Page 307 - Feline Cardiology

Chapter 20: Arterial Thromboembolism 315

The decision to begin long-term anticoagulant
therapy is case and clinician dependent. Although there Box 20.2. Timing of initiation of anticoagulant therapy in
are currently no studies that show these therapies are asymptomatic patients
beneficial, the general consensus is that therapy should Very High risk (begin anticoagulant therapy) Echocardio-
be initiated in cats that have experienced ATE, with most graphic spontaneous contrast or thrombus, prior ATE event
clinicians currently choosing aspirin or clopidogrel
therapy. Beginning therapy in asymptomatic cats is less High risk (consider anticoagulant therapy)
clear cut. In general, therapy is not recommended Severe left atrial enlargement (echocardiographic left atri-
without evidence of heart enlargement (i.e., a cardiac um : aorta >1.9 or subjective severe LAE on radiographs if
murmur alone is not an adequate reason to begin anti- echocardiography not available)
coagulant therapy). See Box 20.2 for factors to consider
before initiating anticoagulant therapy in the asymp- Low risk (anticoagulant therapy not recommended)
tomatic feline patient. Normal left atrial size or mild-moderate left atrial enlarge-
In cardiomyopathic cats with atrial enlargement and ment (echocardiographic, or radiographic if echocardiog-
spontaneous echocardiographic contrast (a change that raphy is not available)
suggests that the patient is at risk for thromboembolic
events), most clinicians recommend prophylactic these results are available, the general consensus is that
therapy. The decision is less clear in cats with heart clopidogrel is likely more effective than aspirin for pre-
disease without evidence of spontaneous echocardio- vention of ATE. However, it is important to weigh the
graphic contrast. Regardless of the underlying heart specific advantages and disadvantages of aspirin and
disease, the main factor in deciding whether to start clopidogrel to choose the best option for the individual
anticoagulant therapy is the severity of atrial dilation. patient and owner.
The authors usually recommend anticoagulation if left Clopidogrel is more expensive than aspirin and it Arterial Thromboembolism
atrial enlargement is severe, depending on discussion should be given with food. In a human study, clopido-
with the owner. With mild to moderate left atrial enlarge- grel was associated with significantly fewer gastrointes-
ment, anticoagulant therapy is rarely recommended tinal tract events than aspirin (27.14% vs 29.82%);
unless there are other factors suggesting the individual however, more adverse dermatologic events were associ-
patient may be at risk. ated with clopidogrel (15.81% vs 13.08%) (Hogan et al.
In those asymptomatic cats that cannot be examined 2004). Clopidogrel administration is objectionable to
by echocardiography, if the radiographic heart size some cats because of its bitter flavor, but most cats toler-
is normal, anticoagulant therapy is not empirically ate the medication in pill pockets or gel caps. It must be
recommended. However, in those cats with significant given daily, so in cats which are particularly difficult to
left atrial dilation on thoracic radiographs (even pill, aspirin administration every third day may be more
when an echocardiogram cannot be performed), empir- reasonable for the owner. Transdermal administration
ical anticoagulant therapy is a reasonable option. of neither clopidogrel nor aspirin has been studied and
Echocardiography is the ideal way to assess left atrial size is not recommended. Some clinicians prefer to avoid
and risk of ATE. See Figure 20.11 for an algorithm aspirin in patients with renal disease because of possible
describing the decision tree for beginning anticoagulant gastric acidity; clopidogrel may be superior in these
therapy in asymptomatic and symptomatic cats with patients as long as it does not alter their appetites.
heart disease. It is also important to reserve therapy for
those patients likely to benefit from it. Otherwise, par- Aspirin
ticularly in patients that are difficult to pill, the risk of As stated above, cats given aspirin orally 1 hour before
patient/owner burnout and noncompliance is great. thrombus occlusion of the aorta had better collateral
circulation than did those cats that did not receive
Antiplatelet Therapies: Clopidogrel, Aspirin, aspirin (Schaub et al. 1982), suggesting aspirin therapy
and Abciximab may be beneficial even during the acute thromboem-
Antiplatelet therapies focus on the principle that expo- bolic event. In cats, aspirin effectively inhibits platelet
sure of blood to subendothelial connective tissue leads function (Greene 1985; Behrend et al. 1996) and is rela-
to rapid platelet activation, platelet plug formation and tively safe; therefore it is a reasonable option for chronic
subsequent thrombus. A clinical trial comparing efficacy therapy. The optimum dose that will inhibit thrombox-
of aspirin and clopidogrel in cats that have experienced ane A production, yet spare prostacyclin synthesis has
ATE is currently underway. The results should identify not yet been established for cats. However, no difference
the optimal therapeutic choice in these patients. Until was detected between low (5 mg/cat q 72 hours, n = 24)