Page 258 - Small Animal Internal Medicine, 6th Edition

230 PART I Cardiovascular System Disorders

persist for a variable time. Tissue necrosis might require associated with many conditions, including systemic and
wound management and skin grafting. Permanent limb endocrine diseases leading to hypercoagulability, neoplasia,
VetBooks.ir deformity develops in some cats, and amputation is occa- aortic disease, and some cardiovascular diseases. However,
in many cases (up to half of dogs with aortic thrombosis in
sionally necessary. Repeated ATE events are common, as is
progressive CHF. Overall, median long-term survival is
Aortic thrombosis appears more prevalent in male compared
approximately 6 to 9 months. some reports) no predisposing abnormality can be found.
with female dogs. It is unclear whether any true breed pre-
PROPHYLAXIS AGAINST ARTERIAL disposition exists, although Greyhounds, Cavalier King
THROMBOEMBOLISM IN CATS Charles Spaniels, and Labradors might be overrepresented.
Prophylactic therapy with an antiplatelet or anticoagulant The most common cause of aortic thrombosis in dogs is
drug is commonly used in cats thought to be at increased protein-losing nephropathy, in which urinary loss of AT
risk for ATE. This includes cats with history of ATE, as well leads to a hypercoaguable state. Similarly, protein-losing
as cats with cardiomyopathy and moderate to severe LA enteropathy could predispose dogs to aortic thrombosis via
enlargement, decreased LA or auricular function, or intra- alimentary loss of AT. Other procoagulant conditions com-
cardiac spontaneous echo-contrast or thrombus on echocar- monly associated with aortic thrombosis in dogs include
diography, However, the efficacy of thromboprophylaxis is hyperadrenocorticism (or recent steroid administration),
unknown, and a strategy that consistently prevents ATE has hypothyroidism, and diabetes mellitus. Neoplasia can result
not been identified. in TE disease either via tumor embolism or by inducing a
Drugs used for ATE prophylaxis include platelet inhibi- paraneoplastic hypercoagulable state. Common neoplasms
tors (clopidogrel or aspirin), LMWH, warfarin, and factor associated with aortic thrombosis include hemangiosar-
Xa antagonists. The antiplatelet drugs are prescribed most coma, pulmonary carcinoma, osteosarcoma, intravascular
commonly, both because they target platelet adhesion (the lymphoma, and adrenal tumors. Diseases directly affecting
most critical factor for thrombus formation in high-shear the aorta, including aortitis, aortic intimal fibrosis, athero-
states), and because platelet inhibitors present a low risk for sclerosis, aortic dissection, or aortic tumors, can also cause
serious hemorrhage and require minimal monitoring. Clopi- aortic thrombosis.
dogrel is preferred over aspirin based on its superior clinical Unlike in cats, common primary structural cardiac dis-
effect in prevention of secondary ATE in cats, although a eases of dogs (cardiomyopathy or degenerative valve disease)
comparison of clopidogrel versus aspirin for prevention of rarely cause thrombosis. The most common cardiac diseases
primary ATE has not been undertaken. Warfarin rarely is associated with systemic thrombotic disease in dogs are
used because of increased bleeding risk, frequent monitoring vegetative endocarditis and cardiac neoplasia. Other car-
required, and lack of demonstrated survival benefit. LMWH diovascular conditions occasionally associated with canine
is expensive and must be given by SC injection, but some thrombotic disease include patent ductus arteriosus (throm-
owners are motivated to do this. Platelet inhibitors can be bosis at the surgical ligation site), arteritis, LA rupture, or
used concurrently with LMWH in cats that are not throm- granulomatous inflammatory erosion into the LA. In the
bocytopenic. No studies have evaluated the efficacy of anti- presence of a right-to-left shunting atrial or ventricular septal
platelet or anticoagulant drugs in prevention of ATE in cats. defect, fragments originating from venous thrombosis could
Therefore empiric decisions about thromboprophylaxis are cross the defect to cause systemic arterial embolization.
clinician-dependent judgments based on risk stratification: Atherosclerosis is uncommon in dogs, but it has been
cats with HCM and severe LA often receive clopidogrel associated with thrombotic disease in this species, as it has
alone, whereas cats with spontaneous echo-contrast, an in people. Endothelial disruption in areas of atherosclerotic
intracardiac thrombus, or history of ATE might receive clop- plaque, hypercholesterolemia, increased PAI-1, and possibly
idogrel in combination with LMWH or a factor Xa other mechanisms could be involved in thrombus formation.
inhibitor. Atherosclerosis may develop with profound hypothyroidism,
hypercholesterolemia, or hyperlipidemia. The aorta, coro-
nary arteries, and other medium to large arteries are affected.
SYSTEMIC ARTERIAL THROMBOSIS Myocardial and cerebral infarctions occur in some cases, and
IN DOGS there is a high rate of interstitial myocardial fibrosis in
affected dogs. Vasculitis related to infectious, inflammatory,
Arterial thrombotic disease in dogs is relatively uncommon immune-mediated, neoplastic, or toxic disease can underlie
compared with cats. However, the true prevalence is thrombosis or embolic events. Arteritis of immune-mediated
unknown and may be underrecognized in dogs because of pathogenesis is described in some young Beagles and other
differences in pathogenesis and clinical presentation. The dogs.
distal aorta is the most commonly reported location, and in
dogs usually results from primary (in situ) thrombus forma- Clinical Features
tion, rather than an acute distant embolic event as in cats. The distal aorta is the most common location for clinically
The development of clinical signs in these dogs is usually recognized TE disease in dogs. Affected dogs typically
more vague and chronic. Aortic thrombosis in dogs has been present for intermittent rear limb lameness or paresis