Syncope

Syncope refers to a sudden, short-term loss of consciousness in dogs, caused by an interruption of blood flow to the brain. The dog suddenly faints and usually regains consciousness within seconds or minutes. Syncope is often an indication of diseases of the cardiovascular system or the nervous system and requires veterinary investigation.

What is syncope?

A syncope occurs when the brain temporarily does not receive enough oxygen, leading to a sudden loss of consciousness. The lack of oxygen arises from reduced or impaired blood flow to the brain, usually due to a problem in the cardiovascular system. As soon as blood flow is restored, the dog typically regains consciousness quickly.

Syncope differs from seizures or epilepsy in that it is caused by inadequate blood flow to the brain, whereas seizures are based on abnormal electrical activity in the brain. During a syncope, muscle spasms or uncontrolled twitching, which are typical of seizures, generally do not occur.

Causes of Syncope in Dogs

Syncope in dogs can be divided into two main categories: cardiovascular diseases and non-cardiac causes.

Cardiovascular Diseases

• Arrhythmias: Irregularities in the heartbeat, such as bradycardia (too slow a heartbeat) or tachycardia (too fast a heartbeat), can impair the heart’s ability to pump sufficient blood and thus oxygen to the brain.
• Valvular heart disease: In mitral insufficiency or other valvular heart diseases, the heart does not function efficiently, which can lead to reduced blood flow to the brain.
• Cardiomyopathy: Dilated cardiomyopathy is a condition in which the heart muscle is weak and enlarged, and the heart is no longer able to pump blood effectively. This condition can lead to repeated episodes of syncope.
• Pulmonary hypertension: Elevated blood pressure in the pulmonary arteries can impair the heart’s ability to pump blood, which can lead to syncope.
• Cardiac tumours: Tumours on the heart or near large blood vessels can obstruct blood flow and trigger syncope.

Non-Cardiac Causes

• Vasovagal response: A vasovagal syncope occurs when the vagus nerve is excessively stimulated, leading to a sudden drop in heart rate and blood pressure. This can occur, for example, under severe stress, pain, or in response to certain stimuli such as violent coughing or sudden movement.
• Hypoglycaemia (low blood sugar): A significantly lowered blood sugar level can impair the brain’s energy supply and cause syncope. Hypoglycaemia frequently occurs in small breeds, puppies, or dogs with diabetes.
• Anaemia: A severe deficiency of red blood cells can impair the brain’s oxygen supply and lead to syncope.
• Heat exhaustion or heatstroke: Overheating can overload the dog’s circulation and lead to circulatory failure, which can trigger syncope.
• Pulmonary embolism: A blood clot in the lung vessels can obstruct blood flow and lead to syncope, as the brain is not adequately supplied with oxygen.

Symptoms of Syncope in Dogs

The symptoms of syncope are sudden and can appear as follows:

• Sudden loss of consciousness: The dog suddenly collapses and remains unconscious for a few seconds to minutes.
• Flaccid body: During syncope, the dog’s body is flaccid, and there are no signs of muscle spasms, as would be the case with a seizure.
• Rapid recovery: After a syncope, the dog typically wakes up quickly and returns to normal behaviour, without confusion or prolonged symptoms.
• Pale mucous membranes: In syncope caused by cardiovascular issues, the dog’s mucous membranes (gums) may appear pale, indicating reduced blood flow.
• Weakness or dizziness: Before or after a syncope, the dog may show signs of weakness or dizziness by staggering or walking unsteadily.

Diagnosis of Syncope

Diagnosing syncope requires a thorough examination by the vet, as the underlying cause must be identified. The following diagnostic steps are commonly performed:

• Medical history and symptom description: The vet will ask for a detailed description of the incident, including the circumstances and symptoms that led to the syncope. This helps to narrow down possible triggers.
• Physical examination: A thorough physical examination, including listening to the heart and lungs, can provide clues about heart murmurs, irregular heartbeats, or breathing problems.
• Blood tests: Blood tests can be carried out to detect signs of anaemia, infections, hypoglycaemia, or other metabolic problems.
• Electrocardiogram (ECG): An ECG measures the electrical activity of the heart and helps to identify arrhythmias that could cause syncope.
• Echocardiography (heart ultrasound): An ultrasound examination of the heart can reveal structural problems such as cardiomyopathy, valvular heart disease, or tumours.
• X-ray and CT: Imaging techniques can be used to examine the lungs and heart more closely, particularly if pulmonary hypertension or pulmonary embolisms are suspected.

Treatment of Syncope in Dogs

The treatment of syncope depends on the underlying cause. In most cases, treatment aims to resolve or control the underlying problem:

• Arrhythmias: If the syncope is caused by an arrhythmia, the vet may prescribe medication to stabilise the heartbeat. In some cases, a pacemaker may also be required.
• Valvular heart disease: For valvular heart disease, medications such as ACE inhibitors, diuretics or blood pressure-lowering drugs may be prescribed to support heart function and alleviate symptoms.
• Hypoglycaemia: In dogs with hypoglycaemia, treatment involves raising the blood sugar level by feeding more frequent, smaller meals or administering glucose preparations.
• Vasovagal syncope: In cases of vasovagal syncope, it is recommended to avoid triggers that cause overstimulation of the vagus nerve. If necessary, medication may be prescribed to stabilise blood pressure or heart rate.
• Anaemia: If anaemia is present, treatment will aim to address the cause of the anaemia, whether through iron supplements, blood transfusions or treating underlying conditions such as parasites or blood loss.
• Heat exhaustion: In cases of heat exhaustion, the dog must be cooled immediately, and fluid therapy may be necessary to stabilise circulation.

Preventing Syncope in Dogs

Preventing syncope generally requires controlling the underlying conditions:

• Regular veterinary examinations: Regular health checks help to identify and treat potential problems at an early stage.
• Monitoring the cardiovascular system: Dogs with heart problems should be monitored regularly, and recommended medications should be administered consistently.
• Balanced nutrition: A balanced diet helps to avoid blood sugar issues or nutrient deficiencies that could lead to syncope.
• Appropriate exercise: Too much or too little exercise can strain the cardiovascular system. A balance in the dog’s activity is particularly important for older dogs or dogs with known heart problems.