A cat with saddle thrombus (aortic thromboembolism) will usually present with weakness or total paralysis in the hind limbs. The hind limbs are often cold to the touch and often the cat will be in severe pain. Usually these symptoms come on suddenly, the cat seems to be perfectly normal and suddenly will be unable to move its hind limbs.
The condition is caused by a blood clot blocking blood flow to the hind legs. The abdominal aorta, which is the large artery which carries blood from the heart to the rear part of the body, divides in the caudal abdomen into two blood vessels called the iliac arteries which supply blood to the hindquarters and rear limbs. The blood clot lodges right at this division and extends a short way into the iliac arteries, giving it the shape of a saddle - hence the term 'saddle thrombus'.
Most cats with a saddle thrombus have an underlying heart condition, such as dilated cardiomyopathy. Dilated cardiomyopathy is a condition where the heart wall weakens and stretches. The stretching of the heart wall allows the chambers in the heart to become much larger than normal, and the chambers no longer completely empty with each heartbeat. Due to the altered blood flow patterns in the heart, blood clots will often form and grow to be quite large. These blood clots can then leave the heart and get stuck in areas where arteries divide - such as the location where the abdominal aorta divides into the iliac arteries.
The number of cats with dilated cardiomyopathy (and saddle thrombus) has decreased over the last few years since the discovery that taurine is an essential nutrient for cats. Taurine is an amino acid found in meats and a deficiency of taurine in cats will often lead to dilated cardiomyopathy. Today, taurine is added to prepared cat foods and so dilated cardiomyopathy is rare in cats eating comercial diets. Dogs make their own taurine and many commercial dog foods do not contain significant amounts of taurine. Dilated cardiomyopathy is sometimes seen in cats whose owners feed dog food in an attempt to save money. Taurine deficiency can also be a problem in cats that are fed a home cooked diet.
Another heart condition that can lead to saddle thrombus is hypertrophic cardiomyopathy, which is the opposite of dilated cardiomyopathy. Hypertrophic cardiomyopathy involves a thickening of the heart walls with a corrosponding decrease in size of the heart chambers. Altered blood flow patterns lead to the formation of blood clots. The exact cause of hypertrophic cardiomyopathy is not known, but there are indications it may be a hereditary condition.
The treatment of saddle thrombus involves giving blood thinners in an attempt to dissolve the clot and supportive care. Pain relief is essential. Oxygen therapy may be helpful. Surgery to remove the blood clot is not usually beneficial. The prognosis for recovery is guarded to poor, many cats with this condition are euthanized. A few cats do recover.
Cats that have had a saddle thrombus once are at great risk of developing the condition again, because the underlying heart condition usually still exists. Long term treatment with anti-clotting drugs may be indicated, as well as diagnosis and treatment of the heart disease.