Peripheral Arterial Embolism

Sudden blockage of a peripheral artery by material travelling from a proximal source. The cardiac source accounts for about 80 to 90%: atrial fibrillation (commonest), left ventricular thrombus (after infarction or in dilated cardiomyopathy), mitral stenosis, prosthetic valves, infective endocarditis and atrial myxoma. Non-cardiac sources: mural thrombus or atheroma in the aorta, aneurysm thrombus (aortic, popliteal), paradoxical embolism through a patent foramen ovale or septal defect, and tumour fragments.

• Emboli lodge at arterial bifurcations: common femoral (about 30 to 40%), iliac (about 10 to 15%), popliteal (about 15 to 20%), aortic bifurcation (saddle embolus, about 5 to 10%), and brachial and axillary arteries in the arm (about 15 to 20%). The previously normal artery has few collaterals, so ischaemia is severe and sudden.
• Outcome: limb salvage in about 75 to 85% with prompt treatment; 30-day mortality about 10 to 25%, mostly from the underlying cardiac disease; amputation about 10 to 20%.
• Reperfusion injury: release of potassium, myoglobin and lactate causes hyperkalaemia, rhabdomyolysis, acute kidney injury and arrhythmia.

• Abrupt pain, pallor, pulselessness, coldness, paraesthesia and weakness (the six Ps with perishing cold). Skin mottling and a sharp line of demarcation develop in hours. Contralateral pulses are usually normal, and there is no history of claudication.
• Cardiac findings: irregularly irregular pulse in atrial fibrillation, murmur of mitral stenosis, prosthetic valve click change, signs of endocarditis.
• Differential diagnosis: acute thrombosis on chronic atherosclerosis (history of claudication, absent contralateral pulses), aortic dissection, thrombosed popliteal aneurysm, trauma, phlegmasia cerulea dolens, cardiogenic shock with low flow, spinal cord infarction, acute neuropathy, and compartment syndrome.
• Complications: limb loss, compartment syndrome, reperfusion injury with hyperkalaemia and acute kidney injury, recurrent embolism, stroke, mesenteric or renal embolism, and death.

• Clinical examination and handheld Doppler (arterial signal present or absent), with ankle pressure. Grade the limb:
  • Viable: no sensory loss or weakness, audible arterial and venous Doppler signals.
  • Marginally threatened: minimal sensory loss of the toes, no weakness, arterial signal often inaudible, venous signal audible.
  • Immediately threatened: sensory loss beyond the toes with rest pain, mild or moderate weakness, arterial signal inaudible.
  • Irreversible: profound anaesthesia, paralysis, absent arterial and venous signals, skin marbling, muscle rigor.
• Do not delay revascularisation for imaging in an immediately threatened limb. CT angiography (arterial and delayed phases) or duplex ultrasonography defines the level and the inflow and outflow; angiography at the time of intervention.
• Search for the source: ECG, 14 to 30 day rhythm monitoring, transthoracic and transoesophageal echocardiography (left atrial appendage, ventricular thrombus, vegetation, patent foramen ovale), CT of the aorta, blood cultures if febrile.
• Blood tests: creatine kinase, potassium, creatinine, lactate, troponin, full blood count, coagulation, group and crossmatch; thrombophilia and antiphospholipid antibodies in patients under 50 or with no cardiac source.

• Immediate measures:
  • Unfractionated heparin 80 units/kg IV bolus (typically 5000 units) then 18 units/kg/h, aPTT 1.5 to 2.5 times control.
  • Analgesia: morphine 2 to 5 mg IV, repeated; oxygen; IV fluids; keep the limb at or just lower than heart level and protect it from pressure and heat; do not elevate, ice or apply heat.
  • Correct hyperkalaemia, acidosis and volume depletion before and after reperfusion.
• Revascularisation (urgent: within 6 hours for an immediately threatened limb):
  • Surgical embolectomy with a balloon embolectomy catheter, usually through a common femoral arteriotomy under local anaesthesia, with on table angiography to confirm outflow. Success is about 80 to 90% for a recent embolus.
  • Catheter directed thrombolysis for viable or marginally threatened limbs and for distal emboli: alteplase 0.5 to 1 mg/h through a multi-side-hole catheter (maximum total about 40 mg), with fibrinogen checked every 4 to 6 hours and the infusion stopped if fibrinogen is less than 1 g/L; repeat angiography every 12 to 24 hours. Aspiration thrombectomy is an alternative.
  • Contraindications to thrombolysis: active bleeding, stroke or neurosurgery within 3 months, intracranial tumour, major surgery or trauma within 3 weeks, severe uncontrolled hypertension (greater than 180/110 mmHg), and an immediately threatened limb that needs rapid reperfusion.
  • If embolectomy fails or the artery is diseased (in situ thrombosis): bypass or endarterectomy with patch.
  • Irreversible ischaemia: primary amputation after resuscitation.
• Fasciotomy (four compartment of the calf) when ischaemia has lasted more than 4 to 6 hours, compartments are tense, there is neurological deficit after reperfusion, or creatine kinase is rising steeply.
• Reperfusion injury:
  • Fluid: 0.9% saline to keep urine output at more than 1 mL/kg/h (200 to 300 mL/h if rhabdomyolysis is severe), with monitoring of potassium, creatine kinase and creatinine every 4 to 6 hours.
  • Hyperkalaemia (potassium greater than 6.5 mmol/L or ECG change): calcium gluconate 10% 10 to 20 mL IV over 10 minutes, soluble insulin 10 units with 25 g glucose IV, salbutamol 10 to 20 mg nebulised; dialysis for refractory cases.
  • Avoid nephrotoxins and iodinated contrast beyond what is needed.
• Source control and prevention of recurrence:
  • Atrial fibrillation: after the procedure continue heparin then give apixaban 5 mg twice daily (2.5 mg twice daily if two of age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more) or warfarin to INR 2.0 to 3.0, lifelong; rate control with bisoprolol 2.5 to 10 mg daily.
  • Left ventricular thrombus: warfarin to INR 2.0 to 3.0 for at least 3 to 6 months.
  • Mitral stenosis or mechanical valve: warfarin (INR 2.5 to 3.5 for a mechanical mitral valve); do not use direct oral anticoagulants.
  • Endocarditis: blood cultures then IV antibiotics and early surgery; send embolus for histology and culture.
  • Atrial myxoma: urgent surgical excision.
  • Paradoxical embolism: anticoagulation, treat the deep vein thrombosis, and consider closure of the patent foramen ovale.
  • Aortic source: anticoagulation, with endovascular or surgical exclusion for recurrence.
  • Heparin induced thrombocytopenia: stop heparin, give argatroban 2 micrograms/kg/min IV (0.5 to 1 microgram/kg/min in hepatic impairment).
• Special groups:
  • Pregnancy: therapeutic enoxaparin 1 mg/kg SC twice daily or unfractionated heparin; surgical embolectomy preferred over thrombolysis; avoid warfarin and direct oral anticoagulants.
  • Elderly and frail: local anaesthesia embolectomy; accept primary amputation sooner when ischaemia is irreversible.
  • Renal impairment: use unfractionated heparin when creatinine clearance is less than 30 mL/min; limit contrast.
  • Cancer: enoxaparin 1 mg/kg twice daily for at least 6 months.
• Red flags: sensory loss spreading proximally, new weakness, tense calf, dark urine, potassium greater than 6.5 mmol/L, bowel or renal pain (visceral emboli).
• Follow up: review at 1 week and 1 month with pulse examination and ankle pressure; echocardiography and rhythm monitoring for the source; anticoagulant monitoring; vascular review if symptoms return.