A saddle thrombus in a cat is a sudden, severely painful blockage of a major blood vessel, medically known as Feline Aortic Thromboembolism (FATE). This event is caused by a blood clot that travels from the heart and lodges in the lower body, resulting in an immediate interruption of blood flow. It represents a life-threatening veterinary emergency that requires urgent, specialized care. The prognosis is often poor, making rapid recognition and intervention absolutely necessary for any chance of survival.
The Physical Event and Location
The term “saddle” refers to the specific anatomical location where the clot lodges. The aorta is the largest artery in the body, carrying oxygenated blood from the heart down the back. This major vessel divides near the cat’s hind legs into the two iliac arteries, which supply blood to the lower body.
The clot travels from the heart until it reaches this split, obstructing blood flow to one or both hind limbs, sitting like a saddle on a horse. This sudden lack of blood supply, or ischemia, causes immediate and intense pain in the hindquarters. The resulting damage from oxygen deprivation rapidly leads to the visible symptoms.
Cardiac Conditions That Lead to Clot Formation
Saddle thrombus cases are a direct, secondary complication of underlying heart disease. The most common cause is Feline Hypertrophic Cardiomyopathy (HCM), where the walls of the heart, particularly the left ventricle, become abnormally thickened. This thickening prevents the heart from relaxing and filling properly, often leading to the enlargement of the left atrium.
This enlarged or poorly functioning left atrium creates turbulent blood flow, allowing blood to pool and become sluggish, a state known as stasis. Within this chamber, microscopic clots form, eventually coalescing into a larger thrombus. A piece of this thrombus can break off, becoming an embolus that travels out of the heart and into the systemic circulation.
The formation of the initial clot often goes unnoticed because many cats with HCM show no outward signs of illness. The saddle thrombus is frequently the first indicator that a cat has a serious, undiagnosed cardiac condition. The presence of “smoke,” or swirling echoes, within the left atrium on an echocardiogram indicates an increased risk for clot formation.
Recognizing the Signs and Immediate Emergency Steps
The onset of a saddle thrombus is sudden and requires immediate recognition. Owners typically observe a sudden inability to use one or both hind legs, often described as paralysis or severe weakness. This physical impairment is accompanied by signs of extreme, acute pain, such as loud vocalization, howling, or rapid, open-mouthed breathing.
Veterinarians use the “5 Ps” to describe the symptoms: Pain, Paralysis, Pulselessness, Poikilothermy (cold limbs), and Pallor (pale or bluish paw pads). The affected hind limbs will feel noticeably cooler to the touch compared to the cat’s front limbs. A weak or absent pulse in the femoral artery of the affected leg is a confirming physical finding.
If a saddle thrombus is suspected, the owner must minimize the cat’s movement and contact an emergency veterinary hospital without delay. Gentle handling is important to prevent further pain and stress. The cat should be transported on a stable, flat surface. Time is a factor, and attempting to self-treat or waiting for improvement is dangerous.
Treatment Strategies and Long-Term Outlook
Upon arrival at the veterinary hospital, the primary goal is aggressive pain management, often involving potent injectable opioid narcotics. Controlling the pain is paramount to stabilizing the cat. Supportive care is also provided, including keeping the cat warm and managing oxygen status, especially if heart failure is present.
The second strategy involves managing or dissolving the clot using medications. This includes anti-clotting medications like clopidogrel to prevent new clots, and sometimes thrombolytic drugs, such as tissue plasminogen activator, to break down the existing clot. Thrombolytic therapy carries significant risks, including a serious complication called reperfusion injury, which occurs when blood flow is restored, potentially releasing toxins that cause severe swelling or cardiac issues.
The long-term outlook remains guarded to poor, with many cats being euthanized due to the severity of pain and high risk of complications. Only about 50% of cats that receive aggressive treatment survive the initial crisis and are discharged. Lifelong management of the underlying heart disease and continued use of anti-coagulant medications are necessary to reduce the high risk of recurrence.