7/16/2015
When Does the Vascular
Waveform Characterization
Impact Clinical Decision Making?
Disclosures
•No conflicts of interest
David Dawson, MD, RPVI, RVT
Professor, Department of Surgery
University of California, Davis
Доверяй, но проверяй
• Russian proverb, a short rhyme,
“doveryai, no proveryai”
• “Trust, but verify”
• Even if source of information
is considered reliable,
additional effort is warranted
to confirm data are accurate,
trustworthy
Clinical Decision Making
1. Evaluation of stenosis
severity
2. Identification of nonfocal arterial narrowing
3. Characterization of nonaxial flow patterns
4. Detection of proximal
occlusive disease
5. Evaluation of steal
physiology
6. Detection of distal
stenosis
7. Organ/tissue perfusion
patterns
8. Assessing arterial
trauma
9. Recognizing alterations
in cardiovascular
hemodynamics
10. Central venous stenosis
President Ronald Reagan
Greater than 50% carotid
bulb stenosis indicated by
PSV ≥ 125 cm/s
Post-stenotic
turbulence
Proximal laminar flow
Increased velocity through stenosis
From Zierler RE in Rutherford’s Vascular Surgery, 8th ed
Post-stenotic turbulence
From Kohler TR in Rutherford’s Vascular Surgery, 8th ed
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1. Stenosis Severity:
Interpretation Clues
• Post-stenotic turbulence confirms the stenosis
is hemodynamically significant
• Velocity elevations without turbulence,
examples:
– Measurement artifact due to angle error
– Moderate increase in flow contralateral to
occlusion (esp. internal carotid artery)
– Normal flow patterns in young people
Waveform Changes with
Arterial Stenosis
• Loss of fluid energy results in delayed
systolic peak, decreased amplitude
• Focal stenosis results in focal velocity
increase
– Greater than 50% stenosis indicated by Vr ≥ 2
• Diffuse stenosis
may not be
associated with
focal velocity increase
Image from Kohler TR in Rutherford’s Vascular Surgery, 8th ed
Patterns of Restenosis After Stenting
• Class I: focal ≤50 mm
– Focal increase in PSV
• Class II: diffuse, >50 mm
Pattern affects outcome of
re-intervention
– Damped waveform
– Drop in distal pressure
• Class III: occlusion
Armstrong EJ, Singh S, Singh GD, Yeo KK, Ludder S, Westin G,
Anderson D, Dawson DL, Pevec WC, Laird JR. Angiographic
characteristics of femoropoplitealin-stent restenosis: association with
long-term outcomes after endovascular intervention. Catheter
Cardiovasc Interv. 2013 Dec 1;82(7):1168-74. doi:
10.1002/ccd.24983. Epub 2013 Jun 3. PubMed PMID: 23630047;
PubMed Central PMCID: PMC3836909
2. Non-Focal Arterial Narrowing:
Interpretation Clues
• Clinical circumstances, symptoms or
hemodynamic changes may increase index of
suspicion
• Diffusely dampened arterial waveforms
• B-mode and color Doppler may help identify
narrowing
From Zierler RE in Rutherford’s Vascular Surgery, 8th ed
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3. Non-Axial Flow Patterns:
Interpretation Clues
Retrograde
Antegrade
• Boundary layer separation in the carotid bulb
confirms a normal finding
• May appear with vessel abnormalities:
– Aneurysm (contributes to mural thrombus
formation)
• May be a normal feature of:
– Anastomoses
– Branch points
Dampened Arterial Waveform
• Femoral artery waveform assessment was “hot
topic” in early days of vascular laboratory
– Technology lacking for direct imaging of inflow vessels
– Peak-to-peak pulsatility index commonly used analytic
measure
Pulsatility Index (PI) =
• Obsolete as primary assessment tool
Right common carotid artery
Damped, low velocity flow
Tardus parvus
Vmax - Vmin
Vmean
Compare to normal contralateral
(left) common carotid artery
waveform and velocity
4. Evaluation for Proximal Stenosis:
Interpretation Clues
• Indirect findings may be of value
– Intrathoracic stenoses
• Brachiocephalic artery
• Proximal common carotid artery
– Iliofemoral stenoses
• Abdominal or pelvic imaging limited by body habitus or
bowel gas
• Comparing PSV and waveform profile to
contralateral artery may be confirmatory
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Reactive Hyperemia
Kliewer MA, Hertzberg BS, Kim DH, Bowie JD, Courneya DL, Carroll BA. Vertebral artery Doppler waveform
changes indicating subclavian steal physiology. AJR Am J Roentgenol. 2000 Mar;174(3):815-9. PubMed PMID:
10701631.
5. Steal: Interpretation Clues
• Waveform variation or asymmetry indicates
abnormality
• Flow reversal may be partial or complete
through cardiac cycle
• “Borderline” steal physiology is augmented
with increased outflow
Kliewer MA, Hertzberg BS, Kim DH, Bowie JD, Courneya DL, Carroll BA. Vertebral artery Doppler
waveform changes indicating subclavian steal physiology. AJR Am J Roentgenol. 2000 Mar;174(3):815-9.
PubMed PMID: 10701631.
Waveform Profile Affected by
Outflow Resistance
• Multi-phasic waveform characteristic of high
resistance outflow
– Forward flow absent during diastole
– Normal in peripheral arteries, external carotid artery,
SMA during fasting
• High resistance pattern in a normally low
resistance vessel indicates distal obstruction
– Stenosis
– Occlusion
– Embolism
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Velocity Waveform Changes
After Bypass for Critical Limb Ischemia
6. Detection of Distal Stenosis:
Interpretation Clues
Early
1
4
2
5
Late
3
Abnormal Organ or Tissue Perfusion
• High resistance to flow may be due to
parenchymal disease (arteriolar), not larger or
medium sized artery occlusion or stenosis
• Cerebral circulation
– Brain death
• Renal artery
– Diabetic nephropathy, hypertensive nephropathy,
other causes
– Renal transplant rejection
Vascular Injury
• Traumatic or iatrogenic
• Acquired arteriovenous fistula
– Increased flow volume
– Increased PSV in artery
– Increased forward diastolic flow (low resistance
pattern)
– Venous pulsatility
• Pseudoaneurysm
– Characteristic to-fro flow pattern
• Expect forward diastolic flow in arteries to
brain, liver, kidneys, and other high-flow
organs
• Absence of diastolic flow can indicate stenosis
beyond access of transducer
• Compare to contralateral artery, when
applicable
• Suggest additional imaging (angiography, CTA,
or MRA) when clinically appropriate
7. Abnormal Organ or Tissue Perfusion:
Interpretation Clues
• Consider the clinical circumstances when
evaluating arterial waveforms
• Always evaluate contralateral side, when
applicable
• Indirect findings of high resistance waveforms
should be considered suggestive, not
diagnostic
8. Arterial Injury:
Interpretation Clues
• Abnormal limb pressure can increase index of
suspicion (and provide complementary
physiologic information)
– Routinely measure API
• Careful evaluation with color Doppler may
identify area for interrogation with pulsed
Doppler
• Compare to waveforms from contralateral limb or
arterial segments remote from suspected injury
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Arterial Pressure and Flow
• Pulsatility and pressure depend on cardiac
function and status of circulation
• Dampened peripheral waveforms are non-specific
finding with shock states
• Doppler velocity waveforms demonstrate
– Rhythm abnormalities
– Artifacts from circulatory assist devices
• Valvular disease may affect pulsatility
– Increased pulsatility or flow reversal with aortic
valvular insufficiency
Common femoral vein
9. Recognizing Alterations in
Cardiovascular Hemodynamics:
Interpretation Clues
• Clinical history may guide interpretation
• Effects from cardiac disease or assist devices
most prominent in proximal arteries
• Abnormal flow patterns are present bilaterally
• Normal velocity criteria for grading stenosis
severity may not apply
Right common femoral vein
Left common femoral vein
Femoral vein, mid thigh
Popliteal vein
Continuous
Phasic with respiration
Augmentation
Augmentation
Posterior tibial vein
ABNORMAL
NORMAL
10. Venous Obstruction:
Interpretation Clues
• Loss of spontaneous and phasic forward flow
suggests more central obstruction
– May be normal finding in periphery
• Continuous flow in vein indicates severe
outflow obstruction
– May prompt more extensive examination
• Compare to contralateral vein at same level
– Important consideration if limited (unilateral)
examination is performed
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Summary: Vascular Waveform Characterization
Often Impacts Clinical Decision Making
1. Evaluation of stenosis
severity
2. Identification of nonfocal arterial narrowing
3. Characterization of nonaxial flow patterns
4. Detection of proximal
occlusive disease
5. Evaluation of steal
physiology
6. Detection of distal
stenosis
7. Organ/tissue perfusion
patterns
8. Assessing arterial
trauma
9. Recognizing alterations
in cardiovascular
hemodynamics
10. Central venous stenosis
When Should Waveforms
Be Evaluated?
As part of every examination!
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