Gradient and pressure recovery of a self-expandable transcatheter aortic valve depends on ascending aorta size: In vitro study.

Objective: In this study we aimed to understand the role of interaction of the Medtronic Evolut R transcatheter aortic valve with the ascending aorta (AA) by evaluating the performance of the valve and the pressure recovery in different AA diameters with the same aortic annulus size. Methods: A 26-mm Medtronic Evolut R valve was tested using a left heart simulator in aortic root models of different AA diameter (D): small (D = 23 mm), medium (D = 28 mm), and large (D = 34 mm) under physiological conditions. Measurements of pressure from upstream to downstream of the valve were performed using a catheter at small intervals to comprehensively assess pressure gradient and pressure recovery. Results: In the small AA, the measured peak and mean pressure gradient at vena contracta were 11.5 ± 0.5 mm Hg and 7.8 ± 0.4 mm Hg, respectively, which was higher (P < .01) compared with the medium (8.1 ± 0.4 mm Hg and 5.2 ± 0.4 mm Hg) and large AAs (7.4 ± 1.0 mm Hg and 5.4 ± 0.6 mm Hg). The net pressure gradient was lower for the case with the medium AA (4.1 ± 1.2 mm Hg) compared with the small AA (4.7 ± 0.8 mm Hg) and large AA (6.1 ± 1.4 mm Hg; P < .01). Conclusions: We have shown that small and large AAs can increase net pressure gradient, because of the direct interaction of the Medtronic Evolut R stent with the AA (in small AA) and introducing higher level of turbulence (in large AA). AA size might need to be considered in the selection of an appropriate device for transcatheter aortic valve replacement.

Effects of MitraClip Therapy on Mitral Flow Patterns and Vortex Formation: An In Vitro Study.

MitraClip transcatheter edge-to-edge repair is used to treat mitral regurgitation (MR). While MR is reduced, diastolic left ventricular flows are altered. An in vitro left heart simulator was used to assess a porcine mitral valve in the native, MR, and MR plus MitraClip cases. Velocity, vorticity, and Reynolds shear stress (RSS) were quantified by particle image velocimetry. Peak velocity increased from 1.20 m/s for native to 1.30 m/s with MR. With MitraClip, two divergent jets of 1.18 and 0.61 m/s emerged. Higher vorticity was observed with MR than native and lessened with MitraClip. MitraClip resulted in shear layer formation and downstream vortex formation. Native RSS decreased from 33 Pa in acceleration to 29 Pa at peak flow, then increased to 31 Pa with deceleration. MR RSS increased from 27 Pa in acceleration to 40 Pa at peak flow to 59 Pa during deceleration. MitraClip RSS increased from 79 Pa in acceleration to 162 Pa during peak flow, then decreased to 45 Pa during deceleration. After MitraClip, two divergent jets of reduced velocity emerged, accompanied by shear layers and recirculation. Chaotic flow developed, resulting in elevated RSS magnitude and coverage. Findings help understand consequences of MitraClip on left ventricular flow dynamics.

Multiple MitraClips: The balancing act between pressure gradient and regurgitation.

OBJECTIVE: Transcatheter mitral valve repair with the MitraClip is used for the symptomatic management of mitral regurgitation (MR). The challenge is reducing MR while avoiding an elevated mitral valve gradient (MVG). This study assesses how multiple MitraClips used to treat MR can affect valve performance. METHODS: Six porcine mitral valves were assessed using an in vitro left heart simulator in the native, moderate-to-severe MR, and severe MR cases. MR cases were tested in the no-MitraClip, 1-MitraClip, and 2-MitraClip configurations. Mitral regurgitant fraction (MRF), MVG, and effective orifice area (EOA) were quantified. RESULTS: Native MRF, MVG, and EOA were 14.22%, 2.59 mm Hg, and 1.64 cm2, respectively. For moderate-to-severe MR, MRF, MVG, and EOA were 34.07%, 3.31 mm Hg, and 2.22 cm2, respectively. Compared with the no-MitraClip case, 1 MitraClip decreased MRF to 18.57% (P < .0001) and EOA to 1.50 cm2 (P = .0002). MVG remained statistically unchanged (3.44 mm Hg). Two MitraClips decreased MRF to 14.26% (P < .0001) and EOA to 1.36 cm2 (P = .0001). MVG remained unchanged (3.29 mm Hg). For severe MR, MRF, MVG, and EOA were 59.79%, 4.98 mm Hg, and 2.73 cm2, respectively. Compared with the no-MitraClip case, 1 MitraClip decreased MRF to 30.72% (P < .0001) and EOA to 1.82 cm2 (P < .0001); MVG remained unchanged (4.03 mm Hg). MVG remained statistically unchanged. Two MitraClips decreased MRF to 23.10% (P < .0001) and EOA to 1.58 cm2 (P < .0001); MVG remained statistically unchanged (3.82 mm Hg). Both MR models yielded no statistical difference between 1 and 2 MitraClips. CONCLUSIONS: There is limited concern regarding elevation of MVG when reducing MR using 1 or 2 MitraClips, although 2 MitraClips did not significantly continue to reduce MRF.

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.

Transcatheter Heart Valves: A Biomaterials Perspective.

Heart valve disease is prevalent throughout the world, and the number of heart valve replacements is expected to increase rapidly in the coming years. Transcatheter heart valve replacement (THVR) provides a safe and minimally invasive means for heart valve replacement in high-risk patients. The latest clinical data demonstrates that THVR is a practical solution for low-risk patients. Despite these promising results, there is no long-term (>20 years) durability data on transcatheter heart valves (THVs), raising concerns about material degeneration and long-term performance. This review presents a detailed account of the materials development for THVRs. It provides a brief overview of THVR, the native valve properties, the criteria for an ideal THV, and how these devices are tested. A comprehensive review of materials and their applications in THVR, including how these materials are fabricated, prepared, and assembled into THVs is presented, followed by a discussion of current and future THVR biomaterial trends. The field of THVR is proliferating, and this review serves as a guide for understanding the development of THVs from a materials science and engineering perspective.

Development of Tissue Engineered Heart Valves for Percutaneous Transcatheter Delivery in a Fetal Ovine Model.

This multidisciplinary work shows the feasibility of replacing the fetal pulmonary valve with a percutaneous, transcatheter, fully biodegradable tissue-engineered heart valve (TEHV), which was studied in vitro through accelerated degradation, mechanical, and hemodynamic testing and in vivo by implantation into a fetal lamb. The TEHV exhibited only trivial stenosis and regurgitation in vitro and no stenosis in vivo by echocardiogram. Following implantation, the fetus matured and was delivered at term. Replacing a stenotic fetal valve with a functional TEHV has the potential to interrupt the development of single-ventricle heart disease by restoring proper flow through the heart.

Fetal Transcatheter Trileaflet Heart Valve Hemodynamics: Implications of Scaling on Valve Mechanics and Turbulence.

The scarcity of data available on the best approach for pulmonary fetal valve replacement or implantation necessitate an investigation on whether practices using adult transcatheter valves could be translated to fetal applications. The objective of this study is to evaluate the hemodynamic characteristics and the turbulent properties of a fetal sized trileaflet transcatheter pulmonary valve in comparison with an adult balloon-expandable valve in order to assess the possibility of designing valves for fetal applications using dynamic similarity. A 6 mm fetal trileaflet valve and a 26 mm SAPIEN 3 valve were assessed in a pulse duplicator. Particle image velocimetry was performed. Pressure gradient (ΔP), effective orifice area (EOA), regurgitant fractions (RF), pinwheeling indices (PI) and turbulent stresses were evaluated. ΔP was 8.56 ± 0.139 and 7.76 ± 0.083 mmHg with fetal valve and SAPIEN respectively (p < 0.0001); EOA was 0.10 ± 0.0007 and 2.1 ± 0.025 cm2 with fetal valve and SAPIEN respectively (p < 0.0001); RF with the fetal valve was 2.35 ± 1.99% and with SAPIEN 10.92 ± 0.11% (p < 0.0001); PI with fetal valve was 0.404 ± 0.01 and with SAPIEN 0.37 ± 0.07; The flow regime with the fetal valve was turbulent and Reynolds numbers reached about 7000 while those with the SAPIEN reached about 20,000 at peak velocity. Turbulent stresses were significantly higher with fetal valve compared with SAPIEN. Instantaneous viscous shear stresses with fetal valve were 5.8 times higher than those obtained with SAPIEN and Reynolds shear stresses were 2.5 times higher during peak systole. The fetal valve implantation leads to a turbulent flow (specific to this particular type and design of valve) regime unlike what is expected of a small valve with different flow properties compared to adult valves.