Syncope: Fainting in Dogs

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Syncope is when a dog loses consciousness for a short time. It happens when the brain doesn't get enough blood and, hence, oxygen.

What Causes Syncope?

Syncope in dogs occurs when the dog loses motor ability and consciousness for a few minutes. Several different things can cause it, including:

• Heart conditions that cause arrhythmias (abnormal heart rates), either too fast (tachycardia) or too slow (bradycardia). For instance, boxer cardiomyopathy, caused by an arrhythmia, is often associated with syncope.
• Sick sinus syndrome, in which the sinoatrial node in the heart (where the electrical impulse governing heart beats are triggered) doesn't work properly, can occur in cocker spaniels, mini Schnauzers, pugs, and dachshunds.
• A vasovagal event, which is triggered by over-excitement or stress that causes the sympathetic nervous system to increase the heart rate and blood pressure temporarily.
• Occasionally, a dog may suffer from situational syncope. That means the dog faints while doing a particular thing such as defecating, coughing, or swallowing.
• Pulling on the collar too hard and interfering with the carotid artery in the neck can cause it.
• Some medications that affect blood pressure may cause syncope.
• Syncope can occur because of low blood sugar, calcium, or sodium.
• Conditions that allow the blood to get too "thick," with a high red blood cell count, can cause fainting.

Diagnosis of Syncope in Dogs

When a dog is having fainting episodes, the veterinarian will take a thorough history from the owner. Sometimes, that can help narrow down the cause. For instance, the syncope may be situational if it always happens when the dog is defecating. It may be vasovagal if it seems excitement-triggered or related to heart disease if it's associated with exercise.

Then, the veterinarian will do a thorough physical exam to look for more clues. Blood work will reveal a low blood sugar or electrolyte level. A heartworm test may be done as well as x-rays or an echocardiogram to evaluate heart size, shape, and function. An ECG can evaluate heart rhythm.

Treatment of Syncope in Dogs

The treatment of syncope depends on the underlying cause. Medications for heart arrhythmias or other heart problems could be necessary. Dogs with sick sinus syndrome may require a pacemaker.

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