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27/11/08
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HEART MONITORS AND LACTATE ANALYSIS
The 2008 Cheltenham Gold Cup winner Denman recently developed a heart problem called atrial fibrillation that is often linked to the oversize of a particular heart chamber (the atrium). Is the heart of this great champion pushing itself so far to the limit that it is struggling to cope?
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QUINE exercise physiology has been subject to major scientific advances over the last three decades. The advent of highspeed treadmills created the opportunity to use more advanced recording techniques and the knowledge obtained from this, combined with that from human athletes, leaves us in a much more informed position as to what exactly goes on inside the racehorse at exercise. With the introduction of new technology such as horse-walkers and allweather gallops, training methods have become more advanced than they were 30 years ago. Nevertheless, this article will question whether trainers should be taking a more scientific approach and using tools such as heart monitors and lactic acid analysis to aid in the daily training of the racehorse. The racing fraternity consider great horses to have great hearts. However, there seems to be a lack of conviction behind this view as hardly anyone this side of the Atlantic scans the hearts of young-stock and only a few monitor cardiac function. The average 500kg racehorse has nearly 50 litres of blood, which the heart pumps throughout the body. The main function of this cardiovascular system is to release carbon dioxide and pick up oxygen in the lungs and spread it throughout the body where it can be released and used. The heart is the centre of this system with its right side pumping blood with low oxygen from the body to the lungs and the left side pumping highly oxygenated blood from the lungs to the body. It stands to reason that a great racehorse needs a good-sized, efficient heart and it should be easy to monitor how much training is stressing the heart, and therefore the horse, by simply recording the heart rate
– yet this is rarely done. The equine heart is a large structure of approximately the same size as a football, which beats quite slowly at rest but which is capable of increasing its resting heart rate by as much as six to ten times when at peak exercise. The horse is the only mammal capable of such an increase (a human is doing well to achieve an increase of three fold) and this perhaps explains why it is such a talented athlete. The heart is situated in the horse’s chest just behind the elbow, almost completely surrounded by the lungs and only a small part of the heart is left uncovered, which is called the cardiac notch. This is the area where the heart makes contact with the left chest wall and so it is the best place to listen to it and to perform cardiac ultrasound. Ultrasound of the heart (echocardiography) enables veterinary surgeons to visualise what is going on in this most central organ. There are several veterinary surgeons, particularly in the United States, who believe that the best racehorses have the most efficient hearts and travel from sale to sale examining yearlings using ultrasound to advise potential purchasers of the ‘best’ hearts on offer. Unfortunately, as anyone who has followed their advice will know, having a heart that looks great on ultrasound examination does not seem to guarantee that the racehorse in question is a champion. The reader can come to their own conclusions as to why, but surely having the ‘best’ heart is only one part in the selection of a future champion. Veterinary surgeons routinely listen to horses’ hearts in an attempt to detect abnormalities such as murmurs. However, should trainers be routinely monitoring heart rate in response to exercise? Not only might they find abnormalities like the atrial
fibrillation seen in Denman, but much more commonly and more importantly, they might get an idea as to whether they have just asked a particular horse to do a little more than they had intended and so could alter its training regime appropriately. There are a small number of heart monitors available on the market but nearly all trainers make the decision that it is a piece of information that they can do without.
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EASURING a horse’s heart rate is straightforward. Simply attach the heart-belt to the horse, turn on the transmitter and monitor the horse’s heart rate on a watch whilst it exercises. The obvious benefit of such a system is that heart rate reflects cardiac output and hence we learn how hard the horse is working. On a daily basis, we watch horses blowing after exercise, we ask the riders how fit they think they are and we weigh the horses. Measuring and recording heart rates in response to exercise could surely provide another useful tool in the training of the racehorse. A horse’s heart rate increases in response to external stress as well as exercise, which can lead to misleading results. For example, a horse may return a higher heart rate during a particular piece of work than truly reflects its fitness if it ‘shied’ at something. The knack is not only learning to read the difference between a false heart rate but understanding the all important recovery rate. In addition, many horsemen could point out with some justification that measuring equine heart rates during a piece of work would only serve to distract their attention from making more important observations – something they have trained
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