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Fainting (syncope) in the dog

Temporary loss of consciousness in dogs can have several causes.

general description

The term syncope comes from the Greek and means syn (“with”) and kopten (“to interrupt”) and is the medical term for fainting. Syncope is a temporary loss of consciousness and muscle tension is released. This is caused by insufficient blood flow and insufficient oxygen saturation in the cerebral vessels of the brain stem. The brainstem is responsible, among other things, for maintaining breathing and circulation. Other causes of loss of consciousness, such as epileptic seizures, should be differentiated from true syncope.

In principle, there are four major causes for syncope:

1. Structural heart or lung diseases

2. Cardiac arrhythmias

3. Acute temporary oxygen deficiency

4. Reflex-Mediated Syncope

Structural heart or lung diseases are diseases that affect the heart muscle tissue or lung tissue and these are also morphologically changed (in terms of its shape). This includes congenital heart diseases, pericardial effusion with cardiac tamponade or pulmonary hypertension due to various causes. In cardiac arrhythmias, the generation and conduction of excitation in the heart muscle is abnormal. An acute temporary oxygen deficiency in dogs can result, for example, from obstruction of the upper respiratory tract or paralysis of the larynx (laryngeal paralysis). The reflex-mediated syncope is caused by a reflex that dilates the blood vessels and / or decreases the heart rate.


How do I distinguish syncope from other disorders of consciousness?

It is usually very difficult to distinguish syncope from another disease with loss of consciousness. It is important to differentiate between syncope and epileptiform seizure (epilepsy / seizure). Above all, the behavior before, during and after the episode is decisive here. Syncope usually follows a triggering event such as exertion, excitement or cough. The animal's muscle tone is usually flaccid during syncope and no urine or feces are passed. After syncope, the animals show normal behavior.

In cases where the syncope or seizure has occurred more frequently, it may be helpful to make a video of the seizure. Occasionally it is also difficult to distinguish conscious weakness from unconsciousness of the animal. Can the animal be called up or addressed? If one is not sure, other differential diagnoses for the symptom weakness can also be considered. The symptoms of weakness can be metabolic-related or, for example, caused by a neuromuscular disease. In contrast to weakness, syncope is episodic and the animal appears completely normal again after syncope even without therapy. Episodic weakness can also occur with hypoglycaemia due to the administration of insulin or due to an insulin-producing tumor.


The clinical examination of a patient with syncope is important to evaluate the cardiovascular condition, as this can give an indication of a heart disease.

A blood laboratory can diagnose other possible causes such as weakness due to hypoglycaemia (low sugar concentration in the blood) or anemia (anemia). Electrolyte disorders such as hyperkalaemia (increased potassium levels in the blood) can explain an abnormal heart rhythm.

After these examinations, an electrocardiogram (EKG) is recommended in a patient with a preliminary report of a syncope. This should be recorded for at least one minute. Since the most common cause of syncope in dogs is a cardiac arrhythmia and arrhythmias can also occur sporadically, it is possible to record an ECG over 24 hours. A “Holter EKG” is used for this. This device can be fixed to the animal for 24 hours with a chest bandage and then analyzed. Further detailed examinations of the heart such as lung x-rays and echocardiography with Doppler are necessary to investigate functional and structural heart diseases


Treatment depends on the underlying syncope disease. If cardiac arrhythmias are present, antiarrhythmic drugs and / or implantation of a pacemaker are necessary, depending on the type of arrhythmia. In the case of situational syncope, such as coughing, the underlying cause must be treated.


The prognosis also depends on the underlying cause of the syncope. In general, cardiac causes have a more cautious prognosis than, for example, cough-related syncope.

When should I contact the vet?

With any kind of syncope.

© Mrs. Dr. Alexandra Rose, Graduate ACVIM, AniCura Animal Clinic Hollabrunn, October 2016