What are the indications and benefits of using Intravascular Ultrasound (IVUS) in patients undergoing Percutaneous Coronary Intervention (PCI)?

Intravascular Ultrasound (IVUS) in Percutaneous Coronary Intervention: Indications and Benefits

Intravascular ultrasound (IVUS) should be routinely used as an essential adjunct to conventional angiography during PCI of specific lesion subsets including left main coronary artery, proximal LAD, complex lesions, and any scenario where angiography may inadequately elucidate coronary anatomy. 1

Key Indications for IVUS in PCI

IVUS has Class 2a recommendations from the American College of Cardiology/American Heart Association/Society for Cardiovascular Angiography and Interventions for:

1. Assessment of intermediate left main coronary artery disease
2. Procedural guidance to reduce ischemic events - particularly in cases of left main or complex coronary artery PCI
3. Determining the mechanism of stent failure 1

Complex Lesion Subsets Where IVUS Provides Greatest Benefit:

• Left main coronary artery lesions
• Proximal LAD lesions
• In-stent restenosis
• Stent thrombosis
• Calcified coronary arteries
• Chronic total occlusions (CTOs)
• Bifurcation lesions 1, 2

Clinical Benefits of IVUS-Guided PCI

Mortality Reduction

• IVUS-guided PCI is associated with lower medium-term mortality compared to angiography-guided PCI in patients with complex lesions (adjusted hazard ratio = 0.89) 3

Reduced Target Vessel Revascularization

• IVUS guidance results in lower rates of target vessel revascularization (adjusted hazard ratio = 0.88) 3

Reduced Major Adverse Cardiac Events (MACE)

• In patients with bifurcation lesions, IVUS-guided PCI shows lower incidence of MACE compared to angiography-guided PCI (OR = 0.55) 4
• The ULTIMATE trial demonstrated that IVUS guidance improved clinically driven target vessel failure compared to angiography-guided PCI (2.9% vs 4.2%) 1

Specific Benefits in Complex Lesions

• In chronic total occlusions, the CTO-IVUS trial reported lower MACE rates with IVUS guidance (2.6% vs 7.1%) 1
• For long lesions (≥28mm), the IVUS-XPL trial showed MACE at 1 year occurred in 2.9% of IVUS-guided group vs 5.8% in angiography-guided group 1

How IVUS Improves PCI Outcomes

Pre-Intervention Assessment

1. Lesion and vessel assessment:

   • Evaluates plaque composition and key lesion characteristics
   • Identifies reference segments and landing zones
   • Helps select optimal stent length and diameter 1

2. Plaque characterization:

   • Identifies vulnerable plaques at risk of future rupture
   • Distinguishes plaque erosion vs rupture in acute coronary syndrome
   • Clarifies complex anatomy (aorto-ostial ambiguity, vessel dissection, intramural hematoma) 1

Lesion Preparation and Stent Deployment

1. Calcification assessment:

   • Detects, localizes, quantifies, and characterizes coronary calcification
   • Guides adjunctive therapies (angioplasty, atherectomy, lithotripsy)
   • Ensures sufficient calcium fracture to facilitate stent delivery 1

2. Stent sizing:

   • Prevents systemic undersizing of stents
   • Provides accurate vessel diameter measurements 1, 5

Post-Procedure Assessment

1. Complication detection:

   • Identifies stent underexpansion, deformation, and malapposition
   • Detects edge dissection, hematoma, and tissue protrusion
   • Rules out geographic miss and inflow/outflow disease 1

2. Optimization criteria (ULTIMATE trial):

   • Minimum lumen area in stented segment >5.0 mm² or 90% of MLA at distal reference
   • <50% plaque burden within 5 mm proximal or distal to stent edge
   • No edge dissection involving media with length >3 mm 1

Practical Implementation Considerations

Technical Aspects

• Imaging should be performed after administration of intracoronary nitroglycerin
• Begin imaging at least 20 mm distal to the area of interest and end at the left main or right coronary artery ostium 1
• If the imaging catheter fails to cross the lesion, low-pressure undersized balloon predilation or atherectomy may facilitate catheter passage 1

Potential Pitfalls and Caveats

1. Procedural risks:

   • Exercise caution when advancing IVUS catheters across severely stenotic lesions or through extremely tortuous anatomy
   • Catheter-related complications can include slow flow, coronary ischemia, dissections, and catheter entrapment 1

2. Specific cautions:

   • Use IVUS with extreme caution in spontaneous coronary artery dissection due to risks of manipulating the dissected coronary artery 1

3. Training requirements:

   • Proper interpretation requires training in recognition of plaque constituents, measurements of lesion and stent optimization parameters, and identification of complications 1

Current Utilization and Recommendations

Despite proven benefits, IVUS utilization remains low (used in <15% of all PCI procedures) 1. Recent data shows increasing trends (from 13.4% in 2014 to 16.5% in 2018 for complex lesions) but with significant inter-hospital variation 3.

The American College of Cardiology recommends that most cardiac catheterization laboratories should ideally have both IVUS and OCT capabilities, with IVUS being the more flexible option that can be utilized in almost all clinical scenarios 1, 2.