Blood Clot

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What is it?

Feline arterial thromboembolism (FATE) occurs when a blood clot blocks the blood flow to part of the body. The most common blockage occurs where the aorta divides to supply blood to the back legs, and this is usually referred to as Feline Aortic Thromboembolism (also abbreviated to FATE). This makes the cat unable to walk and owners often think their cat has been in a road-traffic accident.

Why is it important?

FATE is usually associated with underlying disease, which will need to be treated in addition to the blockage. Heart disease is the most likely cause, although other diseases such as cancer and some types of kidney disease (protein-losing nephropathy) can cause this condition too. The condition is difficult to treat, often recurs and usually has a poor long-term outcome.

What's the risk?

Cats with dilated heart chambers as seen in hypertrophic cardiomyopathy (HCM) are the most likely to develop clots, so although any age or gender of cat can develop FATE, middle-aged to older males are over-represented.

What happens to the animal?

The clinical signs associated with FATE vary depending on the location and size of the clot but they start suddenly. Blood clots can go to many organs including the lungs, brain, kidneys and intestines but the majority of clots occur near the end of the aorta. Aortic thromboembolism blocks the blood flow to the back legs which stops the nerves and muscles from working. Affected legs become paralysed and cold with no pulses and purple (cyanotic) foot pads/nails. The condition is very painful and most cats will vocalise/cry out in distress. In addition to symptoms caused by the clot there will be signs relating to the underlying disease causing it. Cats with heart disease can have fast heart rates, abnormal heart rhythm, heart murmurs and/or rapid breathing with around half of cats being in heart failure. Other underlying diseases may cause a variety of symptoms such as depression, swollen legs, fever, or fluid in the abdomen.

How do you know what's going on?

Diagnosing a thromboembolism in the aorta can typically be done based on clinical signs alone. However, ultrasound can be used to look for the clot within the aorta for confirmation if needed. Thromboembolism in other parts of the body is more challenging but diagnostic imaging with either ultrasound, CT or MRI can be used to locate it. When a thromboembolism has been found, tests should also be performed to find an underlying cause. For heart disease this includes x-rays of the chest and an ultrasound of the heart (echocardiography). Cats with HCM that are susceptible to forming clots have a swelling (dilation) of the left atrium (a heart chamber) on ultrasound.

What can be done?

Cats presenting with thromboembolism of the back legs are often in such extreme pain that most of the time euthanasia is recommended especially when considering the underlying disease involved. Medications can be used to dissolve the clot but the risk of further injury when blood flow is restored is between 40-70% and this can cause death in nearly half of the patients treated. Due to this, treatment to dissolve clots is only usually used when vital organs are affected. Treatment targets different aspects of clot formation. Pain management is essential and requires strong opioid medication. Heparin (a blood thinner) helps prevent the clot getting larger. Blood flow via alternate routes can be improved with the use of aspirin and clopidogrel. Aspirin in high doses is toxic to cats and so should be used carefully. Clopidogrel is more expensive but has been proven to be more effective than aspirin as well as safer. In addition to treating the clot, the underlying disease must also be treated and this will often entail life-long medication.

How can I protect my cat?

Prevention of FATE is aimed at reducing the chance of it happening in the first place. Cats with conditions known to cause clots should be monitored closely and preventative medication started when appropriate. For cats with HCM this decision is made based on echocardiography findings. Cats that have had a clot previously should also receive prophylactic medicine to decrease the risk of recurrence.