Carotid Artery Duplex Evaluation Techniques

Carotid Artery Duplex Evaluation

• Patient's chin is elevated, head turned 45 degrees away from the side being examined.

Equipment

• 7-4 MHz linear array typically used for image quality and visualization.
• Alternative transducers include:
  • 8–5 MHz curvilinear
  • 4–1 MHz sector
  • 5–2 MHz curvilinear

Scanning Technique

• Includes evaluation of:
  • Common carotid arteries (CCAs)
  • Internal carotid arteries (ICAs)
  • External carotid arteries (ECAs)
  • Vertebral arteries
  • Subclavian arteries
• Vessels evaluated in both transverse and longitudinal planes with B-mode imaging, color, and spectral Doppler.

Scanning Technique Tips

• Sweep through carotid system in transverse and longitudinal planes with B-mode imaging.
  • Begin above clavicle and sweep up to angle of jaw.
• Document any identified intraluminal echoes (plaque or other intimal defects).
• Document any other areas of interest.

Color Doppler

• Used to identify:
  • Areas of aliasing or mosaic flow patterns
  • Speckling that could indicate color bruit

Pulsed Wave Spectral Doppler

• Used to:
  • Measure flow velocities
  • Document waveform contours

ICA vs. ECA Differentiation

• ECA has multiple branches within the neck and its spectral waveform will oscillate with “temporal tap.”
• ICA is typically larger and lies posterior to ECA.

Proximal ICA Occlusion

• No obtainable Doppler flow.

ECA Stenosis

• Lesions tend to involve origin and proximal segments.
• Associated with:
  • Focal velocity increase
  • Poststenotic turbulence
  • Dampened distal waveform
• Watch for diffuse increase in velocity as a result of collateralization.

CCA Stenosis

• Can occur in the proximal, mid, or distal segments.
• Significant stenosis associated with:
  • Focal velocity increases
  • Poststenotic turbulence
  • Dampened distal waveforms in both the ICA and ECA
• “Choke lesion” may result in retrograde ECA to supply ICA.

Aortic Valve or Root Stenosis

• Will generate symmetrically abnormal Doppler waveform contour in the bilateral carotid systems.
  • Dampened waveforms throughout both carotid artery systems.
• May also cause bilateral low brachial systolic pressures.
• Brachiocephalic stenosis will only affect the right carotid system.

Special Considerations

• Low cardiac output and poor ejection fraction
• Aortic valvular disease
• Hypertrophic obstructive cardiomyopathy
• Cardiac arrhythmias
• Cardiac assist devices (ventricular assist device [VAD], intra-aortic balloon pump [IABP])

Doppler Flow Velocity

• Primary criterion for classification of stenosis severity.
• Depends on correct Doppler angle (60 degrees or less, parallel to vessel walls).
• Pulsed wave Doppler sample volume should be “swept” through all vessels.

Collateralization

• Posterior-to-anterior
• Side-to-side
• Extracranial-to-intracranial
• May result in increased velocities contralaterally to severe stenosis or occlusion

Criteria for Classification of Disease

• Classification has validated for the ICA ONLY.
• Criteria cannot be applied to CCA or ECA.
• Criteria were developed by comparing duplex results with “gold standard” imaging modalities or surgical findings.

Color and Power Doppler Findings

• Color Doppler displays flow based on frequency shift.
• Power Doppler displays flow based on blood flow amplitude, independent of the direction of blood flow.

Vertebral Artery Stenosis

• Proximal vertebral artery flow has the same pattern as ICA.
  • Low resistance
  • Antegrade flow throughout cardiac cycle
  • Brisk systolic acceleration, sharp peak, and relatively high diastolic flow.
• Proximal vertebral artery stenosis will produce:
  • Abnormal dampened waveforms distally with delayed acceleration and rounded peaks.
  • Possible poststenotic turbulence.
  • No specific criteria should be suspected if focal velocity increase in PSV is >150 cm/s.
• Generally occurs at origin from subclavian artery.
• Resistive or blunted waveforms indicate distal stenosis or occlusion.

Subclavian Steal

• Hemodynamically significant stenosis in the proximal subclavian artery causing changes to vertebral artery flow.
• Results in brachial blood pressure decrease on affected side (more than 15 to 20 mm Hg lower than contralateral arm).
• Causes decreased pressure at the origin of ipsilateral vertebral artery that can lead to reversed flow.
• Vertebral artery flow changes as obstruction progresses:
  • Normal antegrade flow
  • Antegrade flow with deep notch midcardiac cycle
  • Alternating or bidirectional (to-and-fro) flow
  • Complete reversal (fully retrograde) flow

Reactive Hyperemia

• Provocative test used to augment a subclavian steam from “latent” to “complete.”
• Procedure:
  • Blood pressure cuff inflated to suprasystolic blood pressure on affected side.
  • Left inflated for 3 to 5 minutes while vertebral artery is monitored.
  • Cuff is rapidly deflated while ipsilateral vertebral artery is observed.
  • Positive when vertebral artery completely reverses.

This quiz covers the essential techniques and equipment used in a carotid artery duplex evaluation. It includes details about patient positioning, scanning techniques, and the use of color Doppler imaging to assess neck vessels. Test your understanding of the procedures and equipment involved in this important diagnostic method.