Pathologic and electrocardiographic findings in sudden cardiac death in racehorses.
Abstract: Five racehorses in apparently normal condition succumbed to sudden cardiac death (SCD) during or shortly after intensive training exercise. Cardiopathologic examination was performed. In 1 of the 5 horses, the use of an electrocardiogram (ECG) recording taken continuously for 440 sec enabled us to analyze some of the arrhythmias in the terminal event of SCD. The ECG tracing exhibited the R-on-T phenomenon following a pair of ventricular premature contractions (VPCs). The phenomenon rapidly degenerated into ventricular fibrillation, which led to cardiac arrest. In all 5 horses cardiopathologic examination revealed the following lesions: (i) foci of myocardial fibrosis in the right atrium located close to the sinoatrial (SA) node, (ii) fibrotic and/or fibroplastic changes in the upper portion of the interventricular septum, including the atrioventricular (AV) conduction system, and (iii) arterio- and arteriolosclerosis of the SA and AV node vessels. Pathogenetically, the process by which the focal lesions of myocardial ischemia secondary to vascular sclerosis progressed into fibrosis and/or fibroplasia could play a major role in the genesis of arrhythmias. Presumably the fibrotic and/or fibroplastic changes in the area of the AV bundle and its bundle branches are closely related to the onset of fatal ventricular arrhythmias such as VPCs, deteriorating into ventricular fibrillation. SCD in training and racing Thoroughbred horses appears to be due to arrhythmia.
Publication Date: 1999-09-16 PubMed ID: 10487232DOI: 10.1292/jvms.61.921Google Scholar: Lookup
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Summary
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The research focuses on the sudden cardiac death (SCD) in racehorses, occurring during or after rigorous training. Through cardiopathologic examination and electrocardiogram (ECG) recording in one of the five studied horses, the paper discusses the role of arrhythmia in causing these unexpected deaths and the common myocardial fibrosis and fibroplastic changes seen in the horses’ cardiac system.
Methodology
- The researchers investigated the sudden cardiac deaths of five racehorses that were in normal condition but died during or shortly after intensive exercise.
- They conducted a cardiopathologic examination on all five horses to study the pathological changes in their hearts.
- In one particular horse, an electrocardiogram (ECG) was recorded continuously for 440 seconds, allowing for the analysis of arrhythmias during the final moments of SCD.
Findings
- The ECG recording revealed an R-on-T phenomenon following a pair of ventricular premature contractions (VPCs), which quickly declined into ventricular fibrillation, causing cardiac arrest.
- Cardiopathologic examination in all five horses revealed myocardial fibrosis near the sinoatrial (SA) node, fibrotic and/or fibroplastic changes in the interventricular septum (including the atrioventricular – AV – conduction system), and sclerosis in the SA and AV node vessels.
Interpretation & Implication
- The researchers suggested that the progression of focal myocardial ischemia into fibrosis and/or fibroplasia due to vascular sclerosis might be a significant pathogenetic process in arrhythmia development.
- They also hypothesized that the fibrotic and/or fibroplastic changes around the AV bundle and its branches might be closely linked to the initiation of fatal ventricular arrhythmias like VPCs, which deteriorate into ventricular fibrillation.
- The study concludes that SCD in Thoroughbred horses during training or racing appears due to arrhythmias most likely, primarily caused by fibrotic changes in their cardiac system.
Cite This Article
APA
Kiryu K, Machida N, Kashida Y, Yoshihara T, Amada A, Yamamoto T.
(1999).
Pathologic and electrocardiographic findings in sudden cardiac death in racehorses.
J Vet Med Sci, 61(8), 921-928.
https://doi.org/10.1292/jvms.61.921 Publication
Researcher Affiliations
- Department of Veterinary Pathology, Tokyo University of Agriculture and Technology, Fuchu, Japan.
MeSH Terms
- Animals
- Death, Sudden, Cardiac / veterinary
- Electrocardiography / veterinary
- Fibrosis / pathology
- Fibrosis / veterinary
- Horse Diseases / pathology
- Horses
- Myocardium / pathology
Citations
This article has been cited 14 times.- Nath L, Stent A, Elliott A, La Gerche A, Franklin S. Risk Factors for Exercise-Associated Sudden Cardiac Death in Thoroughbred Racehorses. Animals (Basel) 2022 May 18;12(10).
- Ter Woort F, Dubois G, Tansley G, Didier M, Verdegaal L, Franklin S, Van Erck-Westergren E. Validation of an equine fitness tracker: ECG quality and arrhythmia detection. Equine Vet J 2022 Feb 9;55(2):336-43.
- Hellings IR, Skjerve E, Karlstam E, Valheim M, Ihler CF, Fintl C. Racing-associated fatalities in Norwegian and Swedish harness racehorses: Incidence rates, risk factors, and principal postmortem findings. J Vet Intern Med 2022 Mar;36(2):778-786.
- Nath LC, Elliott AD, Weir J, Curl P, Rosanowski SM, Franklin S. Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses. J Vet Intern Med 2021 Mar;35(2):1111-1120.
- Matt CL, Mans C, Doss G, Pinkerton M, Elsmo B. Splenic T-cell lymphoma in a North American River Otter (Lontra canadensis). Open Vet J 2020 Oct;10(3):272-275.
- Goto Asakawa M, Mehmood W, Ali M, Oikawa MA. Idiopathic multifocal myocardial atrophy with fibrosis and fatty infiltration involving Purkinje fibres in a 13-year-old Arabian broodmare: Histopathological features. Vet Med Sci 2021 Jan;7(1):3-8.
- Gimenez F, Hines SA, Evanoff R, Ojo KK, Van Voorhis WC, Maly DJ, Vidadala RSR, Mealey RH. In vitro growth inhibition of Theileria equi by bumped kinase inhibitors. Vet Parasitol 2018 Feb 15;251:90-94.
- Pedersen PJ, Thomsen KB, Olander ER, Hauser F, Tejada Mde L, Poulsen KL, Grubb S, Buhl R, Calloe K, Klaerke DA. Molecular Cloning and Functional Expression of the Equine K+ Channel KV11.1 (Ether à Go-Go-Related/KCNH2 Gene) and the Regulatory Subunit KCNE2 from Equine Myocardium. PLoS One 2015;10(9):e0138320.
- Hiraga A, Sugano S. History of research in Japan on electrocardiography in the racehorse. J Equine Sci 2015;26(1):1-13.
- Sabir IN, Killeen MJ, Goddard CA, Thomas G, Gray S, Grace AA, Huang CL. Transient alterations in transmural repolarization gradients and arrhythmogenicity in hypokalaemic Langendorff-perfused murine hearts. J Physiol 2007 May 15;581(Pt 1):277-89.
- McCrae P, Spong H, Moorehead J, Pearson W. Validation of a smart textile device for long-duration heart rate variability and detection of physiological arrhythmias in resting horses. BMC Vet Res 2025 Nov 19;21(1):675.
- Kapusniak A, Lara NM, Hitchens PL, Bailey S, Nath L, Franklin S. Use of Artificial Intelligence to Detect Cardiac Rhythm Disturbances in Athletes: A Scoping Review. J Vet Intern Med 2025 Nov-Dec;39(6):e70257.
- Avison A, Goderre BG, Pyle WG, Physick-Sheard PW. QT Interval and Cardiac Restitution Ratio Complexity in Standardbred Racehorses From Rest to Maximal Effort: Insights Into Arrhythmia Risk. J Vet Intern Med 2025 Sep-Oct;39(5):e70207.
- Kapusniak A, Nath L, Hebart M, Franklin S. Heritability of sudden cardiac death in Thoroughbred racehorses. Equine Vet J 2025 Mar;57(2):325-332.
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