Saddle Thrombus (Aortic Thrombosis) in Cats

The aorta is the largest blood vessel carrying blood from the heart to the rest of the body. In cats, the area where the aorta splits to supply blood to the hind legs is referred to as the saddle. When a large blood clot lodges in the saddle, it can partially or fully obstruct blood flow to the rear legs, depriving the limbs of oxygen. When this occurs it is referred to as a saddle thrombus or Feline Aortic ThromboEmbolism (FATE). FATE usually goes undetected until oxygen deprivation in the hind legs has already caused severe symptoms, including paralysis and sudden death.

The severity of FATE depends on whether the clot is blocking the blood flow entirely or partially, how quickly care is started, the body temperature of the cat upon hospitalization, and individual details of the specific case.

The prognosis is poor. The condition is often immediately fatal or leads to euthanasia. In cases that are not rapidly fatal, ongoing treatment is necessary and life expectancy is short.

Cats with the level of pain associated with FATE typically stop eating. In these cases, there is the risk of hepatic lipidosis (fatty liver syndrome) which can be fatal. Other symptoms vary depending on the underlying cause of FATE.

In cases where the blood clot is only partially blocking blood flow, especially when the cat is treated promptly, the condition is less severe. However, once the clot is removed, waste products that have built up in the body during the crisis are released into the bloodstream all at once, which is potentially fatal.

In cases where the blood clot is entirely blocking blood flow, especially when care is delayed and the tissues in the hindquarters begin to deteriorate, the condition is usually fatal.

Feline Aortic Thromboembolism (FATE) is a rare, sudden, and very painful life-threatening condition that occurs in cats of all ages and breeds. Some breeds are particularly susceptible to FATE including:

• Maine Coon
• Ragdoll
• Norwegian Forest
• Sphynx
• Abyssinian
• Birmans

Older cats and male cats also are at a greater risk of FATE.

Cats with heart disease (particularly hypertrophic cardiomyopathy) are at the greatest risk of FATE. Cats with lung cancer, bacterial endocarditis, and sepsis are also at risk.

In the majority of cases, the underlying cause of FATE is heart disease. Less often, the cause is cancer, bacterial endocarditis, sepsis, or an unknown cause. In many cases, the underlying condition has often gone unnoticed and FATE is the first indication that there is a problem. Any condition associated with increased risk of blood clotting creates a risk of saddle thrombus.

Once a blood clot has formed, the clot travels through the aorta to the saddle, the place where the aorta divides into smaller vessels that provide blood to the hind limbs of the cat. The clot lodges in these structures, either fully or partially cutting off the blood supply to one or both of the back legs. The back legs become weak or paralyzed, and the tissue is deprived of oxygen.

Diagnosis of FATE is typically based on physical examination. A definitive diagnosis is not necessary, as treatment must be started immediately.

In some cases, or during treatment, other diagnostics may be needed, including:

• Bloodwork
• Urinalysis
• Blood clotting testing
• Diagnostic imaging
• Echocardiogram
• Blood pressure measurement

A curative treatment for FATE has not yet been developed. Removing or dissolving the clot either with anticoagulant medications or surgical intervention has not been determined to change the outcome of FATE, although the treatments do not do any harm and may be attempted.

Treatment focuses on supportive care and monitoring for complications. Treatments include:

• Pain medication
• Encouraging food intake
• Supplementing oxygen
• Assisting with urination and defecation
• Maintaining electrolyte balance
• Providing IV fluids

In cases where the cat survives FATE, the risk of repeated episodes is high. Treatment for the underlying cause as well as ongoing anticoagulant therapy is often necessary for the rest of life.

The prognosis for cats with FATE is poor to grave. In many cases, FATE itself, the aftermath of the crisis, or the underlying cause is fatal. In other cases, humane euthanasia is the only option.

In rare cases, cats survive FATE. After recovery, they typically require lifelong medical management of the underlying condition, typically heart disease. Cats who survive FATE have a significantly reduced life expectancy.

There are no proven preventative measures for FATE. In some cases, cats who are known to have heart disease or lung cancer benefit from anticoagulant therapy, which reduces the risk of blood clots. Regular echocardiograms of at-risk breeds to diagnose heart disease early is recommended.

FATE is rare.

• Nursing care
• Clot removal
• Euthanasia