What does a monophasic waveform in the superficial femoral artery on duplex ultrasound indicate?

Monophasic Waveform at SFA on Duplex Ultrasound

A monophasic waveform in the superficial femoral artery (SFA) on duplex ultrasound indicates hemodynamically significant arterial disease, either at the level of the SFA itself or proximally in the aortoiliac vessels, and signals reduced blood flow that warrants further investigation and management.

What This Finding Means

A monophasic waveform represents a pathologic flow pattern that has lost the normal triphasic or biphasic characteristics of healthy peripheral arteries. This finding indicates:

• Significant stenosis or occlusion either at the site of measurement or upstream 1
• Reduced arterial perfusion with loss of the normal diastolic flow reversal that characterizes healthy peripheral arteries 2
• Increased risk of disease progression and potential limb-threatening ischemia 3

Clinical Significance and Risk Stratification

The presence of a monophasic waveform carries important prognostic implications:

• Bypass graft surveillance: Monophasic flow in a bypass graft or the popliteal artery after femoropopliteal bypass shows a hazard ratio of 2.0 (95% CI: 1.26-3.1) for loss of primary patency 3
• Increased thrombotic risk: Monophasic waveforms create longer particle residence times and larger recirculation zones compared to biphasic/triphasic patterns, increasing atherothrombotic risk 2
• Disease severity marker: In a study of 55 patients with peripheral arterial disease, monophasic waveforms with peak systolic velocity ratio >2:1 were found in 42 patients and correlated with significant stenoses 4

Diagnostic Approach

When you encounter a monophasic waveform at the SFA:

1. Assess the entire arterial tree systematically 5:

   • Examine the common femoral artery waveform to determine if proximal (aortoiliac) disease is present
   • A triphasic CFA waveform has 84.7% negative predictive value for excluding significant aortoiliac disease, but 14% of patients with significant aortoiliac disease still have triphasic waveforms 6
   • Evaluate peak systolic velocities and velocity ratios throughout the SFA

2. Look for specific velocity criteria 7, 8:

   • Peak systolic velocity >300 cm/s suggests high-grade stenosis
   • Peak systolic velocity ratio across a stenosis >3.5 indicates significant narrowing
   • Peak systolic velocity <40-60 cm/s suggests impending graft failure or severe inflow disease

3. Document additional findings 4:

   • Presence of echogenic plaques
   • Corkscrew collaterals (indicating chronic occlusion)
   • Post-stenotic turbulence

Important Caveats

Multisegment disease significantly affects accuracy: When multiple stenoses are present (multisegmental native stenoses), the correlation between velocity ratios and stenosis severity drops from R=0.88 to R=0.78, and diagnostic accuracy decreases 8. The presence of serial lesions makes precise quantification more challenging.

Location matters: Duplex ultrasound has 90-95% sensitivity and specificity for detecting >50% stenosis from the iliac arteries to the popliteal arteries, but accuracy is lower for:

• Iliac arteries (obscured by bowel gas or tortuosity) 5
• Tibial arteries below the knee 9
• Areas with dense calcification 5

Next Steps Based on Clinical Context

For symptomatic patients with lifestyle-limiting claudication 7, 10:

• If revascularization is being considered, proceed with cross-sectional imaging (CTA or MRA) to plan intervention
• Consider invasive angiography if noninvasive imaging is inadequate or contraindicated

For patients with critical limb-threatening ischemia 7, 10:

• Proceed directly to invasive angiography with potential same-session revascularization
• Time is critical to prevent tissue loss

For post-revascularization surveillance 7:

• Monophasic waveforms after bypass indicate need for closer follow-up (every 2-3 months) 9
• Consider repeat intervention to maintain patency

For asymptomatic or stable claudication patients 7:

• Optimize guideline-directed medical therapy
• Structured exercise program
• Serial monitoring with ABI and clinical assessment

The key takeaway: a monophasic waveform is never normal and always indicates hemodynamically significant disease requiring action—whether that's intensified medical management, closer surveillance, or revascularization planning depending on symptom severity and overall clinical context.