Page 1433 - Small Animal Internal Medicine, 6th Edition

CHAPTER 87 Disorders of Hemostasis 1405

THROMBOSIS sighthounds. Decreased activity of the natural anticoagulant
AT plays a major role in the thrombosis seen in dogs with
VetBooks.ir Thrombotic and thromboembolic disorders appear to be protein-losing nephropathy or protein-losing enteropathy;
in addition, humans with hypertension frequently have a
considerably less common in cats and dogs than in humans.
Several situations can result in thrombosis or TE, including
stasis of blood, activation of intravascular coagulation in an high concentration of PAI-1, which in turn inhibits fibrino-
lysis, thus resulting in a net procoagulant effect. This mecha-
area of abnormal or damaged endothelium, decreased activ- nism may also be important in dogs with protein-losing
ity of natural anticoagulants, and decreased or impaired nephropathy and hypertension. The decreased AT activity
fibrinolysis. Thrombosis has been recognized clinically as stems from the fact that this is a relatively small molecule
associated with cardiomyopathy, hyperadrenocorticism, (≈60 kDa) that is easily lost in the urine or gut contents in
protein-losing enteropathy and nephropathy, and IHA. A dogs with either of these two disorders. The thrombosis
syndrome of aortoiliac thrombosis has been recognized pri- commonly seen in dogs with hyperadrenocorticism is likely
marily in Cavalier King Charles Spaniels, Greyhounds, and related to the induction of PAI-1 synthesis by corticosteroids
other sighthound breeds (Goncalves et al., 2008; Lake- (corticosteroids inhibit fibrinolysis). An increased risk for
Bakaar et al., 2012). TE has been recognized in dogs with IHA. Although the
Diagnosing TE is not an easy task. Clinical signs are vari- pathogenesis of these disorders is obscure, the release of
able and include signs associated with parenchymal organ procoagulants from the lysed RBCs has been postulated as a
ischemia (e.g., dyspnea from pulmonary TE, high liver cause; sludging of autoagglutinated RBCs in the microcircu-
enzyme activities in patients with hepatic TE, intermittent lation is also likely to contribute to this procoagulant state.
rear limb claudication in dogs with aortic thrombosis). A Dogs and cats at high risk for thrombosis or TE should
positive D-dimer test has been reported to be associated with receive anticoagulants. The two drugs commonly used in
TE disease in dogs, but that is not my experience. TEG is a cats and dogs at risk for this condition are aspirin and
rapid and sensitive test to diagnose TE disease in some dogs heparin. Coumarin derivatives are commonly used in
(Fig. 87.5); however, in a large proportion of dogs with overt humans, but in dogs and cats they can result in excessive
thrombosis, the TEG tracings are normal. bleeding. In recent reports of human AT deficiency, ana-
Stasis of blood and possibly an irregular endothelial bolic steroids such as stanozolol have also been suggested
surface appear to be the major causes in cats with aortic to decrease the risk of thrombotic disorders because of their
(iliac) TE secondary to hypertrophic cardiomyopathy. Arte- stimulatory effect on the fibrinolytic system. The recogni-
rial pathology and high blood viscosity associated with a tion and management of pulmonary TE are discussed in
high hematocrit are suspected in Greyhounds and other Chapter 22.

A

B
FIG 87.5
(A) Thromboelastograph Hemostasis Analyzer system (TEG) tracing in a normal dog. The
maximum amplitude (MA) provides information on the strength of the clot and is within the
reference range (53.9 mm). (B) TEG tracing in a dog with hypercoagulability. Note that
the MA is 80.3 mm.