Aortic root 3D parametric morphological model from 2D-echo images

Native Sinus Hemodynamics and Thrombosis in Transcatheter Heart Valve: Effect of Implant Depth and Coronary Flow

BACKGROUND

This study aimed to investigate the hemodynamic and anatomic factors associated with sinus thrombosis following transcatheter aortic valve replacement (TAVR), integrating in vivo patient data analysis and in vitro experiments.

METHODS AND RESULTS

Postprocedural, 4-dimensional, multiphase computed tomography data from 211 patients enrolled in the ADAPT-TAVR (Anticoagulation Versus Dual Antiplatelet Therapy for Prevention of Leaflet Thrombosis and Cerebral Embolization After Transcatheter Aortic Valve Replacement) study were analyzed. The prevalence of native sinus thrombosis was examined in relation to valve type, implant depth, and anatomic features. In vitro experiments used particle image velocimetry to observe changes in sinus flow based on the transcatheter heart valves (23-mm SAPIEN3, Edwards Lifesciences; and 29-mm CoreValve, Medtronic) height and coronary artery flow. Native sinus thrombosis was more common in self-expanding valves (39.1% versus 14.9%, P=0.004). In per-cusp analysis of in vivo patient data, adjusted transcatheter heart valve implant depth (odds ratio, 1.2 [95% CI, 1.1-1.3]; P<0.001), noncoronary sinus of Valsalva (odds ratio, 4.0 [95% CI, 2.0-7.8]; P<0.001), sinus inflow diameter (odds ratio, 0.8 [95% CI, 0.6-0.9]; P=0.008), and implanted valve size (odds ratio, 0.8 [95% CI, 0.7-1.0]; P=0.025) were significant factors associated with native sinus thrombosis. In the in vitro experiments, CoreValve showed noticeable flow stasis compared with SAPIEN3. High-positioned SAPIEN3 was linked to reduced velocity within the native sinus of Valsalva. Coronary artery flow led to higher sinus velocity and improved particle washout, reducing sinus thrombosis risk.

CONCLUSIONS

This study provides insights into the relationship between transcatheter heart valve deployment and native sinus thrombosis, emphasizing the role of anatomic factors in relation to the risk of sinus thrombosis.

New indicators for systematic assessment of aortic morphology: a narrative review

In order to prevent the occurrence of aortic adverse events in ascending thoracic aortic aneurysm patients, preventive surgery is the sole option in case of large aneurysm. Identifying high-risk patients timely and accurately requires effective predictive indicators of aortic adverse events and accurate risk stratification thresholds. Absolute diameter measured after a single imaging examination, which has been used as the predictive indicator for decades, has been proved to be ineffective for risk stratification in moderately dilated aorta. Previously, new indicators combining absolute diameters with personalized parameters have been reported to show better predictive power of aortic adverse events than absolute diameters by correcting the effect of these parameters on the diameters. Meanwhile, combining three-dimensional parameters to formulate risk stratification thresholds not only may characterize the aortic risk morphology more precisely, but also predict aortic adverse events more accurately. These new indicators may provide more systematic assessment methods of patients’ risk, formulate more personalized intervention strategies for ascending thoracic aortic aneurysm patients, and also provide a basis for researchers to develop more accurate and effective risk thresholds. We also highlight that the algorithm obtained by combining multiple indicators may be a better choice compared with single indicator, but this still requires the support of more evidence. Due to the particularity of syndromic aortic disease, whether these new indicators can be used for its risk stratification is still uncertain. Therefore, the scope of this manuscript does not include this kind of disease.

A biomechanical model of the pathological aortic valve: simulation of aortic stenosis

Aortic stenosis (AS) disease is a narrowing of the aortic valve (AV) opening which reduces blood flow from the heart causing several health complications. Although a lot of work has been done in AV simulations, most of the efforts have been conducted regarding healthy valves. In this article, a new three-dimensional patient-specific biomechanical model of the valve, based on a parametric formulation of the stenosis that permits the simulation of different degrees of pathology, is presented. The formulation is based on a double approach: the first one is done from the geometric point of view, reducing the effective ejection area of the AV by joining leaflets using a zipper effect to sew them; the second one, in terms of functionality, is based on the modification of AV tissue properties due to the effect of calcifications. Both healthy and stenotic valves were created using patient-specific data and results of the numerical simulation of the valve function are provided. Analysis of the results shows a variation in the first principal stress, geometric orifice area, and blood velocity which were validated against clinical data. Thus, the possibility to create a pipeline which allows the integration of patient-specific data from echocardiographic images and iFR studies to perform finite elements analysis is proved.

Immersogeometric fluid-structure interaction modeling and simulation of transcatheter aortic valve replacement

The transcatheter aortic valve replacement (TAVR) has emerged as a minimally invasive alternative to surgical treatments of valvular heart disease. TAVR offers many advantages, however, the safe anchoring of the transcatheter heart valve (THV) in the patients anatomy is key to a successful procedure. In this paper, we develop and apply a novel immersogeometric fluid-structure interaction (FSI) framework for the modeling and simulation of the TAVR procedure to study the anchoring ability of the THV. To account for physiological realism, methods are proposed to model and couple the main components of the system, including the arterial wall, blood flow, valve leaflets, skirt, and frame. The THV is first crimped and deployed into an idealized ascending aorta. During the FSI simulation, the radial outward force and friction force between the aortic wall and the THV frame are examined over the entire cardiac cycle. The ratio between these two forces is computed and compared with the experimentally estimated coefficient of friction to study the likelihood of valve migration.

Finite element analysis of NiTi self-expandable heart valve stent

Transcatheter aortic valve implantation is a minimally invasive treatment for severe symptomatic aortic valve stenosis. Nitinol stents are proposed for aortic stenosis patients at high risk. In the present study, at different implantation depths in the aortic valve, the crimping and performance of Nitinol stents are investigated. To do so, a constitutive model based on Microplane theory is utilized and implemented through the finite element to express the constitutive characteristics of Nitinol. The self-expanding stent made of NiTi is designed and simulated using the finite element method. To validate the developed model, the obtained results using beam and solid finite element models are compared with those reported in the literature. Superelastic behavior as well as shape memory effect of the Nitinol stent is studied during crimping and deployment. The simulated results show that the produced radial force increases by increasing the implantation depth in a cardiac cycle.

Aortic expansion induces lumen narrrowing in anomalous coronary arteries: a parametric structural finite element analysis

Anomalous aortic origin of coronary arteries (AAOCA) is a congenital disease that can lead to cardiac ischemia during intense physical activity. Although AAOCA is responsible for sudden cardiac death (SCD) among young athletes and soldiers, the mechanisms underlying the coronary occlusion during physical effort still have to be clarified. The present study investigates the correlation between geometric features of the anomaly and coronary lumen narrowing under aortic root dilatations. Idealized parametric computer-aided designed (CAD) models of the aortic root with anomalous and normal coronary are created and static finite element (FE) simulations of increasing aortic root expansions are carried out. Different coronary take-off angles and intramural penetrations are investigated to assess their role on coronary lumen narrowing. Results show that increasing aortic and coronary pressures lead to lumen expansions in normal coronaries, particularly in the proximal tract, while the expansion of anomalous coronary is impaired especially at the ostium. Concerning the geometric features of the anomaly, acute take-off angles cause elongated coronary ostia, with an eccentricity increasing with aortic expansion; the impact of intramural penetration of coronary on its luminal narrowing is limited. The present study provides a proof of concept of the biomechanical reasons underlying the lumen narrowing in AAOCA during aortic expansion, promoting the role of computational simulations as a tool to assess the mechanisms of this pathology.

A systematic approach to 3D echocardiographic assessment of the aortic root

[first paragraph of article]Severe aortic regurgitation (AR) and/or severe abnormalities of the aortic root and the tubular ascending aorta (TAA) are indications for surgical treatment. The correct diagnosis, the choice of optimal treatment, as well as optimal timing of surgery, mainly depend on findings obtained by echocardiography - which is usually the initial diagnostic modality applied in clinical practice. Therefore, an appropriate morphological and functional quantification of the aortic valve (AV) and the aortic root complex is required. Aside from the need of standardization to provide a precise objective evaluation, the use of modern echocardiographic technologies - especially 3D-echocardiography -are less often implemented in clinical routine. The present manuscript focuses on the advantages of transthoracic and transesophageal 3D-echocardiography (TTE, TEE) for an improved assessment of the AV and the aortic root complex to provide accurate and comprehensive measurements for making the correct diagnosis and defining further therapeutic strategies.

Three-dimensional parametric modeling of bicuspid aortopathy and comparison with computational flow predictions

Bicuspid aortic valve (BAV)-associated ascending aneurysmal aortopathy (namely "bicuspid aortopathy") is a heterogeneous disease making surgeon predictions particularly challenging. Computational flow analysis can be used to evaluate the BAV-related hemodynamic disturbances, which likely lead to aneurysm enlargement and progression. However, the anatomic reconstruction process is time consuming so that predicting hemodynamic and structural evolution by computational modeling is unfeasible in routine clinical practice. The aim of the study was to design and develop a parametric program for three-dimensional (3D) representations of aneurysmal aorta and different BAV phenotypes starting from several measures derived by computed-tomography angiography (CTA). Assuming that wall shear stress (WSS) has an important implication on bicuspid aortopathy, computational flow analyses were then performed to estimate how different would such an important parameter be, if a parametric aortic geometry was used as compared to standard geometric reconstructions obtained by CTA scans. Morphologic parameters here documented can be used to rapidly model the aorta and any phenotypes of BAV. t-test and Bland-Altman plot demonstrated that WSS obtained by flow analysis of parametric aortic geometries was in good agreement with that obtained from the flow analysis of CTA-related geometries. The proposed program offers a rapid and automated tool for 3D anatomic representations of bicuspid aortopathy with promising application in routine clinical practice by reducing the amount of time for anatomic reconstructions.

Activities at Thoracic Aortic Research Center, IRCCS Policlinico San Donato

The Thoracic Aortic Research Center (TARC) of the IRCCS Policlinico San Donato (PSD) aims to promote research on thoracic aortic diseases, to disclose the scientific knowledge and clinical experience and to develop new scientific paths within the Hospital and the aortic community, in collaboration with other national and international centres. Thoracic Aortic Research Center collaborates with many centres in both Europe (e.g. University of Utrecht, the Netherlands) and the USA (e.g. University of Michigan). This has led to multiple highly regarded publications in respected cardiovascular journals and has led to several PhD programmes resulting in doctorate degrees. Within Italy, in association with the Bioengineering School of the University of Pavia, TARC has founded the "BETA-lab" (Biomechanics for Endovascular Treatment of the Aorta laboratory), where MDs, Bioengineers, and PhD fellows conduct experimental studies using in vitro/ex vivo models of the physiologic aorta and aortic diseases. Furthermore, a database (iCardiocloud) where the medical imaging of cardiovascular patients from the PSD is structured, for in silico analysis utilizing computational fluid dynamics, and in vitro studies using also 3D printed aortic models. With the role of principal investigator or co-investigator, TARC at PSD has been participating in other several projects, including the International Registry of Acute Aortic Dissection, the International Aortic Arch Surgery Study Group, the European Registry of Endovascular Aortic Repair Complications, the ADSORB and ASSIST trials, and the GREAT registry. International collaborations have included also studies on predictors of aortic growth after dissection with the Yale University and University of Virginia, and on aortic biomarkers with the University of Tokyo.