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Telling the difference between seizures and fainting in pets

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One of the difficulties of my profession is that my patients cannot speak to me. I (Perry Jameson) totally depend on Mom and Dad to describe symptoms.

For certain problems, parents can get so worried and emotional that it clouds their description. One of the more difficult problems to differentiate is the difference between syncope and a seizure.

Syncope is basically a fainting spell and indicates disruption of oxygen supply to the brain. It usually results from a cardiovascular problem that interrupts the delivery of enough oxygenated blood to maintain brain function.

Seizures are caused by either primary brain disease or metabolic disease, which alters brain function.

Primary brain diseases, which may cause seizures, are tumors, inflammation, strokes and trauma. Metabolic causes are problems such as low blood sugar, low blood calcium and liver failure.

A classic syncopal episode is similar to when you or I faint. Usually, people are completely normal prior to the event; they collapse, lose consciousness and are limp. In pets, they are often associated with sudden activity or excitement. Most dogs and cats recover quickly and return to normal within minutes, if not right away.

During a classic seizure, most pets will fall onto their sides, have increased muscle tone and rhythmic muscle contractions, lose consciousness and may urinate and defecate. Often there will be a pre-seizure change in behavior called an aura. Most parents learn to recognize this as an indication a seizure is imminent. Many seizures also are followed by a period of disorientation that may last for minutes, hours or even days.

The difficulty occurs when either the patient does not have a classical seizure or syncopal episode. Also, parents may not observe enough detail to make it easy to differentiate. I was reminded of the difficulty making this distinction last week by Sandy.

She is an 11-year-old Chihuahua whom I had seen one month earlier. I had diagnosed a condition called Cushing’s disease, which is where the adrenal glands are producing too much of their normal hormones. She had the classic symptoms of excessive thirst, increased urination, crazy appetite and hair loss. We started her on therapy and she responded well.

Until Mom called me two weeks later to report an “episode.” While drinking water, she had vocalized, fallen on her side and was limp. Mom was so shaken she could not tell me whether it lasted 30 seconds or 10 minutes. She could not tell me whether Sandy had any muscle activity during the episode. She thought Sandy was “off” for about an hour following the event.

Looking at her record, I had noted a heart murmur the last time we had evaluated her and figured she must have had a syncopal spell related to this.

Many small breed dogs will develop leaky heart valves as they age, and fainting can be a symptom. Pulmonary hypertension (high blood pressure in the lungs but not the rest of the body) is the common cause as it decreases the amount of blood the heart can pump forward, especially following a sudden increase in demand.

The next day, I performed an echo cardiogram but could not document disease significant enough to cause syncope. Blood tests also ruled out metabolic causes of seizures. Mom was worried it was the medications causing a seizure, and even though I had never noted this side effect before, I agreed we should stop as we investigated.

Stopping the medications did not help as she continued to have these spells. The other heart-related cause would be an arrhythmia where the heart beats too fast, erratically or stops altogether, temporarily. Even though not common in this breed, I hooked up a monitor to record her ECG over 24 hours. Once submitted, it takes one to three days to come back.

In the back of my mind, I still suspected pulmonary hypertension even though I could not document any on the echo cardiogram a second time. I started her on a low dose of sildenafil to treat this anyway while we waited for the results. I even had our neurologist look at Sandy to see if she thought it was an atypical seizure and should we do a trial of anti-seizure medication.

She said no to both seizures and medication.

Finally, the results returned and revealed Sandy was having prolonged pauses of her heart rate called sick sinus syndrome. This is where the heart’s own built-in pacemaker temporarily stops for several seconds so the heart does not beat. Since blood is not being pumped forward, the brain does not get oxygen and she passes out.

We will try medications to see if they help, but in the long term, most dogs require the placement of a pace maker. This will pace the heart during those pauses preventing her from fainting.

Syncope and seizure can be tough for us to figure out. Animal parents can help by being as detailed as possible in the description of the event and even better by making a recording of the event with a cellphone video.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to

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