Arterial Embolus and Acute Limb Ischaemia
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Direct answer
An arterial embolus is a clot that travels and lodges at a bifurcation — most often from the heart in atrial fibrillation or after myocardial infarction — producing sudden severe ischaemia of a previously normal limb. The limb shows the six Ps: pain, pallor, pulselessness, paraesthesia, paralysis and poikilothermia, and clinical severity is graded by sensory and motor loss. Treatment is immediate intravenous heparin and emergency embolectomy with a Fogarty balloon catheter, with fasciotomy for reperfusion compartment syndrome.
What you must remember
- Sources in order of exam frequency: the heart in atrial fibrillation, after recent myocardial infarction and from diseased or prosthetic valves; aneurysms and paradoxical emboli account for the rest.
- The six Ps define the syndrome; the commonest landing sites are the aortic bifurcation (saddle embolus with bilateral signs) and the common femoral and popliteal bifurcations.
- The limb is threatened when sensation and motor power are lost — fixed mottling with anaesthesia and rigid muscles means irreversible infarction; calf tenderness on squeeze and rest pain are earlier warnings.
- Management begins with intravenous unfractionated heparin and analgesia at once; the diagnosis in a limb without prior claudication is clinical, and imaging must never delay embolectomy in a threatened limb.
- Balloon catheter embolectomy with a Fogarty catheter is the standard operation; catheter-directed thrombolysis is an alternative in selected cases where the limb is not immediately threatened.
- After revascularisation watch for reperfusion injury — hyperkalaemia, acidosis and myoglobinuria threatening the kidneys — and perform fasciotomy for compartment syndrome; echocardiography then hunts the source.
- Acute-on-chronic thrombosis of an atherosclerotic artery differs from a true embolus: collaterals have developed, the deficit is less dramatic, the limb bears chronic signs, and management leans on revascularising the underlying disease.
Common confusion
The exam repeatedly contrasts embolus with thrombosis-in-situ: the embolic limb was normal until the moment of pain, the source is usually cardiac, and the deficit is maximal at the outset; the thrombotic limb has claudication history, chronic trophic changes and less severe deficit because collaterals pre-exist. Candidates also lose marks by ordering a CT angiogram for an obviously threatened limb — the right answer is heparin plus theatre — and by forgetting fasciotomy after successful embolectomy when the calf is tight.
Exam-focused takeaway
FMGE acute limb ischaemia questions are urgency questions. The sudden pale, pulseless, painful leg in a patient with atrial fibrillation is an embolus: heparin immediately, Fogarty embolectomy urgently, no imaging delay, fasciotomy when the compartments are tight, and monitoring for hyperkalaemia and myoglobinuria after flow returns. Numbness with calf tenderness marks a threatened limb; fixed mottling with paralysis marks a dead one, answered by amputation. The post-event echocardiogram and long-term anticoagulation complete the management pair.
Frequently asked questions
What are the six Ps of acute limb ischaemia?
Pain, pallor, pulselessness, paraesthesia, paralysis and poikilothermia — the classic descriptive set for an acutely ischaemic limb.
What is the commonest source of arterial emboli?
The heart — left atrial thrombus in atrial fibrillation, mural thrombus after myocardial infarction, and vegetations on valves.
What is the immediate management of a threatened limb?
Intravenous unfractionated heparin with analgesia, followed by emergency Fogarty balloon catheter embolectomy without waiting for imaging.
Why is fasciotomy needed after embolectomy?
Reperfusion oedema can precipitate compartment syndrome in the calf, so compartment release is performed when compartments are tense or signs appear.
What systemic danger follows revascularisation?
Reperfusion injury with hyperkalaemia, metabolic acidosis and myoglobinuria causing acute kidney injury — monitor and treat aggressively.
How is embolic acute ischaemia distinguished from thrombosis?
Sudden maximal deficit in a previously normal limb with a cardiac source favours embolus; claudication history, chronic skin changes and collaterals favour thrombosis of diseased artery.