Arterial Thromboembolism (Saddle Thrombus) in Cats

Laurie Anne Walden, DVM

Photo by Kari Shea on Unsplash

Arterial thromboembolism (ATE) in cats has a guarded to poor prognosis and a high mortality/euthanasia rate. In ATE, a blood clot forms in the heart, travels through the circulation, and lodges in an artery. The clot blocks blood flow through that artery, causing significant pain and tissue damage. When the clot blocks an artery supplying a limb, as is usually the case, the limb becomes weak or paralyzed.
 
The most common site for ATE in cats is the aorta at the point where it divides into smaller arteries that supply the rear legs. A clot stuck here takes on the shape of a saddle, so ATE in this location is called a saddle thrombus.
 
Cats with a saddle thrombus have sudden extreme pain and paralysis of the rear legs (usually both rear legs but sometimes just 1). Witnessing their pain and distress can be quite upsetting to their caretakers.
 
Cause
ATE is usually caused by heart disease. Unfortunately, a saddle thrombus can be the very first sign that a cat has heart trouble.
 
The most common type of heart disease in cats—and thus the most common cause of ATE—is hypertrophic cardiomyopathy, an abnormal thickening of the heart muscle. Hypertrophic cardiomyopathy is most common in senior cats but can also affect younger cats. An estimated 15% of all cats and up to 29% of senior cats have hypertrophic cardiomyopathy.[1] Of these cats, a reported 11.3% develop ATE within 10 years after diagnosis.[2]
 
Signs
Signs of ATE usually appear suddenly. A cat with ATE will cry loudly in pain and might vomit. The cat will drag the affected limb or be unable to walk. The affected limb might feel cool to the touch.
 
If the cat’s underlying heart disease has progressed to heart failure, the cat might also have signs like panting or rapid breathing.
 
Diagnosis
ATE can usually be diagnosed with a physical examination. The affected limb is typically cool, the nail beds are bluer or paler than those of the other paws, and the pulse in that limb is absent or weak. A heart murmur might be present. Diagnostic tests can be used to rule out other possible causes, especially if the cat has less obvious signs caused by a partial blockage.
 
Treatment
Many cats with ATE are euthanized before treatment is attempted. Factors linked to a better prognosis include involvement of only 1 limb, ability to move the affected limb, and absence of heart failure (meaning that the heart disease has not yet progressed to the level of heart failure).
 
For cats that receive treatment, the immediate priority is pain control. They also receive anticoagulant medications (blood thinners), treatment for shock and tissue damage, and treatment for heart disease. Cats that don’t have heart failure and survive the first few days in the hospital have a chance of regaining the use of the affected limb once the clot dissolves.
 
Prevention
For cats known to have heart disease, certain findings on echocardiography (heart ultrasound) can indicate an increased risk for ATE. These cats can receive preventive anticoagulant medications. However, many cats with heart disease have no obvious signs, so their heart disease isn’t diagnosed.
 
References
1. Luis Fuentes V, Abbott J, Chetboul V, et al. ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. J Vet Intern Med. 2020;34(3):1062-1077. doi:10.1111/jvim.15745
2. Lo ST, Walker AL, Georges CJ, Li RH, Stern JA. Dual therapy with clopidogrel and rivaroxaban in cats with thromboembolic disease. J Feline Med Surg. 2022;24(4):277-283. doi:10.1177/1098612X211013736
 
Image source: https://unsplash.com/photos/gray-tabby-cat-FilM6ng7VGQ

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