Standardized Protocol for Intravascular Ultrasound-Guided Lithotripsy in Severely Calcified Coronary Lesions

Summary

This protocol presents a standardized, intravascular ultrasound-guided intravascular lithotripsy method for treating severe coronary artery calcification. The goal is to use objective, real-time imaging to precisely size balloons, confirm calcium fractures, and optimize final stent expansion, thereby enhancing procedural safety and efficacy.

Abstract

Severe coronary artery calcification poses a clinical challenge during percutaneous coronary intervention, significantly increasing the risk of stent underexpansion and subsequent adverse cardiovascular events. While intravascular lithotripsy (IVL) uses acoustic pressure waves to modify calcified plaques, its use without precise intracoronary imaging can lead to suboptimal balloon sizing and unpredictable anatomical outcomes. The primary goal of the presented protocol is to detail a standardized, step-by-step methodology for utilizing intravascular ultrasound (IVUS) to guide IVL therapy in patients with heavily calcified coronary lesions. The protocol delineates strict criteria for baseline IVUS evaluation to accurately identify calcium arcs greater than 180° and determine the exact reference vessel diameter, thereby enabling a precise 1:1 IVL balloon-to-artery sizing ratio. Subsequent steps detail the targeted delivery of acoustic pulses at working pressures of 4–6 atm, followed by mandatory post-intervention IVUS pullbacks to visually confirm the induction of multiplanar calcium fractures and ensure optimal final stent apposition. Application of this standardized workflow in a real-world, highly comorbid cohort of 44 patients resulted in a 100% procedural success rate. Quantitative imaging confirmed a statistically significant expansion of the minimum lumen area (MLA) from a baseline of 1.25 mm² ± 0.25 mm² to a final post-stent area of 8.56 mm² ± 0.42 mm², alongside the reduction in severity grade of concentric calcifications. Furthermore, the protocol demonstrated a favorable periprocedural safety profile, with no severe device-related complications, as evidenced by stable cardiac biomarker trajectories and a 0% incidence of major adverse cardiovascular events (MACE) over an extended clinical follow-up period of 6–18 months. Ultimately, adherence to this IVUS-guided IVL protocol provides a reproducible, systematic framework to optimize lesion preparation and facilitate robust stent deployment in complex cardiovascular interventions.

Introduction

The prevalence of coronary artery calcification (CAC) is increasing alongside the global aging of the population and the escalating incidence of metabolic comorbidities, such as diabetes mellitus, dyslipidemia, and chronic kidney disease^1,2. Physiologically, the accumulation of calcium in the arterial wall typically accelerates after age 40, leading to significant alterations in vascular compliance and cardiovascular hemodynamics². In the realm of interventional cardiology, moderate-to-severe CAC presents a significant clinical challenge during percutaneous coronary intervention (PCI)^1,3. Heavily calcified, non-compliant plaques mechanically obstruct the delivery of therapeutic devices, damage the protective polymer coatings of drug-eluting stents, and impair local drug elution kinetics^2,4. Consequently, failure to adequately modify calcified lesions results in incomplete stent expansion and strut malapposition, which are universally recognized as the primary biomechanical drivers of acute stent thrombosis and long-term in-stent restenosis⁵. Furthermore, the presence of severe calcific features serves as a robust, independent predictor of all-cause mortality and major adverse cardiovascular events (MACE)^6,7.

Historically, interventionalists have relied on a variety of plaque-modification strategies to treat severe CAC before stent deployment^1,8. High-pressure and ultra-high-pressure non-compliant balloons, alongside specialized scoring or cutting balloons, are frequently utilized; however, these balloon-based modalities often fail to fracture deep or unusually thick calcium rings and carry an inherent risk of inducing severe barotrauma, vessel dissection, or coronary perforation^1,3. Alternatively, atherectomy devices, such as rotational and orbital atherectomy, effectively ablate superficial calcium^3,4. Nevertheless, these techniques are technically demanding, require a steep learning curve, and are associated with specific periprocedural complications, including thermal injury, guidewire bias, and distal debris embolization that can trigger slow-flow or no-reflow phenomena^1,8. Therefore, there remains a critical clinical need for safer, highly effective modalities to optimize PCI in these complex anatomies⁸.

To overcome the well-documented limitations of traditional ablative technologies, coronary intravascular lithotripsy (IVL) has emerged as a novel addition to the calcium modification armamentarium^3,9. Adapting the fundamental principles of extracorporeal shockwave lithotripsy used for nephrolithiasis, IVL utilizes a fluid-filled balloon catheter to deliver localized, pulsatile acoustic pressure waves directly to the arterial wall3. These sonic waves selectively interact with high-density coronary calcium, safely inducing multiplanar micro-fractures in both superficial and deep calcium deposits while preserving the integrity of the compliant soft vascular tissues^3,9. The landmark Disrupt CAD III prospective, multicenter trial (including its primary endpoint analysis and subsequent follow-ups) firmly established the safety and efficacy profile of IVL, demonstrating a high procedural success rate coupled with a low incidence of periprocedural MACE at both 1-year and 2-year follow-ups^9,10,11. Subsequent robust meta-analyses and large real-world retrospective registries have further corroborated these findings, proving that IVL achieves significant acute luminal gain and remains effective across diverse patient demographics, including highly complex subsets such as calcified left main coronary artery disease^3,12,13.

While IVL provides the necessary mechanical force to alter plaque compliance, the optimization of this therapy relies fundamentally on precise pre- and post-procedural imaging assessment^14,15. Traditional coronary angiography lacks the spatial sensitivity required to accurately quantify the circumferential arc, depth, and longitudinal extent of the calcium burden4. Consequently, intravascular ultrasound (IVUS) has become an indispensable imaging modality for evaluating calcified lesions^15,16. Although optical coherence tomography (OCT) offers superior axial resolution for penetrating and measuring calcium thickness or fracture depth, IVUS was specifically selected as the primary imaging modality for this protocol. IVUS does not require continuous contrast flushing, which is a critical advantage for minimizing the risk of contrast-induced nephropathy in high-risk cohorts with a substantial prevalence of chronic renal insufficiency^4,17. Furthermore, advanced IVUS-derived calcium scoring systems have been validated to successfully predict the likelihood of subsequent stent underexpansion⁵. Crucially, IVUS is instrumental in guiding IVL interventions by facilitating exact 1:1 sizing of the IVL balloon to the reference vessel diameter, monitoring therapeutic efficacy by visualizing discrete calcium fractures, and definitively confirming optimal final stent apposition^5,15,18.

Despite compelling individual evidence supporting IVL and IVUS, standardized clinical protocols that synergize both technologies for routine application remain highly variable1,15. The objective of the present study is to systematically present a standardized, step-by-step IVUS-guided IVL protocol. By investigating a retrospective, single-center cohort of patients with severe, highly angulated coronary calcifications, this methodology aims to outline the procedural reproducibility, essential troubleshooting strategies, and objective criteria for lesion preparation. The prespecified observational endpoints focus on achieving adequate calcium fractures (defined as a complete anatomical discontinuity of the echolucent calcium band) and facilitating optimal final stent expansion. The practical applicability of this protocol is most pronounced in high-risk patient subsets, particularly those with chronic kidney disease requiring zero or minimal contrast volume, elderly patients with highly tortuous anatomies, or scenarios involving severe concentric calcium arcs (>180°) where traditional balloon-based modalities are prone to failure. Furthermore, this standardized workflow provides interventional teams with a highly reproducible, algorithmic decision-making tree to mitigate the risks of stent underexpansion, especially in catheterization laboratories lacking rotational atherectomy infrastructure. While the practical applicability of this standardized IVUS-guided approach is highly relevant for safely managing complex calcified lesions, the primary limitation of this study is its single-arm, observational design without a comparative control group (e.g., rotational atherectomy). Consequently, the clinical outcomes reflect procedural feasibility within a specific cohort rather than proving comparative superiority, and broader generalizability requires validation in future randomized controlled trials.

Protocol

The clinical protocol was performed in compliance with the guidelines of the Ethics Committee of Wuhan Asia Heart Hospital. All patients provided written informed consent before the procedure.

1. Patient selection and evaluation

1. Select patients diagnosed with stable angina pectoris, unstable angina pectoris, or occult coronary artery disease (defined objectively by documented silent ischemia on non-invasive stress testing) who require percutaneous coronary intervention (PCI).
2. Ensure patients meet the angiographic inclusion criteria: presence of severely calcified de novo. coronary lesions with a reference vessel diameter of 2.5–4.0 mm and a lesion length of ≤ 40 mm (restricted to conform to the treatment capacity of a maximum of 80 pulses from a single 12 mm length intravascular lithotripsy (IVL) catheter (see Table of Materials), thereby avoiding confounding adjunctive therapies).
3. Exclude patients presenting with left main coronary artery disease, acute myocardial infarction, hemodynamic instability, complex bypass graft lesions, or pre-existing dissections at the target site.

2. Pre-procedural preparation and angiography

1. Administer a standard dual antiplatelet therapy regimen before the procedure (e.g., a loading dose of 300 mg aspirin combined with 300–600 mg clopidogrel or 180 mg ticagrelor) according to current revascularization guidelines.
2. Establish vascular access via the radial artery as the default strategy. Femoral access is reserved exclusively for complex anatomical variations or radial crossover failure.
3. Administer systemic anticoagulation (e.g., unfractionated heparin at 70–100 U/kg) at the operator's discretion to maintain an activated clotting time (ACT) > 250 s.
4. Perform baseline coronary angiography using multiple orthogonal projections to initially locate and evaluate the target calcified lesion, assess vessel tortuosity, and accurately estimate the lesion length.
   NOTE: In anatomically ambiguous lesions, intracoronary imaging may be cautiously attempted before guidewire crossing to clarify anatomy, provided it does not compromise vessel safety.
5. Adhere strictly to institutional biomedical waste and sharps disposal protocols for the handling of all contaminated invasive equipment throughout the procedure.

3. Baseline intravascular ultrasound (IVUS) assessment

1. Advance a standard 0.014-inch coronary guidewire (see Table of Materials) across the target lesion.
2. Troubleshooting Step: If the baseline IVUS catheter fails to cross the severe calcification, perform gentle pre-dilation utilizing a 1.0 to 1.5 mm semi-compliant balloon to establish a micro-channel before the initial IVUS pullback.
3. CAUTION: When preparing, wiping, or cleaning the IVUS catheter and guidewires, use only a saline wipe or a cotton ball.
   NOTE: Do not use alcohol wipes under any circumstances, as alcohol may compromise the hydrophilic coating of the intravascular devices.
4. Advance the IVUS imaging catheter (see Table of Materials) distal to the target lesion and perform an automated pullback at a constant speed of 0.5 mm/s to the guiding catheter.
5. Assess the calcification severity. Confirm the inclusion criterion by identifying a calcification arc greater than 180° (Grades III or IV) to ensure the protocol is specifically applied to severely resistant concentric calcium.
6. Measure the distal reference vessel diameter accurately using the IVUS console to guide the subsequent selection of the IVL balloon.
7. Determine the reference vessel area by averaging the lumen areas of the most normal-appearing cross-sections within 5 mm proximal and distal to the target lesion.

4. Lesion preparation

1. Perform mandatory pre-dilation of the calcified lesion.
2. Utilize a semi-compliant balloon, non-compliant (NC) balloon, or scoring/cutting balloon (see Table of Materials) sized appropriately to the vessel to establish a preliminary channel.
3. Ensure the lesion is adequately prepared (defined as establishing sufficient patency to allow the smooth delivery of the IVL catheter without requiring excessive pushing force).

5. Intravascular lithotripsy (IVL) procedure

1. Select the appropriate IVL balloon catheter size in a 1:1 ratio based on the IVUS-derived reference vessel diameter (available sizes: 2.5–4.0 mm).
2. Advance the IVL balloon catheter over the guidewire and position it precisely across the most severely calcified segment, utilizing the radiopaque balloon markers under fluoroscopy.
3. Connect the proximal end of the IVL catheter to the generator cable (see Table of Materials).
   NOTE: CAUTION: Acoustic pulse delivery is controlled exclusively via the hand switch on the connector cable.
4. Verify that the operator has clear access to the hand switch.
   NOTE: A foot pedal is not utilized in this system.
5. Inflate the IVL balloon to a sub-nominal pressure of 4 atm to establish initial apposition against the vessel wall.
6. Activate the hand switch to deliver acoustic pulses. Deliver 10 continuous pulses (one cycle) at a frequency of 1 pulse per s.
7. Following the pulse cycle, inflate the balloon to the nominal pressure (6 atm) and actively observe the balloon silhouette under fluoroscopy for full expansion to maximize luminal gain.
8. Deflate the balloon to allow distal blood perfusion.
9. Repeat steps 5.5 through 5.8 as necessary. If the calcified segment is longer than the balloon, reposition the catheter with slight longitudinal overlap (1–2 mm) to ensure contiguous treatment.
10. Deliver additional cycles (up to 80 pulses per catheter) until adequate vessel compliance is achieved.

6. Post-IVL assessment and stent implantation

1. Perform a second IVUS pullback to evaluate the efficacy of the IVL treatment.
2. Carefully inspect the IVUS cross-sections for the presence of longitudinal or transverse calcium fractures (defined objectively as a complete anatomical discontinuity of the echolucent calcium band) and an increase in the minimum lumen area (MLA).
3. If residual stenosis remains > 50% or fluoroscopic balloon expansion is visibly suboptimal, consider delivering additional IVL pulses or utilizing a second IVL catheter.
4. Once adequate lesion preparation is confirmed, deploy an appropriately sized drug-eluting stent (DES) (see Table of Materials) across the target lesion.
5. Perform routine post-dilation using a non-compliant (NC) balloon at high pressure (≥ 14 atm) to ensure full stent expansion.
6. Perform a final IVUS pullback to confirm optimal stent apposition, absence of major edge dissections (e.g., penetrating the media or > 60° in arc), and achievement of adequate final stent expansion (target > 90% compared to the reference vessel area).

7. Data collection and statistical analysis

1. Record all procedural parameters into a standardized electronic clinical database, including IVL balloon sizes, maximum working pressures, total pulse frequencies, and any periprocedural complications (e.g., slow flow, dissection).
   NOTE: Procedural success is defined as successful stent delivery with residual stenosis < 20% and final TIMI 3 flow without severe complications.
2. Collect blood samples post-procedure to monitor high-sensitivity cardiac troponin I (hs-cTNI) and CK-MB levels.
3. Monitor clinical follow-up for 6–18 months to objectively assess Major Adverse Cardiovascular Events (MACE), strictly defined as a composite of cardiac death, non-fatal myocardial infarction, or target vessel revascularization.
4. Perform quantitative IVUS measurements at three designated time points: pre-IVL, post-IVL, and post-stenting. Quantify the minimum lumen area (MLA) by manually tracing the leading edge of the luminal border at the cross-section demonstrating the most severe stenosis.
5. Compile the data and analyze categorical variables using Chi-square or Fisher's exact tests.
   NOTE: The dynamic quantitative changes in MLA across the three continuous procedural timepoints must be analyzed utilizing a Repeated-Measures Analysis of Variance (ANOVA) to ensure methodological rigor. Statistical analyses should be conducted using established statistical analysis software (see Table of Materials). Consider a P. value <0.05 as statistically significant.

Results

Baseline characteristics and comorbidity profile

A total of 44 patients with severe coronary artery calcification were consecutively enrolled in this study. The mean age of the cohort was 67.68 years ± 7.68 years, and 29 patients (65.9%) were male. The clinical presentation was primarily dominated by unstable angina pectoris (61.4%), followed by stable angina (31.8%) and occult angina (6.8%). Importantly, 16 patients (36.4%) presented with concurrent chronic renal insufficienc...

Discussion

The present study evaluated the efficacy and safety of a highly standardized, intravascular ultrasound (IVUS)-guided intravascular lithotripsy (IVL) protocol in a real-world cohort of 44 patients presenting with severe, heavily calcified coronary artery disease. Consistent with the foundational principles of plaque modification, the data demonstrate that targeted acoustic pressure waves, when meticulously sized and evaluated under intracoronary imaging, can safely and effectively fracture dense calcium rings, altering ve...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acoustic Pulse Generator	Shockwave Medical / Johnson & Johnson MedTech	Ref: 80001	IVL energy generator unit
Antiplatelet Drugs		Aspirin (300 mg); Clopidogrel (300–600 mg)	Standard dual antiplatelet therapy
Anticoagulation Agent		Unfractionated Heparin (70–100 U/kg)	Systemic anticoagulant
Cutting/Scoring Balloon	Boston Scientific	Ref: CS-1015	Plaque modification device
Drug-Eluting Stent	Abbott	Ref: DES-3012-R	Metallic coronary stent
Guiding Catheter	Terumo	Ref: GC-6F-RB	6F/7F radial access catheter
IVL Balloon Catheter	Shockwave Medical / Johnson & Johnson MedTech	Ref: IVL-3012-C	Intravascular lithotripsy catheter
IVUS Catheter & System	Philips	Ref: IVUS-PX-40	Intracoronary ultrasound imaging device
Non-Compliant Balloon	Boston Scientific	Ref: NC-B-2512	High-pressure dilation balloon
Saline Wipes		Ref: SW-NON-ALC	Non-alcoholic cleaning materials
Standard Guidewire	Asahi Intecc	Ref: GW-014-S	0.014-inch coronary guidewire
Statistical Analysis Software	IBM	Version: SPSS 26.0 / R 4.2	Data analysis and statistical tool