Aortic Thromboembolism (Saddle Thrombosis) in Cats


What is saddle thrombosis?   What causes it?   What are the symptoms?   How is it diagnosed?  How is it treated?

Saddle thrombosis in cats

What is aortic thromboembolism?

Also known as saddle thrombosis, aortic thromboembolism (abbreviated to ATE or FATE)  is a life-threatening condition in which a blood clot (thrombus) forms in the heart and then all or part of it dislodges and travels down the abdominal aorta where it eventually becomes lodged at the junction of the  iliac arteries of the hind legs which.

Other less common locations the emboli may travel to include the arteries supplying the kidneys, lungs, gastrointestinal tract, forelegs, and brain. However, this article will focus on saddle thrombosis only which affects the rear legs, the term saddle thrombosis is due to the emboli lodging in the junction and draping down into the iliac veins, giving it the appearance of a saddle. Up to 1/3rd of cats with heart disease will develop a blocked artery due to thromboembolism.

The aorta is the largest artery in your cat’s body supplying oxygenated body to the organs. It originates in the left ventricle of the heart, travelling down the abdomen before splitting into the left and right iliac arteries as well as the caudal vein which supplies blood to the back legs and tail. The junction where the aorta splits is known as the aortic bifurcation.  A thrombus is a blood clot which is made up of platelets and fibrin and an embolus is something which travels through a blood vessel until the vessel is too small to let it continue.

saddle thrombosis in cats

What causes aortic thromboembolism?

This condition is devastating, as there is no warning. The majority of cases are due to an underlying heart condition (most often hypertrophic cardiomyopathy) which in many cases many cat owners and veterinarians are unaware of until aortic thromboembolism occurs. Hyperthyroidism and neoplasia may also cause aortic thromboembolism.

Almost all blood clots form in the left atrium of the heart which may be due to a thickening of the atrium wall can cause blood to pool, leading to the formation of these clots, or increased turbulence. At any time a clot formed in the heart can dislodge and travel along the aorta before becoming wedged in the narrower iliac arteries. Once blocked, blood can no longer pass into the iliac arteries. This means tissues in the legs are no longer receiving am adequate (or any) oxygen (known as ischemia), leading to a cascade of biochemical reactions within the cells leading to toxic by-products which ultimately cause cell death. Unfortunately, it doesn’t end there, once the blockage is cleared, all the toxic by-products which have built up are released back into the circulatory system. This is known as reperfusion injury.

Cats of any age or breed can be affected, with a mean age of 8-10 years. The condition is seen slightly more in male cats, probably because of their higher incidence of hypertrophic cardiomyopathy.

What are the symptoms of aortic thromboembolism in cats?

There are five P’s associated with aortic thromboembolism:

  • Pain. Affected cats are in extreme pain with distressed howling/vocalisation and anxiety common symptoms.
  • Paralysis (or weakness) of the hind limbs.
  • Pulselessness – There may be a faint pulse in some cats if there isn’t a complete blockage).
  • Pallor.
  • Poikilothermic – The limbs are cold to the touch.

Other findings may include:

  • Vomiting (prior to ATE)
  • Gait abnormalities
  • Restlessness initially, presumably due to pins and needles type feelings in the leg(s) as blood supply diminishes.
  • Tachypnea (rapid/shallow breathing) with open-mouthed breathing which may be related to pain or heart disease.
  • The paw pads may appear cyanotic (blue).
  • Hard and painful muscles.

Aortic thromboembolism is a medical emergency and veterinary attention must be sought immediately.

How is saddle thrombosis diagnosed?

Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. During the examination, he will check for a pulse in the rear limbs which may be faint or may not be there at all. The leg(s) and feet will feel cold to the touch and may be blue-tinged (more apparent in cats with light coloured paw pads).

  • Abnormal cardiac sounds are a common finding during auscultation due to underlying heart conditions.
  • Your veterinarian may obtain a blood sample from the affected limbs to check the glucose level, which should be reduced in the limbs of cats with aortic thromboembolism compared to normal values from the biochemical profile (see below).
  • Routine tests including complete blood count and biochemical profile will be necessary. These may reveal hyperglycemia (increased blood glucose levels) due to stress, elevated muscle enzymes creatine kinase. Hyperkalemia (high blood potassium) and metabolic acidosis may be seen if reperfusion has occurred.
  • Doppler ultrasound may reveal blockage and/or lack of blood flow.
  • Chest x-rays and/or echocardiogram (ultrasound) to evaluate the size and shape of the heart.
  • If clipped beyond the quick, claws on the affected limb fail to bleed.

If your veterinarian suspects aortic thromboembolism, he will administer strong painkillers quickly as this is an excruciatingly painful condition.

How is saddle thrombosis treated?

Treatment for aortic thromboembolism will include the following:

  • Cats with congestive heart failure will be stabilised, this usually includes oxygen therapy and the drug Furosemide which removes fluid build up.
  • Fluid therapy can help to counteract the toxic effects of byproducts produced during ischemia. Caution must be used when giving fluids to a cat with heart disease.
  • Analgesics such as hydromorphone or buprenorphine to relieve pain.
  • Medications to dissolve the blood clot (thrombolytics).
  • Anticoagulant therapy such as heparin or aspirin is given to thin the blood and help stop additional blood clots forming.
  • Hyperkalemia may be treated with administration of glucose, insulin and in some cases sodium bicarbonate.
  • Cage rest and around the clock nursing care will be required while your cat recovers.

Once your cat has recovered from the thromboembolism, treating the underlying heart condition will be required long term.

Treatment is often unsuccessful. Blood thinners and thrombolytics run the risk of causing bleeding complications. Even if the cat recovers from the initial event, the risk of another clot forming is extremely high. On top of that is usually an underlying heart condition. Many owners elect to euthanise cats with aortic thromboembolism due to the poor outcome.