3D Printing of Carotid Artery and Aortic Arch Anatomy: Implications for Preprocedural Planning and Carotid Stenting

Background. Carotid artery stenting (CAS) has been associated with increased periprocedural stroke in comparison with carotid endarterectomy (CEA). Three-dimensional (3D) printing of aortic arch and carotid artery may aid with preprocedural planning and adaptive learning, possibly reducing procedure-related complications. Methods. Five CAS cases with available computed tomography angiography (CTA) were retrospectively evaluated and 3D-printed models (3D-PMs) were made. One additional case that was 3D printed preprocedurally provided prospective analysis. Standard 3D printing software was used to create a computer-aided image from CTA series that were 3D printed. The models were painted with acrylic paint to highlight anatomical features. The type of aortic arch, common carotid artery (CCA) to internal carotid artery (ICA) angle, and ICA distal landing zone for embolic protection device (EPD) were analyzed. In addition, stent and EPD sizing was determined preprocedurally for the prospective case. Comparisons of 3D-PM were made with 3D-CTA reconstruction and carotid angiography. Results. Of 6 cases, 2 had type III and 4 had type I aortic arches. One case, a failed endovascular approach from femoral artery access site requiring reattempt via right brachial artery, had a CCA to ICA angle >60° and a tortuous innominate artery and distal ICA for EPD. The remaining 5 cases had straight distal landing zones for EPD and <60° CCA to ICA angles with successful first endovascular attempt. Additionally, vessel-specific stent and EPD sizing was appropriately chosen for the 1 prospective case. Conclusions. 3D-PM for CAS offers added value compared with CTA by providing improved perceptual and visual understanding of 3D anatomy.

J INVASIVE CARDIOL 2021;33(9):E723-E729.

Key words: aortic arch, carotid artery, 3D printing

Carotid artery stenting (CAS) is associated with higher periprocedural and non-procedural ipsilateral stroke when compared with carotid endarterectomy (CEA).¹ Etiology for this incidence is related to unfavorable aortic arch type, common carotid artery (CCA) to internal carotid artery (ICA) angulation, tortuous ICA distal landing zone (DLZ) for embolic protection device (EPD), plaque morphology, and other patient-related clinical factors. Computed tomographic angiography (CTA) of the aortic arch and carotid arteries with 3-dimensional (3D) reconstruction is a non-invasive, safe, reliable, and economically valuable imaging modality that can aid with periprocedural planning, although it has limitations. 3D-printed models (3D-PMs) of the aortic arch and carotid arteries from CTA can offer added value by allowing enhanced visual and perceptual understanding of complex anatomy and may reduce procedure-related adverse outcomes by allowing appropriate selection of access site, specific diagnostic and interventional catheters for intraprocedural navigation, better appreciation of arch and carotid tortuosity, and preprocedural stent and EPD sizing.

The 3D slicer software (Surgical Planning Laboratory) was used to generate a computer-aided image from carotid CTA image series. The design was converted into a standard tessellation language (.stl) file, which was uploaded into the Ultimaker 3 software (Create Education Limited) and 3D printed with Ender 3 Pro (Creality 3D) printers at our institution. Fused-deposition modeling, a method whereby heated thermoplastic filament is extruded layer by layer, was utilized using polylactic acid filament. After successful printing of all models, the aortic arch was painted with yellow acrylic paint and the great vessels were painted with red to highlight the anatomy. The type of aortic arch, CCA to ICA angle, and DLZ for EPD were analyzed. The actual CCA to ICA angle was also determined using an online protractor. Lastly, carotid stent and EPD sizes were determined using a manual millimeter caliper preprocedurally for the single prospective case. 3D-CTA and carotid angiograms were compared with 3D-PM for accuracy and feasibility for preprocedural planning.

Six patients with prior CTA who underwent CAS were evaluated and 3D-PMs were printed. Baseline characteristics including clinical history and preprocedure diagnostic non-invasive work-up for each patient are described in Table 1. The print time for each model varied from 16 to 22 hours (Table 2). 3D-PMs of all 6 cases with type of aortic arch, actual CCA to ICA angle measured with an online protractor, ICA-DLZ for EPD, and the respective 3D-CTAs and carotid angiograms for all 5 retrospective (Cases 1-5) and 1 prospective (Case 6) are illustrated. Carotid stent and EPD sizing for the prospective case (Case 6) was accomplished with a manual millimeter caliper and sizing. Clinical value in procedural planning for each case is further described.

Case 1 (Figure 1). 3D-PM reveals a type III aortic arch with a CCA to ICA ratio <60° (actual measured angle, 24°) indicating difficult to engage arch anatomy but without significant ICA tortuosity. The DLZ is straight, further indicating appropriate anatomy for EPD.

Case 2 (Figure 2). 3D-PM shows a type I aortic arch with CCA to ICA angle <60° (actual measured angle, 21°) indicating optimal anatomy for CAS. The DLZ is also straight.

Case 3 (Figure 3). 3D-PM showing a type I aortic arch with CCA to ICA angle <60° (actual measured angle, 13°) and a straight DLZ for EPD.

Case 4 (Figure 4). 3D-PM shows a type I aortic arch with CCA to ICA angle >60° (actual measured angle, 65°). The DLZ for EPD is also noted to be tortuous. Significant distal right ICA tortuosity is confirmed on carotid angiogram, indicating difficult anatomy for endovascular CAS. This was clinically confirmed as the case was a failed first attempt at intervention related to severe innominate artery and distal right ICA tortuosity, which can be appreciated on the 3D-PM. As such, multiple catheters were used with difficulty to engage the right innominate artery, initially with Vitek catheter (Cook Cardiology) and then a Simmons 1 catheter (Cordis Corporation). After advancement of a shuttle sheath over the Simmons 1 catheter, a distal EPD could not be delivered due to severe distal ICA-DLZ tortuosity.

The case was aborted due to hostile anatomy for endovascular intervention and recommended for CEA. The patient opted not to have surgery and thus a second attempt was made via the right brachial artery taking into consideration the hostile anatomy. The right innominate artery was engaged with a standard Judkins Right 4 catheter and a distal EPD was delivered successfully from the support provided by the right brachial artery access.

Appreciation of such anatomy by preprocedural 3D-PM could aid with appropriate access and catheter selection preprocedurally, thus potentially avoiding an unsuccessful procedure.

Case 5 (Figure 5). 3D-PM shows a type III aortic arch and a CCA to ICA angle <60° (actual measured angle, 12°). The prior stent with restenosis is clearly identified and the DLZ for EPD is straight.

Case 6 (Figure 6). 3D-PM shows a type I aortic arch, CCA to ICA angle <60° (actual measured angle, 22°) and the DLZ is straight. This case was the only prospective model printed and allowed for real-time preprocedural planning for stent and EPD sizing. A manual millimeter caliper was used which, as illustrated, showed a CCA diameter of 7.7 mm and distal ICA diameter of 6.7 mm, allowing the preprocedure selection of an 8.0 x 40 mm self-expanding stent and 7.0 mm EPD.

Limitations of carotid angiography. The inherent limitation of angiographic two-dimensional representation of 3D structures, especially in the assessment of complex anatomical varieties, is widely acknowledged. Furthermore, an invasive angiographic procedure is not without risk, as a 4% risk of transient ischemic attack or stroke (of which 1% has shown to be disabling) has been associated with carotid angiography.^2-5 Several patient- and procedure-related factors that increase these risks include age, length of procedure, volume of contrast, number of catheters used, presence of carotid artery stenosis, and prior neurologic deficit. Thus, non-invasive modalities such as CTA, magnetic resonance angiography (MRA), and duplex ultrasound (DUS) have an emerging and dominant role for both diagnostic and case-planning purposes.

Comparison of imaging modalities for carotid disease. DUS is technician dependent and can be inaccurate in difficult anatomies, such as calcific lesions, tortuous arterial course, and “hairline” lumens, leading to overestimation of occlusion. Variable definition for stenosis percentage, which is institution and reader dependent, is another limiting factor.⁶ In comparison with DUS or CTA, limitations of preprocedural imaging with MRA include higher cost, patient discomfort (claustrophobia), or incompatibility due to metal implant. CTA has emerged to be more cost effective than MRA and with a higher accuracy than DUS. In a study of 30 patients for detection of degree of stenosis, dual-source CTA had a sensitivity of 100% and specificity of 97% vs MRA at 100% and 95%, respectively.⁷ Furthermore, in a comparative study of CTA vs conventional angiography in 53 patients, a sensitivity of 87% and specificity of 90% with an accuracy of 89% was seen in diagnosing carotid disease (NASCET [North American Symptomatic Carotid Endarterectomy Trial]criteria >60%) and plaque characterization (ulceration, fatty plaque, fibrosis, occlusion, and calcifications).⁸

3D-CTA can add further value in preprocedural planning, as demonstrated by Wyers et al, where 3D-CTA with reconstruction and analysis of aortic arch and carotid anatomy allowed for preprocedural planning in relation to access site and labeling of borderline vs inappropriate anatomy for endovascular approach. This grouping influenced planning for CAS in 37% of patients and further avoided the risk of angiography by referring directly to CEA in those with hostile anatomies.⁹

Factors associated with lower CAS success. Clinical, anatomical, and patient-related factors associated with higher failure rate of endovascular CAS include: (1) unfavorable aortic arch anatomy; (2) carotid artery angulation or tortuosity rendering EPD deployment difficult; (3) high-risk plaque morphology; and (4) patient-related comorbidity factors.

The CREST trial, which randomized symptomatic and asymptomatic carotid stenosis patients to CAS vs CEA showed an increased rate of periprocedural stroke (4.1% vs 2.3%; P=.01) in elderly patients due to significant vessel tortuosity. Additionally, this trend of increased strokes was seen in the first 30 days, with minimal events occurring between 30 day to 4 years, likely related to procedure-related factors.¹⁰ Aortic arch and carotid anatomies associated with high failure rate or worse clinical outcomes include type II or III arch, bovine arches, angulated ICA, and tortuous CCA.^11-16 Within the SAPHIRE study, independent predictors of stroke or death at 30 days in 1168 patients who underwent CAS with distal EPD included contralateral carotid stenosis, longer carotid plaque, presence of type II or III arch, or a tortuous carotid arterial system.¹⁷

High-risk plaque morphologic characteristics include long (>15 mm) stenosis, ostial lesions, calcified and/or subtotal occlusion lesions, ICA string sign, and common carotid tandem lesions.^18-20 Patient-related factors associated with worse endovascular outcomes include octogenarians, renal disease, history of stroke or transient ischemic attack, recent myocardial infarction, or cardiac surgery indication in addition to carotid intervention.^17-21 A signal for improved outcomes in the elderly has been reported with CEA, which is likely related to significant tortuosity of great vessel and carotid arteries with increasing age along with presence of other comorbid conditions, ie, hypertension, female gender, diabetes, or obesity, which are known to cause arterial tortousity.^15,16,21,22

EPD use in a prospective CAS registry of the Arbeitsgemeinschaft Leitende Kardiologische Krankenhausärzte (ALKK) study group showed lower rates of ipsilateral stroke (1.7% vs 4.1%; P<.01) and lower rate of all non-fatal strokes and death (2.1% vs 4.9%).²³ However, certain anatomical factors, such as tortuous DLZ, not only hinder safe deployment but also lead to difficulty in retrieval of the EPD.^24,25 Carotid tortuosity and hostile anatomy for deployment of distal EPD in 221 symptomatic patients undergoing CAS were associated with an increased risk of stroke, myocardial infarction, death, and all complications.²⁰

CCA to ICA angle is another important predictor of procedural difficulty and failure. CCA to ICA angles of 60° and 73° were associated with unsuccessful carotid wall stent deployment in 2 (6.5%) of 31 symptomatic and asymptomatic CAS patients.²⁶ A CCA to ICA angle greater than 60° was associated with increased 30-day risk of stroke or death in 262 symptomatic patients requiring CAS.²⁷ Thus, severe carotid tortuosity is associated with both increased risk of stroke and failure to complete CAS procedure and knowledge of carotid and aortic arch anatomy and or CCA to ICA angulation preprocedurally can significantly improve both safety and success rate for CAS procedures.^14,27-30

3D printing application in multimedical specialties. 3D printing technology is an emerging technology that has been successfully used in the medical field to aid education and instruction, procedural planning, and advancement of research. It allows for replication of individual anatomy in a precise and predictable manner. For example, bone and cartilage has been 3D printed for replacement and production of customized prosthetics in orthopedics and dental implants and anatomical models used for education and tissue regeneration for stem cell therapeutics in oral and maxillofacial surgery.^31-33 Successful utilization in the field of structural heart disease has allowed understanding of complex anatomical varieties to aid with clinical therapeutics. Current applications include left atrial appendage (LAA) anatomy for accurate device selection in LAA closure procedures, aortic root models for preprocedure planning and mechanism of coronary occlusion during transcatheter aortic valve replacement (TAVR), prediction of post-TAVR paravalvular leaks, and determination of live flow dynamics to predict physiology during valve deployment.^34-36 3D-PMs have also been used for transcatheter mitral valve interventions to assess potential complications or success by accurately duplicating mitral valve apparatus.³⁷ In congenital heart disease, it allows for evaluation of adequate rim tissue for transcatheter atrial septal defect closures.³⁸

3D printing of aortic arch and carotid artery for carotid stenting. 3D-PM of aortic arch and carotid arteries preprocedurally can enhance visual, perceptual, and conceptual understanding of patient anatomy not provided by virtual imaging. 3D-PM was able to accurately predict the type of aortic arch anatomy and CCA to ICA angulation as depicted to anticipate procedural failure and adverse outcomes significantly associated with angles >60°. Additionally, carotid stent size and sizing of distal EPD was also reliably extrapolated as stent undersizing can lead to incomplete revascularization and oversizing may lead to vasospasm and endothelial damage.^39,40 Distal EPD size mismatch can lead to vasospasm and debris embolization.^40,41 Therefore, 3D-PM may prove to be vital in obtaining improved clinical outcomes with carotid interventions, as intravascular imaging is not routinely utilized intraprocedurally to avoid increased risk of adverse outcomes related to higher procedural time and risk of distal embolization. Innominate artery and distal ICA tortuosity can also be better appreciated with a 3D-PM.

Study limitations. The majority of the patients were studied retrospectively and are subject to bias in making clinical inferences. A prospective study comparing aortic arch anatomy and CCA to ICA angles could further add validity in prediction of anticipated procedure related difficulties and clinical outcomes. Stent and EPD sizing was only able to be predicted in 1 patient prospectively and requires a larger study to validate accuracy. Furthermore, correlation of 3D-CTA to 3D-PM in selection of access size, procedural catheters, and stent and EPD devices also requires a prospective blinded comparison.

Preprocedural planning with 3D printing of aortic arch and carotid artery for CAS has the potential to decrease procedural contrast volume, procedure time, and fluoroscopy time. Appropriate access site and procedural catheters can be chosen preprocedurally to increase probability of a successful procedure by better appreciation of aortic arch and carotid anatomy. Additionally, stent sizing and EPD sizing can also be determined preprocedurally, potentially leading to improved clinical outcomes in complex anatomy. All of these findings need to be further validated in a larger prospective clinical study.