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

1. IVUS Tales: From Research to its Clinical application in Contemporary Interventions. Presenter: Islam Bolad Attending: Jose Diez

2. Coronary Angiography • Visual interpretation of coronary angiography exhibits • intraobserver and interobserver variability • (<50%) • Angiography & postmortem histology. • QCA • Glagov phenomenon

3. Am J Cardiol 2002;89(suppl):24B-31B

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

5. 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.

6. 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.

7. 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.

8. 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 22;106(17):2200-6.

9. 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.

10. 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.

11. Resolutions

12. 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.

15. 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.

17. In its distal portion, the anterior interventricular vein (AIV) may branch into two vessels accompanying the LAD on both sides

18. The elliptic shape of the AIV can be appreciated at 3 o'clock in this cross section from the mid LAD

19. LAD/LCx bifurcation, LCx, GCV triangle. Triangle of Brocq & Mouchet

20. 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.

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

23. 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.

24. Veins are associated with RV marginal branches and are characterized by an arching pattern around the RCA.

25. The Endovascular Anatomy. The arterial wall.

26. Different echogenic qualities is due to the relative amount of collagen (1000x reflectance than smooth muscles) and elastin

27. Blood • Speckled pattern that is constantly changing with • systolic and diastolic blood flow alterations • ( > 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.

30. 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.

32. 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.

33. Fibrous Plaque • Plaques with echogenicity that is < 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.

35. 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.

37. 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.

38. 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.

39. 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

41. 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 < 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.

42. Thrombus after stent deployment.

43. Post PTCA and Reopro

44. 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.

46. 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.

48. 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 6;103(5):778. • 2- Int J Cardiovasc Intervent. 2003;5(3):137-42.

50. Quantitative Coronary Ultrasound (QCU)