HISA Study Finds AFib Can Contribute To Sudden Death; Early Detection Key

[Wandering Eyes]

A HISA pilot program released results from a study of advanced cardiac monitoring of Thoroughbreds that shows atrial fibrillation (AF)–traditionally considered a benign, performance-limiting condition–can worsen during exercise, cause a more severe arrhythmia that leads to sudden death, according to a press release from HISA on Thursday. The group said that electrocardiogram data from affected horses that displayed AF both at rest and under exertion, underscores the need for early detection and highlighs the potential of integrating routine cardiac screening into pre-training and pre-race evaluations.

During the first six months of 2025, HISA's Exercise-Associated Sudden Death (EASD) Working Group–launched in October 2023–said that EASD accounted for approximately 8% of racing fatalities and 18% of training fatalities at racetracks subject to HISA rules (and training centers owned by them). Retrospective analysis of cases since HISA's inception shows that more than 50% of cases were likely related to cardiac issues, often classified as “Sudden Cardiac Death.” The majority of these EASD events occurred early in a horse's career, with the highest incidence occurring in horses with zero to five starts.

HISA launched its working group in recognition of the critical importance of addressing and better understanding these risks and preventing EASD. The pilot, led by Dr. Cristobal Navas de Solis, Associate Professor of Cardiology, Ultrasound and Internal Medicine at the University of Pennsylvania School of Veterinary Medicine, and Dr. Sian Durward-Akhurst, Assistant Professor of Genetics, Genomics and Large Animal Internal Medicine at the University of Minnesota College of Veterinary Medicine, is ongoing. The findings were presented at the American College of Veterinary Internal Medicine Forum in Kentucky in summer 2025, among other meetings of specialists in the field.

Dr. Navas de Solis and Dr. Durward-Akhurst partnered with leading experts to investigate underlying causes and develop prevention strategies. Program collaborators include Dr. Mary Durando (Equine Sports Medicine Consultants, U.S.), Dr. Grace Forbes (Racing Victoria, Australia), Dr. Laura Nath (University of Adelaide, Australia) and wearable technology specialists at Arioneo Equimetre (France).

“Integrating cardiac screening into routine evaluations–whether through wearable devices or veterinary exams–could allow trainers and veterinarians to identify at-risk horses before exercise,” said Dr. Karen Hassan, HISA's Compliance and Research Veterinarian and chair of HISA's EASD Working Group. “This opens the door to scalable monitoring protocols and standardized response strategies that could save equine lives.”

The next phase of the program will focus on scalability and the development of real-time cardiac monitoring protocols and risk-based screening criteria. Specifically, AF could be detected either via wearable devices, handheld ECG devices or auscultation by a veterinarian before exercise, allowing trainers to withhold exercise and work with their veterinary team to evaluate affected horses further.

Establishing optimal workflows and tools to be used for rhythm analysis with an emphasis on AF, defining the risk of arrhythmia other than AF and proposing and evaluating a standardized response protocol for cardiac adverse events during exercise will be key components of the next phase of work.

To further educate stakeholders on EASD, a series of educational webinars will be held for horsemen and veterinarians in the coming weeks.

HISA has issued an accompanying Equine Health Advisory on EASD, associated risk factors and what trainers and veterinarians can do to help prevent EASD, which can be found here.

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