Feline Aortic Thromboembolism

🐱 Comprehensive Information on Feline Aortic Thromboembolism (FATE / CATE) for NAVLE Preparation

🔍 Definition and Overview

Feline Aortic Thromboembolism (FATE), also referred to as Cardiogenic Arterial Thromboembolism (CATE) or "saddle thrombus," is a life-threatening condition characterized by the embolization of a cardiac thrombus—most commonly from the left atrium—to the distal aortic trifurcation. It results in acute ischemia of the pelvic limbs and, less commonly, other systemic arteries.

• Prevalence:

  • ~1 in 175 cases in US tertiary centers

  • ~1 in 379 in UK general practices

• Primary cause: Cardiomyopathy in ~90% of cases

  • Most common: Hypertrophic Cardiomyopathy (HCM)

  • Others: Dilated Cardiomyopathy (DCM), Restrictive Cardiomyopathy (RCM), Unclassified Cardiomyopathies

⚙️ Pathophysiology

FATE results from Virchow’s triad:

1. Blood stasis: Due to poor left ventricular filling, leading to left atrial dilation and stagnation.

2. Endothelial injury: Damage to atrial endocardium promotes platelet activation and adhesion.

3. Hypercoagulable state: Includes:

   • ↑ Platelet hypersensitivity

   • ↓ Antithrombin and Protein C

   • ↑ Factor VIII and fibrinogen

🧬 Thrombus Formation:

• Platelet-rich → fibrin-rich thrombus within left atrium

• Embolizes to:

  • Aortic trifurcation (70–75%) → Bilateral hindlimb infarction

  • Unilateral pelvic limb (10–15%)

  • Brachial arteries (~10%)

  • Less common: renal, cerebral, mesenteric arteries

🚨 Clinical Signs

Classic “5 Ps” of acute limb ischemia:

1. Paresis/paralysis

2. Pulselessness

3. Pallor (cyanotic nail beds)

4. Pain

5. Polar (cold limbs)

🩺 Other signs:

• Hindlimb rigidity, absent reflexes, firm painful musculature

• Hypothermia

• Respiratory distress (from CHF or cardiomyopathy)

• Signs of underlying heart disease (dyspnea, gallop rhythm, murmurs)

• Neurologic deficits (if emboli affect CNS)

• Acute renal failure (renal infarction)

🧪 Diagnostics

Clinical Examination:

• Sudden onset of hindlimb paresis/paralysis

• Cyanotic, cold limbs

• Absent femoral pulses

• Pain response in affected limb

Point-of-Care Ultrasound (C-POCUS):

• Enlarged left atrium

• Visualization of intra-atrial thrombi

• Identification of underlying cardiomyopathy

Imaging:

• Thoracic radiographs: Evaluate pulmonary edema or CHF

• Echocardiography: Assess atrial size, myocardial structure

Laboratory Findings:

• ↑ CK, AST, ALT (muscle enzymes)

• Azotemia (pre-renal or renal)

• Hyperkalemia, hyperglycemia, metabolic acidosis

• Elevated lactate in affected limbs (especially >11.5 mmol/L = poor prognosis)

• Hypocalcemia, hypercholesterolemia

💊 Treatment

1. Acute Emergency Management

Analgesia:

• Methadone, fentanyl CRI, buprenorphine, oxymorphone

Cardiopulmonary Stabilization:

• Oxygen supplementation

• Furosemide if pulmonary edema is present

Thromboprophylaxis:

Anticoagulants:

• Unfractionated Heparin (UFH):

  • 250–375 IU/kg IV loading dose

  • 150–250 IU/kg SC q6–8h

• Low Molecular Weight Heparins (LMWH):

  • Dalteparin: 100 IU/kg SC q12h

  • Enoxaparin: 1.0–1.5 mg/kg SC q12h

Thrombolytics (controversial):

• Tissue Plasminogen Activator (t-PA):

  • 0.25–1 mg/kg/hr IV infusion

  • Total dose 1–10 mg/kg

  • High risk of bleeding; no definitive survival benefit

Reperfusion Injury Monitoring:

• Hyperkalemia

• Acidosis

• Bradyarrhythmias → ECG monitoring critical

2. Chronic Management & Prevention of Recurrence

Antiplatelet Therapy:

• Clopidogrel: 18.75 mg PO q24h (first-line)

• Aspirin: 5 mg/cat PO q48h (less effective)

Oral Anticoagulants:

• Rivaroxaban: 0.5–1 mg/kg PO q24h

• Apixaban: Alternative, dose varies

Dual Therapy:

• Clopidogrel + Rivaroxaban offers best protection against recurrence

Warfarin:

• 0.06–0.09 mg/kg PO q24h

• Requires close INR monitoring (target: 2–3)

Supportive Care:

• Nutritional support

• Passive range-of-motion physiotherapy

• Management of concurrent CHF or cardiomyopathy

📊 Prognosis

• Variable; depends on:

  • Number of limbs affected

  • Initial motor function

  • Rectal temp <37°C = poor outcome

  • Limb lactate >11.5 mmol/L = grave prognosis

• Survival to discharge (bilateral): ~37.5%

• Median survival post-discharge: 350–500 days

⚠️ Complications

• Reperfusion injury: Hyperkalemia, acidosis, arrhythmias

• Chronic ischemia: Risk of muscle necrosis, contracture, limb amputation

• Acute kidney injury (from myoglobinuria or hypotension)

✅ Key Takeaways for NAVLE

• FATE is often the first clinical manifestation of cardiomyopathy in cats.

• Left atrial thrombus is the origin in >90% of cases.

• Classic “5 Ps” help identify ischemic neuromyopathy.

• First-line treatment includes clopidogrel; dual therapy is best for recurrence prevention.

• Acute management must include analgesia, anticoagulation, and CHF stabilization.

• Prognosis is guarded to poor, especially with bilateral involvement and hypothermia.

📚 References

• Guillaumin, Julien. Feline aortic thromboembolism: recent advances and future prospects. Journal of Feline Medicine and Surgery. 2024.

• Kittleson, M. D., & Côté, E. (2021). The feline cardiomyopathies II: Hypertrophic cardiomyopathy. Journal of Veterinary Cardiology.

• Merck Veterinary Manual. Heart Disease and Thromboembolism in Cats.