Arterial Thromboembolism: Risks, realities and a rational first-line approachby V. L. Fuentes

Journal of Feline Medicine and Surgery


Small Animals


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Journal of Feline Medicine and Surgery (2012) 14, 459–470

Virginia Luis Fuentes


Risks, realities and a rational first-line approach

Practical relevance: Feline arterial thromboembolism (ATE) is a common but devastating complication of myocardial disease, often necessitating euthanasia. A combination of endothelial dysfunction and blood stasis in the left atrium leads to local platelet activation and thrombus formation. Embolisation of the thrombus results in severe ischaemia of the affected vascular bed.

With the classic ‘saddle thrombus’ presentation of thrombus in the terminal aorta, the diagnosis can usually be made by physical examination.

The prognosis is poor for cats with multiple limbs affected by severe ischaemia, but much better where only one limb is affected or motor function is present.

Patient group: Cats with left atrial enlargement secondary to cardiomyopathy are typically predisposed, although cats with hyperthyroidism, pulmonary neoplasia and supravalvular mitral stenosis may also be at risk.

Management: Analgesia is the main priority, and severe pain should be managed with methadone or a fentanyl constant rate infusion. Congestive heart failure (CHF) requires treatment with furosemide, but tachypnoea due to pain can mimic signs of

CHF. Thrombolytic therapy is not recommended, but antithrombotic treatment should be started as soon as possible. Aspirin and clopidogrel are well tolerated.

Evidence base: Several observational studies of

ATE have been reported. No randomised, blinded, controlled studies have been reported in cats at risk, for either treatment or prevention of ATE, although such a study comparing aspirin and clopidogrel in cats is currently under way.

Virginia Luis Fuentes


DipACVIM DipECVIM-CA (Cardiology)

Department of Veterinary Clinical Sciences,

The Royal Veterinary College,

Hawkshead Lane, North Mymms,

Hatfield, Hertfordshire AL9 7TA, UK


Cats and ATE

Arterial thromboembolism (ATE) occurs when a thrombus formed in one part of the circulation embolises to a peripheral artery (Figure 1).

Arterial blood flow is decreased to tissues distal to the thrombus as a result of mechanical obstruction and vasoconstriction of the collateral blood supply. In cats, the source of the thrombus is generally the left auricular appendage (LAA) (Figure 2). Cats are particularly prone to ATE in comparison with other species, which is partly (but not entirely) explained by their high prevalence of myocardial disease.

Associated conditions

Most cats presenting with ATE have underlying cardiac disease.1,2 Males are over-represented, but this probably reflects the male predisposition to myocardial disease.3 Hypertrophic cardiomyopathy (HCM) is the most common underlying condition associated with

ATE (being the most common type of myocardial disease), but cats with any form of cardiomyopathy (other than arrhythmogenic right ventricular cardiomyopathy) can be presented with ATE. The risk of ATE appears to be greatest with more severe forms of cardiomyopathy, irrespective of the specific type of myocardial disease. Cats with secondary myocardial disease are also at risk, which includes euthyroid cats with treated hyperthyroidism.1 Some congenital heart defects such as supravalvuDOI: 10.1177/1098612X12451547 © ISFM and AAFP 2012

Figure 1 Thrombus (arrow) present in the terminal aorta in a cat presented with ATE


Two video recordings are included in the online version of this article at

DOI: 10.1177/1098612X12451547 at TEXAS SOUTHERN UNIVERSITY on December 13, 2014jfm.sagepub.comDownloaded from 460 JFMS CLINICAL PRACTICE lar mitral stenosis have been associated with

ATE, but this is an uncommon cause.1 There is also a risk of systemic thromboembolism with septic emboli in infective endocarditis, but this is also rare.

The most common non-cardiac cause of

ATE in cats is pulmonary neoplasia, although this is caused by tumour emboli rather than a true thrombus.1 Rarely, no underlying condition is found.

Clinical importance

ATE is probably one of the most distressing conditions encountered in feline practice, particularly as there is often no advance warning.

Owners experience the initial trauma of finding their cat paralysed and in pain, only to face the subsequent devastating news of the poor prognosis. Owners of affected cats are often advised that their pet may not survive the initial episode; or, even if it survives to discharge, may succumb to a future bout of thromboembolism. While both of these statements may be true, it is also true that some cats will regain completely normal motor function following an initial ATE episode, and ATE survivors are more likely to die of congestive heart failure (CHF) than ATE.1

Fortunately, only a minority of cats with cardiomyopathy will go on to develop ATE, but

HCM is sufficiently prevalent that ATE is still a commonly encountered problem in feline practice.

The true prevalence of ATE is not known, as most reports originate from referral institutions. Smith et al reported an overall prevalence of ATE of less than 0.6% of cats seen at

REV IEW / Feline ATE

Figure 2 Echocardiographic image showing a thrombus (arrow) in the left auricular appendage in a cat with HCM and left atrial enlargement. This is a right parasternal short axis view.

Ao = aortic valve, LA = left atrium

The risk of ATE appears to be greatest with more severe forms of cardiomyopathy, irrespective of the specific type of myocardial disease. the Veterinary Teaching Hospital of the University of Minnesota.1 The reported prevalence in cats with HCM varies from 12–21%,4,5 although these are biased population samples that probably reflect a particularly high proportion of symptomatic cats. Recent studies of apparently healthy cats suggest that the prevalence of subclinical HCM may be much higher than previously thought (potentially up to 15% of adult cats),6,7 so the prevalence of ATE in cats with HCM is probably much lower than 12%, as ATE is usually seen only in cats with the most advanced cardiomyopathies. Conversely, many cats presenting with ATE in first opinion practice are euthanased, and are therefore not accounted for in prevalence estimates based on referral populations.