What intervention is needed for a patient with a non-audible posterior tibial pulse after below-knee artery bypass using the greater saphenous vein?

Management of Non-Audible Posterior Tibial Pulse After Below-Knee Artery Bypass

For a patient with a non-audible posterior tibial pulse after below-knee artery bypass using the greater saphenous vein, urgent vascular imaging with duplex ultrasound should be performed to assess graft patency and identify potential complications requiring intervention.

Initial Assessment

When a posterior tibial pulse becomes non-audible after bypass surgery, this requires immediate evaluation as it may indicate graft failure or compromise. The assessment should include:

• Comprehensive vascular examination of all pulses
• Ankle-Brachial Index (ABI) measurement
• Toe pressure and Toe-Brachial Index (TBI) measurement (especially valuable in diabetic patients where ABI may be misleading) 1
• Assessment for signs of acute limb ischemia (pain, pallor, paresthesia, paralysis, poikilothermia)

Diagnostic Workup

First-Line Investigation

• Duplex Ultrasound: This should be the initial imaging modality as it has high correlation with clinical deterioration after both endovascular therapy and bypass 1. It can determine whether the graft is patent, threatened, or occluded, and often identify specific segments of disease.

Additional Imaging Options

• CT Angiography (CTA): If duplex is inconclusive or shows significant abnormalities
• MR Angiography (MRA): Provides excellent imaging of all arterial segments approaching that of DSA, particularly valuable when combined with time-resolved methods 1
• Digital Subtraction Angiography (DSA): May be required if intervention is planned

Intervention Algorithm

Based on imaging findings, follow this decision tree:

1. If graft is patent but compromised:

   • Endovascular intervention (angioplasty/stenting) for focal stenosis
   • Surgical revision for more extensive problems

2. If graft is occluded:

   • Determine timing of occlusion:
     • Acute (<14 days): Consider catheter-directed thrombolysis or mechanical thrombectomy 2
     • Subacute/chronic: Consider surgical revision or new bypass

3. If native vessel disease beyond anastomosis:

   • Consider extension of bypass to more distal target vessel using autogenous vein

Specific Interventions

For Graft Revision

• Autogenous vein should be used preferentially for any revision or extension bypass 1
• If greater saphenous vein is inadequate or unavailable, consider:
  • Lesser saphenous vein through posterior approach 3
  • Arm vein
  • Spliced veins
  • Composite sequential graft (prosthetic to above-knee popliteal with jump graft of autogenous vein to distal vessel) 1

For New Bypass

• Target the most distal artery with continuous flow from above and without significant stenosis 1
• The tibial or pedal artery capable of providing continuous and uncompromised outflow to the foot should be used as the distal anastomosis site 1
• Autogenous vein is strongly preferred with 70% 5-year patency rate compared to only 27% for prosthetic grafts in tibial bypasses 2

Post-Intervention Management

• Antiplatelet therapy should be continued indefinitely unless contraindicated 1
• Regular surveillance with duplex ultrasound for at least 2 years to detect early signs of graft failure 1
• Aggressive risk factor modification (diabetes control, smoking cessation, etc.)

Important Considerations

• The absence of a posterior tibial pulse after bypass may be due to technical issues at the anastomosis, progression of distal disease, or graft failure
• Early intervention for threatened grafts has been shown to improve long-term outcomes and patency 1
• For patients with diabetes, assessment of Charcot neuroarthropathy should be considered if there are signs of foot deformity, as this can complicate vascular assessment 1

Remember that the goal of revascularization is to maximize blood flow to the foot, ideally providing direct pulsatile flow to the wound bed or "angiosome" if wounds are present 1.