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
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.
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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
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.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"