QT Interval and Cardiac Restitution Ratio Complexity in Standardbred Racehorses From Rest to Maximal Effort: Insights Into Arrhythmia Risk.
Abstract: Sudden cardiac death is common in racehorses. Factors associated with the QT interval that could predispose to fatal cardiac arrhythmias are unknown. Cardiac restitution, expressed as a ratio of QT/TQ, has been used in humans to assess arrhythmia risk but has not been described in horses during maximal intensity exercise. Objective: Describe factors associated with the QT interval and cardiac restitution ratio (CRR) in clinically normal Standardbred racehorses under race-day conditions. Methods: Archival electrocardiograms from 42 Standardbred horses during live racing in Ontario. Methods: Observational study performing an automated cardiac restitution analysis. Cardiac cycles were obtained from rest, non-race exercise, non-race recovery, live racing, and post-race recovery periods. Multivariable linear regression analysis was performed with both QT interval and CRR as outcomes of interest. Results: Analysis of 3827 sequential pairs of cardiac cycles was performed. Exercise period and RR interval were highly associated with both QT interval and CRR. Other significant associations varied by exercise period and included: racing gait, sex, age, whether the horse received furosemide, and whether the horse experienced complex ventricular arrhythmias after racing. Interactions between gait and furosemide, and sex and gait were also significant. Conclusions: An automated cardiac restitution analysis is feasible in exercising racehorses. The QT-RR interval relationship is multifactorial, and there are numerous significant associations that must be considered to interpret changes in QT interval and CRR in horses.
© 2025 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
Publication Date: 2025-09-10 PubMed ID: 40926462PubMed Central: PMC12420912DOI: 10.1111/jvim.70207Google Scholar: Lookup
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Cite This Article
APA
Avison A, Goderre BG, Pyle WG, Physick-Sheard PW.
(2025).
QT Interval and Cardiac Restitution Ratio Complexity in Standardbred Racehorses From Rest to Maximal Effort: Insights Into Arrhythmia Risk.
J Vet Intern Med, 39(5), e70207.
https://doi.org/10.1111/jvim.70207 Publication
Researcher Affiliations
- Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
- Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
- IMPART Team Canada, Dalhousie Medicine, Dalhousie University, Saint John, New Brunswick, Canada.
- Women's Health Research Institute, BC Women's Hospital + Health Centre, Vancouver, British Columbia, Canada.
- Department of Population Medicine, Ontario Veterinary College, University of Guelph, Ontario, Canada.
MeSH Terms
- Animals
- Horses / physiology
- Male
- Female
- Arrhythmias, Cardiac / veterinary
- Arrhythmias, Cardiac / physiopathology
- Electrocardiography / veterinary
- Physical Conditioning, Animal / physiology
- Horse Diseases / physiopathology
- Horse Diseases / etiology
- Risk Factors
Grant Funding
- EG2023-09 / Equine Guelph
Conflict of Interest Statement
Authors declare no off‐label use of antimicrobials. The authors declare no conflicts of interest. The software used in the present study is intended to be published in the Biomedical Engineering literature and will be made available at no cost to researchers. There has not been, nor will there be financial gain from the software.
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