Syncope (Fainting) in Dogs

Syncope, or fainting, in dogs can be a very scary thing to witness, especially when it happens unexpectedly. Even as a veterinarian, I must admit that I felt myself starting to panic a bit when I saw my first dog fainting in the veterinary hospital!

There are many potential causes of syncope in dogs, and these causes can range from severe and life-threatening to relatively insignificant. 

Before your mind jumps to a worst-case scenario, it’s important to work with your veterinarian to determine the cause of your dog’s syncopal episodes. Fortunately, with proper treatments, many dogs with syncope go on to lead normal, healthy lives.

What is Syncope in Dogs?

Syncope is the term used to describe fainting in dogs. It is defined as a temporary loss of consciousness that occurs when the brain is not receiving enough oxygen. Just like humans, dogs can experience episodes of syncope or fainting. In most cases, this is due to a temporary decrease in blood flow to the brain.

Syncope in dogs is relatively uncommon. Senior dog syncope is more common than syncope in puppies and younger dogs. Syncope is also seen more frequently in dogs with heart disease.

Causes of Syncope in Dogs

Anything that disrupts blood flow to the brain can lead to syncope. Heart disease is the most significant (and potentially risky) cause of syncope. However, any disruption to your dog’s circulation can potentially cause syncope.  

Stress and fear are relatively common causes of syncope in dogs. In fact, some dogs faint nearly every time that they are taken to the veterinary hospital or grooming salon! Nail trims can trigger syncope in dogs. Episodes of syncope in dogs may also happen after coughing or vomiting.   

Medications that affect the circulatory system and decrease blood pressure can also lead to syncope. These medications include ACE inhibitors, amlodipine, hydralazine, atenolol, and nitrates. Phenothiazine sedatives (such as acepromazine) and diuretics can also increase a dog’s risk of syncope.  

Finally, a variety of heart diseases can cause syncope. Abnormalities of the heart valves and cardiac muscle can interfere with the heart’s ability to move blood throughout the body efficiently. Cardiac arrhythmias can cause periods of decreased circulation to the brain, resulting in syncope. Less common conditions, such as blood clots within the heart and blood vessels, fluid surrounding the heart, and cardiac tumors, can also interfere with a dog’s circulation and result in syncope.

Symptoms of Fainting in Dogs

While syncope may seem like a relatively straightforward condition to recognize, that isn’t always the case. It can be especially challenging to differentiate syncope from a seizure.

In general, the signs of a fainting dog are:

• Sudden loss of consciousness: Your dog may abruptly go from running laps around your backyard to taking a few weak or wobbly steps and suddenly collapsing on their side, unconscious.

• Loss of bladder and/or bowel control: Many (not all) dogs will urinate or defecate on themselves during a syncopal episode.

• Lack of movement: The legs may be either stiff or relaxed, but your dog will generally be relatively still during the period of unconsciousness.

• Rapid recovery: Within a period of seconds to minutes, your dog will recover and carry on with their activities as if nothing happened.

A dog with a seizure, in contrast, will often show several signs that can help distinguish seizures from syncope. Seizures tend to come on relatively gradually, with a dog experiencing several minutes of unusual behavior prior to entering a seizure. During a seizure, dogs typically will “paddle” with their legs, swinging them widely in a rhythmic manner. Finally, when a dog recovers from a seizure, their recovery is typically slow and gradual. They may act disoriented for several minutes to hours after a seizure, in contrast to a dog that “bounces back” almost immediately after fainting.

Other clinical signs will depend on the underlying cause of your dog’s syncope. Dogs with excitement-induced syncope, for example, often show signs of extreme stress or agitation under certain circumstances. Low blood pressure caused by medication may be associated with generalized weakness or lethargy. Dogs with heart disease may exhibit signs of heart failure, including coughing, weakness, lethargy, and weight loss.

Diagnosing Causes of Syncope in Dogs

Your veterinarian will first attempt to determine whether your dog is experiencing syncope or seizures. They will likely ask you a number of questions about your dog’s episodes, including frequency, known triggers, and what happens during and after an episode. 

Taking a video of suspected syncopal episodes in dogs can help you and your veterinarian work together to determine whether your dog is experiencing seizures or syncope.

Your veterinarian will also perform a thorough physical exam. They will check your dog’s pulse and listen carefully to your dog’s heart and lungs. They will also palpate your dog’s abdomen, looking for any evidence of fluid or other abnormalities, and examine the rest of your dog’s body. In some cases, the physical exam can suggest a specific cause for your dog’s syncope.

Diagnostic testing will be guided by your veterinarian’s observations. Common tests for suspected syncope include:

• Complete blood cell count (CBC) and serum biochemistry profile
• Urinalysis
• Chest radiographs (X-rays)
• Electrocardiogram (ECG)
• Ultrasound of the heart
• Blood pressure measurement
• Holter monitor (24-hour ECG monitoring)

Your veterinarian may refer your dog to a veterinary cardiologist for a full cardiology workup.

How to Treat Syncope in Dogs

Effectively treating syncope requires targeting the underlying cause of your dog’s episodes.

In the case of a dog fainting when excited, your veterinarian may talk to you about avoiding triggers that tend to incite syncope in your dog. They may also recommend anti-anxiety medications to reduce your dog’s overall anxiety level and/or working with a veterinary behaviorist to desensitize your dog.

Medication-associated syncope is typically addressed through a change in medication dosing or medication types.

Syncope associated with heart disease often requires medications to promote circulation and address any arrhythmias that may be present. In most cases, your dog will remain on these medications for the rest of their life.

Cost to Treat Fainting in Dogs

Fortunately, most of these treatments are relatively inexpensive. While you may spend several hundred dollars diagnosing the cause of your dog’s syncope, ongoing treatment and monitoring is typically relatively affordable.

Home Remedies for Syncope in Dogs

There are no effective over-the-counter treatments or other home remedies that can be used to treat syncope in dogs. If your dog faints, you should first ensure that your dog has a heartbeat, then attempt to record the episode. If this is your dog’s first episode of syncope or if your dog does not begin to recover within a few seconds, seek veterinary care immediately.

How to Prevent Syncope in Dogs

Preventing fainting in dogs will depend upon the underlying cause.

If you have a dog that faints due to excitement, you may be able to prevent these episodes by avoiding known anxiety triggers.If your dog has heart disease or is on medications that may cause syncope, careful monitoring is the best way to prevent syncope. Any evidence of weakness or ataxia (loss of balance or clumsy walking) could indicate an increased risk of syncope. If your dog appears weak or wobbly, contact your veterinarian to determine whether additional treatments or a change in medication may be beneficial.