Risk Factors for Exercise-Associated Sudden Cardiac Death in Thoroughbred Racehorses.
- Journal Article
Summary
This research aims to identify risk factors for sudden cardiac death (SCD) in Thoroughbred racehorses. The study found that SCD is more likely to occur during training than racing, in horses with fewer lifetime starts and that it is less common in uncastrated males.
Risk Factors for SCD in Thoroughbreds
The study began with the objective of determining the risk factors that contribute to sudden cardiac death in Thoroughbred racehorses. Sudden cardiac death is an important cause of fatalities in racehorses, triggered by cardiac arrhythmias. For this study, a sample of horses with a mandatory post-mortem policy upon death during racing or training was evaluated. The risk factors between horses that suffered from SCD (n=57) and those with other fatal injuries (OFI, n=188) were compared.
- The factors were compared using univariable and multivariable logistic regression and survival years were calculated with the Kaplan-Meier method with a log-rank test.
- The study discovered that horses with SCD were more likely to die during training (74% of the time) than during actual races when compared to horses with OFI (44% of the time).
Other Significant Findings
- Research also revealed that Thoroughbreds with SCD had fewer lifetime starts. The median number of starts was lower for SCD (3) compared to the OFI (9).
- The study also found SCD to be less likely in uncastrated (entire) males.
- The survival in years after SCD was shorter than OFI. The median survival rate for horses with SCD was 3.6 years, lower than the 4.5 years survival of horses with OFI.
Key Takeaways
This study definitively showed that SCD occurs more commonly in training than racing, contradicting the often-held belief that exercise intensity is the primary trigger of SCD. This suggests other factors potentially within the control of trainers could be contributing to the onset of SCD. The researchers observed that SCD typically occurs early in the careers of affected Thoroughbreds indicating that it is essential to monitor horses’ cardiac health right from the start of their careers.
Cite This Article
Publication
Researcher Affiliations
- School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy 5371, Australia.
- Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Werribee 3030, Australia.
- Centre for Heart Rhythm Disorders, University of Adelaide, Adelaide 5005, Australia.
- Baker Heart and Diabetes Institute, Melbourne 3004, Australia.
- School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy 5371, Australia.
Grant Funding
- no number / Racing Victoria
Conflict of Interest Statement
References
- Kiryu K, Machida N, Kashida Y, Yoshihara T, Amada A, Yamamoto T. Pathologic and electrocardiographic findings in sudden cardiac death in racehorses.. J Vet Med Sci 1999 Aug;61(8):921-8.
- Physick-Sheard P, Avison A, Sears W. Factors Associated with Mortality in Ontario Standardbred Racing: 2003-2015.. Animals (Basel) 2021 Apr 5;11(4).
- Physick-Sheard PW, Slack J. Irregular hearts and performance horses.. Equine Vet J 2020 Nov;52(6):782-786.
- Allen SE, Rosanowski SM, Stirk AJ, Verheyen KLP. Description of veterinary events and risk factors for fatality in National Hunt flat racing Thoroughbreds in Great Britain (2000-2013).. Equine Vet J 2017 Nov;49(6):700-705.
- Lyle CH, Uzal FA, McGorum BC, Aida H, Blissitt KJ, Case JT, Charles JT, Gardner I, Horadagoda N, Kusano K, Lam K, Pack JD, Parkin TD, Slocombe RF, Stewart BD, Boden LA. Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings.. Equine Vet J 2011 May;43(3):324-31.
- Boden LA, Charles JA, Slocombe RF, Sandy JR, Finnin PJ, Morton JM, Clarke AF. Sudden death in racing Thoroughbreds in Victoria, Australia.. Equine Vet J 2005 May;37(3):269-71.
- Rosanowski SM, Chang YM, Stirk AJ, Verheyen KL. Descriptive epidemiology of veterinary events in flat racing Thoroughbreds in Great Britain (2000 to 2013).. Equine Vet J 2017 May;49(3):275-281.
- Gelberg HB, Zachary JF, Everitt JI, Jensen RC, Smetzer DL. Sudden death in training and racing Thoroughbred horses.. J Am Vet Med Assoc 1985 Dec 15;187(12):1354-6.
- Molesan A, Wang M, Sun Q, Pierce V, Desideri R, Palmer S, Todhunter R, Kelly K. Cardiac Pathology and Genomics of Sudden Death in Racehorses From New York and Maryland Racetracks.. Vet Pathol 2019 Jul;56(4):576-585.
- 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.
- Corrado D, Zorzi A. Sudden death in athletes.. Int J Cardiol 2017 Jun 15;237:67-70.
- La Gerche A. The Potential Cardiotoxic Effects of Exercise.. Can J Cardiol 2016 Apr;32(4):421-8.
- Finocchiaro G, Papadakis M, Robertus JL, Dhutia H, Steriotis AK, Tome M, Mellor G, Merghani A, Malhotra A, Behr E, Sharma S, Sheppard MN. Etiology of Sudden Death in Sports: Insights From a United Kingdom Regional Registry.. J Am Coll Cardiol 2016 May 10;67(18):2108-2115.
- Lyle CH, Blissitt KJ, Kennedy RN, Mc Gorum BC, Newton JR, Parkin TD, Stirk A, Boden LA. Risk factors for race-associated sudden death in Thoroughbred racehorses in the UK (2000-2007).. Equine Vet J 2012 Jul;44(4):459-65.
- Hitchens PL, Morrice-West AV, Stevenson MA, Whitton RC. Meta-analysis of risk factors for racehorse catastrophic musculoskeletal injury in flat racing.. Vet J 2019 Mar;245:29-40.
- Verheyen KL, Wood JL. Descriptive epidemiology of fractures occurring in British Thoroughbred racehorses in training.. Equine Vet J 2004 Mar;36(2):167-73.
- Rosanowski SM, Chang YM, Stirk AJ, Verheyen KLP. Risk factors for race-day fatality in flat racing Thoroughbreds in Great Britain (2000 to 2013).. PLoS One 2018;13(3):e0194299.
- de Solis CN, Althaus F, Basieux N, Burger D. Sudden death in sport and riding horses during and immediately after exercise: A case series.. Equine Vet J 2018 Sep;50(5):644-648.
- Ely ER, Avella CS, Price JS, Smith RK, Wood JL, Verheyen KL. Descriptive epidemiology of fracture, tendon and suspensory ligament injuries in National Hunt racehorses in training.. Equine Vet J 2009 Apr;41(4):372-8.
- Racing Australia. [(accessed on 2 May 2022)]. Available online: https://www.racingaustralia.horse/
- Australian Studbook. [(accessed on 2 May 2022)]. Available online: https://www.studbook.org.au/
- Dehbi HM, Royston P, Hackshaw A. Life expectancy difference and life expectancy ratio: two measures of treatment effects in randomised trials with non-proportional hazards.. BMJ 2017 May 25;357:j2250.
- Factbook R.A. Table 56. Age of Individual Horses Racing 2004/05–2019/20. 2021. [(accessed on 2 May 2022)]. Available online: http://publishingservices.racingaustralia.horse/otherpublications/FactBook2019-2020/76/
- Navas de Solis C. Exercising arrhythmias and sudden cardiac death in horses: Review of the literature and comparative aspects.. Equine Vet J 2016 Jul;48(4):406-13.
- Boden LA, Anderson GA, Charles JA, Morgan KL, Morton JM, Parkin TD, Slocombe RF, Clarke AF. Risk of fatality and causes of death of Thoroughbred horses associated with racing in Victoria, Australia: 1989-2004.. Equine Vet J 2006 Jul;38(4):312-8.
- Physick-Sheard PW, Avison A, Chappell E, MacIver M. Ontario Racehorse Death Registry, 2003-2015: Descriptive analysis and rates of mortality.. Equine Vet J 2019 Jan;51(1):64-76.
- Palmer S, Gomez AMM, Mohammed HO. Attrition of Thoroughbred and Standardbred racehorses at New York Racetracks due to exercise and non-exercise related fatalities during the 2016 - 2019 racing seasons.. J Equine Vet Sci 2021 Sep;104:103703.
- Verheyen KL. Reducing injuries in racehorses: mission impossible?. Equine Vet J 2013 Jan;45(1):6-7.
- Crawford KL, Ahern BJ, Perkins NR, Phillips CJC, Finnane A. The Effect of Combined Training and Racing High-Speed Exercise History on Musculoskeletal Injuries in Thoroughbred Racehorses: A Systematic Review and Meta-Analysis of the Current Literature.. Animals (Basel) 2020 Nov 11;10(11).
- Morrice-West AV, Hitchens PL, Walmsley EA, Stevenson MA, Whitton RC. Training practices, speed and distances undertaken by Thoroughbred racehorses in Victoria, Australia.. Equine Vet J 2020 Mar;52(2):273-280.
- Ryan N, Marr CM, McGladdery AJ. Survey of cardiac arrhythmias during submaximal and maximal exercise in Thoroughbred racehorses.. Equine Vet J 2005 May;37(3):265-8.
- Marr CM, Franklin S, Garrod G, Wylie C, Smith L, Dukes-McEwan J, Bright J, Allen K. Exercise-associated rhythm disturbances in poorly performing Thoroughbreds: risk factors and association with racing performance.. Equine Vet J 2021 Jul;53(4):656-669.
- Physick-Sheard PW, McGurrin MK. Ventricular arrhythmias during race recovery in Standardbred Racehorses and associations with autonomic activity.. J Vet Intern Med 2010 Sep-Oct;24(5):1158-66.
- De Solis CN, Green C, Sides RH, Seino K, Bayly WM. Arrhythmias in Thoroughbreds During and after Treadmill and Racetrack Exercise. Equine Vet. J. 2016;46:24–25.
- Reef VB, Davidson EJ, Slack J, Stefanovski D. Hypercapnia and hyperlactatemia were positively associated with higher-grade arrhythmias during peak exercise in horses during poor performance evaluation on a high-speed treadmill.. Vet J 2020 Dec;266:105572.
- Whitton RC, Walmsley EA, Wong ASM, Shannon SM, Frazer EJ, Williams NJ, Guerow JF, Hitchens PL. Associations between pre-injury racing history and tibial and humeral fractures in Australian Thoroughbred racehorses.. Vet J 2019 May;247:44-49.
- Corrado D, Schmied C, Basso C, Borjesson M, Schiavon M, Pelliccia A, Vanhees L, Thiene G. Risk of sports: do we need a pre-participation screening for competitive and leisure athletes?. Eur Heart J 2011 Apr;32(8):934-44.
- Karlstam E, Ho SY, Shokrai A, Agren E, Michaëlsson M. Anomalous aortic origin of the left coronary artery in a horse.. Equine Vet J 1999 Jul;31(4):350-2.
- Viu J, Armengou L, Decloedt A, Jose-Cunilleras E. Investigation of ventricular pre-excitation electrocardiographic pattern in two horses: clinical presentation and potential causes.. J Vet Cardiol 2018 Jun;20(3):213-221.
- Jesty SA, Kraus MS, Johnson AL, Gelzer AR, Bartol J. An accessory bypass tract masked by the presence of atrial fibrillation in a horse.. J Vet Cardiol 2011 Mar;13(1):79-83.
- Trachsel DS, Calloe K, Mykkänen AK, Raistakka P, Anttila M, Fredholm M, Tala M, Lamminpää K, Klaerke DA, Buhl R. Exercise-Associated Sudden Death in Finnish Standardbred and Coldblooded Trotters - A Case Series With Pedigree Analysis.. J Equine Vet Sci 2021 Sep;104:103694.
- DeLay J. Postmortem findings in Ontario racehorses, 2003-2015.. J Vet Diagn Invest 2017 Jul;29(4):457-464.
- van de Schoor FR, Aengevaeren VL, Hopman MT, Oxborough DL, George KP, Thompson PD, Eijsvogels TM. Myocardial Fibrosis in Athletes.. Mayo Clin Proc 2016 Nov;91(11):1617-1631.
- La Gerche A, Burns AT, Mooney DJ, Inder WJ, Taylor AJ, Bogaert J, Macisaac AI, Heidbüchel H, Prior DL. Exercise-induced right ventricular dysfunction and structural remodelling in endurance athletes.. Eur Heart J 2012 Apr;33(8):998-1006.
- Abela M, Sharma S. ECG in Athletes. In: Green M., Krahn A., Alqarawi W., editors. Electrocardiography of Inherited Arrhythmias and Cardiomyopathies: From Basic Science to Clinical Practice. Springer International Publishing; Cham, Switzerland: 2020. pp. 137–158.
- Mesirca P, Nakao S, Nissen SD, Forte G, Anderson C, Trussell T, Li J, Cox C, Zi M, Logantha S, Yaar S, Cartensen H, Bidaud I, Stuart L, Soattin L, Morris GM, da Costa Martins PA, Cartwright EJ, Oceandy D, Mangoni ME, Jespersen T, Buhl R, Dobrzynski H, Boyett MR, D'Souza A. Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes.. Circ Res 2021 Jun 25;129(1):e1-e20.
- Chandra N, Bastiaenen R, Papadakis M, Sharma S. Sudden cardiac death in young athletes: practical challenges and diagnostic dilemmas.. J Am Coll Cardiol 2013 Mar 12;61(10):1027-40.
- Van Camp SP, Bloor CM, Mueller FO, Cantu RC, Olson HG. Nontraumatic sports death in high school and college athletes.. Med Sci Sports Exerc 1995 May;27(5):641-7.
- Kiryu K, Nakamura T, Kaneko M, Oikawa M, Yoshihara T. Cardiopathology of sudden cardiac death in the race horse.. Heart Vessels Suppl 1987;2:40-6.
- Eckart RE, Scoville SL, Campbell CL, Shry EA, Stajduhar KC, Potter RN, Pearse LA, Virmani R. Sudden death in young adults: a 25-year review of autopsies in military recruits.. Ann Intern Med 2004 Dec 7;141(11):829-34.
- de Noronha SV, Behr ER, Papadakis M, Ohta-Ogo K, Banya W, Wells J, Cox S, Cox A, Sharma S, Sheppard MN. The importance of specialist cardiac histopathological examination in the investigation of young sudden cardiac deaths.. Europace 2014 Jun;16(6):899-907.
- Hinchcliff KW, Couetil LL, Knight PK, Morley PS, Robinson NE, Sweeney CR, van Erck E. Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement.. J Vet Intern Med 2015 May-Jun;29(3):743-58.
- Takahashi T, Hiraga A, Ohmura H, Kai M, Jones JH. Frequency of and risk factors for epistaxis associated with exercise-induced pulmonary hemorrhage in horses: 251,609 race starts (1992-1997).. J Am Vet Med Assoc 2001 May 1;218(9):1462-4.
- Weideman H, Schoeman SJ, Jordaan GF, Kidd M. Epistaxis related to exercise-induced pulmonary haemorrhage in south African Thoroughbreds.. J S Afr Vet Assoc 2003 Dec;74(4):127-31.
- Morrice-West AV, Hitchens PL, Walmsley EA, Stevenson MA, Wong ASM, Whitton RC. Variation in GPS and accelerometer recorded velocity and stride parameters of galloping Thoroughbred horses.. Equine Vet J 2021 Sep;53(5):1063-1074.
- Frippiat T, van Beckhoven C, Moyse E, Art T. Accuracy of a heart rate monitor for calculating heart rate variability parameters in exercising horses.. J Equine Vet Sci 2021 Sep;104:103716.
- Mott R, Dowell F, Evans N. Use of the Polar V800 and Actiheart 5 heart rate monitors for the assessment of heart rate variability (HRV) in horses. Appl. Anim. Behav. Sci. 2021;241:105401.
- Haughan J, Manriquez M, Cohen N, Robinson M, de Solis CN. Comparison of novel wearable cardiac monitors to yield accurate exercising ECG and heart rate data in horses. Comp. Exerc. Physiol. 2021;17:457–465.
- Ter Woort F, Dubois G, Didier M, Van Erck-Westergren E. Validation of an equine fitness tracker: Heart rate and heart rate variability. Comp. Exerc. Physiol. 2021;17:189–198.
- Mitchell KJ, Schwarzwald CC. Heart rate variability analysis in horses for the diagnosis of arrhythmias.. Vet J 2021 Feb;268:105590.
Citations
This article has been cited 10 times.- Bennet ED, Parkin TDH. Anomalous Incidence of Fatal Musculoskeletal Injury in North American 2-Year-Old Thoroughbred Racehorses in the Year 2020. Animals (Basel) 2023 Aug 9;13(16).
- Gibson MJ, Legg KA, Gee EK, Rogers CW. The Reporting of Racehorse Fatalities in New Zealand Thoroughbred Flat Racing in the 2011/12-2021/22 Seasons. Animals (Basel) 2023 Feb 9;13(4).
- Natterson-Horowitz B, Wright K, Van Steenkiste G, Decloedt A, Gagnon AL, Cai X, Mazmanian A. Arrhythmias across the tree of life: comparative insights for human electrophysiology. Front Cardiovasc Med 2025;12:1652591.
- 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.
- Avison A, Physick-Sheard PW, Pyle WG. Performance horses as a model for exercise-associated cardiac arrhythmias and sudden cardiac death. J Mol Cell Cardiol Plus 2025 Jun;12:100452.
- Bennet ED, Parkin TDH. Novel risk factors associated with fatal musculoskeletal injury in Thoroughbreds in North American racing (2009-2023). Equine Vet J 2026 Jan;58(1):20-30.
- Morrice-West AV, Thomas M, Wong ASM, Flash M, Whitton RC, Hitchens PL. Linkage of jockey falls and injuries with racehorse injuries and fatalities in Thoroughbred flat racing in Victoria, Australia. Front Vet Sci 2024;11:1481016.
- Navas de Solis C, Ramseyer A, Stefanovski D, Haughan J, Solomon CJ, Kirsch K. Association of heart rate variability, exercise intensity and exercising arrhythmias with competition results in eventing horses. Equine Vet J 2025 Nov;57(6):1446-1456.
- 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.
- Nath LC, Elliott A, La Gerche A, Weir J, Forbes G, Thomas G, Franklin S. Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses. J Vet Intern Med 2023 Nov-Dec;37(6):2573-2583.