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The Fragile Fate of FATEs: The Management and Prognosis of Feline Aortic Thromboembolism

Susan Smith, DVM
angell.org/emergency
emergency@angell.org
781-902-8400
MSPCA-Angell West, Waltham

What Is FATE?

With such an ominous acronym as FATE, trepidation about this condition is understandable and warranted. Feline Aortic Thromboembolism (a.k.a. FATE) is a condition of cats in which a large blood clot (or thrombus) has traveled and lodged itself (as an embolus) in an inappropriate location that cuts off the blood supply to parts of the body.  It typically is associated with an acute and distressing presentation in which cats can be hyperventilating, crying out in pain, and are suddenly unable to use their hind legs appropriately.  Because of these sudden and extreme signs, many clients will present their pet to the ER as having endured an unknown trauma. Although there is the potential for recovery with appropriate management, it is important to understand how it happens and the prognosis moving forward.

Why Does FATE Happen?

FATE is most commonly a secondary complication of feline heart disease. Cats with heart disease (such as hypertrophic cardiomyopathy) often have an enlarged chamber of the heart (specifically the left atrium) that promotes stagnant or turbulent blood flow that activates the clotting process and promote clot formation.

Once a blood clot has formed, fragments can migrate from the heart into vessels that supply the front legs and into the aorta. The aorta is the largest artery in the body that runs down the length of the back and splits into arteries to supply the legs. This split is called the saddle and is the most common location for clots to lodge; hence, FATE is also known as “saddle thrombus.” Once lodged, the blood supply to one or both rear legs can be disrupted. Not only does this prevent the leg from moving appropriately, but it also leads to the release of many inflammatory signals and the sensation of extreme pain.

It is important to note that clots can lodge in other parts of the body as well as the saddle, and have equally significant consequences. These areas can include the arteries that supply the front legs, the renal arteries that supply the kidney, and even the cerebral arteries that supply the brain.

It is also important to note that FATE can occur in patients that do not have preexisting heart disease.  In fact, in more than 70% of cats with FATE, it serves as the first sign of heart disease. However, not all cats with heart disease will develop abnormal clots. In one study, 6% of the patients with FATE were identified to have cancer (such as lung tumors) rather than heart disease. It is theorized that changes in platelet function and coagulation can also play a role.

How to Definitively Diagnose FATE?

The physical exam alone can be highly informative in diagnosing our feline patients with this condition. Although it depends on the location of the clot, paresis or paralysis with acute and severe pain are hallmarks of FATE. On physical examination, a pulse may not be appreciable in the affected legs and the paws may be cold with cyanotic (blue-tinged) pads and nail beds confirming loss of blood supply. A low rectal temperature may also be measured. A heart murmur may or may not be auscultable, while some cats may also be in concurrent congestive heart failure in which classic increased breathing with effort and crackles may also be appreciated.  Additionally, a gallop rhythm may be ausculted.

This may be enough to lead to a diagnosis. Differential blood glucose and lactate in an affected limb versus another limb can be performed.  Blood glucose will be lower and lactate will be higher in the affected limb versus a normal limb.  Further work-up if the owner elects to move forward includes bloodwork to assess electrolyte levels and renal function as well as chest x-rays and echocardiogram to ascertain the presence and degree of heart disease and heart failure.

How To Manage FATEs?

FATE is a frustrating disease for the patient, the owner, and the veterinary staff. Most of our current therapies are based on anecdotal treatments. No matter what, if the client elects to move forward with therapy, hospitalization for the first 48 hours is always recommended to not only provide the following therapies, but also to monitor for additional complications such as life-threatening electrolyte disturbances (secondary to reperfusion), arrhythmias, or acute renal failure.

The most critical therapy is pain control in the acute stage. After 24 to 48 hours, the pain may dissipate naturally as the nerves of that limb may begin to lose their function.  However, if reperfusion or incomplete occlusion happens, ongoing or recurrent pain may also be present.

The second most critical therapies aim to prevent further clot formation and to help break down existing clots. Different clinicians will utilize a different combination of medications, but they may include Fragmin (low molecular weight heparin that acts on clotting factors), Plavix (clopidogrel that acts on platelets’ clotting ability), and/or aspirin (that also works on platelets’ clotting ability). The research is still out for how effective these therapies are.

In patients that have concurrent heart failure, diuretics such as Lasix (furosemide) should be administered, and the patient should be kept in an oxygen cage.

Aggressive thrombolytic therapy and surgical removal of the clot are also not usually recommended given that patients with severe heart disease are often poor anesthetic candidates and the effects of spontaneous reperfusion can sometimes be disastrous. However, there are ongoing studies regarding the use of thrombolytics and they may become standard therapy in the future.  Amputation in special circumstances can be considered, but is typically the exception to the rule.

The Long-Term Prognosis

Statistics regarding the prognosis for FATE vary from paper to paper. However, it is widely acknowledged that the prognosis is generally poor. If recovery is achieved from this episode, owners need to be aware that their pet is at an increased risk that another episode could occur in the future and that their pet will likely have heart disease that requires life-long treatments. For these reasons, euthanasia at the time of presentation is the most common outcome.

In patients that are treated, approximately 50% of treated cats typically survive to be discharged from the hospital. The prognosis is worse if they are hypothermic on admit or if there are two or more limbs affected.  If there is evidence of renal failure, the prognosis is grave and euthanasia is strongly recommended.

In the end, the faster and more complete the return to function and sensation of the affected limb(s), the better the short-term prognosis. If complete paralysis persists beyond 48h, the prognosis becomes guarded. However, there have been infrequent instances where complete paralysis lasted for more than 10 days but partial function was eventually regained.  Hence, as long as the toes and foot pads are not gangrenous or completely devoid of blood after 72 hours, therapies can be continued if the owners are willing.

Median survival time for cats surviving 7 days after presentation is 93 days; however, 20% of these cats can have one-year survival times. It is important to note that all of these cats that survived an initial week ultimately died or were euthanized because of cardiac diseases or additional ATE episodes.

Closing Words

Understandably, FATE can be devastating to our patients and our clients. Research is ongoing to discover improved therapies and to gather more information surrounding prognostic indicators.

For more information about Angell’s Emergency/Critical Care service, please visit www.angell.org/emergency. Dr. Smith can be reached at MSPCA-Angell West in Waltham at 781-902-8400, or by e-mailing ssmith@angell.org.

 

References:

Borgeat, K et al. 2014. Arterial Thromboembolism in 250 Cats in General Practice 2004-2012. J Vet Intern Med 28: 102-108.

Borgeat, K et al. 2014. Arterial Thromboembolism in 250 Cats in General Practice 2004-2012. J Vet Intern Med 28: 102-108.

Little, Susan. 2012. The Cat: Clinical medicine and management. Saunders; pg 316-319

Smith, SA. 2003. Arterial thromboembolism in cats: acute crisis in 127 cases (1992-2001) and long-term management with low dose aspirin in 24 cases. J Vet Intern Med 17(1): 73-83.

 

 

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