Saddle Thrombus (Aortic Thrombosis) in Dogs

Key Takeaways

A saddle thrombus is when a large blood clot becomes lodged in the aorta, obstructing blood flow to the hind limbs in dogs.

• The aorta is a large artery which carries blood from the heart to the rest of the body

This rare condition is usually fatal

• Saddle thrombus is associated with heart conditions, circulatory disturbances, and as a rare complication in metabolic disorders

• Symptoms are progressive, developing into hind limb weakness and paralysis

• Other symptoms include severe pain, limbs and feet that are cool to the touch, and reduced mobility

• Diagnostics include physical examination, urinalysis, diagnostic imaging, and bloodwork 

• Treatment includes medication which lessens or prevents blood clotting, alongside targeted treatments directed at the underlying cause

• Even with immediate and aggressive treatment, the prognosis is extremely poor, and euthanasia is common

A Closer Look: What is Saddle Thrombus in Dogs?

The aorta is the major artery that carries blood from the heart to the rest of the body. The area above the hind legs where the aorta branches to supply blood to both appendages is referred to as the “saddle.” When a blood clot gets caught in this junction, it can restrict blood flow to the hind legs, resulting in a saddle thrombus.

A slow-forming clot or chronic saddle thrombus often shows no symptoms at first. Over time, there is a gradual loss of rear leg function. Thrombi that form quickly show sudden symptoms, with rapid development of rear limb dysfunction. In these cases, the condition is both stressful and painful. Other symptoms vary, as a saddle clot may develop alongside other concurrent conditions.

Risk Factors

Aortic thrombosis is rare, but painful and often fatal. It is more common in older dogs, as they have the highest prevalence of underlying conditions that lead to thrombosis. Discovery of the clot may be an indicator of another serious condition. Since the clot cuts off blood supply to the hind limbs and is extremely painful, emergency medical attention is required.

Possible Causes

Blood clots form in response to infections, injuries, diseases, or as a result of irregular blood flow. Conditions associated with a saddle thrombus include: 

Protein loss disorders:  Protein levels are depleted due to excessive losses in the urine or digestive tract. Examples include: 

• Protein-losing enteropathy

• Protein-losing nephropathy

Heart disease/circulatory disturbances, such as:

• Cardiomyopathies

• Bacterial endocarditis

Sepsis

Congenital heart defects

• Congestive heart failure

Rare complication of some metabolic/endocrine diseases, including:

Hyperadrenocorticism

Diabetes mellitus

Hypothyroidism

Pancreatitis 

In addition to gastric dilatation and volvulus and some types of cancer.

In some cases, there is no identifiable underlying cause for the thrombus.

Main Symptoms

As the blood in the aorta clots, blood is unable to reach the hind legs properly. Without blood flow, the tissues are unable to receive oxygen, quickly leading to symptoms such as:

• Limbs or feet that are cool to the touch

Paralysis

Poor mobility/balance (ataxia)

• Loss of function in the rear limbs that worsens over time

Cyanosis of the nail beds (blue coloration to skin)

Testing and Diagnosis

Symptoms are usually enough to diagnose aortic thrombosis, and given the severity of the condition euthanasia is commonly chosen over treatment.

If moving forward with treatment, a full workup is required to discern why the thrombosis developed. Diagnostics include:

• Physical examination

• Diagnostic imaging, including X-rays and ultrasound

• Urinalysis

• Electrocardiogram (ECG)

• Bloodwork, specifically including clotting profiles.

Steps to Recovery

Treatment includes medication to break up the blood clot, such as thrombolytics, antiplatelet therapy, and anticoagulants. Surgical removal of the clot may also be possible with referral to a specialist. Further treatment targeted at the underlying cause of the clot is essential, otherwise there is the potential for recurrence.

It is important to monitor recovery via ultrasound to observe progress in the clot’s disruption, and to catch any complications in restoring proper blood flow. During treatment, pain medications and sedatives are often given to improve patient comfort. 

Saddle thrombus has a very poor prognosis. Even with treatment, the life expectancy once a pet develops a saddle thrombus is measured in months. Pets with saddle thrombi that develop slowly over time may live longer, although treatment is still unlikely to be successful.

Euthanasia is a common choice for animals which develop this kind of blood clot.

Prevention

Appropriate management of chronic conditions which can lead to thrombosis is the most effective way to prevent a clot from developing. Keeping up with regular check upsa and vaccinations is the best way to catch underlying conditions early, especially as dogs age. Blood clots are not contagious.

Is Saddle Thrombus Common in Dogs?

Aortic thrombosis is very rare  in dogs.

Typical Treatment

• Euthanasia

• Medication

• Surgery

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