Electrocardiography in horses – part 1: how to make a good recording

Upon auscultation, cardiac dysrhythmias can be suspected, but electrocardiography is the ultimate diagnostic tool. Electrocardiogram (ECG) recording used to be reserved to specialized centers, but nowadays relatively cheap and small recorders are available to the practitioner in the field. ECGs can therefore be recorded ambulatory and during prolonged periods at rest or even during exercise. The know-how of a good quality recording is mandatory for a correct diagnosis. The basic equipment consists of electrodes, a recorder and a way to display the trace. Self-adhesive electrodes should be used, and positioned along the mean electrical axis of the heart. Small recording devices offer the advantage of allowing recordings during exercise. As the electrical impulse spreads through the heart, the ECG trace shows successively a P wave, a QRS complex and a T wave. T-a waves are not always clearly visible in horses. The positioning of the electrodes may differ for ambulatory, exercise or long-term resting recordings. However, as long as the electrodes are positioned along the mean electrical axis, their exact position is not of crucial importance.