Aortic thromboembolism Flashcards
What are the main differentials for feline aortic thromboembolism
Feline arterial thromboembolism should be differentiated from:
- arterial thrombosis, which forms at the site of a vascular lesion within the arterial system (common in humans, very rare in cats)
- emboli secondary to hypercoagulation, infection or tumors (particularly pulmonary carcinomas)
What is the pathophysiology of ATE
It is accepted that a clot forms within the left heart of cats with myocardial disease (mostly the auricle or atrium), which then breaks off and floats downstream until its diameter exceeds that of the vessel in which it is travelling
Once lodged, the clot not only partially or completely occludes blood flow but more importantly, causes the release of vasoactive substances (serotonin and thromboxane A2) that contribute to vasoconstriction of local vessels that would otherwise form collateral circulation
What is the Virchow’s triad
The exact mechanisms of clot formation are unclear
Virchow’s triad suggests that the likely mechanisms are one or a combination of:
- alterations in endothelial integrity
- blood flow stasis within the dilated atrium/auricle
- changes to the composition of blood such that it becomes hypercoagulable
What are the aims of initial treatment for ATE
The aims of initial treatment should be to:
- alleviate anxiety and pain
- maintain systemic perfusion
- treat congestive heart failure if present
- reduction of further thrombus formation
What is the prognosis for FATE? what are the prognostic factors
ATE is usually associated with a poor prognosis with traditional rates of survival to discharge of 33%
- presence of CHF is not a poor prognosis
Better prognosis factors:
- only one limb is affected
- the cat has only partial loss of limb function
Poor prognosis factors:
- low rectal temperature
- reduced heart rate
- absence of motor function
What are the key facts for clopidogrel
Clopidogrel is a platelet inhibitor that irreversibly anatagonizes ADP receptors on platelets, interfering with primary and secondary platelet aggregation
Clopidogrel is a prodrug, and must be hepatically metabolized to form an active, highly unstable thiol compound (i.e., clopidogrel active metabolie)
- some cats lack the ability to convert clopidogrel into the metabolically active compound rendering the drug ineffective
The drug is given at 18.75 mg, PO, q24h
- for cats < 3 kg, the dose would be 10mg
Clopidogrel appears well tolerated
- occasional vomiting, diarrhea and anorexia that can be ameliorated by giving food concurrently with the drug
- nonregenerative anemia has been reported in some cats receiving long-term therapy
What are the key factors for Rivaroxaban
Rivaroxaban is a Factor Xa inhibitor, affecting both the intrinsic and extrinsic coagulation pathways
It appears safe and effective in producing a dose-dependent prolongation of coagulation times
Suggested dose range is 0.5-1.0 mg/kg/day, PO
Describe the evolution of thrombus formation leading to ATE
Impaired left ventricular filling can result in left atrial dilation, left auricular dysfunction and blood stasis
- this can be identified as spontaneous contrast or smoke on echocardiographic examination
The formation of the intracavitary thrombus begins with platelet activation and aggregation with subsequent release of proaggregating ans vasoconstrictive molecules and initiation of the coagulation cascade
The thrombus is initially platelet-rich but quickly becomes fibrin-rich as the thrombus grows and matures
- as the thrombu ages, it becomes lamellated and superficial portions can break off, or more rarely dislodges in entirety
What is the typical evolution of clinical signs of ATE and what is the therapeutic implication
Clinical signs develop acutely and can worsen but usually remain stagnant or improve over the next several days to 3 weeks
- it is important to strongly encourage owners to consider therapy for at least the first 72 hours
What are the more chronic complications of ATE
Self-mutilation
Limb necrosis requiring amputation
Limb contracture
Residual neurological deficits
How ATE can be prevented
Primary prevention is recommended in cats with:
- an end-systolic left atrial diameter > 17mm
- or left atrium to aortic ratio > 2.0
Primary prevention is also indicated in cats with spontaneous contrast (i.e., smoke) in the left atrium on echocardiography
