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My cat has suddenly gone lame in her hindquarters and seems to be in a lot of pain

What is Feline Aortic Thromboembolism?

Feline Aortic Thromboembolism (ATE) is a condition in cats where a big blood clot settles and blocks the main artery (the aorta) running from the heart to the cat’s hind legs.  The clot typically settles near the pelvis, where the aorta divides into the two main arteries that extend into the legs.

It is almost like the clot itself has two legs extending down into the two main arteries. This type of clot is known as a “saddle clot” or “saddle thrombus”. This condition is typically associated with heart disease in cats.

ATE most commonly occurs in cats with an enlarged left chamber (atrium). The enlarged heart chamber slows down blood flow and over time the red blood cells start clumping together and form a blood clot.

The blood clot is then pushed out of the heart and down the aorta, where it lodges at the point where the aorta branches into the two main arteries (external iliac arteries) extending into the legs. As a result of the clot obstructing the artery, the blood supply to the hind legs is cut off.

What are the symptoms of a saddle thrombus in cats?

  • Sudden Lameness/ Unsteadiness in the hind legs
  • Decreased Activity
  • Over Vocalisation (Painful ‘Meowing’)

Up to 90% of cats show no signs of heart disease before developing this condition and owners often suspect trauma. If the owner is not present right at the onset of the condition, they may come home from work and find their cat paralysed in the hindquarters and dragging its body forward with the front legs. In such instances, it makes perfect sense that one would suspect that the cat had been run over by a car.

When presented to the vet, the tell-tale signs are usually that the hind leg muscles are swollen and very painful to touch. The legs are also cool to the touch because the warm oxygen-rich blood from the heart cannot be pumped down to the legs.

The nail beds will also either be very pale or very dark. With the blood being blocked higher up, the femoral arteries, which are the main arteries on the inside of the leg taking blood to the paws, will have no pulse. The vet will try and feel this pulse on the inside of the hind legs to establish if any blood is still coming through to the legs.

The cat’s rectal temperature will be abnormally low. Many cats are still able to move their tails and control their bladder and stool functions, however, skin sensation and neurological functions i.e. reflexes are absent. Signs of heart failure (heart murmur, difficulty breathing) may accompany the signs.

How is a saddle thrombus diagnosed?

The condition is mostly diagnosed on the typical clinical signs, but to further confirm the diagnosis the vet may cut one of the toenails down to the quick to see if any blood is coming through to the extremities. With a saddle thrombus, the cut nail will either ooze dark blood or not bleed at all.

The vet may also recommend taking radiographs, performing an ECG or doing an echocardiogram (heart scan) with ultrasound to assess the extent off the condition and potential underlying heart failure.

Occasionally the blood clot may lodge further up the aorta and occlude the blood flow to the kidneys as well, in which case the vet may recommend blood tests to evaluate the kidney function.

How is Feline Aortic Thromboembolism treated?

The condition is often treated through cage rest, pain control and drugs which counter blood clots from forming (often in humans referred to as “blood thinners”) and arterial dilators.

Due to the severe pain that this condition causes, Opioids (morphine/fentanyl class) are usually the drugs of choice for controlling the pain. Additionally, the vet may decide to lightly sedate the cat if it is very distressed.

Blood-thinning drugs may theoretically prevent further blood clot formation, while ACP or hydralazine might dilate the blood vessels to aid blood flow to the affected areas. There is however no evidence that these drugs have any benefit over cage rest alone.

Surgical removal of the blood clot carries very high risks and is generally not performed. The concurrent heart failure will also need to be managed. The cat may be kept on a drip for a while and the vet will prescribe medications for it to take for the rest of its life.

If the cat survives past the first few days, it will start regaining its limb function after 10-14 days and will be fully recovered after 4-6 weeks. Some residual deficits may be permanent.

Several drugs such as aspirin, heparin, warfarin have been suggested to prevent blood clots forming in cats diagnosed with heart disease, however, there is no evidence of these drugs being effective and the side effects can be quite severe; thus your vet might opt not to use them at all.

It is important to NEVER use human medication for the treatment of cats unless the vet has prescribed it. Some human medicines like Panado is fatal to cats and one should never treat your cat with a human medication unless it was prescribed by a vet.

If the condition is left unattended, the cat may become permanently paralysed and the skin and muscles may start dying off. This may result in wounds needing surgical treatment or even amputation of a leg. In severe cases, additional blood clots may lodge at various points throughout the rest of the body, ultimately leading to death.

What is the prognosis of a saddle thrombus in cats?

The prognosis is generally guarded, with only 33-50% of affected cats surviving and recovering well enough to be discharged from the hospital. Unfortunately, recurrence of the condition is very common.

Due to the guarded prognosis, the high risk of recurrence, and the presence of heart failure, the decision to euthanise your cat (put to sleep) is often the most humane option.

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