What is Intravascular Ultrasound (IVUS)?
IVUS is a procedure done along with coronary angiography to provide a better anatomical assessment of the coronary artery.
A miniature sound probe (transducer) capable of producing high-frequency sound waves (40-60mHz) mounted on the tip of a coronary catheter is advanced into the coronary artery.
This produces a detailed analysis of the internal layers of the coronary artery, providing important information to your interventional cardiologist that will guide further management.
What is the clinical utility of IVUS?
Coronary Angiography is the gold standard in the diagnosis and assessment of coronary artery disease but it has several limitations:
Normal vs Diffuse disease
Tends to underestimate degree of narrowing in diffuse disease or vessels with positive remodelling
Helps you distinguish normal from abnormal vessels and find the location of disease in patients with a normal angiogram.
Concentric and Eccentric plaques
Must rely on “eyeball” estimate. Assessment of eccentric plaque lesion size especially prone to error based on angle of view.
Helps you get an accurate lumen area to determine lesion significance and stent size.
Calcification of coronary vessels
Less sensitive than IVUS for detecting calcium
Makes the presence of calcium clear, helping to identify lesions that need pre-treatment.
Cannot determine where the dissection begins.
Dissections can be accurately defined.
Difficult to determine
Thrombus can be accurately defined.
Must rely on “eyeball” estimate
Enables you to make lumen and reference vessel measurements that can be used when selecting stent size.
Stent expansion and apposition
Cannot see the vessel wall to verify optimal placement.
User-defined cross-sectional area measurements and views allow verification and documentation of stent placement.
IVUS is thus highly favored by expert interventional cardiologists as an adjunctive tool during coronary angiography and angioplasty.
- 1During coronary angiography
- Shows the presence and amount of plaque in the coronary arteries not well seen during angiography
- Measures the degree of narrowing caused by the plaque
- Provides information on what the plaque is made of (calcium/fibrous tissue/lipids) that will guide the angioplasty
- Helps to assess the cause of restenosis of previous stents
- 2During coronary angioplasty (stenting)
- Guides the choice of the diameter and length of stent to use
- Allow more accurate placement of stent
- Optimization of stent expansion and apposition to the vessel wall
- Reduce the risk of stent restenosis and thrombosis (clotting).
In summary, IVUS helps to:
- Help decide the best therapy option for you
- Guide pre-stenting planning
- Optimize treatment results and reduce stenting complications
Rotational IVUS Image interpretation
- 1Normal Coronary Vessel
- Coronary angiogram – provides only a shadow of the lumen of the artery
- IVUS – Allows visualization of the vessel and lumen
- 2Concentric Mixed Plaque
Information obtainable from IVUS
- Characteristics of the plaque causing the blockage
- Diameter of the vessel
- Minimal lumen diameter and area (MLA)
Utility of the Minimal Lumen Area (MLA)
- Can define a threshold for a significant stenosis to determine the need for catheter-based or surgical intervention
- – MLA < 4 mm2 in LAD, LCX, and RCA vessels > 3 mm in diameter correlates with physiological significance1
- – MLA < 6 mm2 in left main correlates with FFR < 0.75. indicating physiological significance1,2,3
- 3Eccentric Mixed Plaque
Eccentric plaques are distributed non-circumferentially in the vessel; this makes the assessment of disease by angiography especially prone to underestimation or overestimation depending on the angle of view.
Calcium is indicated by very bright areas with acoustic shadowing that blocks out the image behind; this shadowing occurs because the high density of calcium dampens the ultrasound echo.
- 4Fibrous Plaque
Fibrous plaques have an intermediate echogenicity between soft (echolucent) atheromas and highly echogenic calcific plaques. They exhibit little or no acoustic shadowing.
Coronary angioplasty if performed, is usually straightforward as the stent will have minimal/no difficulty expanding the lumen of the narrowed blockage.
- 5Calcified Plaque
Calcium is indicated by very bright areas with acoustic shadowing that blocks out the image behind it. The shadowing occurs because the high density of calcium prevents the ultrasound from passing through.
IVUS is able to pick up calcium more accurately than coronary angiography alone.
Coronary Angioplasty if performed is less straightforward and may require plaque modification using rotablation or shockwave lithiotripsy before stenting can be performed optimally.
- 6Under-expanded Stent
Stent under-expansion has been strongly associated with restenosis (renarrowing of the stent) and stent thrombosis (clot formation within the stent)1.
IVUS-guided coronary angioplasty has been showed to reduce the need for repeat stenting procedures and risk of morbidity and mortality associated with stent thrombosis.
- 7Complications of Coronary Angioplasty
a. Coronary Dissection
Defined as a tear in the vessel wall and it can be seen as a flap with blood flow behind it. It is associated with higher risk of acute stent thrombosis
b. Intraluminal Thrombus
Thrombus is a clot present in patients with an acute heart attack when there is a plaque rupture or when there is insufficient anticoagulation during a coronary angioplasty procedure.
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