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Highlights. Using ECHO and MSCT data, a numerical assessment of hemodynamic effects of paraprosthetic regurgitation following transcatheter aortic valve replacement was performed. A significant increase in the fluid flow, wall and viscous shear stresses in the area of regurgitation is shown. The modeling technique described in the paper can be used prospectively in assessing the optimal treatment modality in terms of predicting the quantitative characteristics of the flow, associated with the risks of destruction of red blood cells and thrombosisAim. To make a numerical assessment of hemodynamic effects of paraprosthetic regurgitation following transcatheter aortic valve replacement based on retrospective clinical data.Methods. The study included echocardiography and multi-slice computed tomography data as input data for modeling one pulsation of a fluid similar in properties to blood. Reconstruction of the paraprosthetic fistula and the ascending aorta was performed in the Mimics medium (Materialise, Belgium). The obtained 3D models were processed in the Salome software (OPEN CASCADE SAS, France), after which they were exported to HELYX-OS (ENGYS, Great Britain) to build a finite element mesh. The flows were modeled using the OpenFOAM software package version 6 (The OpenFOAM Foundation Ltd, UK).Results. The simulation result, expressed quantitatively and qualitatively in the form of diagrams of the measured parameters – fluid flow velocities, wall and viscous shear stresses, shows a significant increase in indicators in the area of paraprosthetic regurgitation. Thus, the velocity in the affected area was 1.9–4.2 m/s, which is 3.8 higher than the average value in the entire computational area. The wall shear stress value was up to 61 Pa in the critical area, which may indicate an increased risk of thrombus formation due to the initiation of the clotting cascade through the von Willebrand factor. The value of viscous shear stress, the main component of the destruction of red blood cells in laminar flow, amounted to 20–26 Pa, which, in general, is not enough for mechanical hemolysis.Conclusion. The modeling technique described in the paper can be used prospectively in assessing the optimal treatment modality in terms of predicting the quantitative characteristics of the flow, associated with the risks of destruction of red blood cells and thrombosis.

Highlights. Non-invasive method for the assessment of the mobility and deformation of the wire element of the bioprosthesis in the cardiac cycle based on the developed mathematical algorithm is presented. Numerical analysis of the behavior of the wire element of the “TiAra” bioprosthesis is shown for the first time. The developed method can be used for other medical devices as well.Aim. To develop a method for non-invasive assessment of the mobility and deformation of the wire element of the aortic heart valve bioprosthesis in the cardiac cycle based on mathematical processing of visual medical data.Methods. Multidetector computed tomography data of patient P. (male, 66 years old), who received the “TiAra” aortic bioprosthesis (NeoCor CJSC, Kemerovo), were used for the study. Using the built-in tools in the Mimics Medical Image Processing Software (Materialize, Belgium), based on the radio density, 5 stages of movement of the wire element of the bioprosthesis were reconstructed in the form of 3D-models. The differences between the models, characterizing deformation in the cardiac cycle, were quantitatively assessed using a proprietary Matlab algorithm (The MathWorks, USA), calculating the distance between similar points. Moreover, obtained data on displacements was used in the numerical study of the stress-strain state of a 3D-model of the wire element by the finite element method in the Abaqus/CAE software (Dassault Systèmes SE, France).Results. The proposed method for assessing the mobility of the wire element made it possible to quantitatively evaluate the biomechanics of the “TiAra” stentless bioprosthesis based on multidetector computed tomography, a non-invasive clinical tool. The movements that the bioprosthesis undergoes during the cardiac cycle (the maximum value is 2.04 mm in the radial direction) are comparable to the movement of the aortic root of a healthy patient. The results of the numerical modeling of the stress state of the wire element did not indicate high amplitudes (peak value – 564 MPa) that would be capable of causing critical damage to the wire. It allows us to confirm the clinical safety of the bioprosthesis in real conditions like asymmetric and uneven loads. Moreover, deformations observed in the bioprosthesis are similar in the amplitude to the displacements of the aortic root described in the literature, which highlights the main feature of the bioprosthesis – ensuring the physiological biomechanics throughout the cardiac cycle.Conclusion. The presented method of qualitative computer assessment of the movement of the wire element of heart valve prosthesis using the “TiAra” bioprosthesis as an example demonstrates its validity as a tool for studying prosthesis functioning.

Highlights. With the use of numerical optimization algorithms, it is possible to qualitatively improve the performance (closing) of the leaflet apparatus of the heart valve prosthesis. Changing the length of the free edge of the lealflet of the prosthesis does not reduce the von Misess stress amplitude and does not change the nature of its distribution on the diagrams.Aim. Numerical study of the stress-strain state of a clinical heart valve prosthesis from the point of view of the impact of physiological loads and determination of ways to optimize the geometry of the biological leaflet apparatus.Methods. The object of study was a three-dimensional model of the UniLine (NeoCor, Russia) clinical prosthesis of the heart valve, size 23 mm, as well as four modifications focused on changing the length of the free edge. The study was carried out using the finite element method with imitation of the full cycle of operation of the leaflet apparatus under physiological conditions (pressure, heart rate). The parameters for the analysis were the qualitative and quantitative characteristics of the stress-strain state of the work of the five studied geometries.Results. It is shown that high stress areas are concentrated in two zones peripheral and free edges, regardless of the geometry. However, quantitatively, the von Mises stress amplitudes differed between the studied models. For example, the leaf shape, conventionally designated as “–10” degrees, demonstrated the smallest amplitude of this indicator relative to the original unmodified leaf model, thus reducing by a maximum of 18.8%. However, for the closed state, this model, on the contrary, showed an increase in the voltage index relative to the initial one by 8.3%. Other modification options showed similar trends.Conclusion. It is shown that despite the initial premise for optimizing the leaflet apparatus – reducing the length of the free edge and eliminating deformations of the closed state, the proposed geometry options did not significantly change the stress distribution map in the material, and also did not allow to significantly reduce the amplitudes of this parameter. Presumably, options for modifying the geometry and/or properties (rigidity, mobility) of another important component of the bioprosthesis, the support frame, which, in addition to the bearing function, provides damping of the hydrodynamic impact on the leaf due to some of its mobility, may become more promising.

A biocompatible thermoelastoplastic, poly(styrene-block-isobutylene-block-styrene), was incorporated with carbon nanotubes. The resulting nanocomposites containing 1, 2, and 4% filler were analyzed by optical microscopy and scanning electronic microscopy, and their strength, elastic-strain properties, contact angle with water, and electrical conductivity were evaluated. Partial heterogeneity in the nanofiller distribution in the macromolecular matrix was revealed. With an increase in the nanotube concentration, the tensile strength increases nonlinearly and the extension ability decreases. Statistically significant differences in the contact angle between the control samples and samples containing 4% carbon nanoparticles were revealed (94.1°± 1.7°and 84.4°± 2.3°, respectively). The electrical conductivity of the samples increases with an increase in the content of nanoparticles. The possibility and conditions of preparing the new promising material for cardiovascular surgery were determined.

The study is devoted to numerical modeling of transcatheter aortic valve implantation (TAVI) from the position of prognostic value in comparison with clinical data. The finite element method implemented in the Abaqus/CAE software and the reconstruction of three-dimensional models based on the computer microtomography of the CoreValve bioprosthesis of a size of 29 mm and the patient-specific data of functional studies (multispiral tomography) were used in the work. The study included three variations in the modeling of the aortic valve prosthesis procedure, which determine the level of detalization of the numerical experiment. All stages of the TAVI process were reproduced: the crimp of the prosthesis, the movement of the delivery system, the interaction of the guide - guidewire with the elements of the “prosthesis-root” of the aorta system, implantation itself. In silico experiment demonstrated significant quantitative and qualitative agreement with the data of intraoperative fluorography and computed tomography after the TAVI procedure. It is shown that the inclusion of additional elements – the guidewire and catheter of the delivery system into the “aortic root” has a positive effect on the convergence of the data with the clinical results. The analysis of the stress-strain state of the elements interacting in the experiment demonstrated a significant contribution to the analyzed parameters of the prosthetic motion stage along the guidewire as part of the delivery system catheter. Nevertheless, a comparison with the results of the clinical evaluation of the TAVI procedure revealed a number of differences in the response of the model of the bioprosthesis at the later stages of modeling, which requires further researches of a level of detalization. The approach is extremely promising both for practitioners and for research work of prosthetic designers, it can be applied in further R&D tasks.

Aim. We analysed the geometry and dynamics of the annulus fibrosus of the mitral valve in normal conditions, with mitral regurgitation of degenerative and ischaemic aetiology based on three-dimensional echocardiography with subsequent mathematical processing.Methods. We included the data of transesophageal three-dimensional echocardiography of 50 patients in the following three groups: 10 patients with degenerative regurgitation, 10 patients with ischaemic mitral regurgitation and 30 patients in the ‘normal’ group without mitral valve pathology. Transesophageal echocardiography was performed using an iE33 expert level equipment (Philips, USA), to quantitatively analyse the anterior-posterior diameter, anterolateral-posterior median diameter, intercommissural diameter, three-dimensional circumference of mitral valve, two-dimensional height of the coaptation zone, leaf height, maximum height, front and back angles of the valves, nonplanar angle, planarity coefficient and ellipticity coefficient. The measurements were performed for both the phases of the cardiac cycle, the period of expulsion of systole and the period of diastole filling, corresponding to the closed and open states of the valve. In addition, the treated data sets were processed in the QLAB programme (Philips, USA) where sets of points describing the geometry of the mitral valve were obtained. Thereafter, we used the in-house algorithm in the MATLAB R2015a environment (MathWorks, Massachusetts, USA). Mathematical models of the anatomy of the annulus rings were obtained for all the three studied groups.Results. A functional study of the mitral valve showed a similar nature of changes in the geometric features of the annulus fibrosus for both the pathologies. The dynamic performance of the fibrous rings during systole-diastole cycle significantly differed among the studied groups. We present the equations for the averaged models of the annulus fibrosus of the groups analysed in the study that can be used in design, verification and computer modelling problems.Conclusion. Pathological changes in the geometry of the mitral valve during ischaemic and degenerative regurgitation work on a similar principle, although there are aetiological differences. However, these pathologies differ when the changes in the geometry of the dynamics of ‘systole-diastole’ are analysed that warrant the use of different approaches and devices for their correction.Received 5 November 2020. Revised 12 December 2020. Accepted 22 December 2020.Funding: The work is supported by a grant of the President of the Russian Federation No. 075-15-2020-067.Conflict of interest: Authors declare no conflict of interest.Author contributionsConception and study design: E.A. Ovcharenko, L.S. BarbarashData collection and analysis: K.Yu. Klyshnikov, I.N. Sizova, N.V. KondyukovaStatistical analysis: K.Yu. KlyshnikovDrafting the article: E.A. Ovcharenko, K.Yu. KlyshnikovCritical revision of the article: E.A. Ovcharenko, K.Yu. Klyshnikov, I.N. Sizova, N.V. KondyukovaFinal approval of the version to be published: E.A. Ovcharenko, K.Yu. Klyshnikov, I.N. Sizova, N.V. Kondyukova, L.S. Barbarash

Sutureless implantation of the mitral valve bioprosthesis using the valve-in-valve method was performed on a large animal (sheep). According to the results of a two-stage implantation (primary implantation of a xenopericardial 26-mm framed bioprosthesis and reimplantation of the developed 23-mm bioprosthesis), minor changes in quantitative indicators were revealed: an increase in the transprosthetic gradient by 1.3 mm Hg and a decrease in the area of the mitral orifice by 21.6%. Considerable reduction in the intervention time by 18 min was achieved (by 40% in comparison with the primary prosthesis). The absence of adverse events in the animal and complications in the post-operative period, as well as physiological hemodynamic indicators indicate the safety of the developed medical device.

Aim: to evaluate the biomechanical remodeling of polymer grafts modified with vascular endothelial growth factor (VEGF) after implantation into rat abdominal aorta.Materials and methods. Vascular grafts of2 mmdiameter were fabricated by electrospinning from polycaprolactone (PCL) and a mixture of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and PCL. The grafts were modified with VEGF by biphasic electrospinning. Morphology of the grafts was assessed by scanning electron microscopy. Physico-mechanical properties of PCL and PHBV/PCL grafts were estimated using uniaxial tensile test and physiological circulating system equipped with state-of-theart ultrasound vascular wall tracking system. Physico-mechanical testing of PCL/VEGF and PHBV/PCL/VEGF was performed before and after implantation into rat abdominal aorta for 6 months. The modeling of coronary artery bypass grafting (CABG) was performed by finite element analysis for modified grafts.Results. Durability of PCL and PHBV/PCL grafts did not differ from that of human internal mammary artery; however, elasticity and stiffness of these grafts were higher compared to internal mammary artery. Viscoelastic properties of the grafts were comparable to those of native blood vessels. Modification of the grafts with VEGF reduced material stiffness. Six months postimplantation, PCL/VEGF and PHBV/PCL/VEGF were integrated with aortic tissue that induced changes in the physico-mechanical properties of the grafts similar to the native vessel. Biomechanical modeling confirmed the functioning of modified grafts in bypass position for CABG.Conclusion. PCL/VEGF and PHBV/PCL/VEGF grafts have satisfactory physico-mechanical properties and can be potentially used in the reconstruction of blood vessels.

Aim. In this article, we report a numerical analysis of the causes and haemodynamic effects of paraprosthetic regurgitation during redo transcatheter prosthesis of the aortic valve with the “valve-in-valve” technique with respect to the predictive value of computer modelling.Methods. We used numerical analysis of haemodynamics for a patient-specific simulation of blood flow in the “valve-in-valve” complex formed from a failed framed and transcatheter self-expanding aortic valve bioprosthesis. The three-dimensional computer models of the aortic root, the frame, and the transcatheter bioprosthesis were reconstructed using the multislice computed tomographic data of patient T. aged 61 years who underwent “valve-in-valve” implantation of a self-expanding valve (CoreValve™; Medtronic, Dublin, Ireland). Computer modelling was performed with the immersed boundary method, considering the haemodynamic characteristics of the patient which were obtained by postoperative transthoracic echocardiography. Qualitative and quantitative indicators of blood flow average and peak blood flow velocities, wall shear, viscous stress, and Reynolds stress were analysed, as were the distributions of these indicators in the blood flow volume of the model. Particular attention was paid to these indicators with regard to the area of observation of the first-degree paraprosthetic regurgitation in the zone of mitral–aortic contact; such regurgitation was clinically observed at 6 months.Results. In numerical simulations, high blood flow velocities in the region of interest (the area of the paraprosthetic blood leakage) as well as stresses (viscous and Reynolds stresses) do not generally cause substantial mechanical destruction of red blood cells because of the short exposure time. In the wall of the fistula, the high shear stress that results from the simulation of high blood flow velocities can initiate thrombosis with the participation of von Willebrand factor in the case of endothelial inflow of the primary bioprosthesis with dysfunction. However, these effects were not clinically observed.Conclusion. As a result of clinically observed first-degree paraprosthetic regurgitation caused by the low position of the CoreValve™ transcatheter prosthesis in relation to the primary frame bioprosthesis, the contact area of the prosthesis-in-prosthesis was reduced. The patient-specific methods used to assess haemodynamic effects arising from transcatheter prosthetics satisfactorily reproduced the clinical picture of paraprosthetic regurgitation and can form the basis of numerical prognostic models of similar interventions.Received 12 June 2019. Revised 31 October 2019. Accepted 6 November 2019.Funding: The research is supported by a grant of the Russian Science Foundation (project No. 18-75-10061).Conflict of interest: Authors declare no conflict of interest.