What does a multiphase subclavian artery on carotid Doppler (duplex ultrasound) indicate?

Understanding Multiphase Subclavian Artery on Carotid Doppler

A multiphase subclavian artery on carotid Doppler ultrasound typically indicates normal arterial flow with preserved triphasic waveform pattern, suggesting absence of significant stenosis in the subclavian artery.

Normal Subclavian Artery Flow Pattern

The term "multiphase" refers to the normal triphasic flow pattern seen in peripheral arteries like the subclavian artery:

• Phase 1: Forward flow during systole (rapid acceleration)
• Phase 2: Brief flow reversal in early diastole
• Phase 3: Low-velocity forward flow during late diastole

This triphasic pattern indicates:

• Normal arterial elasticity
• Low peripheral resistance
• Absence of significant stenosis or occlusion

Clinical Significance

Normal Finding

When a subclavian artery is documented as multiphase on carotid Doppler, this generally represents:

• Normal hemodynamics
• Absence of significant stenosis
• Preserved arterial elasticity
• Adequate distal perfusion

Abnormal Patterns to Compare

In contrast to multiphase flow, abnormal patterns would include:

1. Monophasic flow: Indicates significant stenosis (>70%) with loss of normal triphasic pattern

   • Characterized by continuous forward flow without reversal
   • Seen in severe stenosis or distal to significant obstruction 1

2. Flow reversal: Indicates subclavian steal syndrome

   • Retrograde flow in the vertebral artery
   • Occurs with proximal subclavian stenosis >70% or occlusion 1

3. High-velocity flow: Indicates stenosis

   • Peak systolic velocity >240 cm/s suggests >70% stenosis 2
   • Peak systolic velocity >340 cm/s suggests >70% stenosis according to European guidelines 1

Diagnostic Implications

The finding of multiphase subclavian flow is reassuring and suggests:

• No significant subclavian stenosis: Unlike the monophasic pattern seen with stenosis >50% 1
• No subclavian steal phenomenon: Absence of retrograde vertebral artery flow 1
• No need for intervention: Routine revascularization is not recommended for asymptomatic subclavian artery disease (Class III recommendation) 1

When to Consider Further Evaluation

Despite normal multiphase flow, further evaluation might be warranted if:

• Inter-arm blood pressure difference >15 mmHg (suggests possible subclavian stenosis despite normal waveform) 1
• Symptoms of vertebrobasilar insufficiency during arm exercise
• Presence of periclavicular or infraclavicular bruit 1

Technical Considerations

When interpreting multiphase subclavian flow on carotid Doppler:

• Ensure adequate visualization of the entire subclavian artery
• Compare with contralateral side when available
• Perform dynamic maneuvers (arm abduction/adduction) if symptoms suggest thoracic outlet syndrome 1
• Remember that duplex ultrasound has 90% sensitivity and 94% specificity for identifying significant (>70%) stenosis 1

In summary, a multiphase subclavian artery on carotid Doppler represents normal arterial flow dynamics and is generally a reassuring finding that does not require further intervention in the absence of symptoms or other concerning features.