Background: Atrial fibrillation (AF) impacts performance and horse and jockey safety. Understanding the outcomes of AF identified postrace will better inform regulatory policy. Hypothesis/Objectives: To investigate the outcomes after episodes of AF identified postrace and determine whether affected horses are at increased risk of additional episodes compared to the general racing population. Animals: Total of 4684 Thoroughbred racehorses. Methods: Race records for Thoroughbred horses racing in Hong Kong from 2007 to 2017 were reviewed. Horses that performed below expectation were examined by cardiac auscultation and ECG. Incidence and recurrence of AF were compared between horses with and without a history of AF and between horses with paroxysmal and persistent episodes using Fisher's exact test. Results: There were 96 135 race starts during the study. Atrial fibrillation was identified in 4.9% of horses, with an overall incidence of 2.7 episodes per 1000 starts. The incidence of AF in horses after any previous episode (12.8 per 1000 starts) was higher than for horses with no previous episode (2.4 per 1000 starts; odds ratio [OR], 5.3; 95% confidence interval [CI], 3.8-7.6). Recurrence was seen in 64% of horses previously treated for persistent AF, which was higher than recurrence in horses with paroxysmal AF (23%; OR, 5.9; 95% CI, 1.6-21.2). Median duration between episodes was 343 days (range, 34-1065). Conclusions and Clinical Importance: Thoroughbreds are at increased risk of recurrent AF after both paroxysmal and persistent episodes, but the duration of time between episodes varies widely. These findings support a substantial burden of AF among individual Thoroughbred racehorses.

Cardiac arrhythmias resulting in sudden cardiac death (SCD) are an important cause of racehorse fatalities. The objective of this study was to determine risk factors for SCD in Thoroughbreds by evaluating a sample with a policy of mandatory post-mortem following racing or training fatalities. Risk factors were compared between case horses with SCD (n = 57) and control horses with other fatal injury (OFI, n = 188) by univariable and multivariable logistic regression. Survival in years for horses with SCD was compared to OFI using the Kaplan–Meier method with log rank test. The following variables were most important in the multiple logistic model: Horses with SCD were more likely to die during training than during racing, SCD (42/57, 74%) vs. OFI (82/188, 44%; odds ratio [OR], 95% confidence interval [CI], 2.5, 1.2–5.4; p = 0.01), had fewer lifetime starts, median (interquartile range [IQR]), SCD (3.0 [0.0–9.0]) vs. OFI (9.0 [0.0–22.8]; OR, 95% CI, 0.96, 0.9–1.0; p = 0.02 and were less likely to be entire (uncastrated) males, SCD 9/57 (16%) vs. OFI (46/188, 25%; OR, 95% CI, 0.47, 0.1–0.9; p = 0.03). Survival in years (median (IQR)) for horses with SCD was 3.6 (3.1–4.4), which was shorter than OFI (4.5 [3.1–6.0], hazard ratio, 95%CI, 1.6,1.2–2.3; p < 0.001). SCD occurs more commonly in training than racing, which suggests exercise intensity is less important in precipitating this fatality. In this study, SCD occurred early in the careers of affected horses.

Objective—To determine whether there is evidence of myocardial injury in horses with acute abdominal disease. Design—Prospective case series. Animals—18 healthy horses and 69 horses with acute abdominal disease. Procedures—18 healthy horses had been admitted to the hospital for investigation and were assigned to group 1. Horses examined for acute abdominal disease were assigned to 3 groups: strangulating obstruction, nonstrangulating obstruction, or inflammatory disease (groups 2, 3, and 4, respectively). Heart rate, Hct, and blood lactate and cardiac troponin I (cTnI) concentrations were measured at initial examination. Myocardial function was assessed by echocardiographic measurement of fractional shortening and left ventricular ejection time (LVET). Heart rhythm was evaluated via ECG. Results—The proportion of horses with high (> 0.03 ng/mL) cTnI concentration was significantly greater among horses with strangulating (9/25 [36%]) or inflammatory (9/19 [47%]) lesions, compared with healthy horses (0/18). The proportion of horses with high cTnI concentration was significantly greater among nonsurvivors (12/24 [50%]) than among survivors (10/45 [22%]). Serum cTnI concentration was positively correlated with Hct, heart rate, and blood lactate concentration and negatively correlated with LVET. Conclusions and Clinical Relevance—Evidence of myocardial injury was observed in horses with acute abdominal disease, and this injury was associated with severity of illness. Recognition of myocardial injury could improve treatment of acute abdominal disease in horses.

Background Acute gastrointestinal disease occurs commonly in horses. Novel biomarkers might improve the understanding of SIRS and aid diagnosis and determination of prognosis. Hypotheses Increased plasma concentrations of the biomarkers HMGB‐1 and nucleosomes are associated with severity of gastrointestinal lesions in horses; concentrations of these biomarkers will be greater in horses with lesions more likely to cause SIRS; and will provide additional information compared with standard biomarkers fibrinogen and SAA. Animals Thirty horses with gastrointestinal disease, 22 healthy horses. Methods Prospective study. Plasma samples taken on admission were used for measurement of HMGB‐1, nucleosomes, fibrinogen, and SAA. Values were compared between healthy horses and those with gastrointestinal disease, and between horses with gastrointestinal disease grouped by lesion type (inflammatory, strangulating, and nonstrangulating). Correlations between biomarkers were assessed. Results Plasma concentrations of all biomarkers were significantly higher in horses with gastrointestinal disease compared to healthy horses (P ≤ .001). HMGB‐1 and nucleosomes were significantly higher in inflammatory and strangulating groups compared to healthy horses (3.5‐fold and 5.4‐fold increases, respectively, for HMGB‐1 (P < .05) and 4.8‐fold and 5.6‐fold increases for nucleosomes (P < .05)), but concentrations in the group with nonstrangulating disease did not differ from healthy horses. There was significant correlation between HMGB‐1 and nucleosomes (Spearman's r = 0.623; P < .001), and fibrinogen and SAA (Spearman's r = 0.801; P < .001) but not between other biomarkers. Conclusions and Clinical Importance High mobility group box‐1 and nucleosomes might have use as biomarkers for horses with gastrointestinal disease. Further studies are required to determine kinetics and prognostic value of serial measurements of these biomarkers in horses.