Last year there were some important amendments to the rules of racing for Australian thoroughbreds.
The first change centres on reporting a ‘cardiac arrhythmia’ and the need for the trainer and any person in charge of the horse to report the presence of a cardiac arrhythmia to relevant stewards immediately. The assumption here is that the horse is experiencing, or did experience, atrial fibrillation. There are a number of different ‘cardiac arrhythmias’ that occur in horses, many of which are benign and not related to performance or safety. The code of practice does however state that the arrhythmia must be pathological.
A potential problem with this new code is that the horse after a second event should be examined a qualified veterinary surgeon with specialist qualifications in equine medicine. This person must also have the equipment and skill to be able to perform and interpret an echocardiographic examination and an exercise ECG. There are certainly several individuals in Australia, including several in Western Australia (including Equiimed, Murdoch University, Ascot Equine Vets) who can perform these tasks, but this is not true for all states and territories.
Where a horse is detected with a cardiac arrhythmia, or where a cardiac arrhythmia has been identified, following a race, official trial, jump-out, or at any other time, including, but not limited to, following track work, the trainer and any other person in charge of the horse must; (a) report the detection or identification of a cardiac arrhythmia to the Stewards without delay, and (b) comply with the Racing Australia Code of Practice: Cardiac arrhythmias detected during post-race inspections (as amended from time to time) in respect of any future training of the horse and/or running of the horse in a race, official trial or jump-out.
The policy states:
Where a horse is detected with a pathological cardiac arrhythmia (including atrial fibrillation) on auscultation after a race, official trial and/or jump-out the horse must undergo additional diagnostic procedures to determine the cause of the arrhythmia and a period of rest to allow the horse to recover and be treated if necessary.
The following protocols must be followed according to the number of occasions the horse has been detected with a cardiac arrhythmia.
1. Cardiac arrhythmia (pathological) found for the first time
Where a horse is found to have experienced a pathological cardiac arrhythmia for the first time, the horse must not start in a further race, official trial, or jump-out until the Stewards have received a satisfactory report from a qualified veterinary surgeon which includes the results of: (a) an electrocardiography (ECG) of more than 60 seconds duration performed by that veterinarian whilst the horse is at rest; and (b) a cardiac auscultation performed by that veterinarian within 15 minutes of the horse completing a satisfactory gallop of at least 1000 metres.
2. Cardiac arrhythmia (pathological) found for a second time
Where a horse is found to have experienced a pathological cardiac arrhythmia for a second time, the horse must not start in a further race, official trial, or jump-out until the Stewards have received a satisfactory report from a qualified veterinary surgeon with specialist qualifications in equine medicine which includes the results of: (a) echocardiography performed by that veterinarian at rest; (b) electrocardiography (ECG) performed by that veterinarian at rest and at exercise (see below Notes on obtaining and interpreting an exercising ECG); and (c) any other examination that that veterinarian requests. Following acceptance by the Stewards of the above report, they may grant written permission for the horse to be nominated for and participate in an official trial or jump-out. The horse must not be nominated for a race unless: (a) it trials to the satisfaction of the Stewards in an official trial or jump-out, of at least 1,000 metres; and (b) a qualified veterinary surgeon provides a satisfactory post-trial report that includes the results of cardiac auscultation within 15 minutes of completion of the official trial or jump-out. Following a satisfactory trial or jump-out which only Stewards or Veterinarians officiate at, and upon receiving the satisfactory post-trial veterinary report referred to above, the Stewards may grant written permission for the horse to be nominated for and participate in a race.
3. Cardiac arrhythmia (pathological) found for a third time
Where a horse is found to have experienced a pathological cardiac arrhythmia for a third time, the horse will be ineligible to start in any race, official trial, or jump-out, or be trained, unless otherwise determined by the Stewards in writing.
Notes on obtaining and interpreting an exercising ECG
(a) Exercising ECG should allow evaluation of the rhythm at rest (minimum 60 seconds duration) and a continuous recording during a strenuous exercise test either on a treadmill or track. A heart rate greater than 200 beats per minute should be sustained for a minimum of 60 seconds. The recording should continue until the heart rate of the horse is below 80 beats per minute. Notwithstanding the potential for electrical interference, the recording must be of sufficient quality to allow evaluation of the heart rate, rhythm and morphology of complexes.
(b) Horses with a high number of premature atrial contractions or runs of atrial tachycardia are likely to be at higher risk of developing atrial fibrillation.
(c) Atrial fibrillation causes poor performance. Atrial fibrillation may be associated with ventricular arrhythmias and although unlikely this may result in collapse or death.
(d) Arrhythmia are common in the immediate post exercise period (heart rate 180-220) beats per minute. Although common some arrhythmias can be a cause for concern as horses are known to collapse after finishing a race.
(e) Sinus arrhythmia or occasional monomorphic premature complexes which are overdriven by intense exercise or only occur in the immediate post exercise period are unlikely to cause poor performance or endanger the safety of horse or rider.
(f) Bradyarrhythmia which are not overdriven by exercise are of concern and these horses are not safe to ride.
(g) Premature complexes occurring during intense exercise (heart rate greater than 200 beats per minute) may be a cause for concern.
(h) Features of complex ventricular arrhythmia which are a cause for concern in any phase of the exercise test include; multiform QRS morphology, highly premature R on T timing, repetitive activity (couplets, triplets), paroxysmal or sustained VT, multiform tachycardia and polymorphic tachycardia.
(i) Electrocardiographic findings should be interpreted alongside other clinical findings such as: abnormalities of cardiac chamber size, myocardial thickness or significant valvular regurgitation, haematological and biochemical findings, urinary fractional excretion of electrolytes and upper or lower airway disease.
(j) Other diagnostic tests which may allow further evaluation of the heart include 24-hour ECG monitoring and measurement of cardiac troponin I before and 4 hours after a strenuous exercise test.
