Telemetric Electrocardiography (ECG)
Electrocardiography is used for diagnosing abnormalities of cardiac rhythm. The most common performance limiting arrhythmia in horses is atrial fibrillation. Telemetric electrocardiography allows us to record an ECG over a prolonged period (up to 24 hours or longer). A small unit is attached to a horse via a surcingle or tied to the mane and this box records the trace coming from the electrodes placed on the chest. The trace is recorded onto an SD card or can be watched on a remote computer in real time (from up to 50 metres away). This allows an ECG to be obtained without the horse needing to be tied up or connected to a traditional (paper trace) ECG. It is particularly useful for monitoring the ECG during quinidine treatment for horses with atrial fibrillation and makes this procedure considerably safer.
Echocardiography is ultrasonography of the heart. This is essential for the diagnosis and interpretation of cardiac murmurs which are heard after listening to the heart with a stethoscope. Cardiac murmurs are very common in performance horses and in many cases do not affect performance, however echocardiography is necessary to determine severity. Echocardiography is very accurate for assessment of heart size, which can impact on performance in athletes and can affect prognosis in some cases of valvular regurgitation. Echocardiography is also needed to evaluate fluid around the heart (pericardial effusion).
Similar to the respiratory evaluation, the treadmill is a useful tool for viewing a horse in work and monitoring its cardiac output whilst under pressure. Telemetric electrocardiography can be used to observe and record the cardiac rhythm trace whilst the horse is exercising. This is particularly useful for diagnosing problems that only occur after strenuous exercise, such as some cases of intermittent (paroxysmal) atrial fibrillation or ventricular premature contractions. Echocardiography can be performed immediately after exercise to evaluate for abnormalities of myocardial function which can be subtle if only observed at rest.