Cardiac disease in horses (i.e. atrial fibrillation)

Equine Cardioteam Ghent

The clinic has a specialised Equine CardioTeam GhentCardiac abnormalities such as murmurs or dysrhythmias (= irregular rhythm or arrhythmia) are common in horses. In case of poor performance or loss of performance, a cardiac check-up is advisable. Symptoms of cardiac disease will be more obvious in a sport horse than in a horse kept as a companion animal. Indications for a specialised cardiac examination (echocardiography and electrocardiography) include :

  • emergencies
  • poor performance or loss of performance
  • evaluation of a cardiac murmur
  • irregular heart rhythm (dysrhythmias)
  • swollen legs, ventral oedema, jugular pulsation, …
  • coughing, dyspnoea
  • neonatal foals with persistent cardiac murmurs or foals that are rapidly fatigue
  • in case of an important prepurchase examination


 If a murmur or dysrhythmia is detected by auscultation, a specialized examination is advisable to determine whether this is physiological or pathological. A physiological murmur or dysrhythmia carries no danger for the rider and allows normal use of the horse. A pathological murmur or dysrhythmia can sometimes be treated, for example in case of atrial fibrillation. In some cases, there can be a risk of collapse or sudden death of the horse and the horse is not safe to ride. The severity of a murmur is evaluated by echocardiography.

A Doppler or colour flow echocardiography shows the degree of valvular insufficiency. It is also necessary to assess the diameters and the function of the different cardiac chambers by using two-dimensional, M-mode, tissue Doppler and speckle tracking echocardiography. Horses with a murmur also undergo resting and exercise electrocardiography, as some valvular regurgitations are associated with dysrhythmias.

Evaluating the severity of a dysrhythmia requires electrocardiography at rest and during exercise. The most common dysrhythmia in horses is atrial fibrillation. Most horses with atrial fibrillation have no other cardiac abnormalities such as valvular regurgitation and are thus eligible for treatment. In some horses it is not advisable to ride a horse with atrial fibrillation as this dysrhythmia can cause extremely high cardiac frequencies during exercise. For example, race horses galloping at full speed have a maximal cardiac frequency of 250 beats per minute while horses with atrial fibrillation can develop heart rates of more than 350 beats per minute during stress or exercise. Often, atrial fibrillation is also associated with decreased performance. Treatment is possible in 90% of cases and can be performed either medically or using the more recently developed technique of transvenous electrical cardioversion(TVEC) under general anaesthesia. The success rate of the medical treatment is about 60-80% (with a relatively high risk of developing side effects). The success rate of transvenous electrical cardioversion is about 95% (with very few side effects). Once the cardiac rhythm has returned to the normal regular sinus rhythm, the horse can be ridden again at its previous level of performance.