Ventricular response during lungeing exercise in horses with lone atrial fibrillation

Abstract

Summary 10Reasons for performing the study: Atrial fibrillation (AF) is the most important dysrhythmia 11 affecting performance in horses and has been associated with incoordination, collapse and 12 sudden death. Limited information is available on ventricular response during exercise in 13 horses with lone AF. 14 Objectives: To investigate ventricular response in horses with lone AF during a standardised 15 lungeing exercise test. Results: Individual average heart rate during walk ranged from 42 to 175 bpm, during trot 21 from 89 to 207 bpm, during canter from 141 to 269 bpm, and during gallop from 191 to 311 22 bpm. Individual beat-to-beat maximal heart rate ranged from 248 to 492 bpm. Ventricular 23 premature depolarisations were present in 81% of the horses: at rest (16%), during exercise 24 (69%), and during recovery (2%). In 33% of the horses, broad QRS complexes with R-on-T 25 morphology were found. 26Conclusions: Exercising horses with lone AF frequently develop disproportionate tachycardia. 27In addition, QRS broadening and even R-on-T morphology is frequently found. QRS 28 broadening may originate from ventricular ectopic foci or from aberrant intra-ventricular 29 conduction, for example due to bundle branch block. This might explain the high number of 30 complexes currently classified as ventricular premature depolarisations. 31Potential relevance: Prevalence of QRS broadening and especially R-on-T was very high in 32 horses with AF and was found at low levels of exercise. These dysrhythmias are considered 33 risk factors for the development of ventricular tachycardia and fibrillation and they might 34 explain signs of weakness, collapse or sudden death that have been reported in horses with 35 AF. 36Accepted Article 3

Effect of induced chronic atrial fibrillation on exercise performance in Standardbred trotters

“…Our study identified an extreme increase in HR in the horses during exercise. This finding is in agreement with a previous study, in which a HR of up to 492 bpm was recorded in horses in AF during a submaximal lunging test . A submaximal exercise test performed in warmblood horses in AF also showed an increased HR compared with healthy controls, but it was not as high as the other reported values and our findings.…”

“…The irregular electrical conduction from atria to ventricles as well as the exceedingly fast ventricular response rate during AF have profound effects on ventricular electrophysiology. Three of the 6 horses showed a high number of wide complex tachycardias with R‐on‐T morphology during exercise, and this high prevalence is in agreement with a previous study . In normal Standardbred trotters, the prevalence of single abnormal QRS complexes during racing has been reported at between 0% and 4%, whereas the prevalence in the immediate period after racing is approximately 20% .…”

“…We could not determine whether the abnormal beats were of ventricular origin or if they should have been characterized as aberrant beats originating from the atria. No horses collapsed during the tests, but based on the present and previous studies, horses with AF should undergo exercise testing to determine whether or not they should be used for riding purposes.…”

Pharmacokinetics and electrophysiological effects of sotalol hydrochloride in horses

“…A modified base-apex configuration as described by Verheyen et al (lead II) was used [8]. A modified base-apex configuration as described by Verheyen et al (lead II) was used [8].…”

Equine electrocardiography revisited

“…; Physick‐Sheard and McGurrin ; Verheyen et al . ). Caution and circumspection and careful attention to data quality are essential.…”