Leg Ischaemia (Acute )

hs1

History (Causes) and Examination

• Causes of acute limb ischaemia include 1
  • Acute embolus
    • Atrial fibrillation (most common)
    • Recent myocardial infarction
    • Cardiac valve vegetation
    • Popliteal aneurysm (rarely aortic aneurysm)
    • Paradoxical secondary to deep vein thrombosis (rare)
  • Acute thrombosis
    • Atherosclerosis
    • Prior lower extremity revascularization (angioplasty / stent, bypass graft)
    • Trauma
    • Aortic dissection
• The 6 P’s (paresthesia, pain, pallor, pulselessness, poikilothermia, paralysis) are the classic cardinal signs of acute limb iscahemia 1
• As part of the assessment, patients at risk, with a history or examination suggestive of peripheral arterial disease (PAD) should be assessed with a hand-held Doppler 2 as the quality of the lower extremity pulse examination can vary 1
• In general, the absence of any Doppler signals at the foot or ankle indicates significant ischemia, with a value 1,3

hs2

Computed Tomography Angiogram (CTA)

• Contrast-enhanced CTA is a non-invasive alternative to DSA that requires less radiation, costs less, and has a high diagnostic accuracy 4
• The advantages of speed and easy access make multidetector computed tomographic (MDCT) angiography the investigation of choice in traumatic injury 5
• Modern multi-slice CTA provides 3-dimensional images with an image resolution of about 0.5 to 0.7 mm 4
• MDCT angiography depicts pelvic and leg arteries with good image quality 4,6 and is accurate in showing arterial athero-occlusive disease with reliability similar to DSA 7
• MDCT angiography showed more vascular segments than DSA, particularly within calf vessels 7
• A meta-analysis of the diagnostic performance of CTA in PAD found a pooled sensitivity of 95% (CI, 92% to 97%) and specificity of 96% (CI, 93% to 97%) of diagnosing segmental stenoses of 50% or greater and occlusions in PAD. 8 These findings are similar to the results presented in the meta-analysis of MRA. 4 However, limitations to the meta-analysis of CTA was that the methodological quality of their included 20 studies (11 prospective and 7 retrospective studies and 2 in which the design was unclear) was generally not high, which prevented them from drawing definitive conclusions from those data
• In contrast, the 32 prospective studies in the MRA meta-analysis were of generally high methodological quality. Thus, the evidence that MRA has a high diagnostic accuracy for assessing steno-occlusions in lower-extremity PAD is currently better than that for CTA 4
• Advantages 9
  • Allows for accurate evaluation of short segmental stenosis
  • Shows segments immediately distal to the point of occlusion (supplied by collateral vessels), which are not opacified on DSA
  • Permits the precise evaluation of the vascular wall itself
  • Clearly depict the courses of vessels not only in patent but also in completely occluded segments (such depictions provide useful information for planning interventional radiology revascularization procedures)
  • Allows for the evaluation of arteries with indwelling stents
  • Allows for the detection of extravascular causes of occlusion (e.g. popliteal artery entrapment syndrome, a rare but important cause of exertional leg pain)
• Disadvantages
  • Ionising radiation
  • In general, CTA depicts pelvic and leg arteries with good image quality; however, extensive calcification may hinder assessment of contrast-enhanced residual lumen, especially in the smaller (e.g. tibial) arteries 4,6,10
  • Similar to DSA, CTA carries a risk for anaphylactic reactions and contrast-induced nephropathy because of the iodinated contrast medium 4

hs3

Magnetic Resonance Angiogram (contrast-enhanced MRA)

• Contrast enhanced magnetic resonance angiography (ceMRA) is the most accurate diagnostic technique for the detection of (50% or more) stenosis or occlusion, with most studies reporting sensitivities and specificities of over 90% (based on a “per segment” ” rather than “per patient” analysis) 11,12
• In determining the diagnostic accuracy of duplex ultrasonography, magnetic resonance angiography, and computed tomography angiography, alone or in combination, for the assessment of lower limb peripheral arterial disease; ceMRA seems to be more specific than computed tomography angiography (CTA) in ruling out stenosis >50% and more sensitive than duplex ultrasonography in ruling in stenosis >50% respectively 11
• ceMRA and CTA were generally preferred by patients over contrast angiography (DSA) however this was subject to limited evidence. The review also revealed that magnetic resonance angiography was associated with the highest proportion of adverse events, although these were generally mild, with the most severe events associated with contrast angiography (DSA) 11
• A meta-analysis of 32 clinical trials comparing MRA to CA, the sensitivity and specificity to identify infra-popliteal PAD was 92% and 93% respectively. ceMRA correctly classified 95.3%, over-staged 3.1%, and under-staged 1.6% of arterial segments. It also showed that the pooled sensitivity and specificity for MRA of the tibiofibular arteries was lower than for the aorto-iliac or femoro-popliteal regions, but this difference was small 4
• Limitations to both these reviews were that the primary studies reported the diagnostic accuracy of MRA on a per-segment basis, not a per-patient basis
• A more recently published systematic review and meta-analysis of the diagnostic performance of CTA and ceMRA in patients with critical limb ischaemia and intermittent claudication showed that CTA and ceMRA are accurate techniques for evaluating disease severity of aorto-tibial arteries in patients with critical limb ischaemia and intermittent claudication. No significant differences in the diagnostic performance of the two techniques between patients with critical limb ischaemia and intermittent claudication were found. Methodological quality of studies was moderate to good. Key points identified include 13
  • CTA and ceMRA can both demonstrate arterial disease
  • CTA and CE-MRA can both accurately evaluate arteries in peripheral arterial disease
  • Diagnostic performances of critical limb ischaemia and intermittent claudication are not different
  • Separate imaging technique rather than bolus chase technique of tibial arteries by CE-MRA is preferred
  • CTA and CE-MRA can distinguish confidently between high-grade stenoses and occlusions
• Disadvatages 4,14
  • Claustrophobia
  • Metal artefact from stent deployment (MR angiography cannot depict in-stent patency)
  • Contrast induced nephrogenic systemic fibrosis
  • Incompatibility with AICD and pacing devices
  • Excessive cost
• Patients that should not receive gadolinium-based contrast agents because of the risk for nephrogenic systemic fibrosis include 4
  • Acute or chronic severe renal insufficiency (glomerular filtration rate 2
  • Renal dysfunction due to the hepato-renal syndrome
  • In the perioperative liver transplantation period

hs4

Stages of Acute Limb Ischaemia

• The availability of imaging and the time required to perform and interpret it must be balanced against the urgency for revascularization 15
• If available, non-invasive imaging, with either MR angiography (MRA) or CT angiography (CTA), is now the first choice technique having supplanted catheter angiography for the initial evaluation of peripheral arterial disease in many situations 12
• Gadolinium contrast-enhanced MRA has the most supportive evidence for lower limb arterial assessment, particularly in critical ischaemia 12
• Despite catheter angiography offering the potential benefit of simultaneous therapeutic intervention (thrombolyisis, angioplasty), 1 it exposes the patient to radiation, percutaneous arterial puncture related complications, including haematoma and haemorrhage if thrombolysis is performed, and iodinated contrast related adverse reactions 1,10
• In patients with viable (stage I) or marginally threatened (stage IIa) limbs, it may be reasonable to perform imaging (duplex ultrasonography, computed tomographic angiography, or magnetic resonance angiography) to determine the nature and extent of the occlusion and to plan intervention (Table 1) 10,15
• Patients with immediately threatened limbs (stage IIb) may be taken directly to the operating room where imaging and revascularization can be performed in a single setting as the severity of ischaemia does may not allow time for initial radiological investigation and any delay in treatment can have an adverse effect on clinical outcome 10,15
• Imaging and revascularization are not indicated if the limb is irreversibly damaged (stage III) 15

Stages of Acute Limb Ischaemia 10,15

Data from: SVS / ISCVS, Society of Vascular Surgery / International Society of Cardiovascular Surgery

copyright