Aortic Thromboembolism
Systemic arterial thromboembolism
Also known as: FATE, Feline Aortic Thromboembolism, Saddle Thrombus, Saddle Embolus, Systemic Arterial Thromboembolism
Systemic arterial thromboembolism
Also known as: FATE, Feline Aortic Thromboembolism, Saddle Thrombus, Saddle Embolus, Systemic Arterial Thromboembolism
In short
Aortic thromboembolism, or saddle thrombus, is a sudden, life-threatening emergency in dogs and cats where a blood clot blocks blood flow to the hind limbs. This guide explains the causes, critical warning signs, diagnostic process, and intensive treatment options for this severe cardiovascular condition.

TL;DR. Aortic thromboembolism, commonly known as a saddle thrombus, is a sudden and life-threatening veterinary emergency where a blood clot blocks blood flow to a pet's hind limbs, causing severe pain and paralysis.

A saddle thrombus lodges at the aortic trifurcation, completely blocking blood flow to the hind limbs.
Aortic thromboembolism (ATE)—often referred to as a "saddle thrombus" or feline aortic thromboembolism (FATE) in cats—is one of the most sudden, painful, and severe cardiovascular emergencies in veterinary medicine. The condition occurs when a blood clot (thrombus) forms inside the heart, breaks free, and travels down the main artery of the body (the aorta).
The aorta acts as the primary highway for oxygen-rich blood leaving the heart. As it travels toward the back of the body, it eventually splits into smaller branches that supply blood to each of the hind legs. This split is known as the aortic trifurcation. Because of the narrowing at this fork, a traveling blood clot frequently gets stuck right at the junction, straddling the split like a saddle. This blockage completely or partially cuts off the blood supply to one or both hind limbs, leading to a rapid and devastating lack of oxygen (ischemia) in the leg muscles and nerves.
When tissues are deprived of oxygen and glucose, a cascade of cellular damage begins. Within hours, muscle cells begin to die, a process known as rhabdomyolysis. This cellular breakdown releases dangerous levels of potassium and inflammatory proteins into the local tissues. At the same time, the sciatic and femoral nerves, which run down the hind limbs, are highly sensitive to oxygen deprivation. When their blood supply is cut off, they stop conducting electrical signals, leading to sudden paralysis (paresis) and a loss of reflexes.
For pet owners, understanding this condition is critical because it strikes without warning. A pet who appeared perfectly healthy moments before may suddenly collapse, lose the use of their back legs, and cry out in extreme distress. Immediate veterinary intervention is the only option to manage the intense pain and attempt to restore circulation.
The vast majority of aortic thromboembolism cases are secondary to underlying heart disease. In cats, the primary culprit is hypertrophic cardiomyopathy (HCM), a disease that causes the heart muscle to become abnormally thick. When the heart muscle thickens, the left atrium (one of the upper chambers of the heart) often stretches and enlarges. This enlargement disrupts normal blood flow, causing blood to pool and stagnate in the chamber, which highly predisposes the cat to clot formation.
A leading veterinary internal medicine reference describes this risk:
"Marked LA enlargement is thought to magnify the risk for thromboembolus formation, although TE events occasionally occur in cats with relatively normal LA size. Neoplastic and systemic inflammatory disease are occasionally associated with systemic thromboemboli in cats. Hyperthyroidism may be a risk factor for TE disease in cats independent of its cardiac effects."
Male cats are statistically at a higher risk for developing thromboembolic disease, though this bias is primarily due to the higher prevalence of hypertrophic cardiomyopathy in male felines.
In dogs, the causes of systemic blood clots are often different and are frequently linked to conditions that create a "hypercoagulable state" (a tendency for the blood to clot too easily). These underlying triggers in dogs include:
The clinical signs of a saddle thrombus are dramatic and develop almost instantly. Recognizing these signs immediately can mean the difference between life and death for your pet.

Pale or bluish footpads and cold paws are classic clinical signs of a saddle thrombus.
When you arrive at the emergency clinic, your veterinarian will perform a rapid physical examination focusing on the "five Ps" of vascular obstruction: Pain, Paresis (paralysis), Pulselessness, Pallor (paleness), and Poikilothermia (coldness). If these signs are present in the hind limbs, a presumptive diagnosis of aortic thromboembolism is made immediately, and pain management is started.
To confirm the diagnosis and evaluate the underlying cause, your vet will perform several key diagnostic tests:
"It is important to note that patients who have suffered FATE often exhibit tachypnea that presumably is a manifestation of pain. In this patient population, tachypnea is inconsistently associated with congestion and it is therefore appropriate to obtain thoracic radiographs before administering diuretics to patients with FATE."

Echocardiography is the gold standard for identifying left atrial enlargement and active clot formation.
Treating an aortic thromboembolism is incredibly challenging and requires intensive, round-the-clock hospital care. The primary goals of treatment are to manage the pet's intense pain, prevent the clot from growing, support the cardiovascular system, and monitor for life-threatening complications.
These medications do not dissolve the existing clot, but they are crucial for preventing the clot from getting larger and stopping new clots from forming:
In some cases, physical removal of the clot may be considered, though success rates vary significantly by species:
"Thromboembolus removal using an embolectomy catheter has not been effective in cats but might be more successful in dogs of larger size. Arterial stenting has been used successfully in some dogs with aortic thromboembolism."
The prognosis for pets suffering from an aortic thromboembolism is unfortunately poor. The condition carries a high mortality rate, with approximately 30% of patients dying or failing to survive the initial hospitalization period due to heart failure, severe tissue damage, or the effects of reperfusion injury.
Additionally, approximately 30% of cases result in euthanasia during the acute phase. This decision is often made due to the severe, unmanageable pain the pet experiences, the high financial cost of multi-day intensive care, or the poor long-term outlook for the underlying heart disease.
For pets that do survive the initial crisis and regain use of their limbs, the long-term outlook remains guarded. It can take weeks to months for nerve function to return, and some pets may have permanent deficits, such as "knuckling" (walking on the tops of their paws) or a permanent limp. Because the underlying heart disease or systemic clotting disorder is still present, repeated thromboembolic events are very common. Lifelong medication, frequent veterinary rechecks, and careful home monitoring are required to give these pets the best possible quality of life.
Because aortic thromboembolism is almost always a consequence of an underlying, silent disease, true prevention relies on early detection.
For cats, routine veterinary exams that identify a heart murmur or an abnormal heart rhythm should always be followed up with an echocardiogram. If a veterinary cardiologist detects significant left atrial enlargement before a clot forms, they will typically prescribe preventative medications like clopidogrel to reduce the risk of a future saddle thrombus.
For dogs, managing underlying conditions that cause hypercoagulability—such as treating Cushing's disease or closely monitoring protein-losing kidney diseases—is the most effective way to prevent systemic clots.
Aortic thromboembolism is an absolute, Category 5 veterinary emergency. If you suspect your pet is experiencing a saddle thrombus, do not wait to see if they improve. Drive to the nearest open veterinary hospital or emergency clinic immediately.
Call ahead to let the clinic know you are on your way with a suspected saddle thrombus so they can prepare emergency pain management and oxygen therapy. Watch for these critical red flags:
While any dog or cat can develop a blood clot, certain breeds have documented predispositions to the underlying conditions that cause them.
In cats, breeds prone to hypertrophic cardiomyopathy—such as Maine Coons, Ragdolls, Persians, and Sphynxs—are at a higher risk for FATE.
In dogs, specific breeds have been identified with a higher risk of thromboembolic events:
"PTE [Pulmonary thromboembolism] has also been reported in Cavalier King Charles, with and without underlying mitral valve disease."
If you own one of these predisposed breeds, regular veterinary checkups and proactive screening for cardiac and systemic diseases are essential steps in protecting your pet.
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Aortic thromboembolism, or saddle thrombus, is a sudden, life-threatening emergency in dogs and cats where a blood clot blocks blood flow to the hind limbs. This guide explains the causes, critical warning signs, diagnostic process, and intensive treatment options for this severe cardiovascular condition.
Absent arterial pulse、Acute limb paresis、Pain、Posterior paresis、Azotemia、Cool distal limbs、Cyanotic nailbeds、Dyspnea
Abdominal ultrasonography、Angiography、Doppler studies、Echocardiography、Measurement of muscle enzymes、Thoracic radiography
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
Peqaboo’s AI helps you track symptoms, understand lab reports, and know when to see a vet.
Get the Peqaboo app