What causes acute limb ischemia?

Causes of Acute Limb Ischemia

Acute limb ischemia occurs primarily from two mechanisms: arterial embolism (typically from cardiac sources) or acute thrombosis superimposed on pre-existing atherosclerotic disease. 1

Primary Etiologic Mechanisms

Embolic Occlusion

• Cardiac sources are the most common origin of emboli, particularly in patients with atrial fibrillation, patent foramen ovale, atrial septal defect, or ventricular dysfunction 1
• Emboli typically lodge at arterial bifurcation points where vessel caliber diminishes, such as the common femoral artery, popliteal artery, or aortoiliac bifurcation 1, 2
• Proximal arterial aneurysms can serve as embolic sources, releasing thrombus distally 1
• Embolic occlusions cause more profound ischemia when they interrupt collateral perfusion pathways, particularly when the profunda femoris artery is compromised by embolism to the common femoral artery 1
• A "saddle embolus" at the aortoiliac bifurcation produces bilateral lower-limb ischemia and may cause reversible paraplegia with high mortality 1, 2

Thrombotic Occlusion

• Acute arterial thrombosis superimposed on stenotic atherosclerotic plaque is the second major mechanism 1
• The superficial femoral artery is the most common site of thrombosis, though occlusion can occur anywhere from the aorta to digital arteries 1
• Thrombosis of a lower extremity bypass graft represents another important thrombotic cause 1
• The low-flow state distal to obstructing thrombus encourages both proximal propagation (up to the next large side branch) and distal propagation of thrombus 1

Less Common Causes

• Arterial trauma can precipitate acute ischemia 1
• Popliteal entrapment, cystic adventitial disease, or repetitive trauma may rarely precede arterial thrombosis 1
• Vasospasm and arteritis are nonatherosclerotic causes that should be considered 1
• Atherosclerotic plaque rupture can trigger acute thrombosis 1

Key Distinguishing Features by Etiology

Embolic vs. Thrombotic Presentation

• Embolism tends to present more abruptly than thrombosis, with sudden onset of severe symptoms 1, 3
• Embolic occlusion typically occurs in patients without antecedent claudication and with normal contralateral pulses 3
• Thrombotic occlusion usually presents less severely due to established collateral circulation from chronic atherosclerotic disease 3
• Patients with thrombosis often have a history of claudication and diminished pulses in the contralateral limb 3

Factors Affecting Severity

The severity of acute limb ischemia depends on:

• The location and extent of arterial obstruction 1
• The capacity of collateral vessels to perfuse the ischemic territory 1
• Whether the vascular bed was previously conditioned by collaterals (embolic occlusion in previously normal vessels causes more severe ischemia) 1
• The length of the obstructive lesion, as longer lesions interrupt more collateral pathways 1
• The status of systemic perfusion (cardiac output and peripheral resistance) 1

Critical Clinical Implication

Prompt systemic anticoagulation is mandatory because the low-flow state encourages both proximal and distal thrombus propagation, regardless of whether the initial cause was embolic or thrombotic 1. This represents the rationale for immediate anticoagulation even before definitive diagnosis is established.