Feline aortic thromboembolism (FATE) is one of the most serious medical emergencies vets will see in practice. Owners are shocked by the sudden onset of the condition and the obvious distress they see in their cat. Options for treatment can be limited, and euthanasia is often deemed the kindest course of action. Therefore, in the vast majority of cases, FATE proves fatal. 

But is FATE more survivable than vets had previously thought? A recent paper published by the Journal of Feline Medicine and Surgery has re-examined the survival rates of cats that have undergone treatment for FATE, and it seems there may be a glimmer of hope for some cats affected by this devastating condition.

Table of contents

What causes FATE (Feline aortic thromboembolism)?

In 80% of cases, feline aortic thromboembolism is a complication of cardiomyopathy, a heart condition that, in cats, can often go undetected. Cardiomyopathy causes an enlargement of the left atrium, one of the chambers of the heart, and this enlargement allows blood to ‘sit’ within the chamber before being properly pumped out. This slow-moving blood can clump together and form a blood clot. The blood clot can then travel out of the heart, becoming lodged in the first artery it can’t fit through. Usually in cats, this occurs where the aorta (the main vessel carrying blood away from the heart) divides into two to supply blood to the back legs. The clot blocks the supply of blood to one or both back legs, which is excruciatingly painful. After that, it’s only a matter of hours before the limbs begin to die from a lack of blood flow. 

What happens to cats with a blood clot?

A lack of blood supply to the back legs stops the muscles and nerves from working. Cats lose the use of their back legs almost immediately. And the resulting intense pain may make them cry out in distress. Vets often describe the ‘five P’s’ that aid diagnosis, these being pain, pulselessness, paralysis, pallor (the skin appears white or in some cases, blueish) and poikilothermy (a fancy way to describe the skin as being cool to the touch). 

Since the underlying cause of the blood clot is heart disease in most cases, there may also be other signs at the time of admission, such as a rapid heart rate, heart murmur, or arrhythmia. Over half of cats with FATE are also in heart failure; which may be causing a build-up of fluid in the chest or abdomen too. It’s not surprising that for 90% of cats with this problem, vets and owners agree to euthanase at an early stage. The rationale for this has been that treatment options were limited, and both the short- and long-term prognosis was very poor.  

How does this new paper address the survivability of FATE?

For most vets faced with a painfully paralysed cat, the addition of fluid in the chest would pretty much seal the deal in terms of a decision to euthanise. However, heart failure leading to a build-up of fluid in the chest (‘congestive’ heart failure) has not been associated with a worse prognosis for cats suffering from FATE.

More recent research has also challenged the notion that blood clots cannot be dissolved adequately. A review of survival studies has shown that if a cat survives the initial episode of FATE and gets sent home with appropriate oral medications to ward off a relapse, survival may be much higher than previously thought. 

Retrospective studies have shown that cats may survive up to 350-500 days after leaving the hospital, with the use of rivaroxaban and clopidogrel producing the highest survival times and lowest reoccurrence rates.

Although the prognosis should remain guarded, there are now options available to vets for the treatment of FATE. According to this new data, approximately 40% of cats will survive FATE following treatment, with some veterinary practices reporting 80–90% survival rates, and median survival times of up to 500 days.

It’s important to stress though, that complications during treatment are common. More about that in a moment.

What is the treatment for blood clots in cats? 

Cats will need to be admitted into the hospital to be treated effectively. Pain relief is the first priority. A strong painkiller is required, and often this must be given alongside other pain killers to effectively manage the pain. Many cats will benefit from the administration of oxygen. For cats in heart failure, giving a drug to remove any fluid from the chest is also important.

Medication must then be given to first reduce the risk of the clot getting bigger, and then to start dissolving the clot itself. The key consideration here is the length of time the clot has been present for. If it has been less than six hours since the onset of clinical signs, it could be worth trying this treatment, providing there are no other complicating factors at play. If treatment has been delayed by more than six hours, it is much less likely to be successful. 

Nursing care is extremely important. It can take 2-6 weeks to see an improvement in the function of the back legs, and physiotherapy during this time is essential. 

What are the possible treatment complications for cats with FATE?

Sudden death may occur in around 10-15% of cats affected, usually within the first twelve hours. In about 5% of cases, amputation of a back leg is required, due to irreversible tissue death.

Kidney failure is a common complication and occurs in 30% of cases. 20-50% of cats may develop reperfusion injury. This is a complex inflammatory response that causes further damage to the tissues after blood flow returns. 

The paper says that approximately 40% of cats with FATE who develop complications will survive if appropriate treatment is instituted. However, if an improvement is not noted within the first 24-48 hours, the long-term prognosis should be discussed.

Even after a long and difficult initial recovery, cats may suffer a relapse. However, if cats are sent home with clopidogrel and rivaroxaban as a dual therapy, the risk of a recurrent episode of FATE is cut to 16.7%.

Blood clots in cats – is treatment right for your cat?

The development of new treatment guidelines for feline aortic thromboembolism is certainly good news for cats, where previously very little could be done. If caught early (within six hours of the start of clinical signs), and if there are no other factors affecting recovery, cats suffering an episode of FATE can go on to experience a good quality of life for many months or years.

However, treating this condition may not be the right way forward for every cat… 

It’s important to consider how your cat is likely to cope with a long period of hospitalisation and restricted mobility. There will be a lot of hands-on intervention required, which some cats will struggle to tolerate. The need for regular medication may not suit some cats who enjoy a lot of freedom and outdoor access. They will either need to put up with a more restricted lifestyle or risk not being around when it’s time for their next dose. Remember that cats live in the moment; they do not have the same ability to imagine their future as we do. They do not have the hope that things can improve over time to help motivate them to get through a long period of restriction and recovery. Euthanasia in these circumstances is not the wrong choice to make. 

It’s also worth mentioning that pursuing treatment for FATE will be out of reach for many owners, as costs are likely to mount up extremely quickly. It’s important to have a frank and open discussion about costs with your vet from the outset. 

Recent years have seen advancements in treatment options for cats suffering from FATE. Nevertheless, treatment of cats with FATE remains challenging and complications are common. This is a condition that requires a long discussion with your vet before you decide on the best course of action for your cat.

Sarah Elliott BVetMed MANZCVS (Feline Medicine) MRCVS
5th August 2024