Cardiac Pathology and Genomics of Sudden Death in Racehorses From New York and Maryland Racetracks

Abstract

Postmortem evaluation of racehorses has focused primarily on musculoskeletal injuries; however, horses also die suddenly on the track (sudden death [SD]). Although cardiac conditions are frequently suspected as a cause of death, SD racehorses are often autopsy negative; however, previous studies have been limited due to inconsistent or insufficient cardiac sampling and lack of controls. SD in New York (NY) and Maryland (MD) racehorses was evaluated in an observational case vs control study comparing clinical information, postmortem evaluation including cardiac dissection, and cardiac conduction system histopathology. In the study period, there were 40 cases of SD. In NY, SD occurred in 12% (37/316) of submissions, and 36 (11%) cases of SD were exercise associated (EASD); 3 EASD cases occurred in MD. In NY/MD EASD cases with histologic examination of the heart, 11 of 36 (31%) had significant lesions, including mesenteric artery rupture (1), axial trauma (2), systemic inflammation (2), pulmonary hemorrhage (1), and cardiac disease (5). Mild myocardial fibrosis, mild inflammation, coronary arteriosclerosis, and variation in cardiac nodal connective tissue were present in both SD cases and controls and thus were not considered to be causes of SD. While not excluding a genetic basis for SD, analysis of the genotypes (GGP Equine 70 K Array) of cases and controls did not reveal significant differences in allele frequencies at any locus. Most SD racehorses were autopsy negative; further research using standardized protocols and controls is needed to understand the underlying causes of SD, which is crucial to protecting the viability of racing.

Incidence, recurrence, and outcome of postrace atrial fibrillation in Thoroughbred horses

“…23,24,44 In rodents, myocardial inflammation and fibrosis after exercise training is considered to be a substrate for arrhythmia. [20][21][22] Several studies have reported inflammatory and fibrotic changes in the myocardium of racehorses involving the atria, conduction system and ventricles 3,[45][46][47][48][49] Age is a risk factor for AF in racehorses, 10,12 supporting the effect of volume of training and cardiac remodeling in the promotion of AF in this species. Although exercise likely promotes the onset of AF in horses, individual factors, such as atrial size and microstructural changes affecting electromechanical function, also are important in sustaining AF.…”

Racing‐associated fatalities in Norwegian and Swedish harness racehorses: Incidence rates, risk factors, and principal postmortem findings

“…They included pulmonary edema, congestion and hemorrhage, major vessel rupture, as well as macro‐and microscopic cardiac changes. 1 , 3 , 5 , 9 , 43 , 44 , 45 , 46 , 47 , 48 In most cases, SAD was attributed to acute circulatory failure (30/40 cases), although it was not possible to determine if death was of primary cardiac or pulmonary origin. Other studies report similar findings highlighting the difficulty in interpreting postmortem findings, especially relating to the importance of pulmonary and cardiac changes.…”

“…Other studies report similar findings highlighting the difficulty in interpreting postmortem findings, especially relating to the importance of pulmonary and cardiac changes. 1 , 3 , 5 , 9 , 43 , 48 …”

“…These findings are consistent with previous studies. 1 , 3 , 5 , 9 , 43 , 48 There are contrasting opinions regarding EIPH as a direct cause of sudden death. However, a recent consensus statement from the American College of Veterinary Internal Medicine (ACVIM) stated that there is currently little evidence in the literature that confirms a link between sudden death and EIPH.…”

Idiopathic multifocal myocardial atrophy with fibrosis and fatty infiltration involving Purkinje fibres in a 13‐year‐old Arabian broodmare: Histopathological features

“…Compared with what is known about the pathologies of equine organ systems such as the locomotor, gastrointestinal and nervous systems, data on pathologies of the equine cardiac system are limited. Most recent studies on cardiac pathologies have focused on racehorses, with special attention to sudden death or arrhythmias (Diab, Poppenga, & Uzal, 2017; Kiryu et al, 1999; Kiryu, Nakamura, Kaneko, Oikawa, & Yoshihara, 1987; Lyle et al, 2011; Molesan et al, 2019). Only a few reports on conduction system pathology in nonathletic horses have been published, including cases that resembled arrythmogenic right ventricular cardiomyopathy involving myocardial loss and replacement by fatty or fibrous tissues (Else & Holmes, 1972; Raftery, Garcia, Thompson, & Sutton, 2015).…”