Aortic thromboembolism

Cats may be struck ‘out of the blue’ by a blood clot resulting in dramatic signs (sudden onset of lameness and pain) and potentially devastating damage. The back legs are most often affected, but front legs may also be affected. This is an emergency and if you suspect that your cat has suffered a blood clot, you must seek veterinary help as soon as possible.

The term thromboembolism is made up of two words ‘thrombo’ and ’embolism’. A thrombus is a blood clot within the heart or in a blood vessel; an embolus is something that travels through the bloodstream, lodges in a blood vessel and blocks it. Therefore, thromboembolism is the formation of a blood clot in the circulatory system (thrombus) that breaks loose and is carried by the blood stream until it lodges in a blood vessel and blocks it. The clot may block a vessel anywhere in the body. The more commonly recognized sites are the legs (most frequently the back legs), lungs (pulmonary embolism), the kidneys, the gastrointestinal tract and the brain (stroke).

When a blood vessel becomes blocked, the tissue it normally supplies is deprived of a blood supply (and therefore oxygen). The signs will depend on the location of the affected blood vessel. In the cat, clots most often get stuck in the main blood vessels providing blood supply to the back legs. One or both back legs may be affected. Your cat will be lame or might not be able to stand or use the affected leg or legs at all. The legs may be colder, the muscles may be firm and the nails and foot pads (if not pigmented) may be pale. In the beginning this condition is very painful and your cat might cry, look at or even chew the affected leg(s). The condition comes on very suddenly so a cat may go out of the house apparently completely healthy and later be found on the doorstep unable to stand on their back legs.

If a blood vessel in the lung is blocked, your cat may breathe more heavily, more rapidly and may start to breathe through its mouth (pant). A clot in the brain can cause seizures or altered behavior.

Thromboembolism is an emergency and it is important to get your cat to your vet as soon as possible.

Your veterinarian will suspect a blood clot if your cat has suffered a sudden onset of these signs. However, cats suffering from back injuries or involved in a road traffic accident can show similar signs. Your veterinarian will examine your cat thoroughly and will check for pulses in the legs. If these are absent, it is very likely that your cat has a blocked artery to one (or both) of its legs.

A blocked artery is a serious problem. The reduced blood flow results in a build-up of toxic substances in the tissue. This can be life-threatening, as if the blood supply to an organ is blocked, the function of that organ will be impaired. This can cause changes in the blood which your vet can detect with some simple blood tests.

There are several reasons why blood clots form and although your cat may not have shown any other signs of illness, it is likely that a severe, life-limiting disease is present. Your veterinarian will investigate so as to determine what has caused the clot and what, if any, treatment is appropriate.. Most blood clots in cats are the result of heart disease and your veterinarian may take X-rays of the chest and/or perform an ultrasound investigation of the heart. Some tumors can also cause clots to form and, if your vet suspects this, they might also take X-rays and/or obtain an ultrasound of your cat’s belly.

There are treatments that can be attempted, but it is important to mention that the prognosis is often guarded. If your cat’s pain cannot be controlled, then your vet may advise euthanasia on welfare grounds. If your cat has an underlying condition, such as heart disease, that has  caused the clot, then this also needs to be investigated and treated. Daily treatment with oral anti-coagulants will be necessary for the rest of your cat’s life to help reduce the risk of recurrence.

Your cat may require hospitalisation for several days for pain relief and physiotherapy, so it is also important to discuss potential costs with your vet, as treatment can be expensive.

Once treatment is started long term monitoring will be required to check that treatment is being effective and well tolerated and to follow the progress of the underlying disease.

It depends on the disease which caused the clot in the first instance, and the possible organ damage caused by clots. Sadly, the outlook for cats with thromboembolism is not good. Around one-third of all affected cats do not recover from the initial episode (although in many cases this is because their owner elects for euthanasia). However, depending on the severity (and your veterinarian can advise you on this) it is worth starting treatment to buy some time. If your cat improves over the first few days, there is a chance that further improvement will occur and your cat may recover and have a good quality of life. In cats that do recover, complete function of the affected leg(s) is often not achieved. As most of the underlying diseases which cause clots cannot be cured, your cat is at risk of developing another clot (even if on long-term treatment with anti-coagulation drugs) and around 50% of cats will develop a further thromboembolism.

Thromboembolism is a serious, life-threatening disease, which can come out of the blue. Affected cats will usually have an additional serious underlying disease, which can be treated, but almost certainly not cured. If affected, your cat will be on treatment for the rest of its life and is at risk of developing another clot. Your veterinarian will be able to give you an idea of how badly affected your cat is and whether treatment is worth trying. Cats that do respond to treatment can have a good quality of life and may live for several months or sometimes even years.