Fainting in Dogs

Fainting or syncope is defined as loss of consciousness accompanied by loss of postural tone for a short time because of a temporarily insufficient supply of oxygen or decreased delivery of essential nutrients (e.g. glucose) to the brain. During a fainting episode, a dog will collapse and become limp. The most susceptible breeds are Boxer, Doberman and Great Dane. This syndrome is often associated with cardiac disease and identifying the underlying cause is crucial. 

 Fainting, also called syncope, is a loss of consciousness that is typically due to a lack of normal blood flow to the brain. Fainting in dogs is typically attributed to one of two main problems: neurologic (e.g. to do with the brain or spinal cord) or cardiac (e.g. heart arrhythmias, heart failure etc.).

• Flacid and sudden collapse
• Usually there is no urination or defecation during the episode
• Dog is unresponsive during the episode
• Abrupt and complete recovery
• Pale mucus membranes

Most syncopal events in dogs are due to a temporary reduction in brain blood flow. A decrease in cardiac output or less vascular resistance reduces arterial pressure and may result in reduction of cerebral blood flow. Cardiac diseases are related to two-thirds of the syncope episodes seen in dogs and cats.

Neurological

• Abnormal brain activity

Cardiac

• Abnormal heart rhythms
• Atrioventricular block
• Ventricular tachycardia
• Ventricular fibrillation
• Heart tumors

Others

• Low concentration of glucose, calcium, sodium in blood
• Use of diuretics and vasodilator drugs

Characteristics

• Flaccid and sudden collapse
• Usually there is no urination or defecation during the episode
• Dog is unresponsive during the episode
• Abrupt and complete recovery
• Pale mucus membranes

It is important to provide the veterinarian with as much information about the fainting episode as possible, this will help him/her to distinguish seizures from syncope and to identify the underlying cause. Since most fainting episodes occur in the presence of the dog owner and not of the veterinarian it is important to pay attention to how the dog collapses. Taking a short video, if possible, and showing it to the veterinarian, can be a great way of helping your pet.

Fainting is not a disease but a syndrome or a symptom; therefore, it is very important to identify what is causing the episodes in order to adequately treat the patient. Diagnosis starts with a thorough physical examination and gathering of the patient’s clinical history. Owners should inform the veterinarian about any drugs that the patient is taking.

The veterinarian will start with a thorough physical examination to detect any abnormalities, especially in heart function. Meticulous auscultation and physical exam will allow detection of cardiac disease signs such as a murmur, arrhythmia, pulse deficit or signs of reduced cardiac output such as pale mucous membranes. If there is evidence of cardiovascular disease the following diagnostic test may be needed:

• An electrocardiogram (ECG) to assess resting heart rate and rhythm
• Echocardiography to assess cardiac dimensions and function
• Full haematology and serum biochemistry to assess whether there is evidence of reduced organ perfusion and/or other systemic disease
• Thoracic radiographs to assess whether there are signs of congestive heart failure

Syncope episodes are temporary and reversible; once the cause of syncope has been identified the veterinarian will recommend an appropriate treatment. For example, if an abnormally low heart rate is detected, the dog may need a permanent pacemaker to stimulate heart function. If the episodes were caused by a given medication, treatment withdrawal will probably suffice.

After a fainting episode it is important to detect the cause and to prevent recurrent episodes. It is important to be vigilant of any future episodes and, in such cases, to contact your veterinarian immediately. If cardiac insufficiency was the cause, strenuous exercise should be avoided and the veterinarian’s instructions should be followed rigorously. In these cases, patients tend to have a poor prognosis. Dogs with fainting history will probably need various medical check ups during the year.