Aortic Thromboembolism in Cats

This is characterized by the passing of a blood clot (embolus) from the left side of the heart into the general circulation, where it becomes lodged in an artery. The resulting obstruction to the flow of blood leads to clotting of the artery (thrombosis).

The most common site for blockage is the point at which the abdominal aorta branches into the main arteries that supply the rear legs. Arteries elsewhere in the body can be affected, particularly in the kidneys. Diagnosis of the rear limb problem can be based on signs such as rear limb paralysis, swollen muscles, the absence of a pulse in the groin, and blue nails due to cyanosis. If the renal arteries are blocked, acute kidney failure may result. If a cerebral artery is blocked, seizures may occur. Cats with thrombi can be in quite serious pain.

Formation of a blood clot in the heart and subsequent arterial thromboembolism occurs in about half of all cats suffering from cardiomyopathy. It may be the first indication of heart disease. Suspect this possibility if your cat experiences the sudden onset of weakness in the rear legs. Look for cold legs, bluish skin, and faint or absent pulses in the groin. One leg may be more severely blocked than the other. The colder leg with the weaker pulse is the more severely affected. Ultrasound can be very useful in localizing all potential areas of thrombosis.

Treatment: This depends on the severity of the blockage. Your veterinarian can prescribe medications to try to dissolve the clot. Heparin seems to be the most useful drug for this condition. Aspirin may also be used, and a new product called Fragmin, which is a molecular weight heparin (a version of heparin that is smaller in size - molecular weight - than standard heparin), may also be useful, but it is very expensive and is not approved for use in cats at this time. Clopidogrel is currently being tested at Purdue University to see if it will reduce the recurrence rate of thromboembolism. Surgery has not been found to have a high success rate.

Since these cats are almost always also suffering from severe heart disease, management can be difficult. Potassium levels must be monitored carefully, as the damaged muscles release potassium into the circulation. Kidney function must also be monitored in case a clot lodges in the renal artery and causes acute kidney failure.

Cats who do recover from an initial thrombus are at risk for repeated injuries. Physical therapy may be necessary as healing progresses to restore muscle and joint function. Some cats will develop collateral circulation, where blood vessels grow around the clotted thrombus to provide nutrients and remove toxins in that area, but they are in the minority.

This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.