How to handle feline aortic thromboembolism

A blocked artery caused by a thromboembolus occurs in almost one-third of cats with heart disease, resulting in devastating consequences that often start with pelvic limb paralysis. These clinicians help you detect the blockage, explore newer treatment options, recognize which treatments are not recommended, and identify prevention strategies.

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Aortic thromboembolism (ATE) is a disease process whereby a thrombus is formed, typically in the left atrium. The thrombus then, either in part or as a whole, dislodges and travels (embolizes) through the aorta distally until it reaches an artery of small enough diameter that it can travel no farther. Heart disease is the most common cause of ATE in cats; two separate retrospective studies have identified cardiac disease in more than 90% and in 69% of cats with thromboembolism.1,2 Neoplasia and thyroid disease have also been associated with ATE.

This article discusses alterations in normal hemostasis that may predispose cats to thromboembolism; ATE's clinical presentation, diagnosis, and treatment; and possible prevention strategies.


Thromboembolism is a fairly common and potentially devastating complication of heart disease in cats. ATE has been found in 12% to 28% of cats with hypertrophic cardiomyopathy (HCM) and 27% of cats with unclassified cardiomyopathy.2-5 Less commonly, ATE has been reported in cats with arrhythmogenic right ventricular cardiomyopathy and atrial fibrillation.6,7

1. A photo taken at necropsy of a thrombus lodged at the aortic trifurcation. The cat's head is to the right.
Close to 90% of cats with systemic thromboembolism have a thrombus that lodges in the terminal aorta (aortic trifurcation) (Figures 1 & 2).8 Other potential sites for embolization include brachial, visceral, and cerebral arteries.8,9 Thrombi typically form in the left atrium or left auricle. A dilated left atrium is one of the biggest risk factors for ATE. In a study of cats with HCM, those with ATE had a significantly larger left atrial diameter than those that had congestive heart failure (CHF) alone or had subclinical disease.4 Arterial thromboembolism affects male cats more often than females, but cardiac disease more commonly affects males.2,9

2. The excised thrombus from the cat in Figure 1.
Other diseases associated with thromboembolic disease in cats include neoplasia and thyroid disease. Pulmonary carcinoma causes embolic disease through both thromboembolism and embolization of tumor cells.2,10-12 Since cardiac disease is by far the most common cause of ATE in cats, we focus on ATE secondary to cardiac disease in this article.