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

Prediction of hypoattenuating leaflet thickening in patients underwent transcatheter aortic valves replacement based on clinical factors and 4D-computed tomography morphological characteristics: A retrospective cross-sectional study

BACKGROUND

The rapid increase in the number of transcatheter aortic valve replacement (TAVR) procedures in China and worldwide has led to growing attention to hypoattenuating leaflet thickening (HALT) detected during follow-up by 4D-CT. It's reported that HALT may impact the durability of prosthetic valve. Early identification of these patients and timely deployment of anticoagulant therapy are therefore particularly important.

METHODS

We retrospectively recruited 234 consecutive patients who underwent TAVR procedure in Fuwai Hospital. We collected clinical information and extracted morphological characteristics parameters of the transcatheter heart valve (THV) post TAVR procedure from 4D-CT. LASSO analysis was conducted to select important features. Three models were constructed, encapsulating clinical factors (Model 1), morphological characteristics parameters (Model 2), and all together (Model 3), to identify patients with HALT. Receiver operating characteristic (ROC) curves and decision curve analysis (DCA) were plotted to evaluate the discriminatory ability of models. A nomogram for HALT was developed and verified by bootstrap resampling.

RESULTS

In our study patients, Model 3 (AUC = 0.738) showed higher recognition effectiveness compared to Model 1 (AUC = 0.674, p = 0.032) and Model 2 (AUC = 0.675, p = 0.021). Internal bootstrap validation also showed that Model 3 had a statistical power similar to that of the initial stepwise model (AUC = 0.723 95%CI: 0.661-0.786). Overall, Model 3 was rated best for the identification of HALT in TAVR patients.

CONCLUSION

A comprehensive predictive model combining patient clinical factors with CT-based morphology parameters has superior efficacy in predicting the occurrence of HALT in TAVR patients.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Effect of Leaflet Type and Leaflet-Stent Attachment Height on Transcatheter Aortic Valve Leaflet Thrombosis Potential

Transcatheter aortic valve replacement devices vary in leaflet material and in the height for which leaflets attach to the stented valve frame. Combinations of these features can influence leaflet dynamics, neo-sinus geometries, and fluid dynamics, thereby reducing or exacerbating the potential for blood flow stasis and leaflet thrombosis. To investigate these interconnected relationships, this study evaluated the effects of transcatheter valve leaflet type (porcine vs. bovine pericardium) and the leaflet-stent attachment height (low, mid, and high) on flow stasis and potential for leaflet thrombosis. Transcatheter valve models were manufactured and tested within an aortic simulator under pulsatile left heart hemodynamic conditions. Transvalvular hemodynamics, leaflet kinematics, and flow structures were evaluated by direct measurement, high-speed imaging, and two differing techniques of particle image velocimetry. Transcatheter valves with porcine pericardial leaflets were observed to be less stiff, exhibit a lesser resistance to flow, were associated with reduced regions of neo-sinus flow stasis, and superior sinus washout times. More elevated attachments of the leaflets were associated with less neo-sinus flow stasis. These initial results and observations suggest combinations of leaflet type and stent attachment height may reduce transcatheter aortic valve flow stasis and the potential for leaflet thrombosis.

Impact of calcific aortic valve disease on valve mechanics

The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of forward and reverse flow patterns. Calcific aortic valve disease (CAVD) resulting in compromised valve function and increased pressure overload on the ventricle potentially leading to heart failure if untreated, is the most predominant valve disease. CAVD is a multi-factorial disease involving molecular, tissue and mechanical interactions. In this review, we aim at recapitulating the biomechanical loads on the aortic valve, summarizing the current and most recent research in the field in vitro, in-silico, and in vivo, and offering a clinical perspective on current strategies adopted to mitigate or approach CAVD.

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

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