Initial hydrodynamic study on a new intraaortic axial flow pump: Dynamic aortic valve

Rotary blood pumps have been researched as implantable ventricular assist devices for years. To further reduce the complex of implanted axial pumps, the authors proposed a new concept of intraaortic axial pump, termed previously as “dynamic aortic valve (DAV)”. Instead of being driven by an intraaortic micro-electric motor, it was powered by a magnetic field from outside of body. To ensure the perfusion of coronary artery, the axial flow pump is to be implanted in the position of aortic valve. It could serve as either a blood pump or a mechanical valve depending on the power input. This research tested the feasibility of the new concept in model study. A column, made from permanent magnet, is jointed to an impeller in a concentric way to form a “rotor-impeller”. Supported by a hanging shaft cantilevered in the center of a rigid cage, the rotor-impeller can be turned by the magnetic field in the surrounding space. In the present prototype, the rotor is 8 mm in diameter and 15 mm in length, the impeller has 3 vanes with an outer diameter of 18 mm. The supporting cage is 22 mm in outer diameter and 20 mm in length. When tested, the DAV prototype is inserted into the tube of a mock circuit. The alternative magnetic field is produced by a rotating magnet placed side by side with the rotor-impeller at a distance of 30 mm. Once the alternative magnetic field is presented in the surrounding space, the DAV starts to turn, leading to a pressure difference and liquid flow in the tube. The flow rate or pressure difference is proportioned to rotary speed. At the maximal output of hydraulic power, the flow rate reached 5 L/min against an afterload of 100 mmHg. The maximal pressure difference generated by DAV at a rotation rate of 12600 r/min was 147 mmHg. The preliminary results demonstrated the feasibility of “DAV”, further research on this concept is justifiable.     

Initial hydrodynamic study on a new intraaortic axial flow pump: Dynamic aortic valve

Rotary blood pumps have been researched as implantable ventricular assist devices for years. To further reduce the complex of implanted axial pumps, the authors proposed a new concept of intraaortic axial pump, termed previously as "dynamic aortic valve (DAV)". Instead of being driven by an intraaortic micro-electric motor, it was powered by a magnetic field from outside of body. To ensure the perfusion of coronary artery, the axial flow pump is to be implanted in the position of aortic valve. It could serve as either a blood pump or a mechanical valve depending on the power input. This research tested the feasibility of the new concept in model study. A column, made from permanent magnet, is jointed to an impeller in a concentric way to form a "rotor-impeller". Supported by a hanging shaft cantilevered in the center of a rigid cage, the rotor-impeller can be turned by the magnetic field in the surrounding space. In the present prototype, the rotor is 8 mm in diameter and 15 mm in length, the impeller ha     

Computational assessment of bicuspid aortic valve wall-shear stress: implications for calcific aortic valve disease

The bicuspid aortic valve (BAV) is associated with a high prevalence of calcific aortic valve disease (CAVD). Although abnormal hemodynamics has been proposed as a potential pathogenic contributor, the native BAV hemodynamic stresses remain largely unknown. Fluid-structure interaction models were designed to quantify the regional BAV leaflet wall-shear stress over the course of CAVD. Systolic flow and leaflet dynamics were computed in two-dimensional tricuspid aortic valve (TAV) and type-1 BAV geometries with different degree of asymmetry (10 and 16% eccentricity) using an arbitrary Lagrangian–Eulerian approach. Valvular performance and regional leaflet wallshear stress were quantified in terms of valve effective orifice area (EOA), oscillatory shear index (OSI) and temporal shear magnitude (TSM). The dependence of those characteristics on the degree of leaflet calcification was also investigated. The models predicted an average reduction of 49% in BAV peak-systolic EOA relative to the TAV. Regardless of the anatomy, the leaflet wall-shear stress was side-specific and characterized by high magnitude and pulsatility on the ventricularis and low magnitude and oscillations on the fibrosa. While the TAV and non-coronary BAV leaflets shared similar shear stress characteristics, the base of the fused BAV leaflet fibrosa exhibited strong abnormalities, which were modulated by the degree of calcification (6-fold, 10-fold and 16-fold TSM increase in the normal, mildly and severely calcified BAV, respectively, relative to the normal TAV). This study reveals the existence of major differences in wall-shear stress pulsatility and magnitude on TAV and BAV leaflets. Given the ability of abnormal fluid shear stress to trigger valvular inflammation, the results support the existence of a mechano-etiology of CAVD in the BAV.     

In vitro assessment of the influence of aortic annulus ovality on the hydrodynamic performance of self-expanding transcatheter heart valve prostheses

Background

Although CT-studies as well as intraoperative analyses have described broad anatomic variations of the aortic annulus, which is predominantly found non-circular, commercially available transcatheter aortic heart valve prostheses are circular. In this study, we hypothesize that the in vitro hydrodynamic function of a self-expanding transcatheter heart valve (Medtronic CoreValve^®) assessed in an oval compartment representing the aortic annulus will differ from the conventionally used circular compartment.

Methods

Medtronic CoreValve^® prostheses were tested in specifically designed and fabricated silicone compartments with three degrees of defined ovalities. The measurements were performed in a left heart simulator at three different flow rates. In this setting, regurgitation flow, effective orifice area, and systolic pressure gradient across the valve were determined. In addition, high speed video recordings were taken to investigate leaflet kinematics.

Results

The pressure difference across the prosthesis increased with rising ovality. The effective orifice areas were only slightly impacted. The analyses of the regurgitation showed minor changes and partially lower regurgitation when switching from round to slightly oval settings, followed by strong increases for further ovalization. The high speed videos show minor central leakage and impaired leaflet apposition for strong ovalities, but no leaflet/stentframe contact in any setting.

Conclusion

This study quantifies the influence of oval expansion of transcatheter heart valve prostheses on their hydrodynamic performance. While slight ovalities were well tolerated by a self-expanding prosthesis, more significant ovality led to worsening of prosthesis function and regurgitation.     

Use of a novel acellular xenograft as a patch for aortic annular enlargement during aortic valve replacement

A patient with a history of aortic valve endocarditis and surgical debridement presented with acute congestive heart failure because of severe aortic stenosis. During valve replacement surgery, an aortic annular enlargement was required to overcome a potential patient-prosthesis mismatch. We describe the use of a novel, bioresorbable, acellular xenograft for the enlargement patch. This material is expected to remodel into native patient tissue over time. This case offers an alternative implant for left heart reconstruction using a regenerative patch.     

Intracardiac echocardiographic guidance for hemodynamic assessment in a patient with congenital abnormalities and a prosthetic aortic valve

In this case report, we present the use of intracardiac echocardiography (ICE) for guiding the cardiac catheterization and subsequent hemodynamic investigation in an unusual patient case with multiple congenital abnormalities (bicuspid aortic valve, left cervical aortic arch, two aortic coarctations) and two aortic valve replacement operations in the past. The ICE catheter (AcuNav) permitted us to accurately and safely puncture the interatrial septum and place the Swan-Ganz catheter in the left ventricle; additionally, visualization of the aortic coarctation in the ascending aorta was also achieved.     

Manufacture of small calibre quadruple lamina vascular bypass grafts using a novel automated extrusion-phase-inversion method and nanocomposite polymer

Long-term patency of expanded polytetrafluoroethylene (ePTFE) small calibre cardiovascular bypass prostheses (<6 mm) is poor because of thrombosis and intimal hyperplasia due to low compliance, stimulating the search for elastic alternatives. Wall porosity allows effective post-implantation graft healing, encouraging endothelialisation and a measured fibrovascular response. We have developed a novel poly (carbonate) urethane-based nanocomposite polymer incorporating polyhedral oligomeric silsesquioxane (POSS) nanocages (UCL-NANO?) which shows anti-thrombogenicity and biostability.We report an extrusion-phase-inversion technique for manufacturing uniform-walled porous conduits using UCL-NANO?. Image analysis-aided wall measurement showed that two uniform wall-thicknesses could be specified. Different coagulant conditions revealed the importance of low-temperature phase-inversion for graft integrity. Although minor reduction of pore-size variation resulted from the addition of ethanol or N,N-dimethylacetamide, high concentrations of ethanol as coagulant did not provide uniform porosity throughout the wall. Tensile testing showed the grafts to be elastic with strength being directly proportional to weight. The ultimate strengths achieved were above those expected from haemodynamic conditions, with anisotropy due to the manufacturing process. Elemental analysis by energy-dispersive X-ray analysis did not show a regional variation of POSS on the lumen or outer surface. In conclusion, the automated vertical extrusion–phase-inversion device can reproducibly fabricate uniform-walled small calibre conduits from UCL-NANO?. These elastic microporous grafts demonstrate favourable mechanical integrity for haemodynamic exposure and are currently undergoing in-vivo evaluation of durability and healing properties.     

Hyperlipidaemia and aortic valve disease

PURPOSE OF REVIEW: Degenerative aortic valve stenosis is a common disease in the elderly, and traditional risk factors for atherosclerotic disease including hyperlipidaemia have been associated with the condition in several studies. This review addresses the role of the various risk factors and the potential for intervention. RECENT FINDINGS: The association of lipid abnormalities such as high lipoprotein(a) levels and the presence of the apolipoprotein E4 allele with aortic stenosis, as well as the presence of several inflammatory markers both in plasma and in surgically excised valves, suggest that the stenotic process is driven by many of the same factors behind atherosclerosis. The aortic valves of animals fed a cholesterol-rich diet exhibit many characteristics in common with the early stages of aortic stenosis. This opens up the potential of retarding the process through intervention strategies. SUMMARY: Hyperlipidaemia is associated with degenerative aortic valve stenosis, and the disease resembles the inflammatory process of atherosclerosis. Randomized controlled clinical trials will be needed to demonstrate the role of lipid intervention in patients with this condition.     

Three-dimensional macro-scale assessment of regional and temporal wall shear stress characteristics on aortic valve leaflets

The aortic valve (AV) achieves unidirectional blood flow between the left ventricle and the aorta. Although hemodynamic stresses have been shown to regulate valvular biology, the native wall shear stress (WSS) experienced by AV leaflets remains largely unknown. The objective of this study was to quantify computationally the macro-scale leaflet WSS environment using fluid–structure interaction modeling. An arbitrary Lagrangian–Eulerian approach was implemented to predict valvular flow and leaflet dynamics in a three-dimensional AV geometry subjected to physiologic transvalvular pressure. Local WSS characteristics were quantified in terms of temporal shear magnitude (TSM), oscillatory shear index (OSI) and temporal shear gradient (TSG). The dominant radial WSS predicted on the leaflets exhibited high amplitude and unidirectionality on the ventricularis (TSM>7.50 dyn/cm², OSI < 0.17, TSG>325.54 dyn/cm² s) but low amplitude and bidirectionality on the fibrosa (TSM < 2.73 dyn/cm², OSI>0.38, TSG < 191.17 dyn/cm² s). The radial WSS component computed in the leaflet base, belly and tip demonstrated strong regional variability (ventricularis TSM: 7.50–22.32 dyn/cm², fibrosa TSM: 1.26–2.73 dyn/cm²). While the circumferential WSS exhibited similar spatially dependent magnitude (ventricularis TSM: 1.41–3.40 dyn/cm², fibrosa TSM: 0.42–0.76 dyn/cm²) and side-specific amplitude (ventricularis TSG: 101.73–184.43 dyn/cm² s, fibrosa TSG: 41.92–54.10 dyn/cm² s), its temporal variations were consistently bidirectional (OSI>0.25). This study provides new insights into the role played by leaflet–blood flow interactions in valvular function and critical hemodynamic stress data for the assessment of the hemodynamic theory of AV disease.     

Biomonitoring 2.0: a new paradigm in ecosystem assessment made possible by next-generation DNA sequencing

Biological monitoring has failed to develop from simple binary assessment outcomes of the impacted/unimpacted type, towards more diagnostic frameworks, despite significant scientific effort over the past fifty years. It is our assertion that this is largely because of the limited information content of biological samples processed by traditional morphology-based taxonomy, which is a slow, imprecise process, focused on restricted groups of organisms. We envision a new paradigm in ecosystem assessment, which we refer to as ‘Biomonitoring 2.0’. This new schema employs DNA-based identification of taxa, coupled with high-throughput DNA sequencing on next-generation sequencing platforms. We discuss the transformational nature of DNA-based approaches in biodiversity discovery and ecosystem assessment and outline a path forward for their future widespread application.     

Techniques of aortic valve repair

Similar to mitral repair, newer methods of aortic valve reconstruction are achieving excellent outcomes with an 85% to 90% freedom from valve-related complications at 10 years. The goal of this review is to illustrate these newer and more stable techniques of aortic valve repair. Most patients with aortic insufficiency from either trileaflet or bicuspid aortic valves are candidates for repair, in addition to selected patients with mixed aortic stenosis/insufficiency and aortic root aneurysms. Initially, aggressive commissural annuloplasty is performed to reduce measured valve diameter to 19 to 21 mm. Leaflet prolapse is corrected with plication stitches placed in the free edge of each leaflet adjacent to the Nodulus Arantius. In this regard, the leaflet free edge functions as the chorda tendinea of the aortic valve, and shortening with plication stitches raises the leaflet to a proper "effective height." Leaflet defects are augmented with gluteraldehyde-fixed autologous pericardium, and mild-to-moderate strategically placed spicules of calcium are removed with the cavitron ultrasonic surgical aspirator. Using these methods, most insufficient aortic valves, and many with mixed lesions, can be satisfactorily repaired. Six cases are illustrated in this review, spanning the spectrum of pathologies from annular dilatation without leaflet defects, to standard congenital bicuspid valve with prolapse, to trileaflet prolapse, to unusual bicuspid pathology with calcification, to a moderately calcified trileaflet valve with mixed lesions, and to aortic root aneurysms with severe aortic insufficiency. All valves were repaired using the techniques described above with trivial residual leak and minimal gradients. All repairs have been followed with yearly echocardiography, and valve reconstruction with these methods is now quite stable with excellent late outcomes. Most insufficient aortic valves now can undergo stable repair with minimal late valve-related complications. Greater application of aortic valve repair seems indicated.     

A novel heart valve stent design: mechanical interaction with the aortic root

Percutaneous aortic valve implantation has become an alternative technique to surgical valve replacement in patients with high risk for open chest surgery. Vascular stents clinically used today for non-invasive aortic valve replacement tend, however, to impede the dimension changes of the compliant aortic root over the cardiac cycle. The purpose of the present work is to assess the influence of a novel heart valve stent, designed specifically to limit the traumatism in tissue, on the compliance of the aortic root. A theoretical approach is adopted to model the mechanical behaviour of the different stent parts and assess the compliance modification induced by the stent. The validity of the model is then tested experimentally. Both approaches show that the specific geometry of the stent makes it possible to keep the compliance of the aortic root close to the native root values.