The role of flow stasis in transcatheter aortic valve leaflet thrombosis

Deformation in transcatheter heart valves: Clinical implications and considerations

Transcatheter aortic valve replacement (TAVR) has emerged as a preferred treatment modality for aortic stenosis, marking a significant advancement in cardiac interventions. Transcatheter heart valves (THVs) have also received approval for treating failed bioprosthetic valves and rings across aortic, mitral, tricuspid, and pulmonic positions. Unlike surgically implanted valves, which are sewn into the annulus, THVs are anchored through relative oversizing. Although THVs are designed to function optimally in a fully expanded state, they exhibit a certain degree of tolerance to underexpansion. However, significant deformation beyond this tolerance can adversely affect the valve's hemodynamics and durability, ultimately impacting patient outcomes. Such post-implantation deviations from the valve's intended three-dimensional design are influenced by a variety of physiological and anatomical factors unique to each patient and procedure, leading to underexpansion, eccentric expansion, and vertical deformation. These deformation patterns increase leaflet stress and strain, potentially causing fatigue and damage. This review article delves into the extent of THV deformation, its impact on leaflet function, hypoattenuating leaflet thickening, and structural valve degeneration. It provides an in-depth analysis of deformation specifics in different procedural contexts, including TAVR in native aortic stenosis, aortic and mitral valve-in-valve procedures, and redo-TAVR. Additionally, the review discusses strategies to mitigate THV deformation during the procedure, offering insights into potential solutions to these challenges.

Subjects with carotid webs demonstrate pro-thrombotic hemodynamics compared to subjects with carotid atherosclerosis

Carotid artery webs (CaW) are non-atherosclerotic projections into the vascular lumen and have been linked to up to one-third of cryptogenic strokes in younger patients. Determining how CaW affects local hemodynamics is essential for understanding clot formation and stroke risk. Computational fluid dynamics simulations were used to investigate patient-specific hemodynamics in carotid artery bifurcations with CaW, bifurcations with atherosclerotic lesions having a similar degree of lumen narrowing, and with healthy carotid bifurcations. Simulations were conducted using segmented computed tomography angiography geometries with inlet boundary conditions extracted from 2D phase contrast MRI scans. The study included carotid bifurcations with CaW (n = 13), mild atherosclerosis (n = 7), and healthy bifurcation geometries (n = 6). Hemodynamic parameters associated with vascular dysfunction and clot formation, including shear rate, oscillatory shear index (OSI), low velocity, and flow stasis were calculated and compared between the subject groups. Patients with CaW had significantly larger regions containing low shear rate, high OSI, low velocity, and flow stasis in comparison to subjects with mild atherosclerosis or normal bifurcations. These abnormal hemodynamic metrics in patients with CaW are associated with clot formation and vascular dysfunction and suggest that hemodynamic assessment may be a tool to assess stroke risk in these patients.

Sensitivity of Post-TAVR Hemodynamics to the Distal Aortic Arch Anatomy: A High-Fidelity CFD Study

PURPOSE

Patient-specific simulations of transcatheter aortic valve (TAV) using computational fluid dynamics (CFD) often rely on assumptions regarding proximal and distal anatomy due to the limited availability of high-resolution imaging away from the TAV site and the primary research focus being near the TAV. However, the influence of these anatomical assumptions on computational efficiency and resulting flow characteristics remains uncertain. This study aimed to investigate the impact of different distal aortic arch anatomies-some of them commonly used in literature-on flow and hemodynamics in the vicinity of the TAV using large eddy simulations (LES).

METHODS

Three aortic root anatomical configurations with four representative distal aortic arch types were considered in this study. The arch types included a 90-degree bend, an idealized distal aortic arch anatomy, a clipped version of the idealized distal aortic arch, and an anatomy extruded along the normal of segmented anatomical boundary. Hemodynamic parameters both instantaneous and time-averaged such as Wall Shear Stress (WSS), and Oscillatory Shear Index (OSI) were derived and compared from high-fidelity CFD data.

RESULTS

While there were minor differences in flow and hemodynamics across the configurations examined, they were generally not significant within our region of interest i.e., the aortic root. The choice of extension type had a modest impact on TAV hemodynamics, especially in the vicinity of the TAV with variations observed in local flow patterns and parameters near the TAV. However, these differences were not substantial enough to cause significant deviations in the overall flow and hemodynamic characteristics.

CONCLUSIONS

The results suggest that under the given configuration and boundary conditions, the type of outflow extension had a modest impact on hemodynamics proximal to the TAV. The findings contribute to a better understanding of flow dynamics in TAV configurations, providing insights for future studies in TAV-related experiments as well as numerical simulations. Additionally, they help mitigate the uncertainties associated with patient-specific geometries, offering increased flexibility in computational modeling.

Effect of Ascending Aortic Curvature on Flow in the Sinus and Neo-sinus Following TAVR: A Patient-Specific Study

Patient-specific aortic geometry and its influence on the flow in the vicinity of Transcatheter Aortic Valve (TAV) has been highlighted in numerous studies using both in silico and in vitro experiments. However, there has not yet been a detailed Particle Image Velocimetry (PIV) experiment conducted to quantify the relationship between the geometry, flow downstream of TAV, and the flow in the sinus and the neo-sinus. We tested six different patient-specific aorta models with a 26-mm SAPIEN 3 valve (Edwards Lifesciences, Irvine, CA, USA) in a left heart simulator with coronary flow. Velocities in all three cusps and circulation downstream of TAV were computed to evaluate the influence of the ascending aorta curvature on the flow field. The in vitro analysis showed that the patient-specific aortic curvature had positive correlation to the circulation in the ascending aorta (p = 0.036) and circulation had negative correlation to the particle washout time in the cusps (p = 0.011). These results showed that distinct vortical flow patterns in the ascending aorta as the main jet impinges on the aortic wall causes a recirculation region that facilitates the flow back into the sinus and the neo-sinus, thus reducing the risk of flow stagnation and washout time.

Frequency, Predictors, and Clinical Impact of Valvular and Perivalvular Thrombus After Transcatheter Aortic Valve Replacement

BACKGROUND

Subclinical aortic valve complex (valvular and perivalvular) thrombus is not rare after transcatheter aortic valve replacement (TAVR). The risk factors and clinical implications of these findings remain uncertain.

OBJECTIVES

This study sought to evaluate the frequency, predictors, and clinical outcome of aortic valve complex thrombus after TAVR.

METHODS

In the ADAPT-TAVR (Anticoagulation Versus Dual Antiplatelet Therapy for Prevention of Leaflet Thrombosis and Cerebral Embolization After Transcatheter Aortic Valve Replacement) trial comparing edoxaban vs dual antiplatelet therapy in TAVR patients without an indication for chronic anticoagulation, the frequency of valvular (subclinical leaflet thrombus) and perivalvular (supravalvular, subvalvular, and sinus of Valsalva) thrombus was evaluated by 4-dimensional computed tomography at 6 months. The association of these phenomena with new cerebral thromboembolism on brain magnetic resonance imaging, neurologic and neurocognitive dysfunction, and clinical outcomes was assessed.

RESULTS

Among 211 patients with 6-month computed tomography evaluations, 91 patients (43.1%) had thrombus at any aortic valve complex, 30 (14.2%) patients had leaflet thrombus, and 78 (37.0%) patients had perivalvular thrombus. A small maximum diameter of the stent at the valve level and low body surface area were independent predictors of aortic valve complex and perivalvular thrombus, and decreased renal function was an independent predictor of leaflet thrombus. No significant differences were observed in new cerebral lesions, neurologic or neurocognitive functions, or clinical outcomes among patients with or without valvular or perivalvular thrombus.

CONCLUSIONS

Subclinical aortic valve complex (valvular and perivalvular) thrombus was common in patients who had undergone successful TAVR. However, these imaging phenomena were not associated with new cerebral thromboembolism, neurologic or neurocognitive dysfunction, or adverse clinical outcomes. (Anticoagulation Versus Dual Antiplatelet Therapy for Prevention of Leaflet Thrombosis and Cerebral Embolization After Transcatheter Aortic Valve Replacement [ADAPT-TAVR]; NCT03284827).

Effect of leaflet laceration on transcatheter aortic valve replacement fluid mechanics and comparison with surgical aortic valve replacement

BACKGROUND

Leaflet thrombosis after surgical aortic valve replacement (SAVR) and transcatheter aortic valve replacement (TAVR) may be caused by blood flow stagnation in the native and neosinus regions. To date, aortic leaflet laceration has been used to mitigate coronary obstruction following TAVR; however, its influence on the fluid mechanics of the native and neosinus regions is poorly understood. This in vitro study compared the flow velocities and flow patterns in the setting of SAVR vs TAVR with and without aortic leaflet lacerations.

METHODS

Two valves, (23-mm Perimount and 26-mm SAPIEN 3; Edwards Lifesciences) were studied in a validated mock flow loop under physiologic conditions. Neosinus and native sinus fluid mechanics were quantified using particle image velocimetry in the left and noncoronary cusp, with an increasing number of aortic leaflets lacerated or removed.

RESULTS

Across all conditions, SAVR had the highest average sinus and neosinus velocities, and this value was used as a reference to compare against the TAVR conditions. With an increasing number of leaflets lacerated or removed with TAVR, the average sinus and neosinus velocities increased from 25% to 70% of SAVR flow (100%). Diastolic velocities were substantially augmented by leaflet laceration. Also, the shorter frame of the SAVR led to higher flow velocities compared with the longer frame of the TAVR, even after complete leaflet removal.

CONCLUSIONS

Leaflet laceration augmented TAVR native and neosinus flow fields, approaching that of SAVR. These findings may have potential clinical implications for the use of single or multiple leaflet lacerations to reduce leaflet thrombosis and thus potentially improve TAVR durability.

Early Detection of Risk of Neo-Sinus Blood Stasis Post-Transcatheter Aortic Valve Replacement Using Personalized Hemodynamic Analysis

Background

Despite the demonstrated benefits of transcatheter aortic valve replacement (TAVR), subclinical leaflet thrombosis and hypoattenuated leaflet thickening are commonly seen as initial indications of decreased valve durability and augmented risk of transient ischemic attack.

Methods

We developed a multiscale patient-specific computational framework to quantify metrics of global circulatory function, metrics of global cardiac function, and local cardiac fluid dynamics of the aortic root and coronary arteries.

Results

Based on our findings, TAVR might be associated with a high risk of blood stagnation in the neo-sinus region due to the lack of sufficient blood flow washout during the diastole phase (e.g., maximum blood stasis volume increased by 13, 8, and 2.7 fold in the left coronary cusp, right coronary cusp, and noncoronary cusp, respectively [N = 26]). Moreover, in some patients, TAVR might not be associated with left ventricle load relief (e.g., left ventricle load reduced only by 1.2 % [N = 26]) and diastolic coronary flow improvement (e.g., maximum coronary flow reduced by 4.94%, 15.05%, and 23.59% in the left anterior descending, left circumflex coronary artery, and right coronary artery, respectively, [N = 26]).

Conclusions

The transvalvular pressure gradient amelioration after TAVR might not translate into adequate sinus blood washout, optimal coronary flow, and reduced cardiac stress. Noninvasive personalized computational modeling can facilitate the determination of the most effective revascularization strategy pre-TAVR and monitor leaflet thrombosis and coronary plaque progression post-TAVR.

Mechanical valve thrombosis: current management and differences between guidelines

All foreign bodies inserted in the circulatory system are thrombogenic and require temporary or lifelong antithrombotic therapies to prevent thrombosis. The adequate level of anticoagulation during the first few months determines the long-term durability, particularly for mechanical prostheses;2 however also for biological valves. Suboptimal anticoagulation is the most frequent source of mechanical valve thrombosis (MVT). The patient's clinical presentation decides how mechanical prosthetic valve obstruction is managed. If the mechanical valve thrombosis is obstructive and the patient is in a critical condition with hemodynamic instability, an immediate surgical intervention should be performed. The thrombolytic treatment is an option for left mechanical valve thrombosis in patients who have high surgical risk and no contraindications and also for right heart valve thrombosis. In non-obstructive thrombosis on the mechanical valve, patients can be asymptomatic, requiring optimization of the anticoagulant treatment. Both obstructive and non-obstructive thrombus generated on the mechanical prosthesis can result in embolic events. After anticoagulant treatment, if the thrombus persists the indication is for thrombolytic treatment or redo surgery. Pannus can also cause obstruction of the prosthesis for which surgical treatment is the only option. All these clinical scenarios seem to have a simple solution in terms of surgery vs thrombolysis vs effective anticoagulation, but the real-world clinical experience could be different. For example, the same patient with some common comorbidities, non-obstructive mechanical valve thrombosis, and symptomatic only by repeated systemic embolizations, can go through all these 3 therapeutic options, due to MVT's unpredictable nature. Therefore, treatment indications can intersect both on the time axis and depending on the patient's clinical status and the expertise of the center where he is hospitalized. Moreover, the European and American guidelines show subtle but important differences. The aim of this review was to compare these differences, comment on recent studies and evidence gaps, propose a more pragmatic algorithm combining all current indications, and highlight important research directions for this disease that has dominated already the cardiovascular landscape for more than five decades, but for which there have been no significant recent changes in management.

An In-Vitro Study of the Flow Past a Transcatheter Aortic Valve Using Time-Resolved 3D Particle Tracking

The performance of a transcatheter aortic valve (TAV) can be evaluated by analyzing the flow field downstream of the valve. However, three dimensional flow and pressure fields, and particle residence time, a quantity closely related to thrombosis risk, are challenging to obtain. This experimental study aims to provide a comprehensive 3D measurement of the flow field downstream of an Edwards SAPIEN 3 using time-resolved 3D particle tracking velocimetry (3D PTV) with Shake-the-Box (STB) algorithm. The valve was deployed in an idealized aorta model and tested in a left heart simulator under physiological conditions. Detailed 3D vortical structures, pressure distributions, and particle residence time were obtained by analyzing the 3D particle tracks. Results have shown large-scale retrograde flow entering the sinuses of the TAV at systole, reducing flow stasis there. However, the 3D particle tracks reveal that the retrograde flow has a high residence time and might have already experienced high shear stress near the main jet. Thus by only focusing on the flow in the sinus region is not sufficient to evaluate the leaflet thrombosis risk, and the flow downstream of the valve should be taken into consideration. The unique perspectives offered by 3D PTV are important when evaluating the performance of the TAVs.

Long-term prognostic impact of paravalvular leakage on coronary artery disease requires patient-specific quantification of hemodynamics

Transcatheter aortic valve replacement (TAVR) is a frequently used minimally invasive intervention for patient with aortic stenosis across a broad risk spectrum. While coronary artery disease (CAD) is present in approximately half of TAVR candidates, correlation of post-TAVR complications such as paravalvular leakage (PVL) or misalignment with CAD are not fully understood. For this purpose, we developed a multiscale computational framework based on a patient-specific lumped-parameter algorithm and a 3-D strongly-coupled fluid-structure interaction model to quantify metrics of global circulatory function, metrics of global cardiac function and local cardiac fluid dynamics in 6 patients. Based on our findings, PVL limits the benefits of TAVR and restricts coronary perfusion due to the lack of sufficient coronary blood flow during diastole phase (e.g., maximum coronary flow rate reduced by 21.73%, 21.43% and 21.43% in the left anterior descending (LAD), left circumflex (LCX) and right coronary artery (RCA) respectively (N = 6)). Moreover, PVL may increase the LV load (e.g., LV load increased by 17.57% (N = 6)) and decrease the coronary wall shear stress (e.g., maximum wall shear stress reduced by 20.62%, 21.92%, 22.28% and 25.66% in the left main coronary artery (LMCA), left anterior descending (LAD), left circumflex (LCX) and right coronary artery (RCA) respectively (N = 6)), which could promote atherosclerosis development through loss of the physiological flow-oriented alignment of endothelial cells. This study demonstrated that a rigorously developed personalized image-based computational framework can provide vital insights into underlying mechanics of TAVR and CAD interactions and assist in treatment planning and patient risk stratification in patients.

Effect of Native Aortic Leaflet Geometry Modification on Transcatheter Aortic Valve Neo-sinus and Aortic Sinus Flow: An In-vitro Study

PURPOSE

Leaflet thrombosis is a potentially fatal complication after transcatheter aortic valve replacement (TAVR). Blood flow stagnation in the neo-sinus and aortic sinuses are associated with increased thrombus severity. Native aortic leaflet modification may be a potential strategy to improve the neo-sinus and aortic sinus fluid dynamics. However, limited data exist on the effect of leaflet geometry modification on the flow within the neo-sinus and aortic sinus regions. We evaluate the effect of aortic leaflet modification on the neo-sinus and aortic sinus flow stagnation after simulated TAVR.

METHODS

Particle image velocimetry measurements were performed under nominal (5 LPM) and low (2.5 LPM) cardiac output conditions for an intact leaflet (control) case, and 3 modified leaflet geometries. Aortic leaflet geometry modification via leaflet splay was simulated with increasing splay geometry (leaflet splay distance: 5 mm-narrow, 10 mm-medium, and 20 mm-wide).

RESULTS

Leaflet geometry modification influenced flow features throughout the cardiac cycle, at both cardiac outputs, and allowed for flow communication between the neo-sinus and aortic sinus regions compared to the control. In the aortic sinus, flow stagnation reduced by over 64% at 5LPM, and over 36% at 2.5LPM for all simulated modified leaflet geometries compared to the control. However, only the medium and wide splay geometries enabled a reduction in neo-sinus flow stagnation compared to the control case.

CONCLUSIONS

These findings suggest that aortic leaflet geometry modification (of at least 10 mm leaflet splay distance) may reduce flow stasis and potentially decrease valve thrombosis risk.

Structural analysis of regional transcatheter aortic valve underexpansion and its implications for subclinical leaflet thrombosis

Subclinical leaflet thrombosis has been increasingly recognized following transcatheter aortic valve replacement (TAVR). Determining the risk factors is vital in preventing clinical leaflet thrombosis and ensuring long-term value durability. Clinical data have indicated that regional stent under-expansion of transcatheter aortic valves (TAVs), particularly self-expanding devices, may be associated with an increased risk of subclinical leaflet thrombosis. This study aimed to determine the effects of regional TAV frame under-expansion on leaflet kinematics, leaflet structural characteristics, and explore its impact on the likelihood of leaflet thrombosis. In this study, mild and moderate regional frame under-expansion of a 26-mm CoreValve were examined using experimental testing and computational simulations. The results indicated that regional TAV frame under-expansion impairs leaflet kinematics and reduces the range of motion in leaflets with an angle less than 120°. The reduced range of motion can increase blood stasis on the surface of the TAV leaflets. The results also demonstrated that regional frame under-expansion induced localized high-stress regions in the leaflets close to the fixed boundary edge. The increased mechanical stress can lead to accelerated tissue degeneration. The study improves our understanding of the effects of regional stent under-expansion in TAVR. Post-procedural balloon dilatation of self-expanding TAVs can potentially be advantageous in reducing leaflet distortion and normalizing leaflet stress distribution. Large-scale, prospective, and well-controlled studies are needed to further investigate regional TAV frame under-expansion effects on subclinical leaflet thrombosis and long-term valve durability.

Transcatheter aortic valve thrombosis: a review of potential mechanisms

Transcatheter aortic valve (TAV) thrombosis has been recognized as a significant problem that sometimes occurs as early as within 30 days after valve implantation, leading to increased concerns of stroke and long-term valve durability. In this article, a critical summary of the relevant literature on identifying potential mechanisms of TAV thrombosis from the perspective of the well-known Virchow's triad, which comprises blood flow, foreign materials and blood biochemistry, is presented. Blood flow mechanisms have been the primary focus thus far, with a general consensus on the flow mechanisms with respect to haemodynamic conditions, the influence of TAV placement and expansion and the influence of coronary flow. Less attention has been paid to the influence of blood biochemistry and foreign materials (and related endothelial damage), with little consensus among studies with regards to platelet and/or microparticle levels post-TAV implantation. Finally, we discuss the future outlook for research with unanswered scientific questions.

Heart Valve Biomechanics: The Frontiers of Modeling Modalities and the Expansive Capabilities of Ex Vivo Heart Simulation

The field of heart valve biomechanics is a rapidly expanding, highly clinically relevant area of research. While most valvular pathologies are rooted in biomechanical changes, the technologies for studying these pathologies and identifying treatments have largely been limited. Nonetheless, significant advancements are underway to better understand the biomechanics of heart valves, pathologies, and interventional therapeutics, and these advancements have largely been driven by crucial in silico, ex vivo, and in vivo modeling technologies. These modalities represent cutting-edge abilities for generating novel insights regarding native, disease, and repair physiologies, and each has unique advantages and limitations for advancing study in this field. In particular, novel ex vivo modeling technologies represent an especially promising class of translatable research that leverages the advantages from both in silico and in vivo modeling to provide deep quantitative and qualitative insights on valvular biomechanics. The frontiers of this work are being discovered by innovative research groups that have used creative, interdisciplinary approaches toward recapitulating in vivo physiology, changing the landscape of clinical understanding and practice for cardiovascular surgery and medicine.