The investigation of systolic and diastolic leaflet kinematics of bioprostheses with a new in-vitro test method.

OBJECTIVES: We aimed to investigate leaflet kinematics of bioprostheses with a novel high-speed imaging method. MATERIAL AND METHODS: High-speed-imaging (1000 Hz) was used to evaluate leaflet kinematics of the Carpentier-Edwards Perimount Magna (PM) and Magna Ease (PME) aortic bioprostheses. Both prostheses (diameter 23 mm) were placed inside a model aorta under pulsatile flow conditions. Frequencies (F) and different stroke volumes (S) were simulated. Maximum aortic valve area (AVA), total ejection time (TET), rapid valve opening time (RVOT) and rapid valve closing time (RVCT) as well as opening (OS) and closing (CS) speeds were evaluated. RESULTS: Both bioprostheses showed different results dependent on flow conditions. The test setup was capable of identifying small AVA-differences between both valves (235 vs. 202 mm², F60/S60; 272 vs. 207 mm²; F70/S80), as well as differences in OS and CS (2.36 vs. 1.62 mm²/ms; 2.97 vs. 2.44 mm²/ms, F80/S60). TET was comparable (638 vs. 645 ms F60/S60; 341 vs. 343 ms, F90/S60), while results for RVOT and RVCT were equal, and dependent on frequency and stroke volume. CONCLUSIONS: The novel evaluation method is sensitive to detect differences between valves, although differences were found to be small. PM has a larger visible AVA associated with higher opening and closing speeds in contrast to PME.

Comparison of flow dynamics of Perimount Magna and Magna Ease aortic valve prostheses.

The aim of the present study was to evaluate and compare the in vitro and flow dynamics of the Magna (MB) and the Magna Ease aortic valve bioprosthesis (MEB) within the ascending aorta. A 2D-particle-image-velocimetry (2D-PIV) study was performed to compare the flow dynamics induced by each pericardial Carpentier-Edwards Magna and Magna Ease aortic valve prosthesis in the aortic flow field directly behind the valve. Both prostheses (diameter 23 mm) were placed inside an artificial aorta under pulsatile flow conditions (70 Hz and 70 ml stroke volume). The flow field was evaluated according to velocity, shear strength, and vorticity. Both prostheses showed a jet flow type profile with a maximum velocity of 0.97±0.09 m/s for MB and 0.83±1.8 m/s for MEB. Flow fields of both valves were similar in acceleration, peak flow deceleration and leakage phase. Maximum shear strength was 20,285±11,774 l/s2 for MB and 17,006±8453 l/s2 for MEB. Vorticity was nearly similar for counterclockwise and clockwise rotation in both prostheses, but slightly higher with MB (251±41 l/s and -250±39 l/s vs. 225±48 l/s and -232±48 l/s). The point-of-interest (POI)-analysis revealed a higher velocity for left-sided aortic wall compared to right-sided at MB (0.12±0.09 m/s vs. 0.18±0.10 m/s, p<0.001), but was consistent at MEB (0.09±0.05 m/s vs. 0.08±0.04 m/s, p=0.508), respectively. Velocity, shear strength and vorticity in an in vitro test set-up are lower with MEB compared to MB, thus resulting in improved flow dynamics with a similar flow field, which might have a positive influence on blood rheology and potential valve degeneration.

Development and in vitro characterization of a new artificial flow channel.

To date, cardiac valve diseases are considered as a major public health problem and most frequently, the aortic valve is affected. To treat high-risk patients, catheter-based techniques have been developed recently, avoiding open heart surgery and/or cardiopulmonary bypass. Although these sophisticated and rapidly emerging catheter-based technologies do allow a minimally invasive treatment option of high-risk patients on the one hand, further developments and in vitro testing under physiological conditions are necessary, on the other hand, in order to further optimize them for clinical routines. Therefore, we present the concept of a new multifunctional flow channel, offering (i) the possibility of transapical access; (ii) the simulation of physiological flow conditions; and (iii) the evaluation of the fluid flow by 2D particle image velocimetry within a wide range of parameters.

Numerical simulation of hemodynamics in the ascending aorta induced by different aortic cannulas.

There is still a lack of quantitative information concerning optimal blood flow in the aorta and in the carotid arteries during extracorporeal circulation (ECC). Problems are not only based on the location of the aortic cannula, they are furthermore associated with the cannula design itself and the effects on blood cells and aortic wall shear stresses. We simulated a two-phase fluid flow induced by different cannulas in the ascending aorta during ECC. Three commercially available cannulas were examined according to their influence on red blood cells (RBC). Additionally, mass flow in the carotid vessels and wall shear stresses acting on the aortic wall were evaluated. A constant volume flow of blood (3.4 L/min) was applied. Numerical results demonstrate a strong relation between the mass flow rate in the carotid vessels and the geometry of the aortic outflow cannula. RBC distributions both in the aorta and the carotid vessels changed depending on cannula geometry. Maximum blood velocities, shear stresses on the aortic wall, and the fluid mechanical load acting on RBCs varied depending on each cannula design. This numerical approach demonstrates the significant influence of the cannula design on the distribution of RBCs in the carotid vessels during ECC.

In-vitro investigation of the hemodynamics of the Edwards Sapien transcatheter heart valve.

BACKGROUND AND AIM OF THE STUDY: The study aim was to evaluate the hemodynamic performance of the Sapien transcatheter heart valve (THV) in the ascending aorta, and its influence on the aortic wall in an in-vitro set-up. METHODS: A two-dimensional particle image velocimetry (2D-PIV) study was conducted to evaluate the hemodynamic performance of the Edwards Sapien THV in the aortic flow field (image rate 15 Hz). The prosthesis (diameter 23 mm) was placed inside a mock aorta under pulsatile flow conditions. The velocities, shear strength, vorticity and strain rate were obtained and calculated with a fixed frequency (70 Hz) at constant stroke volume (70 ml). RESULTS: The Sapien THV showed a jet flow-type profile with a maximum velocity of 0.87 +/- 0.16 m/s during peak flow phase (PFP). The jet flow was surrounded by ambilateral vortices with a higher percentage of counterclockwise than clockwise vorticity (335 +/- 66/s versus 277 +/- 44.1/s), analogous to the strain rate (261 +/- 55/s for elongation versus -168 +/- 25/s for contraction). The maximum shear strength was 26,284 +/- 11,550/s2, while the point-of-interest analysis revealed a higher velocity for the bottom aortic wall compared to the upper aortic wall (0.25 +/- 0.05 m/s versus 0.30 +/- 0.04 m/s; p = 0.014). All values were lower during the acceleration and deceleration phases compared to PFP. CONCLUSION: The peak flow of the Sapien THV seems to be slightly higher than that of the native aortic valve, thus imitating near-physiological conditions. That the shear strength, vorticity and strain rate were high during peak flow phase, but low during other phases, might also have an influence on the aortic wall.

Fluid Dynamic Investigation of the ATS 3F Enable Sutureless Heart Valve.

OBJECTIVE: : Currently, sutureless heart valves (SHV) reveal good clinical results during aortic valve replacement. The aim of this study was to evaluate the fluid dynamics of the ATS 3F Enable SHV in the ascending aorta and their influence on the aortic wall in an in vitro setup. METHODS: : A two-dimensional particle image velocimetry study with an image rate of 15 Hz was conducted to evaluate the fluid dynamics of the SHV in the aortic flow field. The prosthesis (diameter, 23 mm) was placed inside a silicone mock aorta under pulsatile flow conditions. Velocities, vorticity, and strain rate were obtained and calculated with a fixed frequency (70 Hz) at constant stroke volume (70 mL). RESULTS: : 3F Enable showed a jet flow type profile with a maximum velocity of 1.01 ± 0.13 m/s during peak flow phase (PFP). The jet flow was surrounded by ambilateral vortices with a slightly higher percentage of clockwise than counterclockwise vorticity (377 ± 57/s vs 389 ± 76/s), strain rate (370 ± 79/s for elongation vs -370 ± 102/s for contraction) was nearly similar. The point-of-interest analysis revealed a higher velocity for bottom compared with upper aortic wall (0.28 ± 0.07 m/s vs 0.31 ± 0.06 m/s, P = 0.024). All values were lower during acceleration and deceleration phase compared with PFP. CONCLUSIONS: : The peak flow of the 3F Enable SHV seems to be little higher compared with native aortic valves, thus simulating nearly physiologic conditions. Vorticity and strain rate are high during PFP and low during other phases and might have an influence on the aortic wall as well.

Cutting precision in a novel aortic valve resection tool. Research in progress.

BACKGROUND: We recently demonstrated the first in-vitro cutting results of a minimal-invasive aortic valve resection tool. The current study was designed to assess the cutting accuracy of this new device improved by the implementation of a linear motor-based propulsion unit. METHODS: Native aortic valves of isolated swine hearts (valve diameter 17.8+/-0.9 mm, mean+/-S.D.) were artificially stenosed and calcified (n=7). Subsequently, valves were resected by the use of a new aortic valve resection tool. The cutting process was performed by fitting the instrument with foldable Nitinol cutting blades (diameter 15 mm) and two software-operated linear motors combined with separated manual rotation. Aortic valve area was measured pre- and postprocedure by software-guided binary area calculation. Aortic valve residue has been determined and the grade of accuracy has been assessed via calculating the average midpoint of the neoannulus. Furthermore, radial deviation of concentricity was calculated and cutting time was measured. RESULTS: Aortic valve resection was successful in all cases and nearly all leaflets (2.5+/-0.4) with a weight of 0.22+/-0.12 g were cut. Aortic valve area increased significantly (0.3+/-0.1 cm(2) vs. 1.1+/-0.2 cm(2), P<0.001) with a mean cutting time of 49.7+/-15.0 s. Mean lateral leaflet rim within the annulus was 3.2+/-3.2 mm. Cutting precision revealed a median deviation of the cutting ring from the desired position of 1.3+/-0.6 mm (y-axis) and 1.4+/-0.5 mm (x-axis). Median center deviation of the cutting ring was 2.6+/-0.8 mm. CONCLUSIONS: The present study clearly confirmed ability of an accelerated cutting of stenotic aortic valve by the aortic valve resection tool. Nearly all leaflets were cut and a small rim was left within the annulus, hence providing an ideal 'landing zone' for the new prosthesis. Nevertheless, the aortic valve resection tool should be enhanced by adding a centering mechanism, thus achieving a more precise cutting process in order to avoid secondary damage.

A new tool for the resection of aortic valves: In-vitro results for turning moments and forces using Nitinol cutting edges.

The use of minimally invasive techniques for aortic valve replacement (AVR) may be limited for severely calcified and degenerated stenotic aortic valves. A quick resection leaving a defined geometry would be advantageous. Therefore, a new minimally invasive resection tool was developed, using rotating foldable cutting edges. This report describes the first experimental in-vitro results of measuring turning moment and forces during cutting of test specimens. Nitinol cutting edges were mounted on a simplified version of the resection instrument. The instrument shaft was combined with an exchangeable gear (1:3.71 vs. 1:5.0), and an exchangeable screw thread for accurate feed motion (0.35 mm or 0.5 mm) was implemented. Furthermore, the option of an added stabilisation body (SB) to prevent strut-torsion during cutting was tested. Tests were performed upon specially designed test specimens, imitating native calcified aortic valves. Resection was successful in all 60 samples (12 samples for each of the five configurations). Mean resection time ranged from 18.7+/-1.0 s (gear 1:3.71, screw thread 0.5, with SB) to 29.3+/-4.6 s (gear 1:5, screw thread 0.35, with SB), mean maximum turning moment ranged from 2.1+/-0.2 Nm (gear 1:3.71, screw thread 0.35, with SB) to 2.8+/-0.4 (gear 1:5, screw thread 0.35, with SB), mean maximum force from 36.0+/-11.3 N (gear 1:3.71, screw thread 0.35, with SB) to 56.3+/-10.5 N (gear 1:3.71, screw thread 0.5, without SB) and mean number of required rotations from 41.3+/-2.9 (gear 1:3.71, screw thread 0.5, with SB) to 59.1+/-3.7 (gear 1:3.71, screw thread 0.35, without SB). In summary, the positive influence of the stabilisation body could be shown. Combining the right parameters, it is possible to limit maximum cutting forces to F(max)<50 N and maximum turning moments to M(max)< 3.0 N.

NiTinol-based cutting edges for endovascular heart valve resection: first in-vitro cutting results.

Machining of shape memory alloys based on Nitinol (NiTi) creates difficulties due to its ductility and severe strain hardening. In this experiment, different cutting edges and grinding parameters were tested to optimize cutting results on NiTi-based blades intended for endovascular heart valve resection. The cutting procedure was performed using two counter-rotating circular NiTi blades of different diameter. A rotating/punching process should be performed. Different shapes (glazed, waved, and saw tooth), different grinding techniques (manual, manual grinder, and precise milling cutter) and additionally various velocities (50 and 200 rpm) were tested on specific test specimens. Cutting forces were measured and cutting quality was examined using digital microscopy. Preliminary tests with rotating blades showed superior results using cutting edges for the punching process (150 N vs. 200 N; n=7). In a second step special test specimens were tested. Maximum cutting-force was 265 N+/-20 N (mean+/-SD; n=7). Subsequently different shapes were tested at 50 and 200 rpm using the rotating/punching method regarding alternate grinding techniques. Cutting forces were 27 N+/-7.7 N for glazed blades (n=7) at 50 rpm and 18 N+/-4.7 N at 200 rpm, waved blades (n=7) required a maximum force of 18 N+/-5 N at 50 rpm and 11 N+/-3.3 N at 200 rpm, whereas saw tooth blades (n=7) needed 17 N+/-12.7 N at 50 rpm and 9 N+/-1.2 N at 200 rpm. Precise cutting quality was only seen when using glazed blades sharpened under accurate conditions with a high-speed milling cutter. Although shape memory alloys based on Nitinol are difficult to process, and well-defined grinding parameters do not exist, acceptable results can be reached using high-speed milling cutters. Best cutting quality can be observed by using glazed blades, performing a rotating/punching process at high velocities. Lower cutting forces can be observed by using other shape-types, however this leads to lower cutting quality. Therefore, further investigations on blade-machining and velocity-testing seem to be necessary to create optimal cutting results.