Aortic Thromboembolism

Published Dec. 21, 2011

Last week I saw a case of aortic thromboembolism in a cat. It ended in euthanasia, and in almost every other way as well, the patient was pretty typical when it comes to this dreaded disease.

Gimli had a two week history of ADR — "ain’t doin’ right," for the uninitiated. His owners could tell he wasn’t feeling well, but when they took him in to their veterinarian, he couldn’t find anything wrong on a basic work up.

Gimli’s owners took him home for monitoring. He continued to be not quite 100%, but was comfortable, eating, etc. So they weren’t too concerned, until WHAMMO, all of a sudden he couldn’t use one of his hind legs and he was howling in agony.

They rushed him back to the vet’s office, where, based on the results of his physical exam — paralysis of a hind leg, a foot that was cool to the touch, poor pulse quality in that leg and excruciating pain — he was diagnosed with a saddle thrombus, otherwise known as aortic thromboembolism or arterial thromboembolic disease.

This disorder most commonly affects cats with heart disease, typically hypertrophic cardiomyopathy, although the heart may appear to be functioning normally on a basic physical exam, as was true in Gimli’s case. Clots begin to form because blood is not circulating normally through the heart chambers. The clots can then break off (at which point they’re called emboli) and travel through the cat’s arteries. A common place for them to lodge is where the aorta divides into two vessels, one supplying blood to each of the hind legs. Depending on the size and exact location of the thrombus (what we call a blood clot that is lodged somewhere it shouldn’t be), a cat may lose some or all of the blood supply to the limb and function of one or both hind legs.

Cats with a saddle thrombus are in excruciating pain. I had one case when I practiced in rural Wyoming where a cat’s owners had to drive over an hour to my clinic with their cat screaming in the back seat of the car. I was nauseous while I waited for them, knowing what they were all going through.

Some cats can recover from aortic thromboembolism, potentially regaining partial or full use of their hind legs. Unfortunately, their long term prognosis is always guarded. A full work-up, including chest X-rays, cardiac ultrasound, and blood pressure testing, is necessary to diagnose and effectively treat the heart disease that usually caused the clot to form in the first place. Therapy includes aggressive pain relief, supportive care (e.g., intravenous fluid therapy), medications to help dissolve existing clots and prevent new ones from forming, and addressing any underlying conditions. Cats that have had one episode of aortic thromboembolism are always at high risk for another.

It was probably this last point that led both Gimli’s and my Wyoming cat’s owners to eventually elect euthanasia. After watching their cats suffer so terribly, I could hardly blame them for choosing the only course that would guarantee that their cats would not have to go through such an ordeal again.