What is an Aortic Thromboembolism?
Reading the hand-out on feline cardiomyopathies may help with your understanding of this condition
An Aortic Thromboembolism (ATE) is an extremely painful, common, life threatening complication of cats with heart disease. It occurs when a blood clot (thrombus) forms (usually in the heart) which then passes down the aorta (the main artery which leaves the heart and lies along the spine before splitting into 2 to go down each leg). The clot then gets lodged in the aorta and blocks the blood supply to one, or both, hind legs. As a result of this blockage, the tissues of the leg/s begin to die. This is why the condition is so painful.
Blockages can also occur in other blood vessels, for example the blood vessels which carry blood to the bowel and/or kidneys.
What are the signs of Aortic Thromboembolism?
Usually the owner will notice a sudden onset weakness or paralysis of one or both hind limbs. The cat is in obvious pain, usually vocalising, and owners often suspect their cat has been in a road accident and have spinal trauma or fractured bones. The cat may be breathing heavily as the pain and stress of the ATE can cause the heart disease (which may not have been diagnosed previously) to worsen suddenly, causing a build up of fluid on the lungs.
What causes an Aortic Thromboembolism?
The condition is most commonly associated with the primary cardiomyopathies (see separate hand-out on heart disease). Three key factors are linked to the development of aortic thromboembolism:
- Damaged cardiac endothelium. The inside lining of the heart is damaged, this encourages platelets to become ‘sticky’
- A hypercoagulable state. This may be present and means that something is causing the blood to be able to clot more easily than normal.
- Intracardiac blood stasis. Due to a cat’s heart condition there is blood inside the heart that isn’t being pumped out. These ‘pools’ of blood within the heart are more likely to clot than blood which is moving.
Other, rarer, causes include liver disease, protein-losing diseases, cancer, kidney disease, Cushing’s disease and bacterial endocarditis (bacterial infection of heart valves)
How is this condition diagnosed?
The condition is often strongly suspected when the vet examines the cat. As well as the pain they will note:
- Weak to absent femoral pulse
- Weak or paralysed hind limb/s
- Pale foot pads or nail beds (though this won’t be visible if these areas are pigmented)
- The affected leg/s are cool to touch
- The limb/s may be stiff as when the muscle begins to die, it contracts
- There may be severe abdominal pain if the bowels are affected, and evidence of kidney failure if the kidney’s blood supply has been disrupted
- The vet may be able to hear a heart murmur
The vet may wish to do an echocardiogram which is where the ultrasound scanner is used to visualise the heart. Heart disease and/or further thrombi may be diagnosed this way, though this is often unnecessary. The ultrasound scanner may also be used to identify the thrombus in the aorta.
A blood test will also be able to support the vet’s suspicion of aortic thromboembolism.
What is the treatment?
Treatment can be intensive, it’s not always successful and, in cases where it is successful, there’s no guarantee the condition won’t reoccur. A large majority of cats who develop aortic thromboembolism are euthanased due to their poor prognosis either due to their heart condition, which can worsen due to the pain and stress of the Aortic Thromboembolism, or the severity of signs in their hind limbs and/or abdomen.
Firstly the cat’s heart condition needs to be stabilised (please see hand-out on feline cardiomyopathies). Strong pain relief will also need to be given.
Ideally, the thrombus needs to be removed. This is either done surgically, or with drugs which will cause the thrombus to break down. Surgery in an unstable patient with a heart condition is very risky and rarely carried out. Thrombolytic drugs (drugs which break down the thrombus) are still in the experimental stage, and currently the risk of undesirable side effects is high.
It is not as easy as simply removing the clot as soon as possible. If the clot is removed too quickly, ‘reperfusion injury’ can occur. This is where all the toxins released by the dying cells in the legs are flushed back into the main circulation by the restarted blood flow, which can cause further illness or death, and may cause other thrombi in the heart to be dislodged and travel down the aorta causing a further embolism.
Most vets will opt to treat medically – to support the cat while it breaks the thrombus down itself. This is done by putting the cat on a drip so that it doesn’t become dehydrated, giving medication to prevent the blood from clotting again (heparin) and, sometimes, giving drugs which cause the blood vessels to dilate, this improves circulation to the affected limb/s via smaller blood vessels (collateral circulation).
Animals who are able to be stabilised recover slowly; it can be more than 3 days before any improvement is seen. These pets will require supportive care at home, including physiotherapy.
It is suggested that if no improvement is seen within one week of stabilisation, or if the limb deteriorates (swelling, gangrene), recovery is unlikely.
Amputation if one limb is affected is an option and the cat will be pain free but, as previously mentioned, the condition commonly reoccurs and can affect the other limb
How can it be prevented?
Prevention is difficult and, for years, giving aspirin every day has been suggested but this has never been scientifically proven to be successful and isn’t recommended.
Heparin therapy is often used to prevent reoccurrence of clot formation.
More recently Warfarin therapy has been used and, although not scientifically proven to work at the moment, early results are encouraging. Animals on Warfarin therapy need close monitoring by the owner and regular blood tests to make sure they’re receiving the correct dose.
Adequate management of the underlying heart disease will also be required to maintain the cat’s quality of life.
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