Sports Medicine

An electrocardiogram (ECG) is the recording of the heart’s electrical impulses. Adhesive patches known as electrodes are placed over the horse’s thoracic region, allowing the heart rate and rhythm to be transmitted to a computer in real time. The recordings are analyzed to determine if the heart is functioning properly and whether any arrhythmias (abnormal heart rhythms) are present. It is not uncommon for athletic horses to experience arrhythmias and although the majority does not usually affect performance, some can seriously affect a horse’s health.

Cardiac arrhythmias can be congenital or can occur as a result of heart disease, systemic disease or metabolic disturbances. An ECG is a simple and painless way to analyze the heart’s electrical activity and distinguish between arrhythmias that are physiological and pathological in nature. It can be performed both at rest and during exercise. Electrodes and wires must be well secured to reduce the amount of interference on the ECG tracing.

At rest a horse’s heart beats approximately 30 to 40 times a minute and during high intensity exercise the heart rate can reach 210-230 beats per minute. Monitoring a horse’s heart rate gives valuable information regarding their fitness levels. A horse whose heart rate increases very suddenly at the onset of exercise and decreases quickly during recovery is generally very fit. A high maximum heart rate may also imply that a horse is very fit, however it may also reflect a horse that is very de-conditioned therefore one should not draw conclusions solely based on heart rate.

Comparisons can be made between pre-season, mid-season and post-season assessments and can provided useful information regarding improvements or regressions made over time. Knowing how fit a horse is can also be useful for making comparisons between different horses to determine how they are responding and adapting to training throughout the season. ECG’s also help determine if the heart is functioning properly, and if arrhythmias are present, where they originate. However the underlying cause of an arrhythmia is not always clear as there may be many possible etiologies; further diagnostic testing is often required.

Blood samples allow us to monitor blood gases, lactate, electrolytes and various cardiac enzymes that are present at the time of sampling. This information gives a greater understanding of the horse’s cardiovascular system and helps determine exactly what is happening in the heart. Knowing the underlying cause of the arrhythmia allows the veterinarian to treat it in an appropriate manner.

Metabolic byproducts also tell us a great deal about a horse’s general health and fitness levels. During high intensity exercise the body works in an anaerobic state, meaning that the muscles are not being supplied with enough oxygen to create the energy it needs. A process known as glycolysis is therefore used to create energy and a byproduct of this process is lactate. The body recycles and clears out lactate, however as exercise intensity increases, production exceeds clearance and lactate begins to accumulate in the blood. This point is referred to as the lactate threshold (LT) and it is very difficult to sustain exercise at this intensity. Anaerobic metabolism provides energy for high-intensity bursts of activity that only last for a short period of time (for example racing).

Blood lactate is often measured in the field for descriptive purposes as it informs us of how hard a horse is working and whether they are in an anaerobic or aerobic state. The more quickly the sample can be drawn following exercise, the more accurate and informative it will be. During recovery, enzymes and other byproducts that build up in the blood begin to be cleared from the system. Training can improve the LT, meaning that exercise can be continued at high intensities for longer periods of time before exhaustion.

Abnormal respiratory noises during exercise are often indicative of upper airway problems. Endoscopes are flexible tubes with a small camera that allow veterinarians to see inside the horse’s airway (throat for example). The scope is inserted into the horse’s nostril and advanced to the pharynx or down to the lungs. Endoscopes are useful for assessing inflammation, irritation, and redness, mucous, obstruction and to determine if the structures are functioning properly.

A limitation of using an endoscope is that evaluations can only be completed at rest and symptoms may not be induced under these conditions. Horses often make noises during intense exercise and to be able to determine what is happening in the airway we need to be able to see inside their throat during exercise.

Read about endoscopic scoring here.

Wireless videoendoscopes (Dynamic Respiratory Scopes or DRS) are even more beneficial as these allow a horse’s upper airways to be assessed during exercise. The scope is inserted into the nostril to view the pharynx (throat). The external end is connected to the horse’s bridle and the accompanying pack is worn by a rider or attached to the tack. A live recording is transmitted to a portable screen. This is an extremely beneficial tool as it allows horses to be examined while exercising in the field and under the exact conditions in which they compete.

• The first video demonstrates the many applications of the DRS Wireless Scope and shows clips from a 'normal' scope.
• The clip below is an abnormal scope showing grade 4 hemiplegia and collapse of the AE fold.

Hyperbaric Oxygen Therapy (HBOT) is a relatively new treatment being used on a variety of chronic conditions and acute injuries in humans, horses and other companion animals. Subjects are placed in a chamber where they are exposed to 100% oxygen at increased pressure. Normal or standard atmospheric pressure is equivalent to 14.7 pounds per square inch (psi). Treatments are generally completed at 29.4 psi, or the pressure equivalent of being 33 feet under water. 

Oxygen is delivered to tissues throughout the body via the blood and is carried by a specific molecule called hemoglobin (Hb). Under normal atmospheric pressures there is a limit to the amount of oxygen that can be carried within the blood; it depends on the amount of red-cell hemoglobin (Hb) in the blood, the amount of oxygen in the air, the lung function and the blood pressure value.

It is believed that treating subjects with 100% oxygen at increased pressure enhances the amount of oxygen available in the blood. Under these conditions there is so much oxygen pressure that the Hb is fully saturated (meaning it carries the maximal amount of oxygen possible) and additional oxygen is dissolved in the plasma thus greatly increasing the total oxygen content of the blood. Persistent infections and slow-healing wounds are often hypoxic, meaning they lack oxygen. The theory is that HBOT promotes the delivery of oxygen to injured tissues working to speed the healing and recovery time and also salvaging tissues that may otherwise be lost from necrosis.

HBOT is most often used for treating infections and soft tissue injuries, however it is being used regularly and for various conditions including chronic infections, neurological injuries, bone infections, intestinal issues and laminitis. There are only a few studies examining the effectiveness of HBOT, however many are using it as an adjunctive therapy in combination with other medical procedures. Treatments range in time but last an average of 90 minutes. Horses are often sedated during their session and tolerate very well the treatment.

Read about Dr. Léguillette's studies on HBOT here.