How should graft thrombosis be monitored after femoral-to-femoral or femoral‑popliteal bypass in an adult peripheral arterial disease patient?

Monitoring for Graft Thrombosis After Femoral-to-Femoral or Femoral-Popliteal Bypass

All patients with infrainguinal bypass grafts require structured surveillance combining clinical assessment, ankle-brachial index (ABI) measurement at every visit, and duplex ultrasound at scheduled intervals—specifically at 4-6 weeks, 6 months, 12 months, and annually thereafter for at least 2 years. 1

Clinical Assessment at Every Visit

Every follow-up visit must include:

• Symptom assessment: Specifically ask about recurrent claudication, rest pain, or new functional limitations, as symptom recurrence is the most important indicator of graft stenosis or occlusion 1
• Vascular examination: Palpate proximal pulses, graft pulses (when accessible), and distal outflow vessel pulses 1
• Skin inspection: Examine closely for new ulceration or gangrene 1
• Functional status: Document walking distance and impact on daily activities 1

Ankle-Brachial Index (ABI) Monitoring

• Measure resting ABI at every follow-up visit in all patients with previous bypass 1
• A change in ABI of ≥0.15 is clinically significant and indicates potential graft stenosis or thrombosis 1, 2
• Post-exercise ABI adds diagnostic value when feasible, as it may reveal hemodynamic compromise not apparent at rest 1, 3

Duplex Ultrasound Surveillance Schedule

For Autogenous Vein Grafts (Femoral-Popliteal)

Duplex ultrasound surveillance is beneficial and should be performed routinely 1:

• Initial baseline scan at 4-6 weeks post-operatively to establish a new baseline for comparison 2
• Follow-up scans at 6 months, 12 months, then annually for at least 2 years 1
• Scan the entire length of the graft with calculation of peak systolic velocities (PSV) and velocity ratios across all identified lesions 1

Critical duplex findings indicating graft-threatening lesions:

• PSV <40-45 cm/s within the graft indicates a graft at risk for failure 1
• End-diastolic velocity <5 cm/s at the conclusion of bypass is a strong predictor of early graft occlusion 1
• PSV >300 cm/s or PSV ratio >3.5 across a stenosis indicates high-grade stenosis requiring consideration for reintervention 1, 2

The rationale for intensive vein graft surveillance: Vein grafts are more likely to develop stenosis before occlusion, unlike synthetic grafts which often occlude without warning 1. Poor compliance with bypass surveillance is an independent risk factor for acute graft thrombosis 1. Secondary patency and limb salvage are significantly improved when graft-threatening lesions are identified and corrected before thrombosis occurs 4.

For Synthetic Grafts (Femoral-Femoral, Prosthetic Femoral-Popliteal)

The effectiveness of routine duplex surveillance for prosthetic grafts is uncertain, though it may be used to characterize mid-graft velocity 1:

• Clinical surveillance with interval history, vascular examination, and ABI measurement (resting and post-exercise when possible) is the standard approach 1
• Timing and efficacy of duplex surveillance for prosthetic grafts have not been ideally defined 1
• Prosthetic grafts often occlude without warning, making detection of pre-occlusive stenosis less reliable than with vein grafts 1

Surveillance Timeline

First 2 years post-operatively is the most critical period, as 80% of all graft failures occur between 1 month and 2 years 2, 5:

• Early failures (<1 month): Usually due to technical error, accounting for approximately 10% of failures 5
• Intermediate failures (1 month to 2 years): Most common period for graft stenosis development, accounting for 80% of failures 5
• Late failures (>2 years): Usually due to progression of native atherosclerosis, accounting for 2-3% of failures annually 5

Thresholds for Reintervention

• Stenosis >70% is a harbinger of poor long-term patency and warrants consideration for reintervention 1, 2
• Recurrent symptoms with hemodynamic compromise (significant ABI drop, high-grade stenosis on duplex) require restudy and repeat intervention 1, 2
• >10% of patients with detectable graft stenosis on initial imaging will occlude in the next 3-6 months 1

Critical Pitfalls to Avoid

• Do not rely solely on symptoms: Duplex may detect significant stenoses not detected by ABI decline or symptom recurrence 1
• Do not use CTA or MRA for routine surveillance in asymptomatic patients, as false positives can lead to unnecessary procedures and these modalities expose patients to radiation or contrast risks 1
• Never use invasive arteriography for surveillance of asymptomatic patients—it is completely inappropriate 1
• Avoid compression of grafts: Waist belts, tight garments, and sleeping positions that compress the graft can cause thrombosis 6
• Ensure medication adherence: Verify antiplatelet therapy and statin compliance at every visit 2, 3

Adjunctive Measures During Surveillance

• Cardiovascular risk factor control: Reassess smoking status, diabetes management, hypertension, and hyperlipidemia at each visit 2
• Continue antiplatelet and statin therapy throughout the surveillance period 2, 3
• Facilitate structured exercise programs to maintain functional gains 1, 2