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Arterial Thromboembolism

Key Points

• Although many authors have suggested a grave outcome associated with feline thromboembolic disease, recent reports
suggest that with aggressive treatment and diligent supportive care, a significant subset of cats can recover and lead good
quality lives.
• Initial therapy is directed at pain management, anticoagulant therapy, and control of congestive heart failure (if present). This
therapy can be instituted immediately and prior to echocardiographic evaluation.
• Chronic therapy typically includes medical management of the underlying heart disease with or without heart failure, and
anticoagulant therapy (typically antiplatelet agents).
• Cats often succumb to heart failure, although recurrence rates for ATE range from 24–75% (Lunsford and Mackin 2007).
• Prevention of ATE in asymptomatic cats should be considered when risk factors suggest ATE is likely (significant left
atrial enlargement [LA : Ao > 1.9 with echocardiography or severe LA enlargement radiographically if an echocardiogram
is not possible] or when spontaneous echogenic contrast is visible in the left atrium (echocardiographically). However,
anticoagulation is not generally recommended if these findings are not present (e.g., feline patient with a murmur and normal
heart size).

INTRODUCTION obstructive effect, vasoactive mediators released by the
clot result in constriction of collateral vessels. It is
Arterial thromboembolism (ATE) has long been associ- believed that these vasoactive mediators, rather than the
ated with cardiomyopathy. The syndrome is most often obstruction to blood flow, are primarily responsible for
associated with hypertrophic cardiomyopathy (HCM), the clinical signs associated with feline ATE. This theory
likely because this is the most common type of heart is supported by the fact that ligation of the distal aorta
disease in cats. One study found the prevalence of HCM in cats fails to reproduce the clinical syndrome (Butler
to be 14.5% in a population of asymptomatic cats 1971; Imhoff and Tashjian 1961), and clinical signs are
(n = 103). Although a majority (89–92%) of cats with ameliorated if cyproheptadine, a serotonin antagonist,
ATE have cardiogenic emboli, neoplasia (in particular is administered prior to thrombus formation (Olmstead
bronchogenic carcinoma), was the cause of ATE in 5% and Butler 1977). Similarly, aspirin therapy (resulting in
of cats, and 3% of cats had no identifiable cause of the thromboxane inhibition) prior to a surgically produced
ATE (Smith et al. 2003; Laste and Harpster 1995) aortic thrombosis preserves collateral circulation
Thrombosis is the formation of a clot within a cardiac (Schaub et al. 1982).
chamber or blood vessel. Thrombi may be located within
the left atrium, left ventricle, or both. Embolization PATHOPHYSIOLOGY AND GROSS PATHOLOGY
occurs when a clot is carried by blood flow to lodge in
a vessel (Figure 20.1). In cats, most thromboembolisms Pathophysiology
involve the left heart and systemic arteries, which causes Virchow’s triad describes the three prerequisites required
obstruction of the affected artery. In addition to this for thrombogenesis:

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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