Embolus versus thrombus - acute limb ischaemia
Acute limb ischaemia (ALI) is a sudden reduction in arterial perfusion of a limb that threatens viability. It is a surgical emergency - without timely revascularisation extensive tissue necrosis can occur (classically within about 6 hours).
The two common causes are an embolic arterial occlusion from a distant source and in‑situ thrombosis on pre‑existing peripheral arterial disease (PAD). Distinguishing the two guides immediate investigation, likely source control and the revascularisation strategy vascular teams will consider (NICE CG147).
Pathophysiology and common causes
- Embolus: material (usually thrombus) formed elsewhere (often the heart) lodges in a distal artery. Common cardiac sources include atrial fibrillation (AF), mural thrombus after myocardial infarction, prosthetic valves and infective endocarditis. Emboli cause abrupt cessation of flow and marked ischaemia in territories with poor collaterals.
- Thrombus (in situ on PAD): thrombus forms on an atherosclerotic, stenosed or previously partially occluded arterial segment. Chronic PAD usually has developed collaterals, so deterioration can be more gradual and less florid initially.
Clinical presentation
- Key signs:
- Severe limb pain
- Pallor of the limb
- Absent or reduced distal pulses
- Paresthesia or sensory deficit
- Motor deficit or paralysis (late and ominous)
- Cool, clammy or mottled limb with delayed capillary refill
- Timing is the single most helpful discriminator: