FELINE AORTIC THROMBOEMBOLISM (FATE)
One tends to feel apprehensive about a condition with the acronym: FATE and rightly so. FATE (Feline Aortic Thromboembolism) is a dramatic and painful condition with serious implications. It comes on suddenly and appears to paralyze the cat, causing one or both rear legs to become useless and even noticeably cold. The cat will hyperventilate and cry out with extreme pain. Despite the extreme presentation, the cat may be able to recover from the episode but it is important to understand how this came to be in order to make decisions.
A thrombus is a large blood clot.
WHAT IS A “SADDLE THROMBUS?”
(original graphic by marvistavet.com)
The aorta is the largest artery in the body. It stems from the heart itself, where it arches back and runs down the length of the back, ultimately splitting into the arteries supplying the back legs. The split where the aorta becomes the left and right iliac arteries is called the “saddle.”
A “saddle thrombus” is a blood clot that breaks off from a larger blood clot in the heart, travels down the aorta and lodges at the “saddle.” Not only is the blood supply to one or both rear legs cut off but a metabolic cascade results leading to the release of assorted inflammatory mediators (especially serotonin). The muscles of the rear legs become hard, the foot pads become bluish in color, and the condition is extremely painful. The inflammatory mediators readily lead to circulatory shock.
72% of cats with a saddle thrombus have both rear legs affected.
WHERE THE SADDLE THROMBUS CAME FROM
The saddle thrombus comes from a larger clot in the left atrium of the heart. This obviously begs the question as to why there would be a large blood clot in a cat’s heart. In fact, 89% of cats with a saddle thrombus have heart disease. Heart disease leads to turbulent blood flow which encourages the formation of clots.
Arrow shows a large clot in the left atrium of a cat with a saddle thrombus.
To see a video of an echocardiographic imaging of a person who presented with recurrent postural syncope, looking much like it would in a cat, click here. The clot in her left atrium looks like a round ball moving around.
In 76% of cats with saddle thrombus, the FATE episode was the very first sign of heart disease.
HOW BAD IS THIS SITUATION?
The outcome is variable but has potential to be very bad. Let's review the possibilities.
BEST CASE SCENARIO (THROMBUS RECOVERY AND NO HEART FAILURE): A cat with a thrombus that only partially blocks circulation or dissolves rapidly may be showing tremendous improvement in a couple of days. This scenario sounds pretty good but remember there is an underlying heart disease to contend with. If the heart disease does not include active heart failure, there is a good chance heart failure will erupt in the future and the owner must learn how to watch for signs. There will definitely need to be medication for to prevent future thromboembolism. Further, the patient at home may need some nursing care until maximum rear leg function returns. While many cats regain full function, the should be prepared for a cat that never regains complete function. It may take several weeks to determine the extent of recovery.
THERE IS ABOUT A ONE IN FOUR CHANCE THAT THE CAT WILL HAVE ANOTHER SADDLE THROMBUS EPISODE IN THE FUTURE.
THROMBUS RECOVERY WITH HEART FAILURE: In this scenario, the cat presents not only with the pain and paralysis of the saddle thrombus but also in active heart failure. Even if the thrombus situation resolves relatively promptly with signs of limb function recovery and resolution of pain after a couple of days, there is still a life-threatening cardiac crisis to contend with. The heart failure alone may be lethal in the short term but let's assume the heart failure can be controlled quickly with medication AND the recovery from the thrombus is in progress. The cat will need heart medication, blood thinners, and nursing care while the rear legs recover. Median survival of saddle thrombus cats with heart failure is 77 days while median survival of saddle thrombus cats without heart failure is 223 days.
TISSUE DAMAGE FROM THE THROMBUS: The good news is that permanent limb damage is the exception and not the rule but it is possible. Some cats will lose skin or even muscle from the circulatory compromise. About 5% of cats will have tissue damage appearing as an open wound. As circulation returns, this sort of injury should heal. Another 5% will have more serious damage and the occasional cat will require amputation of a limb.
RAPID DEATH FROM THE TISSUE DAMAGE OR HEART FAILURE: Many cats will die in the hospital. Some are simply overcome by their heart failure. Some will throw another blood clot or multiple clots to a less survivable location such as the brain or lung blood vessels. Some will suffer what is called a "reperfusion injury" when, as circulation returns to the limbs, toxic biochemicals from the limbs enters the main body of the circulation. Large amounts of potassium released from dying cells can be enough to fibrillate the already diseased heart. A saddle thrombus is a serious event. Is this lethal event likely to happen? It turns out the best predictive parameter is the body temperature at the time of presentation to the hospital. Cats with an initial body temperature over 98.9 F have a greater than 50% chance of avoiding this disaster and getting well enough to return home.
SADDLE THROMBUS IN THE ABSENCE OF HEART DISEASE: We have discussed saddle thrombus in terms of heart disease so far but it turns out there are other ways to get an aortic thromboembolism. While 89% of cats have heart disease, 6% will have cancer, 3% will have no apparent reason for their thrombus. The cats with cancer usually have lung cancer, which is discovered when chest radiographs are taken to assess heart disease. Lung cancer is not the only type of tumor that can induce a state promoting inappropriate clotting, though, so if heart disease is not found, a tumor search should be initiated with abdominal ultrasound. In this scenario, obviously the cat must contend with the thrombus recovery and medication to prevent future embolism, PLUS the newly discovered cancer and whatever treatments are available to address that.
THROMBUS HIGHER UP: In some cats the thrombus lodges higher up in the aorta, not where the aorta splits to serve the two rear legs but where branches split off to serve the two kidneys. If the kidney's lose their blood supply acute renal failure develops and a particularly rapidly lethal uremic toxin build up occurs. This scenario is fortunately uncommon but needs to be recognized if it is present. Affected cats will have a drastic reduction in urine production and high levels of renal toxins on their blood tests.
EUTHANASIA: Because of the potential for repeat saddle thrombus episodes, need for regular medication administration at home, potential long term treatment of heart disease, not to mention the seriousness & painfulness of the cat’s initial predicament, 25% of pet owners elect euthanasia without attempting treatment.
HERE ARE SOME STATISTICS THAT HAVE BEEN ASSEMBLED:
WHAT TO EXPECT AT THE VETERINARY HOSPITAL
The doctor will needquickly determine if the cat has a saddle thrombus or some other reason for rear limb paralysis and pain. The saddle thrombus patient will have cold rear feet, with a bluish or purplish color of the pads when compared to the front feet. Sometimes a toenail will be clipped short on a rear toe to check for bleeding. The diagnosis is often clinched by comparing a blood glucose level taken from the front of the body against one taken from the rear legs. Pain control is generally initiated while these preliminary evaluations are being preformed. Obviously, the initial body temperature is recorded so as to assist in making a prognosis and assessing the severity of the situation.
Once the cat is more comfortable, more comprehensive blood testing can be performed and chest radiographs can be taken. In doing this, the cat is assessed for the kidney toxins, toxins related to poor circulation, general biochemical body function, stress, heart failure, and possible lung cancer. If heart failure is present, diuretics will be needed to relieve extra fluid from the circulation and ease the burden on the weakened heart. There is controversy about using injectable blood thinners but many hospitals will begin them and later transition to oral clopidogrel, aspirin or both.
Most cats will present to their regular veterinarian's office for initial care. The question will arise as to whether 24 hour care is needed or likely to be worth the extra expense, stress of travel to a specialty center etc. The benefit of the specialty center includes the ability to continue pain relieving medications overnight and to watch for and address sudden exacerbations with regard to heart failure or new embolisms. The cat will also need an assessment by a veterinary cardiologist to assess the underlying heart disease and prescribe medications as indicated. Many specialty centers will have a cardiologist on-site so this is another reason to transfer sooner rather than later. Of course, not every community has a specialty center conveniently located so the echocardiogram may need to be addressed by a mobile specialist, by telemedicine (over the internet), or even by a skilled non-specialist.
The cat will need to be hospitalized for at least a couple of days and possibly for as long as a week for pain management and to establish comfort and appetite before release from the hospital. Owners will need to be able to give medication and nursing care as needed.
Page last updated: 2/12/2017