Acute Limb Ischemia

Epidemiology

Risk Factors

  • Aortic Atherosclerosis
  • Aortic Dissection
  • Arterial Trauma
  • Atrial Fibrillation
  • Deep Venous Thrombosis (DVT): increases risk of paradoxical embolism
  • Large Vessel Aneurysm: aortic, popliteal, etc
  • Prior Lower Extremity Revascularization: angioplasty, stent, bypass graft
  • Recent Myocardial Infarction

Etiology

Arterial Embolism

Source of Arterial Embolism

  • Cardiac Source: most arterial emboli originate from a cardiac source
    • Atrial Fibrillation/Flutter (see Atrial Fibrillation, [[Atrial Fibrillation]] and Atrial Flutter, [[Atrial Flutter]])
    • Atrial Myxoma (see Atrial Myxoma, [[Atrial Myxoma]]): usually located in the left atrium
    • Endocarditis (see Endocarditis, [[Endocarditis]])
      • Infectious Endocarditis
      • Non-Infectious (Marantic) Endocarditis: due to systemic lupus erythematosus (SLE), RA, malignancy, sepsis, severe burns
    • Left Atrial/Left Atrial Appendage Thrombus (see Intracardiac Thrombus, [[Intracardiac Thrombus]])
    • Left Ventricular Thrombus (see Intracardiac Thrombus, [[Intracardiac Thrombus]])
      • Myocardial Infarction with Left Ventricular Aneurysm (see Left Ventricular Aneurysm, [[Left Ventricular Aneurysm]]): usually antero-apical with associated decreased systolic function
      • Left Ventricular Dysfunction/Cardiomyopathy with Decreased Cardiac Output (see Congestive Heart Failure, [[Congestive Heart Failure]])
    • Mechanical Prosthetic Mitral/Aortic Valve: usually in the setting of inadequate anticoagulation
    • Mitral Annular Calcification
    • Papillary Fibroelastoma: cardiac tumor usually found on the mitral/aortic valves
  • Arterial Source: account for 20% of arterial emboli
    • Aneurysm
    • Aortic Atherosclerotic Plaque: risk of embolization is increased with increased plaque thickness, plaque ulceration or mobility, and cardiovascular procedures (cardiac catheterization/intra-aortic balloon pump/cardiac surgery may dislodge the plaque)
  • Paradoxical Embolism: account for 2-4% of arterial emboli
    • Epidemiology
      • Patients with paradoxical embolization are typically younger (mean age: 39) than patients with other types of arterial thromboembolization (mean age: 68)
      • Patients with paradoxical embolization typically have little evidence of cardiac or peripheral arterial disease
    • Mechanism: venous thrombosis that traverses a right-to-left intracardiac shunt (patent foramen ovale, atrial septal defect, atrial septal aneurysm)
    • Venous Sources
      • Upper/Lower Extremity Deep Venous Thrombosis (DVT)

Destination of Arterial Embolism

  • General Comments
    • Lower extremities are affected more commonly than upper extremities
    • Emboli commonly lodge in sites of arterial narrowing: at atherosclerotic plaques or bifurcation points (common femoral bifurcation, common iliac bifurcation, popliteal artery bifurcation)
  • Femoral Artery: 28% of cases
  • Upper Extremity Artery: 20% of cases
  • Aortoiliac: 18% of cases
  • Popliteal Artery: 17% of cases
  • Visceral Artery: 9% of cases
  • Other Artery: 9% of cases

Arterial Thrombosis

  • General Comments
    • Arterial thrombosis usually occurs at the site of an atherosclerotic plaque, in arterial aneurysms, at the site or within a prior revascularization (stents, grafts), or in a vein bypass (usually at a site of venous abnormality)
  • Aneurysm with Thrombosis
  • Arteritis (see Vasculitis, [[Vasculitis]])
  • Atherosclerotic Plaque: the degree of limb ischemia in a patient with pre-existing atherosclerotic plaques in the affected distribution may be less severe, due to the prior development of collateral circulation
  • Entrapment Syndrome
  • Ergotism (see Ergotism, [[Ergotism]])
  • Hypercoagulable State: arterial thrombosis may occur in these patients even in normal limb arteries
  • Low-Flow State
  • Vascular Grafts/Stents

Arterial Trauma

  • Blunt Arterial Trauma
  • Penetrating Arterial Trauma
  • Iatrogenic Arterial Trauma
    • Cardiac Catheterization: incidence of arterial complications following cardiac catheterization (hematoma, pseudoaneurysm, arteriovenous fistula, arterial occlusion, cholesterol emboli syndrome) is between 1.5-9%
      • Arterial occlusions can occur due to intimal flaps/dissections or embolization of thrombus from the arterial sheath site

Arteriolar/Arterial Compression Due to Compartment Syndrome (see Compartment Syndrome, [[Compartment Syndrome]])

  • Phlegmasia Cerulea Dolens (see Deep Venous Thrombosis, [[Deep Venous Thrombosis]]): acute massive venous thrombosis with obstructed venous drainage of lower extremity -> may result in arterial compression and acute limb ischemia
  • Any Other Etiology of Compartment Syndrome

Physiology

  • Acute Arterial Occlusion: with a sudden decrease in limb perfusion that results in a potential threat to limb viability
  • Atheroemboli vs Thromboemboli
    • Compared to thromboemboli, atheroemboli are much less likely to produce acute limb ischemia, more commonly resulting in small vessel occlusion with features such as digital ischemia and livedo reticularis (see Cholesterol Emboli Syndrome, [[Cholesterol Emboli Syndrome]])

Diagnosis

  • Trans-Thoracic Echocardiogram (TTE): useful as the first study to identify cardiac sources of arterial emboli
  • Trans-Esophageal Echocardiogram (TEE): useful to identify cardiac sources of arterial emboli in cases where trans-thoracic echocardiogram is inconclusive or poor quality
  • Ankle-Brachial Index (ABI): value <0.4 indicates significant ischemia
  • Wrist-Brachial Index (WBI): useful
  • Upper Extremity/Lower Extremity Arterial Duplex Ultrasound: useful
  • Computed Tomography (CT) Angiogram: diagnostic
  • Magnetic Resonance (MR) Angiogram: diagnostic
  • Angiogram with Digital Subtraction Angiography: diagnostic
    • Features which allow differentiation between embolism and thrombosis
      • Embolism: sharp cutoff with rounded reverse meniscus sign, intraluminal filling defect, presence of multiple filling defects, absence of collateral circulation
      • Thrombosis: sharp or tapered (but not rounded) cutoff, diffuse atherosclerosis with collateral circulation

Clinical Classification of Acute Limb Ischemia

  • Viable
    • Mild Pain
    • Intact Capillary Refill
    • No Motor Deficit
    • No Sensory Deficit
    • Audible Arterial Doppler
    • Audible Venous Dopplers
  • Threatened
    • Severe Pain
    • Delayed Capillary Refill
    • Partial Motor Deficit
    • Partial Sensory Deficit
    • Inaudible Arterial Doppler
    • Audible Venous Dopplers
  • Non-Viable
    • Variable Pain
    • Absent Capillary Refill
    • Complete Motor Deficit
    • Complete Sensory Deficit
    • Inaudible Arterial Doppler
    • Inaudible Venous Dopplers

Clinical Manifestations

General Comments

  • Patient with Underlying Peripheral Arterial Disease: symptoms may develop acutely or subacutely (even presenting with gradual progression of symptoms in some cases)
  • Patient without Underlying Peripheral Arterial Disease: typically present acutely with classical presentation of 6 P‘s
    • Pain
    • Pulseless
    • Parasthesias
    • Pallor
    • Poikilothermia
    • Paralysis

Rheumatologic/Orthopedic manifestations

  • Acute Limb Pain (see Acute Limb Pain, [[Acute Limb Pain]])
    • Usually distal in the lower extremity and progresses proximally with increased duration of ischemia
    • Usually gradually increases in severity: however, later in course, pain may decrease due to ischemic sensory loss
    • In contrast, acute compartment syndrome must be ruled out as the etiology of extremity pain (it usually manifests with leg swelling and leg pain elicited by passive stretch or palpation of the muscles) (see Compartment Syndrome, [[Compartment Syndrome]])
  • Parasthesias/Anesthesia (see Parasthesias, [[Parasthesias]] and Anesthesia, [[Anesthesia]])
    • The anterior compartment of the lower leg is most sensitive to ischemia: sensory deficits over the dorsal foot are an early sign of acute vascular insufficiency
    • Anesthesia occurs late in the course
  • Motor Weakness/Paralysis (see Weakness, [[Weakness]] and Paralysis, [[Paralysis]])
    • Motor weakness may occur earlier in the course
    • Paralysis occurs late in the course
  • Ischemic Ulcers (see Mucocutaneous Ulcers, [[Mucocutaneous Ulcers]]): presence usually indicates chronic vascular insufficiency
  • Gangrene (see Gangrene, [[Gangrene]]): occurs late in course
  • Pallor: pale skin
    • The point of arterial occlusion is usually one joint above the line of demarcation between the normal and ischemic tissue
  • Polikilothermia: cool skin
  • Poor Skin Perfusion: poor capillary refill
  • Pulselessness: handheld Dopplers may be required to assess arterial flow in the lower extremities
  • Rhabdomyolysis/Compartment Syndrome (see Rhabdomyolysis, [[Rhabdomyolysis]] and Compartment Syndrome, [[Compartment Syndrome]]): occurs late in course

Treatment Based Upon Clinical Classification

Viable

  • Urgent Diagnostic Work-Up
    • Duplex Ultrasound
    • CT Angiogram
    • MR Angiogram
    • Angiogram with Digital Subtraction Angiography
  • Anticoagulation: indicated early (usually before diagnostic procedures are performed)
    • Heparin Drip (see Heparin, [[Heparin]])
  • Catheter-Directed Thrombolytics: may be used in non-surgical candidates, patients with easily-remedied emboli, etc
  • Emergent Surgical Revascularization: may be used

Threatened

  • Emergency Surgical Revascularization: indicated
    • Irreversible changes may occur within 4-6 hrs of an embolic event

Non-Viable

  • Prompt Amputation: indicated

References

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