IVUS Tales: From Research to its Clinical application in Contemporary Interventions'

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IVUS Tales From Research to its Clinical
application in Contemporary Interventions.

• Presenter Islam Bolad
• Attending Jose Diez

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Coronary Angiography

• Visual interpretation of coronary angiography
  exhibits
• intraobserver and interobserver variability
• (lt50)
• Angiography postmortem histology.
• QCA
• Glagov phenomenon

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Am J Cardiol 200289(suppl)24B-31B
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IVUS

• Vessel wall vs. lumen.
• Internal electronic distance scale

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IVUS Technology

• Real time high resolution imaging.
• 2D tomographic assessments of vessels
• Also longitudinal and 3D computer asssited
• reconstruction.
• Allows assessment of total vessel lumen and
• plaque dimension in vivo.

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• Two main IVUS systems are currently in use
• 1- A mechanical system that contains a flexible
• imaging cable which rotates a single
  transducer
• at its tip inside an echo-lucent distal
  sheath.
• 2- An electronic solid state catheter system with
  
• multiple imaging elements at its distal tip,
  providing
• cross sectional imaging by sequentially
  activating
• the imaging elements in a circular way.
• 1 is usually smaller than 2.

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• IVUS catheters max. diameter 2.6-3 Fr (0.89-1mm)
• Motorized pull back of transducer (0.25-1mm/sec,
• usually 0.5mm/sec)
• Volumetric measurement.
• Imaging frequencies increased- improved
  qualitative
• assessment of atherosclerotic plaques.
• - Soft, low echogenecity
• - Fibrous, high echogenicity
• - Calcified, high echogenicity with
  acoustic
• shadowing/ reverberations.

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• Recently, more advanced IVUS plaque
• characterization has been introduced.
• 1- Analysis of the backscatter IVUS
  radiofrequency
• data provided a color coded mapping based on
• the different backscatter signals among the
  tissue
• types (virtual histology).
• - Allows examination of the different plaque
• components in more details (fibrous,
  fibro-lipidic,
• calcium, lipid core)

Nair et al Circulation. 2002 Oct
22106(17)2200-6.
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• 2- Intravascular elastography.
• IVUS radiofrequency acquired at different
  levels
• of intravascular pressure can measure tissue
  strain
• reflecting the mechanical properties of the
  vessel
• wall.
• - Help identify vulnerable plaque prior to
  rupture.
• Both techniques require further validation.

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Technical Aspects

• Transducers with US frequencies ranging between
• 20-50 MHz are used (usually 30MHz).
• High frequencies provide excellent theoretical
• resolution, as US wavelength which determines
• the maximum resolution is inversely
  proportional
• to frequency.
• AT 30MHz, the wavelength is 50µm, which permits
• an axial resolution of 100µm. Lateral
  resolution
• 250µm.

Metz JA et al.
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Resolutions
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Perivascular Landmarks.

• A well defined imaging protocol is vital for
  proper
• IVUS interpretation in the coronary tree.
• Slow pullback from distal to proximal vessel.
• Perivascular markings are important reference
• for axial position and tomographic orientation
• within the artery.
• Important for reproducibility of examination
  within
• same segment.

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LAD

• Diagonals
• Anterior Interventricular Vein.
• - Left of proximal and mid LAD in 85. D1 D2
• emerge from LAD on same side of vein.
• - Right of LAD in 15 and crosses it near
  bifurcation
• of the LCx.
• - In 30, the AIV branches into 2 beyond D2.

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In its distal portion, the anterior
interventricular vein (AIV) may branch into two
vessels accompanying the LAD on both sides
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The elliptic shape of the AIV can be appreciated
at 3 o'clock in this cross section from the mid
LAD
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LAD/LCx bifurcation, LCx, GCV triangle. Triangle
of Brocq Mouchet
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LCx

• Distally, Cx is accompanied by posterior LV vein
• Proximally, Cx is accompained and crossed by
• great cardiac vein.
• GCV posterior LV vein form coronary sinus,
• best visualized from distal RCA.
• GCV runs superior to Cx , just inferior to LA
• appendage.

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The great cardiac vein is seen best from the
proximal Cx as a large, almost clear structure
filled with fine blood speckle.
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RCA

• Translational effect (like CX) as it is an AV
  groove
• artery.
• The marginal veins (in contrast to LAD) cross
  over
• artery in an arcing pattern.
• Usually, small amount of fluid near the crux.

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Veins are associated with RV marginal branches
and are characterized by an arching pattern
around the RCA.
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The Endovascular Anatomy. The arterial wall.
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Different echogenic qualities is due to the
relative amount of collagen (1000x reflectance
than smooth muscles) and elastin
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Blood

• Speckled pattern that is constantly changing
  with
• systolic and diastolic blood flow alterations
• ( gt echogenic in systole).
• In real-time imaging, lumen/ intima has distinct
  
• appearance in still frames blood speckle can
  have
• a pattern similar to plaque.
• Blood stagnation proximal to a stenosis may have
• a similar effect. Saline flush can clear the
  lumen
• temporarily.

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Calcific Plaque

• Calcific plaque is the simplest tissue type to
  identify
• Bright reflection of intense signal attenuation.
• Ghost Arcsor reverbrations.
• Calcification is seen in 60-80 of target
  lesions
• using IVUS compared to 30-40 by angiography.
• 180 degrees of vascular circumference must be
• calcified before it can be visualized by
  angiography.

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• Sometimes, shadowing with no bright reflections
• occurs in calcified lesions.
• IVUS imaging of calcium is angle dependent, and
  the
• calcific plaque itself is imaged only when the
  beam is
• perpendicular
• Acosutic shadowing can occur in the absence of
• calcium in the presence of dense fibrous
  tissue.
• Therefore it is correct to refer to lesions with
• shadowing on IVUS as fibrocalcific. This
  distinction
• does not have major clinical implication.

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Fibrous Plaque

• Plaques with echogenicity that is lt bright than
• than calcium, but higher than that from muscle
  or
• fat tissue.
• In general, brightness of fibrous tissue is
  similar
• to that of adventitia.
• No reverebrations.

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Fatty Plaque

• Radiolucent, and has a soft grey-scale
  appearance
• on IVUS.
• Radiolucent areas within fibrous plaques reflect
• accumulation of lipid.
• Shadowing from a heavily fibrotic plaque can be
• mistaken for lipid.

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Plaque distribution and remodeling

• Significant plaque burden (30-40) normal
• arteries by angiography.
• Positive remodeling.
• Concentric / focal remodeling.
• Positive remodeling is exhausted when 50 of the
• lumen is occupied by plaque, and further growth
• results in lumen encroachment.

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RCA IVUS from segments 5mm apart without vessel
branching between them. A- Small vessel with some
element of focal calcification. B- Dramatic
vessel remodeling in a fibrofatty lesion.
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• Negative remodeling / de-remodeling.
• Commonly seen as part of restenosis process
• following PCI.
• Vessel scarring shrinkage may in some caces
• contribute significantly to late lumen loss
  after PTCA

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Endovascular Entities. Thrombus.
One of the most difficult tissue types to
identify by IVUS

• Sparkling pattern on real time IVUS imaging.
• Presence of microchannels, echodensity lt 50
• of the surrounding adventitia and deep Ca are
• clues to the correct diagnosis of thrombus.
• Sometimes, lobular or cauliflower-like
  appearance.
• Identification of thrombus after stenting may
• sometimes be vital.

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Thrombus after stent deployment.
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Post PTCA and Reopro
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False Lumen

• Recognition of 3 layered appearance (true
  lumen),
• observation of slower and more echogenic blood
• reflectance (commonly in false lumen) and
• identification of branches taking off from true
  lumen
• provide clues to discriminate the 2 lumina.
• Contrast material injection can sometimes be
• helpful because the echogenic patterns from
• contrast hung-up and takes longer to evacuate
• a false lumen.

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Aneurysms

• Useful in discriminating between true and false
• aneurysms.
• Histologically, presence of media differentiates
• true from false aneurysms.
• In true aneurysms, the media is thinned and
• expanded but fully encompasses the perimeter
• of the aneurysm.

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Black Holes

• Initially described following brachytherapy.
• Thought to represent tissue is acellular and
  necrotic
• and lacks connective tissue elements1.
• Kay et al2 showed that it is tissue rich in
• proteoglycans while poor in mature collagen
  elastin
• Now seen with DES.
• 1- Circulation. 2001 Feb 6103(5)778.
• 2- Int J Cardiovasc Intervent.
  20035(3)137-42.

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Quantitative Coronary Ultrasound (QCU)
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Evaluating Intermediate Coronary Lesions.

• Abizaid et al compared various IVUS parameters
• with CFR.
• Linear relation between CFR and minimum LCSA.
• They defined minimum LCSA as 4mm2 and
• demonstrated concordance of 89 with CFR
• (abnormal CFR lt2).

Am J Cardiol. 1998 Aug 1582(4)423-8.
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• Nishioka et al compared IVUS parameter with
• nuclear perfusion imaging.
• They found that minimum LCSA 4mm2 had
• sensitivity of 88 and specificity of 90 for
  predicting
• reversible perfusion defect.
• Other IVUS parameters (eg area stenosis)
• performed less well.

J Am Coll Cardiol. 1999 Jun33(7)1870-8
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• Takagi et al compared IVUS parameters with FFR
• for determining functional significance of
  moderate
• lesions.
• Strong correlation between minimum LCSA and FFR
• Using cutoff of 3mm2 to define abnormal minimum
• LCSA and lt 0.75 to define abnormal FFR, the
• investigators found IVUS had a sensitivity of
  83
• and specificity of 92 for detecting ischemia
• producing lesions based on FFR.

Circulation. 1999 Jul 20100(3)250-5.
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• Briguori et al compared IVUS with FFR only in
• patients with intermediate lesions.
• IVUS minimum LCSA was significantly related to
• FFR (r0.41, plt0.004).
• The sensitivity and specificity of minimum IVUS
• LCSA of 4mm2 for predicting FFR 0.75 were
• 92 and 56.

Am J Cardiol. 2001 Jan 1587(2)136-41.
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What about the LMS?

• Jasti et al examined 55 patients with an
  angiographically
• ambiguous LMCS, a pressure guidewire was used to
  calculate
• FFR, and IVUS parameters were calculated after
  automatic
• pullback.

• IVUS MLD 3.80.61 mm, MLA 7.652.9 mm2,
  cross-
• sectional narrowing (CSN) 5913, , and area
  stenosis (AS)
• 4719.

Circulation. 20041102831-2836
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• Regression analysis demonstrated strong
  correlations between
• FFR and MLD as well as between FFR and MLA.
• Compared with FFR as the "gold standard," an MLD
  of 2.8
• mm had the highest sensitivity and specificity
  (93 and 98,
• respectively) for determining the significance
  of an LMCS,
• followed by an MLA of 5.9 mm2 (93 and 95,
  respectively).

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• Fassa et al performed IVUS on 121 patients with
• angiographically normal LMSs to determine the
• lower range of normal minimum lumen area (MLA),
  
• defined as the mean - 2 SD.
• They also conducted IVUS studies on 214 patients
  
• with angiographically indeterminate LMS
  lesions, and
• deferral of revascularization was recommended
  when
• the MLA was larger than this predetermined
  value.

J Am Coll Cardiol. 2005 Jan 1845(2)204-11
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• In the normal LMSs group, LCSA was 16.254.3
  mm2.
• The lower N value (mean MLA-2SD) was 7.65mm2.

• 7.5mm2 was used as the lower range of normal.

• The majority of patients lt 7.5 underwent revasc.
• Follow-up (mean 3.32.0 yrs) showed no
  significant
• difference in MACE between patients with an MLA
  
• lt7.5 mm2 who underwent revascularization and
• those with an MLA 7.5 mm2 deferred for
• revascularization (p 0.28).
• Based on outcome, the best cut-off MLA by ROC
• was 9.6 mm2.

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Limitations of IVUS

• Ring-down artifact.
• Caused by transducer oscillation filling the
  area
• immediately adjacent to the catheter with
  noise,
• making this area unavailable for imaging.
• Seen as bright halo of variable thickness
  surrounding
• the catheter.

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• NURD
• Occurs when the rotating transducer inside the
• US catheter is exposed to frictional forces
• (eg catheter bending, hemostatic valve too
  tight)
• Portions of the images are stretched or
  compacted
• Catheter manipulation eliminates artifact.
• Can be a problem in calcific arteries.
• NURD does not occur in solid state design
• (advantage over mechanical design).

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Image Quantification Errors

• Catheter positioning.
• Catheter angulation, especially in large
  arteries.
• Can alter vessel geometry.

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Ghost Images

• Occurs when structures of high echogenicity are
• imaged (eg Calcium, stent struts)
• Appear of the side of the transducer that is
  opposite
• the bright structure being imaged.

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Summary

• Gold standard for vessel visualization.
• Led to new insights into the pathophysiology of
• coronary plaque accumulation.
• Advances in technology will certainly
  revolutionalize
• this imaging modality.