The largest artery in the body that is the main “highway” for the propagation of oxygenated blood from thr heart to the tissues is the aorta. The feline aorta leaves the heart with oxygen rich blood and courses through the chest and ultimately through the abdomen heading toward the tail. At the level of the pelvis, the aorta splits into two smaller arteries that ultimately supply blood to the tissues of each leg. It is at this split where formed clots can get lodged, leading to a severe medical emergency called a saddle thrombus.
Saddle thrombus is exclusively a feline phenomena, causing a severe situation where the lodged clot cuts off blood supply to the legs. The lack of nutrient rich, oxygen rich blood reaching the tissues of the legs leads to severe pain, disuse of the legs and severe damage to the tissues, blood vessels, and nerves.
Typically, cats that are predisposed to saddle thrombus have underlying cardiac disease that increases turbulence to the flow of blood through the heart. This increased turbulence makes these patients more prone to the formation of clots. Cats with hyper-thyroidism are prone to a cardiac condition called hypertrophic cardiomyopathy. Therefore, saddle thrombus tends to be associated with cats that have hyperthyroidism.
Cats that have formed a saddle thrombus typically appear paralyzed, unable to move the rear legs. They are often vocalizing due to severe pain. When touched, the back legs are often cold and stiff, and sometimes there is panting and trouble breathing.
Due to the time sensitive nature of the irreversible consequences of saddle thrombus, as well as the severe pain that saddle thrombus causes, it is strongly recommended that one seek immediate veterinary care for one’s cat if saddle thrombus is suspected.
Saddle thrombus is diagnosed by a combination of history, presentation, cold/stiff rear legs, and lack of any palpable pulses in the rear legs. Chest x-rays will often indicate evidence of cardiac disease, and even congestive heart failure.
Prognosis is poor for saddle thrombus, even when found early. Treatment is geared toward managing pain and re-establishing blood supply to the legs through the use of IV clot busters such as heparin, or surgical removal of the clot. In many cases, however, the damage to the tissues, blood vessels, and nerves of the rear limbs is too severe and irreversible for treatment to offer a return quality of life, leaving euthanasia the most humane option for the patient.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 6/3/2014