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Equine veterinary journal2026; doi: 10.1002/evj.70166

Exercising electrocardiograms from Thoroughbred racehorses with exercise associated sudden death.

Abstract: Exercise associated sudden death (EASD), defined as a fatal collapse in a closely monitored and previously presumed clinically healthy horse that occurs during exercise or within approximately 1 h after exercise, is disproportionately more common in equine than in human athletes. Objective: To describe ECGs from EASD cases in Thoroughbred racehorses. Methods: Retrospective case series. Methods: An international call for potential cases was made through direct contact with relevant racing authorities requesting that trainers of horses which had experienced EASD consent to researchers gaining access to any available ECG data recorded with a wearable device prior to or during EASD events. ECGs were evaluated by a single observer and the findings were described and summarised. Results: Eleven horses, with a total of 24 readable ECGs (median [range] 2 [1-4]/horse) were identified. Four horses were wearing an ECG at the time of death; 3 had atrial fibrillation (AF) throughout the recording that led to malignant arrhythmias and death, and the 4th had couplets and triplets with R on T, ventricular fibrillation, and death in the late recovery period. The other seven horses had ECGs recorded 4-462 days before death. One of these horses had AF throughout the recording and died 9 days later. Late recovery arrhythmias were identified in 5 recordings from 3 additional horses. Conclusions: Small number of horses with EASD were sampled, and use of a single lead ECG limited information on arrhythmia origin. Conclusions: ECG screening to detect AF before horses train or race has the potential to reduce EASD incidence. More information is needed for risk stratification of late recovery and other arrhythmias.
© 2026 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2026-04-21 PubMed ID: 42012310DOI: 10.1002/evj.70166Google Scholar: Lookup
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Summary

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Overview

  • The study investigated the electrocardiograms (ECGs) of Thoroughbred racehorses that experienced exercise-associated sudden death (EASD) to identify cardiac arrhythmias related to these fatal events.

Background

  • EASD refers to the sudden, fatal collapse of a horse during exercise or within about an hour afterward, despite the horse appearing healthy beforehand.
  • This phenomenon occurs more frequently in horses compared to human athletes.
  • Understanding the cardiac electrical activity during these events may help identify causes and potential preventative measures.

Study Objective

  • To describe the ECG patterns in Thoroughbred racehorses that suffered from EASD.

Methods

  • The study was a retrospective case series.
  • Researchers issued an international call to racing authorities to request access to ECG data from horses that had EASD.
  • Trainers of affected horses consented to share ECG data recorded with wearable devices before or during the fatal events.
  • A single observer analyzed all the available ECG recordings to ensure consistency in interpretation.

Results

  • Data from 11 horses were collected, with 24 readable ECGs in total (median of 2 per horse, ranging from 1 to 4 recordings).
  • Four horses were wearing ECG devices at the time of death:
    • Three of these showed atrial fibrillation (AF) throughout the ECG recording. These AF cases progressed to malignant arrhythmias and death.
    • The fourth horse’s ECG revealed couplets and triplets with “R on T” phenomenon, ventricular fibrillation, and eventual death during the late recovery period after exercise.
  • The remaining seven horses had ECGs recorded days to months (4 to 462 days) prior to death:
    • One had persistent atrial fibrillation and died 9 days later.
    • Late recovery arrhythmias were noted in five recordings from three horses, indicating abnormalities occurring after exercise in the recovery phase.

Conclusions

  • The study sample was small, and the ECG recordings utilized a single lead, limiting detailed analysis of where arrhythmias originated within the heart.
  • Atrial fibrillation detected by ECG appears strongly linked with subsequent exercise-associated sudden death in these horses.
  • Routine ECG screening to detect atrial fibrillation before horses train or race could potentially reduce the risk of EASD by identifying at-risk horses.
  • Arrhythmias occurring during the late recovery phase post-exercise also seem significant, but further information is necessary to assess how these contribute to risk.
  • Overall, improved monitoring and risk stratification based on ECG findings could enhance safety in equine athletics.

Cite This Article

APA
Navas de Solis C, Durando M, Nath L, Durward-Akhurst S. (2026). Exercising electrocardiograms from Thoroughbred racehorses with exercise associated sudden death. Equine Vet J. https://doi.org/10.1002/evj.70166

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Navas de Solis, Cristobal
  • School of Veterinary Medicine, Clinical Studies New Bolton Center, University of Pennsylvania, Kennett Square, Pennsylvania, USA.
Durando, M
  • Equine Sports Medicine Consultants, Newark, Delaware, USA.
Nath, L
  • School of Animal & Veterinary Sciences, University of Adelaide, Adelaide, South Australia, Australia.
Durward-Akhurst, S
  • Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, Minnesota, USA.

Grant Funding

  • Horseracing Integrity and Safety Authority
  • 1UM1TR004405-01A1 / National Institutes of Health (NIH) K12
  • K12TR004373 / National Institutes of Health (NIH) K12

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