs in dogs.

Treating Stubborn Cardiac Arrhythmias-Looking Toward the Future

As animals can develop significant side effects or remain refractory while on antiarrhythmic medical therapy for tachyarrhythmias, interventional therapies are progressively being explored. This review will highlight the principles and utilities of implantable cardioverter-defibrillators, electrophysiological mapping and catheter ablation, three-dimensional electroanatomical mapping, and stereotactic arrhythmia radiotherapy. In particular, three-dimensional electroanatomical mapping is emerging as an adjunct electrophysiology tool to facilitate activation, substrate, and pace mapping for intuitive analysis of complex tachyarrhythmias. Unlike antiarrhythmic medications, these modalities offer potential for decreasing risk of sudden death and even permanent termination of tachyarrhythmias.

Three-dimensional electroanatomical mapping for guidance of pulmonary vein isolation as treatment for persistent atrial fibrillation in a dog

A two-year and four-month, male German Shepherd was referred for exercise intolerance and panting. Irregular heart auscultation (250 beats per minute (bpm)) and pulse deficits were noted on physical exam. Electrocardiogram (ECG) showed irregular, narrow-QRS tachycardia without P waves compatible with coarse atrial fibrillation (AF). A 24-h ECG showed sustained AF (mean ventricular response rate 92 bpm). Echocardiography showed no structural abnormalities. Given the young age and presence of AF-related symptoms, rhythm control was preferred. Transthoracic electrical cardioversion was successfully performed six weeks later but AF recurred within 24-h. Sotalol was started but discontinued due to poor tolerance and AF persisted. Seven months after AF diagnosis, radiofrequency catheter ablation (RFCA) aiming for pulmonary vein isolation was performed under general anaesthesia. After transseptal puncture, three-dimensional electroanatomical mapping of the left atrium was performed. Point-by-point pulmonary vein isolation was achieved by RFCA. Seventy-eight RFCA lesions were placed in the left atrium encircling the three pulmonary vein ostia followed by electrical cardioversion. No complications occurred and the dog was discharged with amiodarone. In the immediate post-operative phase, there was recurrence of persistent AF requiring electrical cardioversion. Furthermore, at one month after the ablation, the dog experienced a single and transient paroxysm of AF. Since then, stable sinus rhythm (SR) was retained on daily ECG monitoring at home and confirmed by 24-h ECG three months post-operatively. Amiodarone was stopped subsequently. At the time of writing (one year post-operative), the dog remains in SR with normal exercise tolerance.

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.

Feasibility of electroanatomic mapping and radiofrequency catheter ablation in Boxer dogs with symptomatic ventricular tachycardia

Background

Treatment for Boxers with ventricular tachycardia (VT) is limited. Electroanatomic mapping (EAM) facilitates identification of arrhythmogenic substrate for radiofrequency catheter ablation (RFCA).

Objective

Describe the use of EAM to guide RFCA in Boxers with VT.

Animals

Five client‐owned Boxers with symptomatic VT or persistent VT despite antiarrhythmic medications.

Methods

Case series evaluating clinical, EAM, and before and after RFCA Holter data.

Results

Sustained VT was inducible in 3 dogs, but required aggressive stimulation protocols. Low‐voltage areas consistent with electroanatomic scar were found in 2 dogs, located at the right ventricular (RV) outflow tract and cranial RV. Two dogs had a focal activation pattern of VT and 1 dog had a reentrant mechanism. After RFCA, all dogs no longer collapsed and had fewer runs of VT, 3 of which had 0 runs of VT. Number of ventricular premature beats increased in 3 dogs and decreased in 2 dogs, 1 of which had nearly complete resolution of all arrhythmias. Procedural complications included ventricular fibrillation (n = 2) with successful defibrillation, bruising or hemorrhage at the vascular access site (n = 4), retroperitoneal hemorrhage (n = 1), aortic and mitral regurgitation (n = 1), onset of frequent supraventricular tachycardia (n = 1), and persistent right pelvic limb lameness (n = 1).

Conclusions and Clinical Importance

Electroanatomic mapping and RFCA are feasible in Boxers with VT. Based on this small cohort, RFCA may help decrease runs of VT and improve clinical signs. The anatomic substrate and electrophysiologic mechanisms are variable and require further study.

Three-dimensional electroanatomic mapping and radiofrequency catheter ablation of ventricular arrhythmia in a dog without structural heart disease

A 1.5-year-old, female-spayed mix-breed dog was presented with recurrent episodes of shaking and excessive panting attributed to drug-refractory ventricular arrhythmia (VA) characterized predominantly by incessant periods of ventricular bigeminy. The VA had a narrow QRS morphology, suggestive of an origin near the His bundle or fascicular system. Diagnostic evaluation found no structural heart disease or underlying etiology. Three-dimensional electroanatomic mapping and radiofrequency catheter ablation were pursued. Voltage mapping demonstrated normal bi-ventricular voltage (≥1.5 mV) without any fractionated or multicomponent electrograms, indicating the absence of ventricular myocardial scar. Pace mapping identified an endocardial origin of the VA at the basal anterior septum of the left ventricle, distal to the His bundle and near the left bundle branch. Two ablation lesions were delivered to this site, and a left bundle branch block was temporarily induced. The dog recovered uneventfully. One month later, the owners reported a remarkable improvement in clinical signs, and follow-up 48-h Holter monitor found complete resolution of VA.

Radiofrequency catheter ablation of accessory pathways in the dog: the Italian experience (2008-2016)

INTRODUCTION

Accessory pathways (APs) in dogs are mostly right-sided, display nondecremental conduction, and mediate atrioventricular reciprocating tachycardias (AVRTs). Radiofrequency catheter ablation (RFCA) is considered the first-line therapy in human patients to abolish electrical conduction along APs.

ANIMALS

Seventy-six consecutive client-owned dogs.

MATERIAL AND METHODS

Retrospective study to describe the precise anatomical distribution and the electrophysiologic characteristics of APs in a large population of dogs and to evaluate long-term success and complication rates of RFCA.

RESULTS

Eighty-three APs were identified in 76 dogs (92.1% with single APs and 7.9% with multiple APs); 96.4% were right-sided, 3.6% left-sided. Conduction along the APs was unidirectional and retrograde in 68.7% of the cases and bidirectional in 31.3%. Accessory pathways presented retrograde decremental properties in 6.5% of the cases. They mediated orthodromic AVRT in 92.1% of the cases and permanent junctional reciprocating tachycardia in 6.5%. In one case, no AVRT could be induced. In 97.4% of dogs, RFCA was attempted with an acute success rate of 100%. In 7.7% of cases, recurrence of the tachycardia occurred within 18 months, followed by a second definitively successful ablation. A major complication requiring pacemaker implantation was identified in 2.6% of dogs.

DISCUSSION

Accessory pathway distribution and electrophysiologic properties in these 76 dogs were similar to previous report. Long-term success and complication rates of RFCA in dogs appeared very similar to results of humans.

CONCLUSION

Radiofrequency catheter ablation of APs can be performed with a high success rate and low incidence of complications.

Phenotypic description of cardiac findings in a population of Dogue de Bordeaux with an emphasis on atrial fibrillation

The aim of this study was to describe the clinical phenotype of Dogue de Bordeaux (DdB) referred for cardiac investigation, with particular reference to the prevalence of atrial fibrillation and associated features. Review of canine medical records of two United Kingdom veterinary referral hospitals identified 64 DdB with available echocardiographic and electrocardiographic (ECG)/Holter data. Atrial fibrillation was documented in 25 (39%) dogs and supraventricular tachycardia was recorded in five (7.8%) dogs. In a subset of 34 dogs, excluding congenital heart disease (n=17), presence of a cardiac mass (n=7) and non-cardiac neoplasia (n=6), 19 (56%) dogs had atrial fibrillation, with a median heart rate of 200 beats per min (bpm) on presentation. Atrial fibrillation was inconsistently associated with cardiac chamber remodelling, but was frequently associated with systolic dysfunction (13/19, 68.4%) and right sided atrial or ventricular dilatation (14/19, 73.7%) in dogs with atrial fibrillation in this subset. No dogs in this subset had right sided atrial or ventricular dilatation in the absence of supraventricular arrhythmia or systolic dysfunction. The absence of structural heart disease in some dogs with supraventricular arrhythmias suggests that an underlying primary arrhythmic process might be responsible for initiating remodelling, although a primary cardiomyopathy cannot be ruled out.

Experimental model of focal atrial tachycardia: clinical correlates

BACKGROUND

The mechanisms underlying focal atrial tachycardia (AT) are unclear.

METHODS

In 14 pentobarbital anesthetized dogs, a right thoracotomy allowed electrical stimulation (ES) of the anterior right ganglionated plexi (ARGP). After ES was applied to the ARGP at baseline, atropine, 1 mg/cc, was injected into the ARGP and repeat stimulation applied. After a left thoracotomy (n = 8), a similar procedure was followed by atropine injected into the superior left (SL) GP.

RESULTS

ES (0.6-3.2 V) applied to the ARGP and SLGP caused an average reduction in sinus rate from 151 ± 14/min to 60 ± 11/min. At ≥4.5 V atrial fibrillation (AF) was induced (duration 48 ± 14 seconds). After injection of atropine into the ARGP or SLGP, ES applied to these GP induced no slowing of the sinus rate. Runs of AT were induced at an average voltage of 10 ± 2 V in 14 experiments (duration ≥4 minutes). AT was localized by ice mapping or by 3D noncontact mapping to the crista terminalis (n = 6), AV junction (n = 2) or a focal site at the left superior pulmonary vein (6). In AT lasting <4 minutes (n = 2), epinephrine injected into the GP significantly increased the AT duration. In 4/4 experiments, sustained AT could be terminated by intravenous esmolol.

CONCLUSIONS

Atropine injected into the ARGP or SLGP promotes ES-induced AT whose duration is increased by adrenergic agonists and terminated by beta blockade. Presumably cholinergic blockade and accentuated release of adrenergic neurotransmitters provide the AT mechanism. The induced AT was found to be localized at sites similar to those reported clinically.