What is arteriovenous duplex ultrasound?

What is Arteriovenous (AV) Duplex Ultrasound?

Arteriovenous duplex ultrasound is a noninvasive imaging technique that combines real-time B-mode (grayscale) anatomic imaging with Doppler flow analysis to simultaneously visualize blood vessels and measure blood flow velocity, direction, and patterns in both arteries and veins. 1

Technical Components

Duplex ultrasound integrates two imaging modalities:

• B-mode imaging provides real-time grayscale cross-sectional images of vessel anatomy, including vessel walls, lumen diameter, and surrounding soft tissues 2
• Doppler analysis measures blood flow velocity, direction, and hemodynamic characteristics through spectral waveform analysis 1, 3
• Color flow Doppler superimposes color-coded flow information onto the grayscale image, with colors indicating flow direction and intensity reflecting velocity 2, 4

Clinical Applications

AV duplex is the standard diagnostic tool for evaluating vascular disease throughout the body:

Arterial Assessment

• Carotid artery stenosis: Measures peak systolic velocity and velocity ratios to quantify stenosis severity (50-69% stenosis: PSV 125-230 cm/s; 70-99% stenosis: higher velocities with ICA/CCA ratio 2-4) 1
• Peripheral artery disease: Evaluates lower extremity arterial stenosis and occlusion, though accuracy declines below the knee 1, 5
• Arteriovenous malformations: Identifies fast-flow lesions showing arterial waveforms in draining veins without solid tissue mass 1

Venous Assessment

• Deep venous thrombosis: Standard imaging test for suspected lower extremity DVT, with comprehensive protocols from thigh to ankle 1
• Venous malformations: Detects slow-flow or absent flow in anechoic spaces, distinguishing from arterial lesions 1
• Dialysis access surveillance: Monitors arteriovenous fistula function by measuring flow volume and detecting stenosis 6, 7

Vascular Malformations

• Distinguishes low-flow from fast-flow lesions: Venous and lymphatic malformations show minimal or absent Doppler signal, while AVMs/AVFs demonstrate high-velocity arterial flow 1
• Characterizes lesion composition: Identifies solid versus cystic components and presence of phleboliths 1

Key Advantages Over Standard B-Mode Ultrasound

Duplex provides hemodynamic information that standard B-mode cannot:

• Flow velocity quantification enables stenosis grading and functional assessment 1, 6
• Distinguishes vascular from avascular lesions, improving diagnostic specificity 6
• Real-time dynamic assessment during provocative maneuvers (e.g., thoracic outlet syndrome evaluation) 1
• Noninvasive and without radiation or contrast risks, making it ideal for serial monitoring 2, 3

Important Limitations and Pitfalls

Dense arterial calcification can completely obscure flow signals, particularly in diabetic patients or those with chronic kidney disease, creating false-negative results 5

Accuracy declines in infrageniculate vessels, with only moderate agreement (κ=0.4-0.6) between duplex and angiography for tibial and peroneal arteries 5

Technical factors limit reliability:

• Deep vessel location, obesity, and edema reduce acoustic windows 5
• Operator-dependent technique requires dedicated trained personnel 1
• Slow flow in severely diseased vessels may fall below detection threshold 5

Multiple sequential stenoses reduce diagnostic accuracy, necessitating cross-sectional imaging (CTA/MRA) for comprehensive assessment 5

When Duplex Alone Is Insufficient

Cross-sectional imaging (CTA or MRA) is required when:

• Planning tibial-level revascularization or distal bypass surgery 1, 5
• Duplex shows monophasic waveforms or non-visualized vessels, mandating anatomic confirmation 5
• Critical limb-threatening ischemia requires precise anatomic mapping for intervention 1
• Evaluating deeper pathology such as thoracic outlet compression or Pancoast tumor 1

Clinical Context for Ordering

Duplex ultrasound is appropriate for:

• Suspected vascular stenosis or occlusion requiring hemodynamic confirmation 1
• Surveillance after vascular intervention (combined with ABI monitoring) 1
• Distinguishing vascular malformation types before definitive imaging 1
• Evaluating dialysis access dysfunction 6, 7

Duplex should not replace cross-sectional imaging when anatomic detail determines revascularization strategy, particularly for infrageniculate disease 1, 5