What is IVUS (Intravascular Ultrasound) in patients with suspected or known coronary artery disease?

What is IVUS (Intravascular Ultrasound)?

IVUS is a catheter-based coronary imaging technique that uses high-frequency ultrasound (20-60 MHz) to generate real-time, 360-degree cross-sectional images of coronary arteries, providing detailed visualization of both the vessel lumen and arterial wall structure that cannot be seen with angiography alone. 1

Technical Fundamentals

IVUS employs a piezoelectric crystalline transducer mounted on an intravascular catheter to transmit ultrasound pulses that reflect differentially across varied tissue structures. 1 The system generates gray-scale cross-sectional images where:

• Echogenic structures (fibrous tissue, calcifications) produce bright hyperechogenic signals 1
• Echolucent structures (lipid collections) produce low-intensity hypoechogenic signals 1
• Spatial resolution ranges from 20-60 MHz depending on the catheter system 1

Two conventional engineering designs exist: solid-state catheters with phased array transducer elements arranged circularly, and mechanical-state catheters utilizing a solitary rotating component. 1 Both come in over-the-wire and monorail configurations. 1

Automated pullback at constant rates (0.5-10 mm/s) is preferable to manual pullback as it allows accurate measurement of lesion length. 1

Clinical Applications in PCI

Pre-Intervention Assessment

IVUS is reasonable for determining the adequacy of coronary stent deployment, including extent of stent apposition and minimum luminal diameter within the stent (Class IIa, Level B). 1

IVUS provides critical pre-intervention assessment of plaque composition, lesion characteristics, and identification of optimal reference segments for stent placement. 2 This prevents systematic undersizing of stents and helps select optimal stent length and diameter. 2

IVUS should be performed after administration of intracoronary nitroglycerin, beginning at least 20mm distal to the area of interest and ending at the vessel ostium. 2

Specific Indications (Class IIa)

IVUS is reasonable for: 1

• Determining mechanism of stent restenosis (inadequate expansion versus neointimal proliferation) to enable appropriate therapy selection (Level B) 1
• Evaluating coronary obstruction at locations difficult to image angiographically in patients with suspected flow-limiting stenosis (Level C) 1
• Assessing suboptimal angiographic results after PCI (Level C) 1
• Establishing presence and distribution of coronary calcium when rotational atherectomy is contemplated (Level C) 1
• Determining plaque location and circumferential distribution for directional coronary atherectomy guidance (Level B) 1

Optimization Criteria

Post-PCI IVUS optimization requires: 2

• Minimum lumen area (MLA) in the stented segment >5.0 mm² or 90% of the MLA at distal reference segments 2
• <50% plaque burden within 5mm proximal or distal to stent edge 2
• No edge dissection involving the media with length >3mm 2

Advantages Over Angiography

Unlike coronary angiography which displays only the contrast-filled luminal silhouette, IVUS images the vessel wall, revealing the true extent of coronary plaque that angiography commonly underestimates. 3

IVUS demonstrates atherosclerotic plaques in 80% of angiographically normal coronary segments in patients with coronary artery disease. 4 In one study, 16 of 20 patients (80%) with angiographically normal segments proximal to target lesions had plaque detected by IVUS. 4

IVUS-guided angioplasty reduces final residual plaque area from 51% to 34%, despite a final angiographic percent stenosis of 0%. 1

Complex Lesion Subsets

IVUS guidance is particularly valuable in complex coronary situations: 3

• Left main stem disease - some consider IVUS almost mandatory 3
• Ostial stenoses 3
• Bifurcation stenoses 3
• Chronic total occlusions - helps resolve proximal cap ambiguity and guides true-lumen wiring 2
• Heavily calcified lesions - IVUS-based scoring systems identify stenoses at risk for stent under-expansion requiring adjunctive modification 2

Outcomes Data

Recent randomized trials demonstrate IVUS guidance improves clinical outcomes in complex disease: 1

• ULTIMATE trial: IVUS guidance reduced target vessel failure at 12 months (2.9% vs 4.2%; HR 0.530; P=0.019) 1
• IVUS-XPL trial: MACE at 1 year occurred in 2.9% IVUS-guided vs 5.8% angiography-guided (HR 0.48; P=0.007) 1
• CTO-IVUS trial: Lower MACE rates with IVUS guidance (2.6% vs 7.1%; P=0.035; HR 0.35) 1

Meta-analyses show IVUS guidance reduces target lesion revascularization, target vessel revascularization, MACE, cardiovascular mortality, and stent thrombosis compared with angiographic guidance alone. 1

Special Clinical Scenarios

In MINOCA (myocardial infarction with non-obstructive coronary arteries), IVUS or OCT is recommended to identify unrecognized causes such as thrombus, plaque rupture or erosion, or spontaneous coronary artery dissection (Class I, Level C). 1, 5

In heart transplant patients, IVUS has emerged as the gold standard for early detection of cardiac allograft vasculopathy, with IVUS in conjunction with coronary angiography at baseline (4-6 weeks) and 1 year after transplant being a Class IIa recommendation (Level B). 1 IVUS findings predict mortality and major adverse cardiac events even when angiograms are normal. 1

In congenital or acquired coronary abnormalities, IVUS affords precise sequential cross-sectional imaging particularly useful in stenosis of anomalous vessels in their intramural course. 1

Current Utilization and Barriers

Despite multiple randomized trials, meta-analyses, and registries supporting IVUS use, overall adoption remains low at <15% of all PCI procedures. 1, 2 Explanations include unfamiliarity with imaging equipment, knowledge gaps in interpretation, perception of increased procedural times, lack of adequate reimbursement, and need for further definitive trials. 1

IVUS is not necessary for all stent procedures - the French Stent Registry of 2900 patients treated without IVUS reported a subacute closure rate of 1.8%, and the STARS trial showed 0.6% subacute closure with optimal stent implantation without IVUS. 1 However, IVUS evaluation appears warranted in high-risk procedures (multiple stents, impaired flow, marginal angiographic appearance). 1

Important Caveats

IVUS should be used cautiously in spontaneous coronary artery dissection due to risks of manipulating the dissected artery. 2

Air bubbles between the catheter sheath and IVUS transducer can degrade image quality. 2

Stent malapposition should be distinguished from stent underexpansion, as most acute malapposition resolves over time without affecting long-term stent failure rates. 2