Feline Aortic Thromboembolism

FATE
(Feline Aortic Thromboembolism)
(also called “Saddle Thrombus”)

One tends to feel apprehensive about a condition with the acronym: FATE. Rightly so. FATE (Feline Aortic Thromboembolism) is a serious and painful condition with serious implications. It comes on suddenly and appears to paralyze the cat, causing one or both rear legs to become useless and even noticeably cold. The cat will hyperventilate and cry out with extreme pain. Despite the extreme presentation, the cat may be able to recover from the episode but it is important to understand how this came to be in order to make decisions.

A thrombus is a large blood clot.
An embolism is a small blood clot lodged in an inopportune location.

WHAT IS A “SADDLE THROMBUS?”

saddle location

(original graphic by marvistavet.com)

The aorta is the largest artery in the body. It stems from the heart itself, where it arches back and runs down the length of the back, ultimately splitting into the arteries supplying the back legs. The split where the aorta becomes the left and right iliac arteries is called the “saddle.”

A “saddle thrombus” is a blood clot that breaks off from a larger blood clot in the heart, travels down the aorta and lodges at the “saddle.” Not only is the blood supply to one or both rear legs cut off but a metabolic cascade results leading to the release of assorted inflammatory mediators (especially serotonin). The muscles of the rear legs become hard, the foot pads become bluish in color, and the condition is extremely painful. The inflammatory mediators readily lead to circulatory shock.

72% of cats with a saddle thrombus have both rear legs affected.

WHERE THE SADDLE THROMBUS CAME FROM

The saddle thrombus comes from a larger clot in the left atrium of the heart. This obviously begs the question as to why there would be a large blood clot in a cat’s heart. In fact, 89% of cats with a saddle thrombus have heart disease. Heart disease leads to turbulent blood flow which encourages the formation of clots.

saddle thrombus

Arrow shows a large clot in the left atrium of a cat with a saddle thrombus.
Image courtesy of Veterinary Specialists of the Valley and the North Hollywood Animal Care Center

Not every cat with heart disease will form an abnormal clot, in fact most will not; but there is presently no clear way to predict which cats will form these clots and which ones will not. In cats with hypertrophic cardiomyopathy, the most common form of feline heart disease, the size of the left atrium is one factor that is considered. The presence of “smoke” in the atrium during echocardiography is another factor. (“Smoke” being whispy material seen in the circulating blood). Both these factors are considered controversial.

To see a video of an echocardiographic imaging of a person who presented with recurrent postural syncope, looking much like it would in a cat, click here. The clot in her left atrium looks like a round ball moving around.

In 76% of cats with saddle thrombus, the FATE episode was the very first sign of heart disease.

WILL THE CAT REGAIN NORMAL USE OF HIS LEGS?

The cat with a saddle thrombus is very likely in shock. There is a question of survival from the shock as well as a question of whether or not actual heart failure is present. Obviously, heart failure is potentially life threatening as is circulatory shock. Assuming everything goes well, that heart failure and/or shock are either not present or are readily controlled, one still ends up with a cat with heart disease and big blood clot that could spit off another embolism at any time. Because of the potential for repeat episodes and need for long term treatment of heart disease, not to mention the seriousness of the cat’s predicament, 25% of pet owners elect euthanasia without attempting treatment.

Of the remaining cats who get treatment, the following statistics have been published:

  • 50% of treated cats survived to be discharged from the hospital.
     
  • The median hospitalization time was 2 days.
     
  • The median survival time of cats that did not present in heart failure was 223 days.
     
  • The median survival time of cats that did present in heart failure was 77 days.
     
  • Of cats who used aspirin as their main clot prevention drug after discharge, 25% of them had at least one more FATE episode at some point (usually in 6-12 months)
     
  • Occasionally a cat would lose tissue from loss of blood supply or even require limb amputation but these turn out to be exceptions to the rule. Most cats recover normal limb function after their FATE episode.

Expect limb function to begin to improve after 2-3 weeks. The cat may require a great deal of nursing care until he/she is able to walk.

For information on care of the paralyzed pet click here.

WHAT TO EXPECT AT THE VETERINARY HOSPITAL

Once the doctor determines that the cat most likely has a saddle thrombus, further diagnostics will be needed as well as treatment. The cat will need medication for the pain and medication to reduce the ability to clot. Usually treatment is started with injections and changed to oral after the cat is eating. The pain of the condition generally is subsiding after the first 24 hours and the muscles become softer after 2-3 days.

Cats with a rectal temperature of 98.9º or higher have a 50% or higher chance of survival.
Body temperature turns out to be a very important parameter for prognosis.

Fluid therapy is tricky as the heart will be sensitive to being overloaded but the circulatory shock will need intravenous fluids. There is a bit of a “tightrope” to walk. This is one of the pitfalls in therapy for this condition.

Expect radiographs of the chest to be needed to help determine if heart failure is present. It can be difficult to tell if the cat is in heart failure. Almost every cat with a saddle thrombus will appear to pant or at least will breathe rapidly simply from the pain of the condition so this normally useful parameter is not helpful. Radiographs will help look for fluid in or around the lungs that would indicate that heart failure therapy is needed in addition to treatment for the saddle thrombus. Further, 6% of cats with a saddle thrombus do not have heart disease and have cancer instead. In most of these cancer cases a lung tumor will be present; chest radiographs serve to identify this type of cancer.

Blood tests will also be needed to assess the cat’s general health and ability to tolerate medication. It is common to find evidence of liver cell death on basic blood tests (a common event after circulatory shock). Kidney function is also often compromised by the shock and must be assessed. Elevated potassium levels tend to bode poorly for survival.

Echocardiography is the cornerstone diagnostic of feline heart disease and should be done as soon as the patient is stable enough for it. This will allow for classification of the cat’s heart disease and determine what long term medicines are needed.

At the present time there is controversy over what medications are best used to prevent future episodes. Obviously, abnormal bleeding tendency is as dangerous as abnormal clotting tendency. Aspirin is readily available, inexpensive, and is probably the most commonly recommended medication for this situation. It is important to know how to dose it as cats metabolize aspirin extremely slowly; be sure to follow your veterinarian’s recommendations. Clopidrogrel (Plavix®) is becoming more popular for feline use. Low Molecular Weight Heparin injections are another choice but it is more difficult to balance bleeding and clotting tendencies. The jury is still out as to which treatments work best or if simply doing nothing is a viable option.

Page posted: 2/29/2012
Page last updated: 9/1/2014