Studies on the causes of exercise associated sudden death (EASD) are urgently needed and validation and assessment of wearable technology is vital in this effort1. Wearable devices capable of recording ECGs are used in training in Great Britain (GB) but were not previously permitted in racing. The regulatory steps taken to enable the use of a device during jump races in GB for a pilot study are outlined. To date, 6 horses have worn the device on 4 racecourses; 2 hurdle, 1 chase and 3 National Hunt flat races. Six Thoroughbreds (3 mares, 3 geldings, aged 4-9 years, median 5.5 years) with no cardiac murmurs grade >3/6 and normal serum and red blood cell potassium, magnesium and serum cardiac troponin I concentrations were included. Single lead ECGs were obtained during racing and one training session (median 5, range 2 – 25 days pre-race). ECG findings were described by one operator (CMM). ECG quality during the race was graded subjectively as good 2, moderate 3, poor 1. On raceday, all horses had premature depolarisations (PD) and 3 horses (all had jumped) had >5PD during racing, a finding which has been suggested as a cut-off for clinical significance previously. Pairs, triplets and/or runs were noted. Training sessions resulted in lower peak heart rates than racing (median 214, 210-222 bpm, p = 0.01); 5 horses had rhythm disturbances but only one horse showed 1 paired PD in recovery, otherwise arrhythmias seen in training were isolated PD.
The study is limited by its small sample size but demonstrates rhythm disturbances in racehorses are common, but arrhythmia burden is higher during racing than training, particularly when jumping. Further longitudinal studies are needed to understand the range of arrhythmias which occurs in healthy horses racing successfully and to develop criteria for clinical interpretation of racing ECGs.