Aortic thromboembolism (saddle thrombus) is a relatively common complication associated with heart disease. The most common heart disease in cats is hypertrophic cardiomyopathy. The walls of the diseased heart allow the formation of clots in the left atrium, the upper chamber of the heart. These clots then become dislodged and travel down the aorta, the main vessel leaving the heart. Clots most often become lodged at the base of the aorta when it divides into the arteries that supply blood to the rear legs. This causes a sudden onset of inability to use the rear legs, dragging the rear legs and cold paws. Cats often howl and cry in pain.
Clots may also lodge anywhere in the body including the arteries to the kidneys, intestines, front arms or brain. If affecting the front arms, usually the right front arm is affected.
After the clot lodges in the vessel, it almost always dissolves on its own over time, although it may cause severe nerve and muscle damage. This damage may not be reversible. For this reason, it is recommended that your cat receive immediate treatment for saddle thrombus.
Following treatment, about 35 to 40 percent of cats are able to walk again, usually within three weeks of the episode. Unfortunately, a significant number of cats do not survive the heart failure that often accompanies saddle thrombus. Other cats may not survive the muscle and nerve damage that occurrs with the clot.
Cats that do survive an episode of saddle thrombus unfortunately have a 90 percent chance of recurrence within six months.
Other diseases may cause sudden onset of dragging rear legs. These include:
Intervertebral disk disease
Tumor of the spinal cord
Pelvic fracture
Traumatic injury
