IVUS – LM & Bifurcation MCQs – What we should know

IVUS in Left Main & Bifurcation PCI — 50 FAQs

Basics & Principles

1. What is IVUS?
   Intravascular ultrasound is an intracoronary imaging modality that provides cross-sectional vessel anatomy using ultrasound.
2. Why is IVUS preferred in left main disease?
   Because angiography underestimates plaque due to positive remodeling, and IVUS shows true vessel size (EEM).
3. What does EEM represent on IVUS?
   External elastic membrane area represents the true vessel size.
4. What is plaque burden on IVUS?
   (Plaque + media area / EEM area) × 100.
5. What plaque burden indicates high risk?
   ≥70% plaque burden is associated with adverse outcomes.

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Left Main Cut-offs

6. What IVUS MLA safely allows deferral of LM revascularization?
   ≥6.0 mm² (LITRO trial).
7. What LM MLA is clearly significant?
   <4.5 mm² is generally hemodynamically significant.
8. What is the LM gray zone MLA?
   4.5–6.0 mm².
9. Which LM segment usually has the smallest MLA?
   Distal left main bifurcation.
10. Why is physiology still useful in LM disease?
    IVUS gives anatomy; FFR/iFR confirm functional significance.

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Bifurcation-Specific Concepts

11. Why is IVUS critical in bifurcation PCI?
    It defines plaque distribution and predicts carina shift.
12. Which IVUS parameter predicts side-branch compromise?
    Side-branch minimal lumen area (MLA).
13. What SB MLA suggests high risk of compromise?
    <3.5–4.0 mm² (context dependent).
14. What does IVUS guide in proximal optimization technique (POT)?
    True proximal vessel diameter based on EEM.
15. Which reference should be used for POT sizing?
    Proximal EEM diameter, not angiography.

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PCI Optimization

16. What is the strongest IVUS predictor of stent failure?
    Stent under-expansion.
17. What is the target MSA for LM PCI?
    Approximately ≥8–9 mm² (segment dependent).
18. What is the target MSA for non-LM PCI?
    ≥5.0–5.5 mm².
19. What stent expansion percentage is considered adequate?
    ≥90% of the reference lumen area.
20. Is mild malapposition always clinically significant?
    No, isolated mild malapposition is often benign.

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Calcification & Lesion Preparation

21. How does IVUS identify calcium?
    Hyperechoic arc with acoustic shadowing.
22. Why is IVUS useful in calcified LM lesions?
    It defines calcium arc and depth to plan atherectomy or IVL.
23. What calcium arc suggests need for plaque modification?

180° arc, especially with thick calcium.

24. Can IVUS measure calcium thickness accurately?
    Limited; OCT is superior for thickness measurement.
25. Which modality is preferred for calcium depth assessment?
    IVUS.

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Trials & Evidence

26. Which trial validated IVUS-guided LM deferral?
    LITRO trial.
27. Which trial showed reduced MACE with IVUS-guided PCI?
    ULTIMATE trial.
28. Which trial focused on long lesions and IVUS guidance?
    IVUS-XPL trial.
29. Which registry showed reduced stent thrombosis with IVUS?
    ADAPT-DES.
30. Which bifurcation trial benefits from IVUS optimization?
    DK-CRUSH trials.

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IVUS vs OCT

31. Why is OCT less suitable for LM disease?
    Poor EEM visualization and need for contrast flush.
32. Which modality has higher resolution?
    OCT.
33. Which modality has greater tissue penetration?
    IVUS.
34. Which modality is better for stent malapposition?
    OCT.
35. Which modality is safer in renal dysfunction?
    IVUS.

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In-Stent Restenosis (ISR)

36. What can IVUS differentiate in ISR?
    Under-expansion vs neoatherosclerosis.
37. Which ISR mechanism is mechanical?
    Under-expanded stent.
38. Which ISR mechanism is biological?
    Neoatherosclerosis.
39. Why is IVUS important in LM ISR?
    Guides treatment strategy by identifying failure mechanism.
40. Can IVUS detect late-acquired malapposition?
    Yes, often due to positive remodeling.

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Practical & Guideline-Based

41. When should IVUS be used in LM PCI?
    Both pre-PCI and post-PCI.
42. ESC guideline class for IVUS-guided PCI in complex lesions?
    Class IIa.
43. Is IVUS mandatory for LM PCI?
    Strongly recommended, though not mandatory.
44. Does IVUS increase procedure time significantly?
    No, usually modest increase with experience.
45. Does IVUS reduce contrast use?
    Yes, by reducing repeat angiographic injections.

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Exam & Viva Pearls

46. Single most important principle of IVUS-guided PCI?
    Adequate stent expansion.
47. Most common angiographic error corrected by IVUS?
    Stent undersizing.
48. Why does angiography underestimate LM disease?
    Positive remodeling.
49. Best modality to size LM stents accurately?
    IVUS.
50. Key exam takeaway comparing IVUS vs OCT?
    IVUS = vessel size & plaque burden; OCT = surface detail & stent biology.

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IVUS in Left Main & Bifurcation PCI — 50 One-Liners (NEET SS / DM)

1. IVUS provides true vessel size by visualizing the external elastic membrane (EEM).
2. Angiography underestimates left main disease due to positive remodeling.
3. Left main MLA ≥6.0 mm² allows safe deferral of revascularization (LITRO trial).
4. Left main MLA <4.5 mm² is generally hemodynamically significant.
5. The gray zone for left main MLA lies between 4.5 and 6.0 mm².
6. Plaque burden ≥70% on IVUS is associated with high-risk coronary lesions.
7. IVUS plaque burden is calculated as (plaque + media)/EEM area ×100.
8. Distal left main is the most frequent site of minimal lumen area.
9. IVUS correlates better with FFR than angiography in left main disease.
10. IVUS is preferred over OCT for left main imaging due to superior penetration.
11. In bifurcation PCI, IVUS defines plaque distribution and predicts carina shift.
12. Side-branch MLA on IVUS predicts risk of side-branch compromise.
13. Side-branch MLA <3.5–4.0 mm² suggests higher risk after main-branch stenting.
14. Proximal Optimization Technique (POT) sizing should be based on proximal EEM.
15. IVUS is the best modality to guide POT in left main bifurcation PCI.
16. Stent under-expansion is the strongest IVUS predictor of restenosis and thrombosis.
17. Adequate stent expansion is defined as ≥90% of reference lumen area.
18. Target minimal stent area in left main PCI is approximately ≥8–9 mm².
19. Target minimal stent area in non-left-main PCI is ≥5.0–5.5 mm².
20. Isolated mild stent malapposition is often clinically benign.
21. IVUS detects calcium as a hyperechoic arc with acoustic shadowing.
22. Calcium arc >180° on IVUS suggests need for plaque modification.
23. IVUS is superior to OCT for assessing calcium depth.
24. OCT is superior to IVUS for measuring calcium thickness.
25. IVUS guides selection of atherectomy or intravascular lithotripsy.
26. IVUS differentiates mechanical from biological causes of in-stent restenosis.
27. Under-expanded stent is a mechanical cause of ISR.
28. Neoatherosclerosis is a biological cause of ISR.
29. Late-acquired stent malapposition is often due to positive remodeling.
30. IVUS is essential in evaluating left main in-stent restenosis.
31. The LITRO trial validated IVUS-guided deferral of left main PCI.
32. The ULTIMATE trial showed reduced MACE with IVUS-guided PCI.
33. The IVUS-XPL trial demonstrated benefit in long coronary lesions.
34. ADAPT-DES showed reduced stent thrombosis with IVUS guidance.
35. IVUS optimization improves outcomes in DK-CRUSH bifurcation techniques.
36. IVUS is recommended both before and after left main PCI.
37. ESC guidelines give IVUS-guided PCI a Class IIa recommendation in complex lesions.
38. IVUS reduces contrast usage compared with angiography-guided PCI alone.
39. IVUS is safer than OCT in patients with renal dysfunction.
40. OCT requires contrast for blood clearance, IVUS does not.
41. IVUS axial resolution is approximately 100–150 μm.
42. OCT axial resolution is approximately 10–20 μm.
43. IVUS is preferred for ostial and proximal coronary lesions.
44. OCT is preferred for detailed stent edge and malapposition assessment.
45. IVUS is superior for imaging long lesions and chronic total occlusions.
46. The single most important principle of IVUS-guided PCI is optimal stent expansion.
47. Most angiographic sizing errors are corrected by IVUS.
48. IVUS improves procedural planning in complex coronary anatomy.
49. IVUS complements, but does not replace, physiological assessment.
50. For NEET SS / DM exams: IVUS equals vessel sizing and plaque burden, OCT equals stent detail.