Implantation Depth and Rotational Orientation Effect on Valve-in-Valve Hemodynamics and Sinus Flow

Analysis of Energy and Pressure in the Sinus with Different Blood Pressures after Bioprosthetic Aortic Valve Replacement

PURPOSE

To investigate the effect of changing systolic and diastolic blood pressures (SBP and DBP, respectively) on sinus flow and valvular and epicardial coronary flow dynamics after TAVR and SAVR.

METHODS

SAPIEN 3 and Magna valves were deployed in an idealized aortic root model as part of a pulse duplicating left heart flow loop simulator. Different combinations of SBP and DBP were applied to the test setup and the resulting change in total coronary flow from baseline (120/60 mmHg), effective orifice area (EOA), and left ventricular (LV) workload, with each combination, was assessed. In addition, particle image velocimetry was used to assess the Laplacian of pressure (∇ 2 P ) in the sinus, coronary and main flow velocities, the energy dissipation rate (EDR) in the sinus and the LV workload.

RESULTS

This study shows that under an elevated SBP, there is an increase in the total coronary flow, EOA, LV workload, peak velocities downstream of the valve,∇ 2 P , and EDR. With an elevated DBP, there was an increase in the total coronary flow and∇ 2 P . However, EOA and LV workload decreased with an increase in DBP, and EDR increased with a decrease in DBP.

CONCLUSIONS

Blood pressure alters the hemodynamics in the sinus and downstream flow following aortic valve replacement, potentially influencing outcomes in some patients.

Cardiac computed tomography post-transcatheter aortic valve replacement

Transcatheter aortic valve replacement (TAVR) is performed to treat aortic stenosis and is increasingly being utilised in the low-to-intermediate-risk population. Currently, attention has shifted towards long-term outcomes, complications and lifelong maintenance of the bioprosthesis. Some patients with TAVR in-situ may develop significant coronary artery disease over time requiring invasive coronary angiography, which may be problematic with the TAVR bioprosthesis in close proximity to the coronary ostia. In addition, younger patients may require a second transcatheter heart valve (THV) to 'replace' their in-situ THV because of gradual structural valve degeneration. Implantation of a second THV carries a risk of coronary obstruction, thereby requiring comprehensive pre-procedural planning. Unlike in the pre-TAVR period, cardiac CT angiography in the post-TAVR period is not well established. However, post-TAVR cardiac CT is being increasingly utilised to evaluate mechanisms for structural valve degeneration and complications, including leaflet thrombosis. Post-TAVR CT is also expected to have a significant role in risk-stratifying and planning future invasive procedures including coronary angiography and valve-in-valve interventions. Overall, there is emerging evidence for post-TAVR CT to be eventually incorporated into long-term TAVR monitoring and lifelong planning.

Effect of Blood Pressure Levels on Sinus Hemodynamics in Relation to Calcification After Bioprosthetic Aortic Valve Replacement

Coexisting hypertension and aortic stenosis are common. Some studies showed that elevated blood pressures may be associated with progression of calcific aortic valve disease (CAVD) while others showed no correlation. Flow dynamics in the sinuses of Valsalva are considered key factors in the progression of CAVD. While the relationship between hemodynamics and CAVD is not yet fully understood, it has been demonstrated that they are tightly correlated. This study aims to investigate the effect of changing systolic and diastolic blood pressures (SBP and DBP, respectively) on sinus hemodynamics in relation to potential initiation or progression of CAVD after aortic valve replacement (AVR). Evolut R, SAPIEN 3 and Magna valves were deployed in an aortic root under pulsatile conditions. Using particle image velocimetry, the hemodynamics in the sinus were assessed. The velocity, vorticity, circulation ( Γ ) and shear stress were calculated. This study shows that under elevated SBP and DBP, velocity, vorticity, and shear stress nearby the leaflets increased. Additionally, larger fluctuations of Γ and area under the curve throughout the cardiac cycle were observed. Elevated blood pressures are associated with higher velocity, vorticity, and shear stress near the leaflets which may initiate or accelerate pro-calcific changes in the prosthetic leaflets leading to bioprosthetic valve degeneration.

Decoding thrombosis through code: a review of computational models

From the molecular level up to a blood vessel, thrombosis and hemostasis involves many interconnected biochemical and biophysical processes over a wide range of length and time scales. Computational modeling has gained eminence in offering insights into these processes beyond what can be obtained from in vitro or in vivo experiments, or clinical measurements. The multiscale and multiphysics nature of thrombosis has inspired a wide range of modeling approaches that aim to address how a thrombus forms and dismantles. Here, we review recent advances in computational modeling with a focus on platelet-based thrombosis. We attempt to summarize the diverse range of modeling efforts straddling the wide-spectrum of physical phenomena, length scales, and time scales; highlighting key advancements and insights from existing studies. Potential information gleaned from models is discussed, ranging from identification of thrombus-prone regions in patient-specific vasculature to modeling thrombus deformation and embolization in response to fluid forces. Furthermore, we highlight several limitations of current models, future directions in the field, and opportunities for clinical translation, to illustrate the state-of-the-art. There are a plethora of opportunity areas for which models can be expanded, ranging from topics of thromboinflammation to platelet production and clearance. Through successes demonstrated in existing studies described here, as well as continued advancements in computational methodologies and computer processing speeds and memory, in silico investigations in thrombosis are poised to bring about significant knowledge growth in the years to come.

Contemporary issues and lifetime management in patients underwent transcatheter aortic valve replacement

Latest clinical trials have indicated favorable outcomes following transcatheter aortic valve replacement (TAVR) in low surgical risk patients with severe aortic stenosis. However, there are unanswered questions particularly in younger patients with longer life expectancy. While current evidence are limited to short duration of clinical follow-up, there are certain factors which may impair patients clinical outcomes and quality-of-life at long-term. Contemporary issues in the current TAVR era include prosthesis-patient mismatch, heart failure hospitalization, subclinical thrombosis, future coronary access, and valve durability. In this review, the authors review available evidence and discuss each remaining issues and theoretical treatment strategies in lifetime management of TAVR patients.

Deformation of Transcatheter Heart Valve Following Valve-in-Valve Transcatheter Aortic Valve Replacement: Implications for Hemodynamics

BACKGROUND

Valve-in-valve (ViV) transcatheter aortic valve replacement (TAVR) may be associated with adverse hemodynamics, which might affect clinical outcomes.

OBJECTIVES

This study sought to evaluate the extent and predictors of transcatheter heart valve (THV) deformity in ViV TAVR and the relation to postprocedural hemodynamics.

METHODS

We examined 53 patients who underwent ViV TAVR in surgical heart valves with self-expanding Evolut prostheses. THV deformation was examined using cardiac computed tomography prospectively performed 30 days after ViV TAVR, and correlated with 30-day echocardiographic hemodynamic data.

RESULTS

Near complete expansion of the functional portion of the implanted ViV prostheses (ie, >90%) was observed in 16 (30.2%) patients. Factors related to greater expansion of the functional portion and consequently larger neosinus volume were absence of polymer surgical frame, higher implantation and use of balloon aortic valvuloplasty or bioprosthetic valve fracture during the procedure (all P < 0.05). Underexpansion of the functional portion, but not the valve inflow frame, was closely associated with mean gradient and effective orifice area at 30 days on echocardiography, with and without adjustment for the sizes of the THV and surgical heart valve.

CONCLUSIONS

Underexpansion of the functional portion of THV prostheses is common during ViV TAVR, occurs more frequently with deep implantation and the presence of a polymer surgical stent frame, and is associated with worse postprocedural hemodynamics. Procedural techniques, such as higher implantation and balloon postdilatation, may be used to help overcome problems with THV underexpansion and improve clinical outcomes.

On the Three-dimensionality of Flow in the Neo-sinus and its Implications for Subclinical Leaflet Thrombosis

OBJECTIVES

Subclinical leaflet thrombosis is a silent phenomenon commonly observed following transcatheter aortic valve implantation (TAVI). Leaflet thrombosis is associated with ischaemic complications and structural valve deterioration. Prior studies have shown that blood stasis in neo-sinus contributes to the initiation and growth of subclinical leaflet thrombosis. This study aimed to quantify temporal and spatial characteristics of the flow field from a fundamental perspective.

METHODS

in vitro experimental analysis and fluid-solid interaction simulations were employed to characterize the flow field of a transcatheter aortic valve (TAV) with an intra-annular design in a pulse duplicator. Blood residence time (BRT) and flow-induced viscous shear stress were measured in the neo-sinus and on the surface of TAV leaflets.

RESULTS

Temporal and spatial velocity variations were observed in neo-sinus, indicating that the flow is time-dependent and fully three-dimensional. The degree of blood stasis in the neo-sinus (bulk fluid) and on the surface of the TAV leaflets highly depends on the local flow characteristics. Regional flow variation in the neo-sinus resulted in substantial variations in BRT magnitude in the neo-sinus and on the surface of the TAV leaflet. Areas with a high degree of blood stasis were observed near the fixed boundary edge of the leaflets.

CONCLUSIONS

The study indicated that leaflet motion is a primary driver of flow in neo-sinus. Considering the substantial variations in BRT magnitude in the neo-sinus (bulk fluid), blood stasis should be quantified locally on the surface of foreign (valve) materials to avoid errors in forecasting the risk of subclinical leaflet thrombosis in patients undergoing TAVI.

Rationale, Definitions, Techniques, and Outcomes of Commissural Alignment in TAVR: From the ALIGN-TAVR Consortium

Given the expanding indications of transcatheter aortic valve replacement (TAVR) in younger patients with longer life expectancies, the ability to perform postprocedural coronary access represents a priority in their lifetime management. A growing body of evidence suggests that commissural (and perhaps coronary) alignment in TAVR impacts coronary access and valve hemodynamics as well as coronary flow and access after redo-TAVR. Recent studies have provided modified delivery system insertion and rotation techniques to obtain commissural alignment with available transcatheter heart valve devices. Moreover, patient-specific preprocedural planning and postprocedural imaging tools have been developed to facilitate and evaluate commissural alignment. Future efforts should aim to refine transcatheter heart valve and delivery system designs to make neocommissural alignment easier and more reproducible. The aim of this review is to present an in-depth insight of commissural alignment in TAVR, including its rationale, standardized definitions, technical steps, outcomes, and future directions.

Subclinical Leaflet Thrombosis and Anticoagulation After Transcatheter Aortic Valve Replacement: A Review

Importance

Subclinical leaflet thrombosis affects approximately 15% of patients after transcatheter aortic valve replacement (TAVR). The pathophysiology and clinical significance of leaflet thrombosis remain incompletely understood. Defining the optimal management strategy in patients who are asymptomatic, including the role for oral anticoagulation (OAC), is a key challenge for the field.

Observations

Three recent randomized trials have evaluated the role of OAC in patients after TAVR. These studies have confirmed prior observational data suggesting that OAC is effective at prevention of subclinical leaflet thrombosis. Overall, however, OAC does not lead to a clinical benefit over the period studied, and in some patients may be harmful owing to bleeding risk.

Conclusions and Relevance

Strategies for identification of patients in whom the benefit of OAC outweighs the risks are required for optimization of long-term outcome after TAVR. This requires clearer insights into the mechanisms of asymptomatic leaflet thrombosis, its clinical significance, and patient-specific risks of bleeding and structural valve degeneration.

Comparison of performance of self-expanding and balloon-expandable transcatheter aortic valves

Objective

Methods

Results

Conclusions

Neosinus and Sinus Flow After Self-Expanding and Balloon-Expandable Transcatheter Aortic Valve Replacement

OBJECTIVES

The aim of this study was to evaluate flow dynamics in the aortic sinus and the neosinus (NS) after transcatheter heart valve (THV) implantation in valve-in-valve (ViV).

BACKGROUND

Leaflet thrombosis may occur on THVs and affect performance and durability. Differences in flow dynamics may affect the risk for leaflet thrombosis.

METHODS

Hemodynamic assessment following THV implantation in a surgical aortic valve was performed in a left heart simulator under pulsatile physiological conditions. Assessment was performed using a 23-mm polymeric surgical aortic valve (not diseased) and multiple THV platforms, including self-expanding devices (26-mm Evolut, 23-mm Allegra, small ACURATE neo) and a balloon-expandable device (23-mm SAPIEN 3). Particle image velocimetry was performed to assess flow in the sinus and NS. Sinus and NS washout, shear stress, and velocity were calculated.

RESULTS

Sinus and NS washout was fastest and approximately 1 cardiac cycle for each with the Evolut, ACURATE neo, and Allegra compared with the SAPIEN 3, with washout in 2 and 3 cardiac cycles, respectively. The Allegra showed the largest shear stress distribution in the sinus, followed by the SAPIEN 3. In the NS, all 4 valves showed equal likelihoods of occurrence of shear stress <1 Pa, but the Allegra showed the highest likelihoods of occurrence for shear stress >1 Pa. The velocities in the sinus and NS were 0.05, 0.078, 0.080, and 0.075 m/s for Evolut, SAPIEN 3, ACURATE neo, and Allegra ViV, respectively.

CONCLUSIONS

Sinus and NS flow dynamics differ substantially among THVs after ViV. Self-expanding supra-annular valves seem to have faster washouts compared with an equivalent-size balloon-expandable THV.

Impact of blood pressure on coronary perfusion and valvular hemodynamics after aortic valve replacement

OBJECTIVE

Our objective was to evaluate the impact of various blood pressures (BPs) on coronary perfusion and valvular hemodynamics following aortic valve replacement (AVR).

BACKGROUND

Lower systolic and diastolic (SBP/DBP) pressures from the recommended optimal target range of SBP < 120-130 mmHg and DBP < 80 mmHg after AVR have been independently associated with increased cardiovascular and all-cause mortality.

METHODS

The hemodynamic assessment of a 26 mm SAPIEN 3 transcatheter aortic valve (TAV), 29 mm Evolut R TAV, and 25 mm Magna Ease surgical aortic valve (SAV) was performed in a pulsed left heart simulator with varying SBP, DBP, and heart rate (HR) conditions (60 and 120 bpm) at 5 L/min cardiac output (CO). Average coronary flow (CF), effective orifice areas (EOAs), and valvulo-arterial impedance (Zva) were calculated.

RESULTS

At HR of 60 bpm, at SBP < 120 mmHg and DBP < 60 mmHg, CF decreased below the physiological lower limit with several different valves. Zva and EOA were found to increase and decrease respectively with increasing SBP and DBP. The same results were found with an HR of 120 bpm. The trends of CF variation with BP were similar in all valves however the drop below the lower physiological CF limit was valve dependent.

CONCLUSION

In a controlled in vitro system, with different aortic valve prostheses in place, CF decreased below the physiologic minimum when SBP and DBP were in the range targeted by blood pressure guidelines. Combined with recent observations from patients treated with AVR, these findings underscore the need for additional studies to identify the optimal BP in patients treated with AVR for AS.

Predictive Model for Thrombus Formation After Transcatheter Valve Replacement

PURPOSE

Leaflet thrombosis is a significant adverse event after transcatheter aortic valve (TAV) replacement (TAVR). The purpose of our study was to present a semi-empirical, mathematical model that links patient-specific anatomic, valve, and flow parameters to predict likelihood of leaflet thrombosis.

METHODS

The two main energy sources of neo-sinus (NS) washout after TAVR include the jet flow downstream of the TAV and NS geometric change in volume due to the leaflets opening and closing. Both are highly dependent on patient anatomic and hemodynamic factors. As rotation of blood flow is prevalent in both the sinus of Valsalva and then the NS, we adopted the vorticity flux or circulation (Г) as a metric quantifying overall washout. Leaflet thrombus volumes were segmented based on hypo-attenuating leaflet thickening (HALT) in post-TAVR patient's gated computed tomography. Г was assessed using dimensional scaling as well as computational fluid dynamics (CFD) respectively and correlated to the thrombosis volumes using sensitivity and specificity analysis.

RESULTS

Г in the NS, that accounted for patient flow and anatomic conditions derived from scaling arguments significantly better predicted the occurrence of leaflet thrombus than CFD derived measures such as stasis volumes or wall shear stress. Given results from the six patient datasets considered herein, a threshold Г value of 28.0 yielded a sensitivity and specificity of 100% where patients with Gamma < 28 developed valve thrombosis. A 10% error in measurements of all variables can bring the sensitivity specificity down to 87%.

CONCLUSION

A predictive model relating likelihood of valve thrombosis using Г in the NS was developed with promising sensitivity and specificity. With further studies and improvements, this predictive technology may lead to alerting physicians on the risk for thrombus formation following TAVR.

Effect of Left and Right Coronary Flow Waveforms on Aortic Sinus Hemodynamics and Leaflet Shear Stress: Correlation with Calcification Locations

Coronary flow induces hemodynamic alterations in the aortic sinus region. The objectives of this study are to: (1) investigate the differences among sinus hemodynamics and leaflet wall shear stresses engendered by the left versus right versus non-coronary flow and (2) correlate respective wall shear stresses with leaflet calcification in patients. A left heart simulator flow loop with a tunable coronary circuit provided physiological coronary flow waveforms corresponding to the left coronary cusp case (LCC), right coronary cusp case (RCC), and non-coronary cusp case (NCC). High spatio-temporal resolution particle image velocimetry was conducted to quantify leaflet wall shear stress and sinus vorticity fields and to measure aortic leaflet tip kinematics. Thirty-one patients with severe calcific aortic valve disease were segmented from CT data for the calcific volumes in their respective left, right, and non-coronary cusps. Leaflet tip position during systole shows the RCC has a wider leaflet opening compared to LCC and NCC. Velocity and vorticity fields combined with leaflet position data show that sinus vorticity is diminished (peak ~ 43 s-1) in the LCC while RCC and NCC maintain high vorticity (~ 1200 and ~ 950 s-1 respectively). WSS magnitudes greater than 0.3 Pa show 20 and 81% greater occurrences in the LCC and RCC respectively compared to NCC. Significant differences [X2 (2, n = 31) = 7.31, p = 0.0258] between the calcification levels in each cusp of the patient population. Coronary flow differences between LCC, RCC, and NCC show significant impact on leaflet kinematics and sinus flow hemodynamics. Clinical data correlations of the coronary flow cases indicate the left coronary cusp has a higher likelihood of calcification compared to the right.

Anatomical Characteristics Associated With Hypoattenuated Leaflet Thickening in Low-Risk Patients Undergoing Transcatheter Aortic Valve Replacement

BACKGROUND/PURPOSE

This sub-analysis of the prospective Low Risk TAVR (LRT) trial determined anatomical characteristics associated with hypoattenuated leaflet thickening (HALT), which may contribute to early transcatheter heart valve (THV) degeneration.

METHODS/MATERIALS

The LRT trial enrolled 200 low-risk patients between February 2016 and February 2018. All subjects underwent baseline and 30-day CT studies, analyzed by an independent core laboratory. Additional measurements, namely THV expansion, eccentricity, depth, and commissural alignment, were made by consensus of three independent readers. HALT was observed only in the Sapien 3 THV, so Evolut valves were excluded from this analysis.

RESULTS

In the LRT trial, 177 subjects received Sapien 3 THVs, of whom 167 (94.3%) had interpretable 30-day CTs and were eligible for this analysis. Twenty-six subjects had HALT (15.6%). Baseline characteristics were similar between groups. There was no difference in THV size implanted and baseline aortic-root geometry between groups. In patients who developed HALT, THV implantation depth was shallower than in patients who did not develop HALT (2.6 ± 1.1 mm HALT versus 3.3 ± 1.8 mm no-HALT, p = 0.03). There were more patients in the HALT group with commissural malalignment (40% vs. 28%; p = 0.25), but this did not reach statistical significance. In a univariable regression model, no predetermined variables were shown to independently predict the development of HALT.

CONCLUSIONS

This study did not find anatomical or THV implantation characteristics that predicted the development of HALT at 30 days. This study cannot exclude subtle effects or interaction between factors because of the small number of events.

In-Vitro Assessment of the Effects of Transcatheter Aortic Valve Leaflet Design on Neo-Sinus Geometry and Flow

Transcatheter aortic valve (TAV) leaflet thrombosis is a clinical risk with potentially fatal consequences. Studies have identified neo-sinus flow stasis as a cause of leaflet thrombosis. Flow stasis is influenced by the TAV leaflets, which affect the local fluid dynamics in the aortic sinus and neo-sinus. This study evaluated the effects of TAV leaflet features on the neo-sinus flow as a measure of leaflet thrombosis risk. Five TAVs of varied leaflet length and insertion height were tested in a simulator. Hydrodynamics and leaflet kinematics through en-phase imaging were quantified. Velocity fields were assessed using high-speed particle image velocimetry. Regions of flow stasis and particle residence times (PRTs) were quantified. TAVs with shorter leaflet length exhibited larger orifice areas and lower transvalvular pressure gradients. Shorter leaflet length and increased leaflet insertion TAVs additionally exhibited lower neo-sinus PRTs (0.44 ± 0.21 vs 2.83 ± 0.48 cycles, p < 0.05) and higher neo-sinus peak velocities (0.15 ± 0.009 vs 0.07 ± 0.005 m/s, p < 0.05) than TAVs with longer leaflet length and lower leaflet insertion. The average neo-sinus volume positively correlated with PRT(r = 0.810, p < 0.001), and extent of flow stasis (r = 0.682, p < 0.05). These results suggest that a small neo-sinus volume may reduce flow stagnation and particle residence, potentially reducing the risk of leaflet thrombosis. We propose that leaflet design features might be proactively controlled in the design of future transcatheter aortic valves.

Sinus Hemodynamics After Transcatheter Aortic Valve in Transcatheter Aortic Valve

BACKGROUND

This study evaluated the effect of transcatheter aortic valve (TAV)-in-TAV on sinus hemodynamics and washout. With TAV becoming the standard procedure for aortic valve replacement and with the limited valve durability, a second intervention is necessary (TAV-in-TAV) after first TAV failure.

METHODS

Six arrangements of TAV-in-TAV were chosen for this study as follows: (1) Evolut 23 (Medtronic, Minneapolis, MN) in Evolut 26, (2) Evolut 23 in SAPIEN 3 23 (Edwards Lifesciences, Irvine, CA), (3) Evolut 26 in Evolut 26, (4) Evolut 26 in SAPIEN 23, (5) SAPIEN 3 23 in Evolut 26, and (6) SAPIEN 3 23 in SAPIEN 3 23. These TAV-in-TAV configurations were assessed in a pulse duplicator. Particle image velocimetry was performed.

RESULTS

During systole, (1) the highest velocity was found with SAPIEN-in-SAPIEN (0.7 m/s) and the lowest was with Evolut 26-in-Evolut 26 (0.2 m/s); (2) the highest shear stress magnitude near the leaflet was with Evolut 23-in-SAPIEN (1.45 Pa) and the lowest was with Evolut 26-in-Evolut 26 (0.55 Pa); and (3) washout was almost equal in all sinuses of these cases (<2.5 cycles).

CONCLUSIONS

This study shows that TAV-in-TAV is highly dependent on the valve that is originally implanted and the valve to be implanted. Washout is not significantly degraded after TAV-in-TAV compared with valve-in-valve and TAV replacement. Further studies are needed to optimize valve size and selection.

Hemodynamics inside the neo- and native sinus after TAVR: Effects of implant depth and cardiac output on flow field and coronary flow

Transcatheter aortic valve replacement (TAVR) has emerged as a widely used therapy for aortic valve diseases. With TAVR, flow hemodynamics may change leading to areas of flow stagnation prone to thrombosis risk. The neo-sinus, created by introducing a prosthesis inside the diseased native valve, may prompt leaflet thrombosis due to areas of flow stasis. This study attempted to understand the effect of different prosthesis implant depths on the flow field within the neo- and native sinus and on the coronary perfusion. Experiments were performed inside an in vitro pulse duplicator producing physiological conditions according to ISO 5840-1:2015 standard. Flow fields were obtained for two cardiac outputs (CO) using particle image velocimetry (PIV). Washout was calculated as a measure of flow stasis. The two main results are: a lower implant position and a lower CO/frequency led to better native sinus washout, but worsened neo-sinus washout. In contrast, a higher implant position led to higher coronary flow (for higher CO/frequency). No significant effect of implant depth on coronary flow was observed for lower CO/frequency. In summary, a higher implant position using this self-expanding prosthesis is associated with reduced neo-sinus flow stasis. Hereby, washout of the native sinus, as well as coronary flow, are dependent on cardiac output.

Impact of Leaflet Laceration on Transcatheter Aortic Valve-in-Valve Washout: BASILICA to Solve Neosinus and Sinus Stasis

OBJECTIVES

The aim of this study was to evaluate any potential leaflet washout benefits after bioprosthetic or native aortic scallop intentional laceration to prevent iatrogenic coronary artery obstruction during TAVR (BASILICA) in transcatheter valve-in-valve (ViV) in the context of leaflet thrombosis.

BACKGROUND

Leaflet thrombosis after transcatheter aortic valve replacement is secondary to flow stasis in both the sinus and neosinus. Strategies to improve washout and ameliorate neosinus and sinus flow velocities may have the potential to mitigate the occurrence of clinical and subclinical leaflet thrombosis.

METHODS

A 23-mm Edwards SAPIEN 3 and a 26-mm Medtronic Evolut were deployed in a 23-mm transparent surgical aortic valve model before and after leaflet laceration. The valves were placed in the aortic position of a pulse duplicator flow loop. Particle image velocimetry was performed to quantify sinus flow hemodynamic status. A tracing fluorescent dye was injected to evaluate the number of cycles to washout in both regions of interest.

RESULTS

The leaflet laceration procedure led to an increase in the velocities in the sinus and the neosinus by 50% for Evolut ViV and 61.9% for SAPIEN 3 ViV. In addition, leaflet laceration led to a reduction in overall cycles to washout in the neosinus by at least 56% with the Evolut and 54.5% with the SAPIEN 3 and in the sinus by at least 16.7% with the Evolut and 60.8% with the SAPIEN.

CONCLUSIONS

Leaflet laceration using a BASILICA-type approach may hold the potential to mitigate neosinus and sinus flow stasis. Controlled in vivo trials are necessary to establish the potential benefit of BASILICA to reduce the occurrence of leaflet thrombosis.

Modeling risk of coronary obstruction during transcatheter aortic valve replacement

OBJECTIVE

In this study we aimed to evaluate risk of coronary obstruction during transcatheter aortic valve replacement and develop improved criteria based on computational modeling.

METHODS

Patient specific 3-dimensional models were constructed and validated for 28 patients out of 600 patients who were flagged as high risk for coronary obstruction (defined as meeting coronary ostium height < 14 mm and/or sinus of Valsalva diameter [SOVd] < 30 mm). The models consisted finite element analysis to predict the post- transcatheter aortic valve replacement native cusp apposition relative to the coronary ostium and were validated in vitro. The distance from cusp to coronary ostium (DLC) was derived from the 3-dimensional models and indexed with the coronary artery diameter to yield a fractional obstruction measure (DLC/d).

RESULTS

Twenty-two out of 28 high-risk patients successfully underwent transcatheter aortic valve replacement without coronary obstruction and 6 did not. DLC/d between the 2 groups was significantly different (P < .00078), whereas neither coronary ostium height nor SOVd were significantly different (P > .32). A cutoff of DLC/d < 0.7 was predictive with 100% sensitivity and 95.7% specificity. The optimal sensitivity and specificity of coronary ostium height and SOVd in this high-risk group was only 60% and 40%, respectively, for cutoff coronary ostium height of 10 mm and SOVd of 30.5 mm.

CONCLUSIONS

Three-dimensional modeling has the potential to enable more patients to be safely treated with transcatheter aortic valve replacement who have a low-lying coronary ostium or small SOVd. DLC/d is more predictive of obstruction than coronary ostium height and SOVd.

Does transcatheter aortic valve alignment matter?

Objective

This study investigates the effect of transcatheter aortic valve (TAV) angular alignment on the postprocedure haemodynamics. TAV implantation has emerged as an effective alternative to surgery when treating valve dysfunction. However, the benefit of avoiding surgery is paid back by the inability to remove the native diseased leaflets and accurately position the device in relation to the aortic root, and the literature has shown the root anatomy and substitute position can play an essential role on valve function.

Methods

A commercial TAV was placed in a silicone mock aortic root in vitro, including mock native leaflets, and either aligned commissure-to-commissure or in maximum misalignment. Haemodynamic performance data at various stroke volumes were measured, and Particle Image Velocimetry analysis was performed at a typical stroke volume for rest conditions. The two configurations were also studied without mock native leaflets, for comparison with previous in vitro studies.

Results

Haemodynamic performance data were similar for all configurations. However, imaging analysis indicated that valve misalignment resulted in the central jet flow not extending to the root wall in the native commissures’ vicinity, replaced by a low shear flow, and a reduction of upper sinus flow of 40%, increasing flow stagnation in the sinus.

Conclusions

TAV misalignment did not result in a significant change in valve hydrodynamic performance, but determined some change in the fluid flow patterns, which may promote pathological scenarios, such as increased thrombogenicity of blood flow within the sinuses of Valsalva, and plaque formation around the lumen of the sinotubular junction.

The hemodynamics of transcatheter aortic valves in transcatheter aortic valves

BACKGROUND

The durability of transcatheter aortic valves (TAVs) remains their greatest disadvantage, given that fixed tissue leaflets are not immune to structural degeneration from calcification and thrombosis. Therefore, a second intervention is necessary, especially given that TAV in low-risk patients has shown noninferior outcomes compared with surgery. This study aimed to assess the hemodynamic and turbulent properties of the flow downstream with different TAV-in-TAV configurations, to offer basic hemodynamic guidance for future interventions when currently implanted valves structurally degrade.

METHODS

Six TAV-in-TAV configurations were chosen: 23 mm Evolut-in-26 mm Evolut, 23 mm Evolut-in-23 mm SAPIEN 3, 26 mm Evolut-in-26 mm Evolut, 26 mm Evolut-in-23 mm SAPIEN 3, 23 mm SAPIEN3-in-26 mm Evolut, and 23 mm SAPIEN3-in-23 mm SAPIEN 3. Their hemodynamic performance was assessed in a pulse duplicator for 100 cycles. High-speed imaging and particle image velocimetry were performed to assess turbulence. Effective orifice area (EOA), pinwheeling index (PI), and Reynolds shear stress (RSS) were evaluated.

RESULTS

The largest mean EOA was obtained with 23 mm SAPIEN-in-26 mm Evolut (2.07 ± 0.06 cm²), and the smallest was obtained with 23 mm Evolut-in-23 mm SAPIEN (1.50 ± 0.04 cm²) (P < .001). The highest mean PI was obtained with SAPIEN-in-SAPIEN (26.5 ± 2.00%), and the lowest was obtained with 26 mm Evolut-in-26 mm Evolut (7.5 ± 1.6%) (P < .01). At peak systole, the least detrimental RSS range was obtained with 23 mm Evolut-in-26 mm Evolut (up to ∼340 Pa), and the most detrimental RSS range was obtained with 23 mm Evolut-in-SAPIEN (∼900 Pa) (P < .01).

CONCLUSIONS

This study shows that best hemodynamic parameters are TAV-specific (implanted and to be implanted). In addition, it shows that RSS levels, which are indicative of turbulence levels and associated with blood damage, are 2- to 3-fold higher after TAV-in-TAV.

Modeling of the Instantaneous Transvalvular Pressure Gradient in Aortic Stenosis

The simplified and modified Bernoulli equations break down in estimating the true pressure gradient across the stenotic aortic valve due to their over simplifying assumptions of steady and inviscid conditions as well as the fundamental nature in which aortic valves are different than idealized orifices. Nevertheless, despite having newer models based on time-dependent momentum balance across an orifice, the simplified and modified Bernoulli continue to be the clinical standard because to date, they remain the only models clinically implementable. The objective of this study is to (1) illustrate the fundamental considerations necessary to accurately model the time-dependent instantaneous pressure gradient across a fixed orifice and (2) propose empirical corrections when applying orifice based models to severely stenotic aortic valves. We introduce a general model to predict the time-dependent instantaneous pressure gradient across an orifice that explicitly model the Reynolds number dependence of both the steady and unsteady terms. The accuracy of this general model is assessed with respect to previous models through pulse duplicator experiments on a round orifice model as well as an explanted stenotic surgical aortic valve both with geometric areas of 0.6 cm2 (less than 1 cm2 which is the threshold for stenosis determination) over cardiac outputs of 3 and 5 L/min and heart rates of 60, 90 and 120 bpm. The model and the raw experimental data corresponding to the orifice showed good agreement over a wide range of cardiac outputs and heart rates (R2 exceeding 0.91). The derived average and peak transvalvular pressure gradients also demonstrated good agreement with no significant differences between the respective peaks (p > 0.09). The new model proposed holds promise with its physical and closed form representation of pressure drop, however accurate modeling of the time-variability of the valve area is necessary for the model to be applied on stenotic valves.

Valve-in-Valve TAVR: State-of-the-Art Review

An increasing number of surgically implanted bioprostheses will require re-intervention for structural valve deterioration. Valve-in-valve transcatheter aortic valve replacement (ViV TAVR) has become an alternative to reoperative surgery, currently approved for high-risk and inoperable patients. Challenges to the technique include higher rates of prosthesis–patient mismatch and coronary obstruction, compared to native valve TAVR. Herein, we review results of ViV TAVR and novel techniques to overcome the aforementioned challenges.

Impact of BASILICA on Sinus and Neo-Sinus Hemodynamics after Valve-in-Valve with and without Coronary Flow

BACKGROUND/PURPOSE

This study aims at evaluating the impact of BASILICA on neo-sinus and sinus hemodynamics with and without coronary flow. Leaflet thrombosis after valve-in-valve (ViV) may compromise not only leaflet mobility but also affect valve durability and performance.

METHODS/MATERIALS

In a 23 mm transparent surgical aortic valve model, a 23 mm Edwards SAPIEN 3 and a 26 mm Medtronic Evolut were deployed before and after leaflet laceration, in models with and without coronary flow. Neo-sinus and sinus hemodynamics were evaluated in the aortic position of a pulse duplicator and particle image velocimetry was performed in order to quantify sinus flow hemodynamics along with sinus and neo-sinus washout.

RESULTS

BASILICA-type leaflet laceration procedure led to (a) an increase in the velocities in the sinus and the neo-sinus by 50% for Evolut ViV with and without coronary flow, 70% for non-coronary SAPIEN 3 ViV and 10% for coronary SAPIEN 3 ViV, and (b) an improvement in overall washout up to 2 cycles in the neo-sinus and 0.5 cycles in the sinus.

CONCLUSIONS

A BASILICA-type leaflet laceration approach may improve sinus and neo-sinus hemodynamics through decreasing flow stasis and enabling less confined blood flow. BASILICA confers coronary sinus flow patterns to the non-coronary sinus.

In vitro hemodynamic assessment of a novel polymeric transcatheter aortic valve

Transcatheter aortic valve replacement (TAVR) is a life-saving alternative to surgical intervention. However, the identification of features associated with poor outcomes, including residual paravalvular leakage (PVL), leaflet calcification, and subclinical leaflet thrombosis, are cause to be concerned about valve durablilty (Mylotte and Piazza, 2015a, 2015b; Dasi et al., 2017; Makkar et al., 2015; Kheradvar et al., 2015a). The aim of this study is to optimize the potential of a hyaluronan (HA) enhanced polymeric transcatheter aortic valve (HA-TAV) that has promised to reduce blood damage causing-turbulent flow while maintaining durability. HA-enhanced linear low-density polyethylene (LLDPE) leaflets were sutured to novel cobalt chromium stents, size 26 mm balloon expandable stents. Hemodynamic performance was assessed in a left heart simulator under physiological pressure and flow conditions and compared to a 26 mm Medtronic Evolut and 26 mm Edwards SAPIEN 3. High-speed imaging and particle image velocimetry (PIV) were performed. The HA-TAV demonstrated an effective orifice area (EOA) within one standard deviation of the leading valve, SAPIEN 3.The regurgitant fraction (RF) of the HA-TAV (11.23 ± 0.55%) is decreased in comparison the Evolut (15.74 ± 0.73%) and slightly higher than the SAPIEN 3 (10.92 ± 0.11%), which is considered trace regurgitation according to valve standards. A decreased number of higher principal Reynolds shear stresses were shown for the HA-TAV at each cardiac phase. The HA-TAV is directly comparable and in some cases superior to the leading commercially available prosthetic heart valves in in-vitro hemodynamic testing.

A case study on implantation strategies to mitigate coronary obstruction in a patient receiving transcatheter aortic valve replacement

Coronary obstruction is a life threatening complication during and post-transcatheter aortic valve replacement (TAVR). The objective of this preliminary work is to investigate the mechanisms underlying coronary obstruction in a patient after TAVR, in whom coronary obstruction was confirmed in addition to highlighting the importance of pre-procedural planning. The aortic root of an 80-year old male patient with coronary obstruction during TAVR-where a 29 mm SAPIEN 3 was deployed-was segmented from Computed Tomography scans and 3D-printed with compliant material. Flow and pressure data were acquired in this 3D-printed model in-vitro using a pulse duplicator under physiological conditions for the cases: a 29 mm SAPIEN 3, a 26 mm SAPIEN 3 expanded with a 29 mm balloon, and a 31 mm Medtronic-CoreValve deployed annularly, supra and sub-annularly respectively. Only the CoreValve in sub-annular axial position and the 29 mm SAPIEN 3 yielded pressure gradients (PG) lower than 10 mmHg (6.76 ± 0.52 and 5.72 ± 0.13 mmHg respectively) while the 26 mm SAPIEN 3, CoreValve in normal and supra-annular positions yielded higher PGs (15.5 ± 0.48, 12.2 ± 0.15 and 10.8 ± 0.24 mmHg respectively). 29 mm SAPIEN 3 implantation yielded an FFR value of 45.7 ± 0.6%. However, 31 mm CoreValve in any of the three different annular positions yielded FFR values going from 89.6 ± 1.1% in supra-annular position to 98.3 ± 1.1% in sub-annular position. Implantation with a 26 mm SAPIEN 3 expanded with a 29 mm balloon also yielded an FFR of 92.1 ± 1.2%. Coronary obstruction in this patient could have been prevented through usage of different valve types and/or through usage of a different combination of valve size-balloon sizes.

A turbulence in vitro assessment of On-X and St Jude Medical prostheses

OBJECTIVE

The objective of this study was to investigate and compare the hemodynamic and turbulence characteristics upon implantation of St Jude Medical (SJM) (St Jude Medical, St Paul, Minn) and On-X (On-X Life Technologies, Kennesaw, Ga) bileaflet mechanical valves. Both valves are considered highly successful bileaflet mechanical valves characterized by good clinical outcomes despite their numerous design differences. Although thromboembolism remains the main disadvantage of bileaflet mechanical valves, On-X valves have been shown to need less anticoagulation therapy.

METHODS

Hemodynamic assessment of a 23-mm On-X bileaflet mechanical valve and a 23-mm bileaflet SJM valve implanted in an aortic root was performed under pulsatile physiologic conditions. Time-resolved and phase-locked particle-image-velocimetry images and high-speed imaging data were acquired. Pressure gradients, effective orifice areas, dimensionless area index, leaflet position tracking, velocity, and principal Reynolds shear stress were calculated.

RESULTS

Pressure gradient for the On-X valve was 4.15 ± 0.099 mm Hg versus 4.75 ± 0.048 mm Hg for SJM (P < .001). Effective orifice area for the On-X valve was 2.61 ± 0.045 cm² versus 2.36 ± 0.022 cm² for SJM (P < .001). Area index was higher with SJM (0.87 ± 0.008) than with On-X (0.73 ± 0.013) (P < .001). On-X showed fluctuating leaflet behavior during systole, whereas SJM leaflets were stable. At peak systole, the maximal velocity with On-X was 1.86 m/s versus 2.33 m/s with SJM. Reynolds shear stress was higher with On-X compared with SJM at peak systole (95 vs 72 Pa). Higher velocity fluctuation was noted with the On-X valve.

CONCLUSIONS

This study shows that despite the design differences that characterize the On-X valve, the hemodynamic and turbulence parameters were not necessarily improved compared with SJM.

Spatiotemporal Complexity of the Aortic Sinus Vortex as a Function of Leaflet Calcification

Several studies have shown the variation of aortic sinus structures' hemodynamics with different flow and geometric characteristics. They have also correlated aortic sinus hemodynamics with the progression and evolution of calcific aortic valve disease (CAVD). This study aims at visualizing aortic sinus fluid structure variations as functions of different leaflet calcification degrees and assessing their potential relationship with CAVD. A degenerated 23 mm Carpentier-Edwards Perimount Magna valve extracted from a redo-surgery patient was implanted in an aortic root model and tested in a pulse duplicator left heart simulator. The valve has 3 leaflets with 3 different levels of calcium distribution: mild, moderate and severe. High-speed imaging and particle image velocimetry were performed to assess sinus vortices, leaflet tip position and velocity along with shear stress. Results have shown that (a) aortic sinus vortices initiation, entrapment and evolution varied with different calcified leaflet exposure; (b) higher velocities in the sinus were calculated with the mildly calcified leaflet compared to the moderately and severely calcified ones; (c) during systole, the mildly calcified leaflet sinus case shows the most spread-out and higher ranges of shear stress probabilities and highest magnitudes going from (- 1.5 to + 1.8 Pa) compared with (- 1.0 to + 1.0 Pa) for moderately and severely calcified leaflets. The higher the calcification degree the lower the shear stress range and likelihoods of having higher shear stress. This holds in diastole as well. This study shows the impact of calcification on the aortic sinus flow structures.

Sinus Hemodynamics Variation with Tilted Transcatheter Aortic Valve Deployments

Leaflet thrombosis is a complication associated with transcatheter aortic valve (TAV) replacement (TAVR) correlated with sinus flow stasis. Sinus hemodynamics are important because they dictate shear stress and washout necessary to avoid stasis on TAV leaflets. Sinus flow is controlled by TAV axial deployment position but little is known regarding TAV axis misalignment effect. This study aims to elucidate TAV angular misalignment with respect to aortic root axis effect on sinus flow stasis potentially leading to leaflet thrombosis. Sinus hemodynamics were assessed in vitro using particle-image velocimetry in three different angular misalignments with respect to aorta axis: untilted, tilted away from the sinus and tilted towards sinus. A 26 mm Edwards SAPIEN3 was implanted in a 3D printed model of an anatomically realistic aortic root. TAV hemodynamics, sinus vortex tracking, leaflet shear stress probability density functions, and sinus blood time to washout were calculated. While pressure gradients differed insignificantly, blood velocity and vorticity decreased significantly in both tilted cases sinuses. Shear stress probability near the leaflet decreases with tilt indicating stasis. TAV tilted away from the sinus is the most unfavorable scenario with poor washout. TAV axial misalignment adds to factors list that could influence leaflet thrombosis risk through modifying sinus hemodynamics and washout.

Reduction of Pressure Gradient and Turbulence Using Vortex Generators in Prosthetic Heart Valves

Blood damage and platelet activation are inherent problems with present day bi-leaflet mechanical heart valve designs. Passive flow control through different arrangements of vortex generators (VG) as means of improving pressure gradients and reducing turbulence are investigated. Rectangular VG arrays were mounted on the downstream surfaces of a 23 mm 3D printed mechanical valve. The effect of VGs on the resulting flow structures were assessed under pulsatile physiological flow conditions where high resolution particle image velocimetry measurement was performed. The co-rotating VGs showed lower Reynolds shear stresses and improved pressure gradients (PG) compared with the counter-rotating ones and the no-VG control one (that showed higher turbulence). RSS was found 38.13 ± 0.89, 12.95 ± 0.32, 15.75 ± 0.71, 24.54 ± 0.84 and 16.33 ± 0.58 Pa for the control, co-rotating VGs, 8 counter-rotating VGs, 4 far-spaced VGs and 4 closely-spaced VGs, respectively. PG of 10.45 ± 0.94 mmHg was obtained with co-rotating VGs and the difference was significant compared with the other configurations (control 14.88 ± 0.4 mmHg; 8 counter-rotating VGs 13.76 ± 0.51 mmHg; 4 far-spaced VGs 13.84 ± 0.09 mmHg; and 4 closely-spaced VGs 15.37 ± 0.16 mmHg). Co-rotating VGs for this application induce a more delayed flow separation and a more homogenized and streamlined transition of flow compared with the counter-rotating VGs. Passive flow control techniques deployed on BHMVs is potentially beneficial as significant control of flow at small length scales without inducing large-scale design modifications of the valve.

Principles of TAVR valve design, modelling, and testing

INTRODUCTION

Transcatheter aortic valve replacement (TAVR) has emerged as an effective minimally-invasive alternative to surgical valve replacement in medium- to high-risk, elderly patients with calcific aortic valve disease and severe aortic stenosis. The rapid growth of the TAVR devices market has led to a high variety of designs, each aiming to address persistent complications associated with TAVR valves that may hamper the anticipated expansion of TAVR utility.

AREAS COVERED

Here we outline the challenges and the technical demands that TAVR devices need to address for achieving the desired expansion, and review design aspects of selected, latest generation, TAVR valves of both clinically-used and investigational devices. We further review in detail some of the up-to-date modeling and testing approaches for TAVR, both computationally and experimentally, and additionally discuss those as complementary approaches to the ISO 5840-3 standard. A comprehensive survey of the prior and up-to-date literature was conducted to cover the most pertaining issues and challenges that TAVR technology faces.

EXPERT COMMENTARY

The expansion of TAVR over SAVR and to new indications seems more promising than ever. With new challenges to come, new TAV design approaches, and materials used, are expected to emerge, and novel testing/modeling methods to be developed.

Sinus Hemodynamics in Representative Stenotic Native Bicuspid and Tricuspid Aortic Valves: An In-Vitro Study

(1) The study’s objective is to assess sinus hemodynamics differences between stenotic native bicuspid aortic valve (BAV) and native tricuspid aortic valve (TrAV) sinuses in order to assess sinus flow shear and vorticity dynamics in these common pathological states of the aortic valve. (2) Representative patient-specific aortic roots with BAV and TrAV were selected, segmented, and 3D printed. The flow dynamics within the sinus were assessed in-vitro using particle image velocimetry in a left heart simulator at physiological pressure and flow conditions. Hemodynamic data calculations, vortex tracking, shear stress probability density functions and sinus washout calculations based on Lagrangian particle tracking were performed. (3) (a) At peak systole, velocity and vorticity in BAV reach 0.67 ± 0.02 m/s and 374 ± 5 s−1 versus 0.49 ± 0.03 m/s and 293 ± 3 s−1 in TrAV; (b) Aortic sinus vortex is slower to form but conserved in BAV sinus; (c) BAV shear stresses exceed those of TrAV (1.05 Pa versus 0.8 Pa); (d) Complete TrAV washout was achieved after 1.5 cycles while it was not for BAV. 4) In conclusion, sinus hemodynamics dependence on the different native aortic valve types and sinus morphologies was clearly highlighted in this study.

On the Significance of Systolic Flow Waveform on Aortic Valve Energy Loss

This study aims to quantitatively and qualitatively assess energy dissipation in the aortic valve as a function of systolic aortic flow waveform representing pathologies where flow time-to-peak is delayed. A bioprosthetic valve was tested in the aortic position of a left-heart simulator under physiological pressure and flow conditions. The flow loop piston pump was programmed to generate three different flow waveforms each with a different peak time annotated as early peak (EP) with a rapid acceleration, mid peak (MP) and late peak (LP) with a rapid deceleration. Energy dissipation was calculated from flow and pressure measurements while sinus vorticity dynamics were evaluated using time-resolved planar particle image velocimetry. Average pressure gradients during systole are found 30.2 ± 0.19, 30.7 ± 0.25 and 32.9 ± 0.29 mmHg and average dissipation over systole is found 0.95 ± 0.026, 1.05 ± 0.034 and 1.25 ± 0.043 W for EP, MP and LP respectively. As systole's acceleration phase is slower, sinus vortices are more likely to form, necessitating more energy exchange from shear layers inducing more viscous dissipation. EP found in healthy individuals is superior in terms of reducing energy dissipation and increasing aortic valve efficiency. In the context of possible left ventricular dysfunction and aortic stenosis, this means that delayed time-to-peak in the aortic flow waveform seen is not compensatory.

Stented valve dynamic behavior induced by polyester fiber leaflet material in transcatheter aortic valve devices

OBJECTIVE

This study aims at assessing the global dynamic behavior, elastic deformability, closing energy and turbulence of rigid versus deformable stented (RS vs DS) valve systems with deformable and rigid textile materials (DT vs RT) through studying the stent-valve interaction compared to a bioprosthetic material in transcatheter aortic valves (TAV).

METHODS

Three 19 mm stented textile TAV designs (RS-DT, RS-RT and DS-RT) with different stent and leaflet properties were tested and compared with a control bioprosthetic TAV (RS-DB) in a left heart simulator flow loop under physiological pressure and flow. Particle Image Velocimetry and high speed imaging were performed. Pressure gradients (PG), leakage fractions (LF), Pinwheeling indices (PI), closing energy (E) and Reynolds shear stresses (RSS) were calculated.

RESULTS

(a) PGs and LFs were 11.86 ± 0.51 mmHg, 11.70 ± 0.34%; 8.84 ± 0.40 mmHg, 29.80 ± 0.76%; 11.59 ± 0.12 mmHg, 14.23 ± 1.64%; and 7.05 ± 0.09 mmHg, 12.08 ± 0.45% % for RS-DB, RS-DT, RS-RT and DS-RT respectively. (b) PIs were 15.79 ± 2.34%, 4.36 ± 0.84%, 2.47 ± 0.51% and 2.03 ± 0.33% for RS-DB, RS-DT, RS-RT and DS-RT respectively. (c) E is lowest for DS-RT (0.0010 ± 0.0002 J) followed by RS-RT (0.0017 ± 0.0002 J), RS-DB (0.0023 ± 0.0004 J) and highest with RS-DT (0.0036 ± 0.0007 J). (d) At peak systole lowest RSS was obtained with RS-DT (87.82 ± 0.58 Pa) and highest with DS-RT (122.98 ± 1.87 Pa).

CONCLUSION

PGs, LFs, PIs and E were improved with DS-RT compared to other textile TAVs and RS-DB. Despite achieving more RSS than the rest of TAVs, DS-RT still falls within the same range of RSS produced by the other 2 valves and control exceeding the threshold for platelet activation.

Impact of patient-specific morphologies on sinus flow stasis in transcatheter aortic valve replacement: An in vitro study

OBJECTIVE

The goal of this study is to evaluate how sinus flow patterns after transcatheter aortic valve replacement in realistic representative patient roots vary. Sinus flow can affect transcatheter aortic valve operation and likely leaflet thrombosis occurrence due to stasis and poor washout. How the interaction between transcatheter aortic valve and representative patient aortic roots affects sinus hemodynamics is important to establish for future individualization of transcatheter aortic valve replacement therapy.

METHODS

Two representative patient aortic roots were selected, segmented and 3-dimensional printed followed by deployment of Medtronic CoreValve (Medtronic Inc, Irvine, Calif) and Edwards SAPIEN (Edwards Lifesciences, Irvine Calif) transcatheter aortic valves. Sinus hemodynamics were assessed in vitro using high spatio-temporal resolution particle-image-velocimetry. Detailed sinus vortex tracking, shear stress probability density functions, and sinus washout were evaluated and assessed as a function of valve type and representative patient morphology as independent case studies.

RESULTS

Peak velocity in the sinus with SAPIEN valve was approximately 3 times higher than with CoreValve for both models (0.30 ± 0.02 m/s and 0.34 ± 0.041 m/s vs 0.13 ± 0.01 m/s and 0.10 ± 0.02 m/s) (P < .01). Between representative patient models, vorticity magnitudes were significantly different (75 ± 1.1 s^-1, 77 ± 3.2 s^-1, 109 ± 2.3 s^-1, and 250 ± 4.1 s^-1) (P < .01) regardless of valve type. Sinus blood washout characteristic as a function of cardiac cycles was strongly both patient related and valve specific. Fluid dynamics favored shear stresses and washout characteristics due to a smaller sinus and sinotubular junction, further amplified by the SAPIEN valve.

CONCLUSIONS

Sinus flow dynamics are highly sensitive to aortic root characteristics and transcatheter aortic valve aortic root interaction. Differences in sinus-flow washout and stasis regions between representative patient models may be reflected in different risks of leaflet thrombosis or valve degeneration.

An in vitro evaluation of turbulence after transcatheter aortic valve implantation

BACKGROUND

This study aimed at assessment of post-transcatheter aortic valve (TAV) replacement hemodynamics and turbulence when a same-size SAPIEN 3 (Edwards Lifesciences Corp, Irvine, Calif) and Medtronic Evolut (Minneapolis, Minn) were implanted in a rigid aortic root with physiological dimensions and in a representative root with calcific leaflets obtained from patient computed tomography scans.

METHODS

TAV hemodynamics were studied by placing a SAPIEN 3 26-mm and an Evolut 26-mm in rigid aortic roots and representative root with calcific leaflets under physiological conditions. Hemodynamics were assessed using high-fidelity particle image velocimetry and high-speed imaging. Transvalvular pressure gradients (PGs), pinwheeling indices, and Reynolds shear stress (RSS) were calculated.

RESULTS

(1) PGs obtained with the Evolut and the SAPIEN 3 were comparable among the different models (10.5 ± 0.15 mm Hg vs 7.76 ± 0.083 mm Hg in the rigid model along with 13.9 ± 0.19 mm Hg vs 5.0 ± 0.09 mm Hg in representative root with calcific leaflets obtained from patient computed tomography scans respectively); (2) more pinwheeling was found in the SAPIEN 3 than the Evolut (0.231 ± 0.057 vs 0.201 ± 0.05 in the representative root with calcific leaflets and 0.366 ± 0.067 vs 0.122 ± 0.045 in the rigid model); (3) higher rates of RSS were found in the Evolut (161.27 ± 3.45 vs 122.84 ± 1.76 Pa in representative root with calcific leaflets and 337.22 ± 7.05 vs 157.91 ± 1.80 Pa in rigid models). More lateral fluctuations were found in representative root with calcific leaflets.

CONCLUSIONS

(1) Comparable PGs were found among the TAVs in different models; (2) pinwheeling indices were found to be different between both TAVs; (3) turbulence patterns among both TAVs translated according to RSS were different. Rigid aortic models yield more conservative estimates of turbulence; (4) both TAVs exhibit peak maximal RSS that exceeds platelet activation 100 Pa threshold limit.

Effect of severe bioprosthetic valve tissue ingrowth and inflow calcification on valve-in-valve performance

While in vivo studies clearly demonstrate that supra-annular Valve-in-Valve (ViV) implantation provides the highest probability for optimal post-ViV pressure gradients (PG), there is still no physical insight into explaining anomalies where some supra-annular ViV implantations yield high pressure gradients while some sub-annular implantations yield low pressure gradients. The aim of this study is to explain how severe tissue ingrowth and calcification (TIC) in a surgical aortic valve (SAV) can be one physical mechanism leading to anomalous ViV performance characteristic. The ViV hemodynamic performance was evaluated as a function of axial positioning -9.8, -6.2, 0, and +6 mm in SAVs with and without TIC. Effective orifice area (EOA) and PG were compared. Leaflet high-speed imaging and particle image velocimetry were performed to elucidate flutter and forward jet characteristics. ViV without TIC showed significantly lower PG and greater EOA (p < 0.01). EOA and PG improve with supra-annular deployment (p < 0.01) while for ViV with TIC, EOA and PG worsen as the deployment varies from -9.8 mm to 0 mm (p < 0.01) only to recover at + 6 mm (p < 0.01). Separated jet flow at the TIC site, and consequently induced stronger TAV leaflet fluttering highlight the dynamic compromising nature of TIC on jet width and performance reduction. We conclude that the inflow TIC greatly influence ViV performance due to dynamic effects that results in a real anomalous performance characteristic different than that seen in most ViV in vivo. Further in vivo studies are needed to evaluate ViV outcomes in the presence of severe TIC in SAVs.