How Can We Help a Patient With a Small Failing Bioprosthesis?

Effects of different valve-in-valve positions on the hydrodynamic properties of transcatheter aortic valves

OBJECTIVE

With the rise of transcatheter aortic valve-in-valve (ViV) procedures for high-risk patients with degenerated surgical aortic valves, precise positioning of the transcatheter heart valve (THV) within the surgical heart valve (SHV) is crucial for optimal functional outcomes. This study aims to explore the impact of implantation depth on functional outcomes post-ViV in a controlled in vitro setting.

METHODS

This study focused on the impact of valve positioning on fluid dynamics characteristics and subsequent ViV procedural outcomes. Rigorous in vitro experiments measured the structural parameters of the surgical valves, and based on these, the appropriate Taurus Elite valves were selected for pulse flow testing under simulated conditions of varying heart rates and cardiac outputs. Fluid dynamic evaluations were conducted on Taurus Elite THVs in sizes 21, 23, 26, 29 mm and SHVs from two brands: Hancock II (Medtronic, USA) and BalMedic (Balance Medical, China) across a range of diameters. In-depth analysis was performed at a cardiac output (CO) of 5 L/min and heart rate (HR) of 70 bpm, focusing on key metrics such as transvalvular pressure gradient (TVPG), effective orifice area (EOA), and total regurgitation fraction (TRF) at implantation depths of -2.5, 0, 2.5, and 5 mm to gain insights into the dynamic interaction between THV placement and hemodynamic performance. Anchoring force tests were also conducted for SHV-THV combinations at -2.5 and 0 mm depths to ensure safety of implantation.

RESULTS

Significant differences were observed in TVPG, EOA, and TRF across various SHV brands and sizes, emphasizing the importance of THV positioning. Specifically, Taurus Elite23 demonstrated superior TVPG performance at various depths compared to Taurus Elite21, indicating a better match with BalMedic19 and Hancock II21, especially at implantation depths ranging from -2.5 to 0 mm. Taurus Elite29 showed the lowest TVPG across all tested depths, making it the preferred choice for BalMedic25 and Hancock II27. These findings highlight the importance of selecting the appropriate THV model and determining the optimal implantation depth for different SHVs.

CONCLUSIONS

In different surgical valves, both the model and implantation depth of the interventional valve can affect its hemodynamic performance and valve opening-closing morphology. The recommended implantation of the interventional valve as shallowly as possible in this study has guiding significance in clinical valve-in-valve surgeries.

A multimodal approach to predict prosthesis-patient mismatch in patients undergoing valve-in-valve trans-catheter aortic valve implantation

AIMS

The valve-in-valve transcatheter-aortic-valve-implantation (VIV-TAVI) represents an emerging procedure for the treatment of degenerated aortic bio-prostheses, and the occurrence of patient-prosthesis mismatch (PPM) after VIV-TAVI might affect its clinical efficacy. This study aimed to test a multimodal imaging approach to predict PPM risk during the TAVI planning phase and assess its clinical predictivity in VIV-TAVI procedures.

METHODS

Consecutive patients undergoing VIV-TAVI procedures at our Institution over 6 years were screened and those treated by self-expandable supra-annular valves were selected. The effective orifice area (EOA) was calculated with a hybrid Gorlin equation combining echocardiographic data with invasive hemodynamic assessment. Severe PPM was defined according to such original multimodality assessment as EOAi≤0.65 cm2/m2 (if BMI < 30 kg/m2) or < 0.55 cm2/m2 (if BMI ≥ 30 kg/m2). The primary endpoint was a composite of all-cause mortality and valve-related re-hospitalization during the clinical follow-up.

RESULTS

A total of 40 VIV-TAVI was included in the analysis. According to the pre-specified multimodal imaging modality assessment, 18 patients (45.0 %) had severe PPM. Among all baseline clinical and anatomical characteristics, estimated glomerular filtration rate before VIV-TAVI (OR 0.872, 95%CI[0.765-0.994],p = 0.040), the echocardiographic pre-procedural ≥moderate AR (OR 0.023, 95%CI[0.001-0.964],p = 0.048), the MSCT-derived effective internal area (OR 0.958, 95%CI[0.919-0.999],p = 0.046) and the implantation depth (OR 2.050, 95%CI[1.028-4.086],p = 0.041) resulted as independent predictors of severe PPM at multivariable logistic analysis. At a mean follow-up of 630 days, patients with severe PPM showed a higher incidence of the primary endpoint (9.1%vs.44.4 %;p = 0.023).

CONCLUSION

In VIV-TAVI using self-expandable supra-annular valves, a multimodal imaging approach might improve clinical outcome predicting severe PPM occurrence.

Transcatether Aortic Valve Implantation to Treat Degenerated Surgical Bioprosthesis: Focus on the Specific Procedural Challenges

Actually transcatheter aortic valve implantation within failed surgically bioprosthetic valves (VIV-TAVI) is an established procedure in patients at high risk for repeat surgical aortic valve intervention. Although less invasive than surgical reintervention, VIV-TAVI procedure offers potential challenges, such as higher rates of prosthesis-patient mismatch and coronary obstruction. Thus, optimal procedural planning plays an important role to minimize the risk of procedure complications. In this review, we describe the key points of a VIV-TAVI procedure to optimize outcomes and reduce the risk of procedure complications.

The role of flow stasis in transcatheter aortic valve leaflet thrombosis

OBJECTIVE

With the recent expanded indication for transcatheter aortic valve replacement to low-risk surgical patients, thrombus formation in the neosinus is of particular interest due to concerns of reduced leaflet motion and long-term transcatheter heart valve durability. Although flow stasis likely plays a role, a direct connection between neosinus flow stasis and thrombus severity is yet to be established.

METHODS

Patients (n = 23) were selected to minimize potential confounding factors related to thrombus formation. Patient-specific 3-dimensional reconstructed in vitro models were created to replicate in vivo anatomy and valve deployment using the patient-specific cardiac output and idealized coronary flows. Dye was injected into each neosinus to quantify washout time as a measure of flow stasis.

RESULTS

Flow stasis (washout time) showed a significant, positive correlation with thrombus volume in the neosinus (rho = 0.621, P < .0001). Neither thrombus volume nor washout time was significantly different in the left, right, and noncoronary neosinuses (P ≥ .54).

CONCLUSIONS

This is the first patient-specific study correlating flow stasis with thrombus volume in the neosinus post-transcatheter aortic valve replacement across multiple valve types and sizes. Neosinus-specific factors create hemodynamic and thrombotic variability within individual patients. Measurement of neosinus flow stasis may guide strategies to improve outcomes in transcatheter aortic valve replacement.

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.

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.

Matched comparison of next- and early-generation balloon-expandable transcatheter heart valve implantations in failed surgical aortic bioprostheses

AIMS

Transcatheter valve-in-valve implantation (VinV) is established for the treatment of degenerated surgical bioprostheses in patients at high operative risk. Our aim was to report on the first large assessment of VinV with next-generation balloon-expandable transcatheter heart valves.

METHODS AND RESULTS

After SAPIEN XT or SAPIEN 3 VinV, 514 patients were analysed using an inverse probability of treatment weighting. Standardised clinical and haemodynamic outcomes were compared, and core laboratory evaluation of implantation depth was performed. Thirty-day all-cause mortality was 0.6% and 3.5% for SAPIEN 3 and SAPIEN XT (p=0.077). Residual transprosthetic gradient ≥20 mmHg was observed in 38.3% (SAPIEN 3) and 35.7% (SAPIEN XT) of patients (p=0.627) with increased rates in small bioprostheses (≤21 mm true ID). In SAPIEN 3 VinV, low implantation depth >20% THV stent frame length was associated with a higher rate of elevated transaortic gradients (p=0.048). Similarly, an implantation depth >5 mm was linked to more pacemaker implantations (p=0.01). Overall, a trend towards higher pacemaker implantation rates was observed after SAPIEN 3 VinV (6% vs. 2.5% in SAPIEN XT, p=0.071).

CONCLUSIONS

Transcatheter aortic VinV with the balloon-expandable SAPIEN XT or SAPIEN 3 was similarly safe and effective. However, residual stenosis remains a concern, particularly in smaller bioprostheses and with increasing implantation depth.

Optimising the Haemodynamics of Aortic Valve-in-valve Procedures

Bioprosthetic surgical valves are increasingly implanted during cardiac surgery, instead of mechanical valves. These tissue valves are associated with limited durability and as a result transcatheter valve-in-valve procedures are performed to treat failed bioprostheses. A relatively common adverse event of aortic valve-in-valve procedures is residual stenosis. Larger surgical valve size, supra-annular transcatheter heart valve type, as well as higher transcatheter heart valve implantation depth, have all been shown to reduce the incidence of elevated post-procedural gradients. With greater understanding of technical considerations and surgical planning, valve-in-valve procedures could be more effective and eventually may become the standard of care for our increasingly ageing and comorbid population with failed surgical bioprostheses.

Valve thrombosis following transcatheter aortic valve replacement: significance of blood stasis on the leaflets

OBJECTIVES

Leaflet thrombosis following transcatheter aortic valve replacement (TAVR) and valve-in-valve (ViV) procedures has been increasingly recognized. However, the factors affecting the post-TAVR/ViV thrombosis are not fully understood. This study aimed to investigate the effect of the geometric confinement of transcatheter aortic valve (TAV) on blood residence time (BRT) on the TAV leaflets and in turn on the post-TAVR valve thrombosis.

METHODS

Two computational models, representing a surgical bioprosthesis and a TAV, were developed to study the effect of the geometric confinement on BRT on the leaflets in ViV setting/TAVR Intra-annular positioning. 3D flow fields were obtained via a one-way fluid-solid interaction modelling approach validated by experimental testing. BRT was compared between the two models by quantification and statistical analysis of the residence time of randomly distributed particles in close proximity of the leaflets.

RESULTS

Significantly longer BRT on the leaflets was observed in the TAV compared to the surgical valve during different stages of the cardiac cycle. During forward flow, the mean value of BRT was found to be 39% higher in the TAV compared to the surgical bioprosthesis ( P <  0.0001). During diastole, specifically from end-systole to mid-diastole and from mid-diastole to the beginning of systole, the amount by which the mean BRT was higher for TAV compared to the surgical valve was 150% and 40%, respectively ( P <  0.0005).

CONCLUSIONS

The geometric confinement of TAV by the failed bioprosthesis or the calcified native valve increases the BRT on the TAV leaflets. This may act as a permissive factor in valve thrombosis.

ACC/AATS/AHA/ASE/EACTS/HVS/SCA/SCAI/SCCT/SCMR/STS 2017 Appropriate use criteria for the treatment of patients with severe aortic stenosis

The American College of Cardiology collaborated with the American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, European Association for Cardio-Thoracic Surgery, Heart Valve Society, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons to develop and evaluate Appropriate Use Criteria (AUC) for the treatment of patients with severe aortic stenosis (AS). This is the first AUC to address the topic of AS and its treatment options, including surgical aortic valve replacement and transcatheter aortic valve replacement. A number of common patient scenarios experienced in daily practice were developed along with assumptions and definitions for those scenarios, which were all created using guidelines, clinical trial data and expert opinion in the field of AS. The '2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines' [1] and its 2017 focused update paper [2] were used as the primary guiding references in developing these indications. The Writing Group identified 95 clinical scenarios based on patient symptoms and clinical presentation, and up to 6 potential treatment options for those patients. A separate, independent Rating Panel was asked to score each indication from 1 to 9, with 1-3 categorized as 'Rarely Appropriate', 4-6 as 'May Be Appropriate' and 7-9 as 'Appropriate'. After considering factors such as symptom status, left ventricular function, surgical risk, and the presence of concomitant coronary or other valve disease, the Rating Panel determined that either surgical aortic valve replacement or transcatheter aortic valve replacement is appropriate in most patients with symptomatic AS at intermediate or high surgical risk; however, situations commonly arise in clinical practice in which the indications for surgical aortic valve replacement or transcatheter aortic valve replacement are less clear, including situations in which one form of valve replacement would appear reasonable when the other is less so, as do other circumstances in which neither intervention is the suitable treatment option. The purpose of this AUC is to provide guidance to clinicians in the care of patients with severe AS by identifying the reasonable treatment and intervention options available based on the myriad clinical scenarios with which patients present. This AUC document also serves as an educational and quality improvement tool to identify patterns of care and reduce the number of rarely appropriate interventions in clinical practice.

ACC/AATS/AHA/ASE/EACTS/HVS/SCA/SCAI/SCCT/SCMR/STS 2017 Appropriate Use Criteria for the Treatment of Patients With Severe Aortic Stenosis: A Report of the American College of Cardiology Appropriate Use Criteria Task Force, American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, European Association for Cardio-Thoracic Surgery, Heart Valve Society, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons

The American College of Cardiology collaborated with the American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, European Association for Cardio-Thoracic Surgery, Heart Valve Society, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons to develop and evaluate Appropriate Use Criteria (AUC) for the treatment of patients with severe aortic stenosis (AS). This is the first AUC to address the topic of AS and its treatment options, including surgical aortic valve replacement (SAVR) and transcatheter aortic valve replacement (TAVR). A number of common patient scenarios experienced in daily practice were developed along with assumptions and definitions for those scenarios, which were all created using guidelines, clinical trial data, and expert opinion in the field of AS. The 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines(1) and its 2017 focused update paper (2) were used as the primary guiding references in developing these indications. The writing group identified 95 clinical scenarios based on patient symptoms and clinical presentation, and up to 6 potential treatment options for those patients. A separate, independent rating panel was asked to score each indication from 1 to 9, with 1-3 categorized as "Rarely Appropriate," 4-6 as "May Be Appropriate," and 7-9 as "Appropriate." After considering factors such as symptom status, left ventricular (LV) function, surgical risk, and the presence of concomitant coronary or other valve disease, the rating panel determined that either SAVR or TAVR is Appropriate in most patients with symptomatic AS at intermediate or high surgical risk; however, situations commonly arise in clinical practice in which the indications for SAVR or TAVR are less clear, including situations in which 1 form of valve replacement would appear reasonable when the other is less so, as do other circumstances in which neither intervention is the suitable treatment option. The purpose of this AUC is to provide guidance to clinicians in the care of patients with severe AS by identifying the reasonable treatment and intervention options available based on the myriad clinical scenarios with which patients present. This AUC document also serves as an educational and quality improvement tool to identify patterns of care and reduce the number of rarely appropriate interventions in clinical practice.

Aortic Valve Bioprostheses: Leaflet Immobility and Valve Thrombosis

Leaflet immobility and valve thrombosis have been reported with both transcatheter and surgical aortic valve bioprostheses. The relationships between these abnormalities and their incidence, time course, clinical significance, predisposing factors, optimal imaging modality, and current therapeutic options remain uncertain but are rapidly evolving. Four-dimensional computerized tomographic imaging has been determined to have the highest sensitivity in studies evaluating leaflet immobility and valve thrombosis. Echocardiography is also used during surveillance, but it appears to be less sensitive. The definitive diagnosis of valve thrombosis is based on a combination of diagnostic 4-dimensional computerized tomographic imaging findings, resolution of imaging abnormalities, and elevated transcatheter gradients with anticoagulation or surgical or pathological confirmation. Uncertainty about the incidence and clinical significance of the findings is the basis of 2 US Food and Drug Administration-approved studies comparing transcatheter and surgical aortic valve replacement with a subset undergoing surveillance 4-dimensional computerized tomographic imaging. Given the expansion of transcatheter aortic valve procedures, including potentially lower-risk patients, the resolution of these uncertainties is critical.

The Fluid Mechanics of Transcatheter Heart Valve Leaflet Thrombosis in the Neosinus

BACKGROUND

Transcatheter heart valve (THV) thrombosis has been increasingly reported. In these studies, thrombus quantification has been based on a 2-dimensional assessment of a 3-dimensional phenomenon.

METHODS

Postprocedural, 4-dimensional, volume-rendered CT data of patients with CoreValve, Evolut R, and SAPIEN 3 transcatheter aortic valve replacement enrolled in the RESOLVE study (Assessment of Transcatheter and Surgical Aortic Bioprosthetic Valve Dysfunction With Multimodality Imaging and Its Treatment with Anticoagulation) were included in this analysis. Patients on anticoagulation were excluded. SAPIEN 3 and CoreValve/Evolut R patients with and without hypoattenuated leaflet thickening were included to study differences between groups. Patients were classified as having THV thrombosis if there was any evidence of hypoattenuated leaflet thickening. Anatomic and THV deployment geometries were analyzed, and thrombus volumes were computed through manual 3-dimensional reconstruction. We aimed to identify and evaluate risk factors that contribute to THV thrombosis through the combination of retrospective clinical data analysis and in vitro imaging in the space between the native and THV leaflets (neosinus).

RESULTS

SAPIEN 3 valves with leaflet thrombosis were on average 10% further expanded (by diameter) than those without (95.5±5.2% versus 85.4±3.9%; P<0.001). However, this relationship was not evident with the CoreValve/Evolut R. In CoreValve/Evolut Rs with thrombosis, the thrombus volume increased linearly with implant depth (R²=0.7, P<0.001). This finding was not seen in the SAPIEN 3. The in vitro analysis showed that a supraannular THV deployment resulted in a nearly 7-fold decrease in stagnation zone size (velocities <0.1 m/s) when compared with an intraannular deployment. In addition, the in vitro model indicated that the size of the stagnation zone increased as cardiac output decreased.

CONCLUSIONS

Although transcatheter aortic valve replacement thrombosis is a multifactorial process involving foreign materials, patient-specific blood chemistry, and complex flow patterns, our study indicates that deployed THV geometry may have implications on the occurrence of thrombosis. In addition, a supraannular neosinus may reduce thrombosis risk because of reduced flow stasis. Although additional prospective studies are needed to further develop strategies for minimizing thrombus burden, these results may help identify patients at higher thrombosis risk and aid in the development of next-generation devices with reduced thrombosis risk.

Choice of Balloon-Expandable Versus Self-Expanding Transcatheter Aortic Valve Impacts Hemodynamics Differently According to Aortic Annular Size

We sought to determine whether balloon-expandable valve (BEV) and self-expanding valve (SEV) affect valve hemodynamics differently according to native aortic annulus size. Transcatheter aortic valve replacement can achieve superior prosthetic valve hemodynamics compared with surgical aortic valve replacement, particularly in patients with small aortic annulus. One hundred ninety-three consecutive transcatheter aortic valve replacement patients were grouped into tertiles defined by computed tomography derived aortic annulus systolic perimeter. The predischarge echocardiogram was analyzed for prosthetic valve hemodynamics. Tertile perimeter cutoffs were 73 and 80 mm. STS score decreased as annulus size increased (7.8% vs 7.6% vs 6.0%, p ≤0.05 for small, medium, and large annulus, respectively). In patients with small aortic annulus, SEV was associated with significantly higher dimensionless index (0.64 vs 0.53, p = 0.02) and lower peak velocity (1.8 vs 2.4 m/sec, p <0.001) and a trend toward lower mean gradient (7.5 vs 10.0 mm Hg, p = 0.07) compared with BEV. These differences were attenuated and absent in patients with medium and large annulus, respectively. Few patients had moderate/severe paravalvular leak, with no association with valve type or annulus size. There was no difference in mortality between tertiles or valve type at 30 days or 1 year. There was no association between aortic annulus perimeter and 1-year mortality by univariate analysis (hazard ratio 1.00, 95% CI 0.95 to 1.05, p = 0.86) or multivariate analysis (hazard ratio 1.02, 95% CI 0.95 to 1.09, p = 0.60). In conclusion, SEV hemodynamics was superior to BEV in patients with small aortic annulus. This difference was diminished in patients with larger aortic annulus. This study highlights the importance of valve selection in patients with small aortic annulus.

Effect of transcatheter aortic valve size and position on valve-in-valve hemodynamics: An in vitro study

OBJECTIVE

Transcatheter heart valve implantation in failed aortic bioprostheses (valve-in-valve [ViV]) is an increasingly used therapeutic option for high-risk patients. However, high postprocedural gradients are a significant limitation of aortic ViV. Our objective was to evaluate Medtronic CoreValve Evolut R ViV hemodynamics in relation to the degree of device oversizing and depth of implantation.

METHODS

Evolut R devices of 23 and 26 mm were implanted within 21-, 23-, and 25-mm Hancock II bioprostheses. Small and gradual changes in implantation depth were attempted. Hemodynamic testing was performed in a pulse duplicator under ISO-5840 standard.

RESULTS

A total of 47 bench-testing experiments were performed. The mean gradient of the 26-mm Evolut R in 23- and 25-mm Hancock II was lower than 23-mm Evolut R (P < .001). However, the mean gradient of 26-mm Evolut R in 21-mm Hancock II bioprostheses R (ranging from 21.30 ± 0.23 to 24.30 ± 0.22 mm Hg) was worse than 23-mm Evolut R (ranging from 15.94 ± 0.18 to 20.35 ± 0.16 mm Hg, P < .001). Furthermore, our results suggest that supra-annular implantation of 23-mm and 26-mm Evolut R devices within the bioprostheses can lead to lower gradient and improved leaflet coaptation. Regardless of implantation depth, superior transvalvular gradient is expected with 26-mm Evolut R than 23-mm Evolut R in a nonstenotic Hancock II with a true internal diameter > 17.5 mm.

CONCLUSIONS

The current comprehensive bench-testing assessment demonstrates the importance of both transcatheter heart valve size and device position for the attainment of optimal hemodynamics during ViV procedures. Additional in vitro testing may be required to develop hemodynamics-based guidelines for device sizing in ViV procedures in degenerated surgical bioprostheses.

On the Mechanics of Transcatheter Aortic Valve Replacement

Transcatheter aortic valves (TAVs) represent the latest advances in prosthetic heart valve technology. TAVs are truly transformational as they bring the benefit of heart valve replacement to patients that would otherwise not be operated on. Nevertheless, like any new device technology, the high expectations are dampened with growing concerns arising from frequent complications that develop in patients, indicating that the technology is far from being mature. Some of the most common complications that plague current TAV devices include malpositioning, crimp-induced leaflet damage, paravalvular leak, thrombosis, conduction abnormalities and prosthesis-patient mismatch. In this article, we provide an in-depth review of the current state-of-the-art pertaining the mechanics of TAVs while highlighting various studies guiding clinicians, regulatory agencies, and next-generation device designers.

The Effect of Valve-in-Valve Implantation Height on Sinus Flow

Valve-in-valve transcatheter aortic valve replacement (VIV-TAVR) has proven to be a successful treatment for high risk patients with failing aortic surgical bioprostheses. However, thrombus formation on the leaflets of the valve has emerged as a major issue in such procedures, posing a risk of restenosis, thromboembolism, and reduced durability. In this work we attempted to understand the effect of deployment position of the transcatheter heart valve (THV) on the spatio-temporal flow field within the sinus in VIV-TAVR. Experiments were performed in an in vitro pulsatile left heart simulator using high-speed Particle Image Velocimetry (PIV) to measure the flow field in the sinus region. The time-resolved velocity data was used to understand the qualitative and quantitative flow patterns. In addition, a particle tracking technique was used to evaluate relative thrombosis risk via sinus washout. The velocity data demonstrate that implantation position directly affects sinus flow patterns, leading to increased flow stagnation with increasing deployment height. The particle tracking simulations showed that implantation position directly affected washout time, with the highest implantation resulting in the least washout. These results clearly demonstrate the flow pattern and flow stagnation in the sinus is sensitive to THV position. It is, therefore, important for the interventional cardiologist and cardiac surgeon to consider how deployment position could impact flow stagnation during VIV-TAVR.