INTRAVASCULAR ULTRASOUND

1. INTRAVASCULAR ULTRASOUND Sripal Bangalore, M.D., M.H.A. and Deepak L. Bhatt, M.D., M.P.H., F.A.H.A

2. Overview • Intravascular Ultrasound (IVUS) • Rationale for use • Indications • Equipment • Technique • Image Interpretation • Qualitative Analysis • Quantitative Analysis • Artifacts

3. Rationale for use • Advantages of IVUS: • Precise quantification of disease extent and severity • Good intra/inter observer correlation • High resolution • Ability to assess plaque characteristics • 360 degree measurement • Images the vessel wall • Accurate sizing of vessel Limitations of angiography: • Under/over estimation of lesion extent and severity • Poor intra/inter observer correlation • Low resolution • Less sensitive to assess plaque characteristics • Two dimensional • Images the lumen and not the vessel wall • QCA measurements prone to magnification errors

4. Indications Class IIa • IVUS is reasonable for the assessment of angiographically indeterminate left main CAD. (Level of Evidence: B) • IVUS and coronary angiography are reasonable 4 to 6 weeks and 1 year after cardiac transplantation to exclude donor CAD, detect rapidly progressive cardiac allograft vasculopathy, and provide prognostic information. (Level of Evidence: B) • IVUS is reasonable to determine the mechanism of stent restenosis. (Level of Evidence: C) Levine GN, et al. 2011 ACCF/AHA/SCAI guideline for percutaneous coronary intervention. Circulation. 2011;124:2574-2609.

5. Indications Class IIb • IVUS may be reasonable for the assessment of non–left main coronary arteries with angiographically intermediate coronary stenoses (50% to 70% diameter stenosis). (Level of Evidence: B) • IVUS may be considered for guidance of coronary stent implantation, particularly in cases of left main coronary artery stenting. (Level of Evidence: B) • IVUS may be reasonable to determine the mechanism of stent thrombosis. (Level of Evidence: C) Levine GN, et al. 2011 ACCF/AHA/SCAI guideline for percutaneous coronary intervention. Circulation. 2011;124:2574-2609.

6. Indications Class III NO BENEFIT • IVUS for routine lesion assessment is not recommended when revascularization with PCI or CABG is not being contemplated. (Level of Evidence: C) Levine GN, et al. 2011 ACCF/AHA/SCAI guideline for percutaneous coronary intervention. Circulation. 2011;124:2574-2609.

7. Equipment Mechanical IVUS System: • A single rotating transducer driven by a flexible drive cable • Smaller size compared to solid state systems • More artifacts – Guidewire, NURD, etc. • Higher resolution Solid State System: • Annular array of multiple (64) imaging elements providing imaging by sequentially activating the imaging elements • Larger size compared to mechanical systems • Less artifacts • Ring-down artifact

8. Technique • Anticoagulation: bivalirudin or heparin as per routine clinical practice • 6Fr guide catheter to engage the coronary ostium • Standard 0.014 inch guidewire to cross the lesion • Intracoronary nitroglycerin before acquisition of IVUS images to prevent artifacts from catheter induced coronary spasm • A well defined imaging protocol is vital for proper IVUS interpretation and reproducibility • Imaging should be acquired starting at least 10 mm distal to the lesion and preferably at the site of a branch vessel (as a reference marker) with pullback to the proximal vessel

9. Technique • Pullback using motorized transducer pullback (usually at 0.5 mm/s) can be used to survey the artery all the way back to the aorta • Manual transducer pullback can then be used to better interrogate areas of interest • The guiding catheter should be disengaged from the coronary ostium while interrogating an ostial lesion • The motorized pullback technique allows for L-mode (longitudinal) display and estimation of lesion length

10. Image Interpretation - Qualitative • Proximal and distal reference segments and the lesion should be identified • Proximal reference: The site with the largest lumen proximal to a stenosis but within the same segment (usually within 10 mm of the stenosis with no major intervening branches) • Distal reference: The site with the largest lumen distal to a stenosis but within the same segment (usually within 10 mm of the stenosis with no intervening branches) • Normal structures: Look for branches, veins and pericardium

11. Image Interpretation - Qualitative Intima Anterior Interventricular Vein Media IVUS Catheter Adventitia Guidewire IVUS of Proximal LAD Trilaminar Image • Innermost layer (intima): Relatively echogenic compared with lumen or media and is comprised of intima, atheroma, and internal elastic lamina • Middle layer (media): Less echogenic than the intima • Outer layer (adventitia and periadventitial tissue): Relatively echogenic compared with media

12. Image Interpretation-Qualitative Acoustic shadowing Calcium Branch vessel IVUS of LAD

13. Plaque Characterization Soft Plaque - Concentric Soft Plaque - Eccentric • Soft Plaque • Hypoechoic compared to adventitia • High lipid content

14. Plaque Characterization • Fibrous Plaque • Similar/more echogenicity compared with adventitia • Rarely produce acoustic shadowing • Most common type of plaque

15. Plaque Characterization Shadowing 1800 Arc of Calcium 3600 Arc of Calcium • Fibrocalcific Plaque • Hyperechoic compared to adventitia • Acoustic shadowing seen • 1800 of calcification must be present before it can be visualized by angiography

16. Thrombus • Thrombus • Echolucent or variable grey scale appearance • Usually layered, lobulated, or pedunculated • Micro-channels are occasionally present • Diagnosis of thrombus by IVUS is always PRESUMPTIVE Stent Strut Thrombus Subacute stent thrombosis (IVUS after mechanical thrombus aspiration)

17. Dissection • Classification of Coronary Dissection • Intimal • Medial • Adventitial • Intramural Hematoma • Intra-stent Angiographic and IVUS images of the LAD (1-4): Arrow points at the intimal flap. IVUS catheter is in the true lumen. The false lumen is filled with contrast (black-image 1), blood (gray-image 4) and both contrast and blood (images 2 and 3) Reproduced with permission from Ohlmann, P. et al. Circulation 2006;113:e403-e405 • True Lumen (TL): 3-layer appearance (intima, media, adventitia); branches communicating with the lumen • False Lumen (FL): Not all layers are present; branches do not communicate with the lumen

18. Plaque Rupture Plaque rupture at the shoulder Fibrous cap Lipid core Reproduced with permission from Tanaka, A. et al. Circulation 2002;105:2148-2152

19. Ulcerated Plaque A and B show ulcerated plaque. Follow up IVUS 21 months later shows the same ulcerated plaque (non healed). Reproduced with permission from Rioufol, G. et al. Circulation 2004;110:2875-2880

20. Intramural Hematoma Intramural Hematoma IVUS of LAD • Intramural Hematoma • Accumulation of blood within medial space • Displacement of internal elastic membrane inwards and EEM outwards

21. Aneurysms Prox Reference • True aneurysm: Includes all layers of the vessel wall with an EEM and lumen diameter ≥ 50% larger than the proximal reference segment • Pseudoaneurysm: Does not include all layers of vessel wall and with disruption of the EEM True Aneurysm Coronary angiogram and IVUS imaging of left circumflex artery Reproduced with permission from Noguchi, T. et al. Circulation 1999;99:162-163

22. Myocardial Bridge Systole Diastole The white arrows point to a ‘half-moon’ like crest shaped area of the bridge which maintains its shape during systole Reproduced with permission from Oxford University Press - Ge, J. et al. EHJ 1999; 20: 1707–1716

23. Stent Malapposition Stent malapposition (white arrows): 1 or more struts clearly separated from vessel wall with evidence of blood speckles behind the strut Reproduce with permission from Shah, V. M. et al. Circulation 2002;106:1753-1755

24. Restenosis: Neointimal Hyperplasia Neointimal hyperplasia Stent Struts Neointimal hyperplasia in the gap between two stents Reproduced with permission from Tanabe, K. et al. Circulation 2003;107:559-564

25. Image Interpretation - Quantitative • Quantitative measurements are performed from “leading edge to leading edge” EEM CSA Lumen CSA Maximal Lumen Diameter Minimal Lumen Diameter Max Plaque Thickness

26. Image Interpretation - Quantitative • Definitions • Proximal reference: The site with the largest lumen proximal to a stenosis but within the same segment (usually within 10 mm of the stenosis with no major intervening branches) • Distal reference: The site with the largest lumen distal to a stenosis but within the same segment (usually within 10 mm of the stenosis with no intervening branches) • Largest reference: The largest of either the proximal or distal reference sites • Average reference lumen size: The average value of lumen size at the proximal and distal reference sites

27. Image Interpretation - Quantitative • Definitions • Lumen CSA: The area bounded by the luminal border • Minimum lumen diameter: The shortest diameter through the center point of the lumen • Maximum lumen diameter: The longest diameter through the center point of the lumen • Lumen eccentricity: Max lumen dia - Min lumen diameter Max lumen diameter • Lumen area stenosis: Ref lumen CSA - Min lumen CSA Ref lumen CSA • EEM CSA: The area bounded by the external elastic membrane border

28. Image Interpretation - Quantitative • Definitions • Atheroma (plaque+media) CSA: EEM CSA - lumen CSA • Max atheroma (plaque+media) thickness: The largest distance from the intimal leading edge to the EEM • Min atheroma (plaque+media) thickness: The shortest distance from intimal leading edge to the EEM • Atheroma eccentricity: (max atheroma thickness – min atheroma thickness)/max atheroma thickness • Atheroma burden: Plaque + media CSA • EEM CSA • Remodeling index: Lesion EEM CSA Ref EEM CSA Remodeling index > 1.05  Positive remodeling Remodeling index < 0.95  Negative remodeling Remodeling index 0.95-1.05  No remodeling

29. Remodeling Negative Remodeling Positive Remodeling Reproduced with permission from Dangas, G. et al. Circulation 1999;99:3149-3154

30. Image Interpretation - Quantitative * Hanekamp et al. Circulation 1999;99:1015–21 ** Pijls et al. Circulation 2002;105:2950–4

31. Artifacts: NURD • Non Uniform Rotational Distortion • Seen with mechanical transducers and results from mechanical binding of the drive cable that rotates the transducer (due to frictional forces) • Due to excessive vessel tortuosity, catheter twisting, calcified arteries, or excessive tightening of the hemostatic valve (O-ring) • Smudging of portions of the image • Fix: Loosening the O-ring

32. Artifacts: Ring-down • Ring Down Artifact • Produced by acoustic oscillations in the transducer • Bright halos around the catheter • Creates a zone of uncertainty around the transducer • Less with solid state transducers • Fix: Adjusting the time gain control

33. Artifacts: Blood Speckle • Blood Speckle Artifact • Due to increased transducer frequency or decreased velocity of blood (in the region of severe stenosis) • Increased intensity of blood speckle makes delineation of lumen difficult as well as identification of plaques • Fix: Adjusting the time gain control or flushing the catheter with saline or contrast

34. Artifacts: Guidewire • Guide Wire Artifact • Seen mainly with mechanical transducers • Acoustic shadow < 120 arc