Aortic Thromboembolism in Cats: Deep Welfare Guide
Pathophysiology
Feline aortic thromboembolism (ATE, also called 'saddle thrombus') occurs when a blood clot, usually originating from the left atrium in cats with hypertrophic cardiomyopathy (HCM) or other cardiac disease, lodges at the aortic trifurcation. This blocks blood flow to the hindlimbs, causing ischaemia of hindlimb muscles and peripheral nerves. The resulting inflammation and pain are severe. ATE occurs without warning in cats that may have appeared outwardly well.
Acute Welfare Emergency
ATE presents as sudden onset hindlimb paralysis or paresis with severe pain. Affected cats are in extreme distress: vocalising, panting, dragging hindlimbs, and unable to stand. Hindlimbs are cold, cyanotic, and have absent pulses. The distress is compounded by cardiovascular instability. Pain management is the immediate welfare priority; the condition is terrifying for both the cat and owners.
Prognosis and Welfare Decisions
ATE carries a poor short-term prognosis: many cats die or are euthanised within 24-48 hours due to cardiac failure or overwhelming pain. Survivors face a difficult recovery period and high recurrence risk. Factors affecting prognosis: degree of limb involvement (bilateral worse than unilateral), cardiac function, and temperature of affected limbs. The decision between aggressive treatment and euthanasia is profoundly difficult and must be made with compassionate owner support.
Treatment and Recovery
For cats where treatment is pursued: pain management (opioids; avoid aspirin in acute phase); supportive care (warmth, IV fluids if cardiac status allows); anti-thrombotic therapy (clopidogrel, heparin); and cardiac management for underlying disease. Limb reperfusion (when it occurs) causes ischaemia-reperfusion injury and can worsen pain and hyperkalaemia transiently. Long-term survivors require lifelong anti-thrombotic therapy and cardiac management.
Prevention in At-Risk Cats
Cats with HCM (particularly those with left atrial enlargement >1.7cm or spontaneous echo contrast 'smoke') are at highest ATE risk. Clopidogrel (Plavix) reduces the risk of first ATE and recurrence; it is the current standard of care for high-risk cats. The FATCAT study showed clopidogrel superior to aspirin for prevention. Regular cardiac monitoring of known HCM cats allows identification of deteriorating left atrial size and appropriate escalation of preventive therapy.