Feline Aortic Thromboembolism (FATE)

Care Pathway

1. Planning & Triage

Receptionist Telephone Triage

  • Prioritise as an Emergency: Advise the owner this is a veterinary emergency requiring immediate assessment
  • Advise Minimal Stress: Instruct the owner to handle the cat as little as possible and ensure transport is swift, quiet and stress-free
  • Manage Expectations: Inform the owner that this is a very serious condition and that initial priorities are pain relief and stabilisation
  • Red Flags requiring immediate assessment:
    • Sudden hind-limb paralysis with pain or cold limbs
    • Dyspnoea or open-mouth breathing
    • Collapse or unresponsiveness

In-Clinic Triage & Initial Plan

Core Triage Principle

FATE is an extremely painful and life-threatening emergency. The primary goals are to provide immediate, effective analgesia and anxiolysis while providing low-stress oxygen therapy and assessing for concurrent congestive heart failure (CHF).

Prepare for Arrival

  • Prepare a quiet, low-stress kennel or oxygen cage
  • Gather equipment for oxygen therapy (flow-by, mask, cage)
  • Draw up analgesics (e.g., methadone) and sedatives
  • Ready equipment for i/v access if possible with minimal stress
  • Ensure emergency CHF drugs (furosemide) and thoracocentesis kit are accessible
  • Have monitoring equipment ready (Doppler, ECG, BP monitor)

Immediate Triage Actions

  • Move the patient directly to the prepared low-stress area
  • Provide immediate flow-by oxygen while minimising handling
  • Administer analgesia and anxiolysis as the first priority
  • Perform a rapid, hands-off ABC assessment, focusing on respiratory rate/effort
  • Assess for the '5 Ps' (Pain, Paralysis, Pulselessness, Pallor, Poikilothermy)
  • If stable enough, perform a quick T-POCUS scan to check for CHF

2. Presentation & Risk Factors

Causes & Risk Factors

  • Cause: Thrombi form in the heart (usually left atrium), dislodge and obstruct a peripheral artery, most commonly the aortic trifurcation ('saddle thrombus')
  • Underlying Disease: Most cats have underlying cardiomyopathy (e.g., HCM, RCM, DCM), but many have no prior clinical signs of heart disease
  • Other Causes: Hyperthyroidism and neoplasia (e.g., pulmonary carcinoma) are less common causes
  • Risk Factors: Middle-aged cats, male bias, previous ATE, visible atrial thrombus or spontaneous echo contrast on echocardiogram

Key Clinical Features

Hallmark (The 5 Ps):

  • Pain (severe, acute onset)
  • Paresis or paralysis (typically hindlimbs)
  • Pulselessness (absent femoral/pedal pulses)
  • Pallor (pale or cyanotic nail beds/pads)
  • Poikilothermy (cold limbs)
  • Most cats have no known history of cardiac disease; a murmur or gallop may be the first sign
  • Presentation: Often peracute, with owners reporting howling then dragging one or both hindlimbs
  • Respiratory: Tachypnoea or open-mouth breathing may be due to pain, stress or concurrent CHF

3. Diagnostics

Diagnostic Approach

  • Primary Diagnosis: Based on the classic clinical findings (the 5 Ps)
  • Initial management is often based on clinical examination alone, as extensive investigation may be unsafe in a dyspnoeic or painful patient
  • Definitive diagnosis involves documenting the arterial occlusion and identifying the underlying cardiac disease
First-line Investigations

Thoracic Imaging (T-POCUS & Radiography)

  • T-POCUS: Rapid, low-stress tool to assess for CHF. Can detect pleural effusion, B-lines and enlarged left atrium
  • Radiography: Useful for detecting cardiomegaly and pulmonary oedema
  • AVOID forcing dyspnoeic cats into lateral recumbency

Blood Flow Evaluation

  • Use a Doppler transducer over the dorsal pedal or palmar artery
  • Absence of an arterial signal is highly suggestive of ATE
  • The presence of arterial blood flow does not exclude ATE

ECG

  • May reveal arrhythmias due to underlying cardiomyopathy
  • Continuous ECG is essential for detecting the effects of hyperkalaemia during reperfusion
  • Hyperkalaemia changes:
    • Bradycardia, tall/tented T waves, widened QRS, absent P waves
  • Use ECG pads instead of crocodile clips
Investigations to Consider

Biochemistry & Electrolytes

  • Biochemistry: Marked elevations in muscle enzymes (CK, AST), azotaemia, hyperlactaemia, hyperglycaemia
  • Electrolytes: Hyperkalaemia, hyperphosphataemia and hypocalcaemia are common, especially with reperfusion
  • Consider serial monitoring of potassium in the first 24-48 hours

Comprehensive Echocardiography

  • Gold standard for identifying underlying cardiomyopathy, assessing its severity and visualising intracardiac thrombi or spontaneous echo contrast
  • Best performed once the patient is stable

Contextualised Care: Limb Lactate & Glucose Measurement

  • Measurement of lactate and glucose differences between affected and unaffected limbs can support a diagnosis
  • This is rarely essential in practice, as clinical signs and ultrasound are the primary diagnostic tools
  • May be considered in equivocal cases or where rapid, safe analysis is possible
Differential Diagnosis
  • Acute spinal or limb injury: Including fractures or severe trauma
  • Spinal compression: From neoplasia, abscess or intervertebral disc disease
  • Alternative embolic disease: Caused by inflammatory disease, sepsis, neoplasia or fibrocartilaginous emboli (FCE)
  • Other causes of acute pain: Such as bite wounds or abscesses

4. Treatment Protocol

Immediate Supportive Care

Analgesia & Anxiolysis

  • This is the highest priority
  • Full mu-opioid agonists are required (e.g., Methadone)
  • Buprenorphine may be insufficient for the initial severe pain
  • Consider a fentanyl CRI for profound or ongoing pain
  • AVOID i/m injections into affected, poorly perfused limbs

CHF & Oxygen Management

  • Oxygen: Indicated for any respiratory distress; use flow-by or an oxygen cage
  • CHF: If confirmed, give furosemide boluses, titrating to effect based on respiratory rate
  • Thoracocentesis: Perform immediately for significant pleural effusion
  • AVOID diuretics for tachypnoea due to pain alone

Hyperkalaemia Management

  • Treat if severe hyperkalaemia or associated ECG changes are present
  • This is typically a sign of reperfusion injury
  • Treatment includes calcium gluconate (cardioprotective) and/or insulin-dextrose therapy
  • AVOID fluids until CHF is excluded
Thrombus Management

Antiplatelet Thromboprophylaxis (All Cats)

  • Goal: Prevent further clot formation and reduce risk of recurrence
  • Indicated for all cats post-FATE; give as soon as the cat is stable enough to swallow
  • First-line Monotherapy: Clopidogrel is proven superior to aspirin for preventing recurrence
  • Alternative Monotherapy: Rivaroxaban has shown equivalent recurrence and survival versus clopidogrel
  • SELECTED HIGH-RISK or RECURRENT CASES: Consider dual therapy (Clopidogrel + Rivaroxaban)

Decision Point: Adjunctive Anticoagulant Therapy?

  • May be considered to prevent propagation of the existing thrombus during initial stabilisation
  • Reasonable to use if:
    • The cat is hospitalised and not yet eating
    • There is concern about ongoing thrombus formation
    • Thrombolysis is not being given but clot stabilisation is desired
  • Efficacy is not fully established for these agents in FATE

Contextualised Care: Thrombolysis – Specialist Use Only

  • Only considered <6 h from onset, if bilateral occlusion and the cat is otherwise stable
  • High risk of fatal reperfusion injury. A 2022 study showed no survival benefit
  • Always consider “primum non nocere” (first do no harm)
CRITICAL SAFETY NOTE: Vasodilators such as acepromazine are NOT recommended. They are ineffective at restoring circulation and may exacerbate hypotension and shock

Contextualised Care: Discussing Euthanasia

  • Euthanasia is always a consideration, particularly if intractable pain or if intensive care is unavailable

5. Monitoring & Complications

Key Monitoring Parameters

  • Limb Perfusion: Limb temperature, colour of pads/nail beds, presence of pulses (Doppler)
  • Pain Score: Crucial for titrating analgesia
  • Respiratory: Sleeping/resting respiratory rate and effort to monitor for CHF
  • Hydration & Perfusion: Blood pressure, heart rate, urine output
  • Electrolytes: Serial potassium checks for reperfusion injury
  • Renal Values: Monitor for azotaemia

Potential Complications

  • Congestive heart failure (CHF)
  • Reperfusion injury (leading to severe hyperkalaemia and metabolic acidosis)
  • Acute kidney injury (AKI)
  • Local tissue necrosis, requiring limb amputation
  • Self-mutilation of affected limbs
  • Recurrence of thromboembolism

6. Nursing Care

Key Nursing Considerations

Pain Management & Stress Reduction
  • Perform regular, validated pain scoring to ensure analgesia is effective
  • Handle patients minimally and gently, using low-stress techniques
  • Ensure the patient is housed in a quiet, calm environment away from dogs
Limb Care & Mobility
  • Assess limb temperature, colour and swelling regularly
  • Once pain is controlled, gently perform passive range of motion (PROM) exercises to improve circulation and reduce stiffness
  • Protect devitalised limbs from trauma and monitor for signs of self-mutilation or pressure sores
  • Provide thick, soft, padded bedding (e.g., Vetbed) to support affected limbs
Monitoring for CHF
  • Monitor sleeping/resting respiratory rate (SRR/RRR) frequently (target <30 breaths/min)
  • Report any increase in rate, effort or the onset of open-mouth breathing immediately
  • Auscultate the chest for crackles or muffled heart sounds
Monitoring for Reperfusion Injury
  • Be vigilant for signs of reperfusion, which can occur 6-48 hours after presentation
  • Signs include worsening depression, collapse and bradycardia
  • Monitor electrolytes (especially potassium) and ECG for changes indicative of hyperkalaemia
Hygiene & Elimination
  • Monitor for urination and defecation; many cats are incontinent initially
  • Keep the patient clean and dry to prevent urine scald, especially around the perineum
  • Gently express the bladder if the cat is unable to urinate, but only if instructed by the vet
Nutritional & Hydration Support
  • Ensure fresh food and water are easily accessible without the cat needing to stand
  • Tempt the cat with warmed, strong-smelling foods
  • Inform the vet if the cat is not eating, as assisted feeding may be required once stable
  • Monitor hydration status, as cats with CHF may not receive i/v fluids

7. Prognosis

~35% Survival to Discharge Rate
146 days Median Time to Recurrence
  • The long-term prognosis for most cats is poor due to underlying heart disease and high recurrence rate
  • Euthanasia at the time of presentation is common
  • Negative Prognostic Indicators: Low rectal temperature (<37.2°C), more than one limb affected, presence of CHF, no motor function
  • Positive Prognostic Indicators: Single limb affected, voluntary limb movement on presentation
  • In the 1-year-long FATCAT study, recurrence occurred in 19/39 (49%) cats receiving clopidogrel
  • Recovery of limb function can take hours to weeks and may not be complete
  • Median survival time is significantly shorter in cats with concurrent CHF (77 days) vs those without (223 days)

8. Drug Dose Tables

Drug Class / Use Drug Dose Notes
Analgesia Methadone 0.1–0.3 mg/kg i/v or 0.1–0.5 mg/kg i/m
  • Full mu-opioid agonist; ideal for severe pain
  • Can be given transmucosally (0.6 mg/kg)
Buprenorphine 0.02–0.04 mg/kg i/v or i/m q6h
  • May be insufficient for initial severe pain
  • Use once pain is better controlled
Fentanyl 3–5 µg/kg i/v bolus, then 5 µg/kg/hr CRI
  • For severe, refractory pain
CHF Management Furosemide 1–4 mg/kg i/v or i/m q1-4h
  • Dose based on severity of CHF
  • Titrate based on respiratory rate improvement
Thromboprophylaxis Clopidogrel 18.75 mg/cat p/o q24h
  • First-line antiplatelet therapy
  • Consider 37.5 mg loading dose
Rivaroxaban 2.5 mg/cat p/o q24h
  • Factor Xa inhibitor; reasonable alternative to clopidogrel
Aspirin 5 mg/kg p/o q72h
  • Not recommended as sole agent
  • Used in some dual antiplatelet protocols
Anticoagulants Unfractionated Heparin 250 IU/kg s/c q6h
  • Efficacy not established; limited evidence
Dalteparin 75 IU/kg s/c q6h
  • Low-molecular-weight heparin; limited evidence

9. Supporting documents

Links

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