Abstract: The remodeling of the dilatated valve annulus with a prosthetic ring for the repair of valve insufficiency is a well-established concept in mitral valve surgery, and may also be suitable for aortic valve reconstruction. In this study, two models of prosthetic aortic annuloplasty devices were investigated.
Abstract: OBJECTIVES: An IgG and granulocyte-activating immune response with secondary dystrophic calcification might be the reason glutaraldehyde (GA)-fixed xenograft valves fail, especially in young patients, who are more immunocompetent than the elderly. Titanium nanocoating on GA-fixed bovine pericardium was tested for its ability to prevent major immunoreactions. METHODS: The immune activity of platelets from GA-fixed bovine pericardium with different treatment procedures was evaluated using the blood from 5 human donors: group I (n = 5), GA fixed as the control; group 2 (n = 5), detoxified with 10% citric acid; group 3 (n = 5), 10% citric acid, aldehyde-dehydrogenase, and a physical plasma treatment; and group 4 (n = 5), treated the same as group 3, but with an additional titanium coat 30 nm in thickness. Titanium deposition was visualized using scanning electron microscopy. IgG deposits (iC3b) were shown by immunostaining and documented as colored pixels (red). The pixels were evaluated electronically. Attracted granulocytes (polymorphonuclear leukocytes) were counted in front of the titanium-coated surface. RESULTS: IC3b deposits and polymorphonuclear leukocytes within control group 1 were defined as 100%; in group 2, iC3b was 149% ± 34% and polymorphonuclear leukocytes were 89%, in group 3, IC3b was 102% ± 24% and polymorphonuclear leukocytes were 47%; and in group 4, IC3b had decreased to 38.49% ± 21% (P < .05) and polymorphonuclear leukocyte activation had decreased to 6.3% (P ≤ .01). CONCLUSIONS: Titanium coating significantly reduced the iC3b and granulocyte activating immune response of GA-fixed pericardium. Therefore, it might prevent relevant immunorejection and increase the durability of GA-fixed bioprosthetic heart valves.
Abstract: The use of stentless bioprostheses for aortic valve replacement provides excellent haemodynamics; however, these valves bear the potential risk of progressive regurgitation over time. To overcome this disadvantage, a new generation of pericardial stentless prostheses has been developed. This study aims to assess the tolerance of such bioprotheses against progressive sinotubular junction dilatation.
Abstract: Aortic cross-clamping during cardiac operations may injure the vessel wall and cause tissue lesions. This experimental study analyses the influence of the intravascular and external pressure and the duration of aortic cross-clamping on endothelial tissue damage. Fresh porcine aortas (n=20) were tested with intravascular pressures from 30 to 80 mmHg. The external clamp pressure, necessary to occlude the aorta, was applied by using the second cog of a commercial aortic clamp and cross-clamping was performed for 1 and 30 min. The observed pressure curves were compared to the histological findings. For occlusion of the aorta, an external pressure of at least 10-fold higher than the intravascular pressure (max. 812 mmHg) had to be applied. After 30 min of clamping, a complete endothelial destruction was observed, irrespective of intra-aortic pressure. The aortic media remained intact. After 1 min clamping, fractions of intact endothelial cells were left, ranging from 40 to 70% at different intra-aortic pressures. These results indicate that endothelial tissue lesions due to aortic cross-clamping are not avoidable, even in moderate clamp application. The duration of aortic cross-clamping but not intravascular pressure is the pivotal factor. The integrity of the aortic media can be preserved if low-force cross-clamping is achieved.
Abstract: PURPOSE: We describe a new prosthetic graft aiming to restore normal valve configuration in systemic circulation. In vitro evaluation data and first clinical results are presented. DESCRIPTION: The aortic valve consists of three separate leaflets and sinuses of Valsalva interconnected through three straight interleaflet triangles. This shape has important implications on valve function. EVALUATION: In vitro tests showed nearly normal hemodynamics, although root distensibility was decreased and bending deformation of the leaflets was increased due to the nonflexibility of the graft material. However, the anatomical shape of the aortic root was well preserved in vitro and also in vivo without contact of leaflets to the prosthesis wall. CONCLUSIONS: This new sinus prosthesis maintains normal configuration of the aortic root with three distinct sinuses of Valsalva and straight commissural pillars in systemic circulation. The noncompliant material induces abnormal leaflet bending during systole, but leaflets do not collide with the wall of prosthesis.
Abstract: A major concern with mechanical heart valve prostheses is still the need for lifelong anticoagulation to prevent valve thrombosis and thrombembolism. Knowledge of the localization of initial thrombus formation on the prosthesis may help to improve valve design. Since observation of early clot deposition in vivo is difficult, the aim of this study was a detailed assessment of the initial stages of thrombus formation at bileaflet mechanical heart valves by means of an in-vitro clotting model. Four different bileaflet mechanical heart valves (St. Jude Medical, CarboMedics, ATS and On-X) were investigated in a mock circulation in aortic position using enzyme-activated milk resembling blood clotting potential. Initial development of clot formation on the valves was documented photographically and frequency of occurrence was analyzed for both location and valve type. For the bileaflet valves, clot depositions could be found in a distinct pattern similar in all types. In initial stages, clots developed downstream of the leaflets near the orifice ring, 61.5+/-5.8% of which were hinge associated, but 38.5+/-5.8% were located isolated laterally and medially remote of the hinge region, providing new information on thrombus formation potentially useful for improvement of valve design.
Abstract: Defective heart valves are often replaced by implants in open-heart surgery. Both mechanical and biological implants are available. Among biological implants, xenograft ones-i.e., valves grafted from animals such as pigs, are widely used. Good implants should exhibit certain typical anatomical and functional characteristics to successfully replace the native tissue. Here, we describe a video-based system for measuring quality parameters of xenograft heart valve implants, including the area of the orifice and the fluttering of the valves' leaflets, i.e., their flaps (or cusps). Our system employs automatic methods that provide a precise and reproducible way to infer the quality of an implant. The automatic analysis of both a valve's orifice and the fluttering of its leaflets offers a more comprehensive quality assessment than current, mostly manual methods. We focus on valves with three leaflets, i.e., aortic, pulmonary, and tricuspid valves.
Abstract: BACKGROUND: Valve competence in valve-sparing aortic root replacement has been described as being influenced by commissural height as well as graft size. The aim of this study was to investigate the impact of a gradual reduction of commissural height and graft diameter on aortic insufficiency under physiological conditions in an IN VITRO model. METHODS: Porcine aortic valves were reimplanted into a tubular graft and a native commissural height was obtained. Subsequently the height was reduced by 10 % and 20 %, respectively. To investigate the impact of graft size, a 30 % reduction of the prosthesis diameter was carried out in valves with both native and reduced commissural heights. All conditions were investigated under pulsatile flow simulation and static pressure exposure. RESULTS: Reduction of commissural height caused regurgitation at both 10 % and 20 % lower heights, which was more pronounced in grafts with 20 % reduction. Graft undersizing resulted in significant reflux, with regurgitation even occurring with valves in a native commissural position. CONCLUSIONS: Valve competence is impaired both by the reduction of commissural height and by reduced graft size. In particular, reimplantation of aortic valves into undersized grafts promotes valve insufficiency even if commissural height is well adjusted.
Abstract: In this study, we report on our first experience with the construction of a valve using autologous vena cava tissue for right ventricular outflow tract reconstruction. Simulating the clinical situation valves were built from tubular pieces of porcine inferior vena cava placed in a PTFE tube and investigated in a pulsatile flow simulator. Based on the given vena cava dimensions, conduits were constructed with diameters of 19 mm in bicuspid or tricuspid and 22 mm and 24 mm in bicuspid configuration. The lowest pressure gradients were observed in the 22 mm vena cava valves in bicuspid configuration (8.6+/-0.5 mmHg) compared to 24 mm valves (10.6+/-0.9 mmHg, P=0.0004) and 19 mm valves (13.4+/-1.5 mmHg, P=0.005). No differences could be found between 19 mm bicuspid and tricuspid valves. Concerning valve opening movements, a complete opening in the 19 mm and a nearly unhindered opening in 22 mm valves were registered. In 24 mm valves opening was incomplete. Leakage was increased in 19 mm bicuspid valves due to leaflet prolapse. In conclusion, construction of a valve mechanism from vena cava tissue is feasible. The in-vitro hemodynamic results are encouraging, animal experiments are ongoing to investigate the midterm function of these valves.
Abstract: BACKGROUND AND AIM OF THE STUDY: Although, in small aortic annulus or aortic annulus calcification, it is recommended that valves are implanted in a tilted position, mechanical valves show impaired hemodynamic performance when positioned in this way. To date, no investigations have been conducted with biological valves implanted in a tilted position. METHODS: Measurements were performed in a pulsatile flow simulator. The aortic roots were mounted in a fluid reservoir and tested with bioprosthetic valves implanted in the regular position (21 mm; n = 7) or at a 200 tilt (23 mm; n = 7). Additional 21 mm valves were implanted in both positions with a systemic pressure of 120/80 mmHg. Subsequently, the valves were implanted into a glass model and flow visualization monitored by adding air bubbles illuminated with a laser diode. RESULTS: The 21 mm valves showed a slightly higher transvalvular gradient in the tilted than in the regular position, while 23 mm valves in a tilted position showed a lower gradient than 21 mm valves in the regular position. Flow in the regular position was seen to be straight and central, but in the tilted position was diverted and impacted on the aortic wall. Vortex formation in the tilted position was more pronounced than in the regular position, with certain low-flow areas being observed. CONCLUSION: The implantation of a one size-larger bioprosthetic valve at a 20 degree tilt in a small aortic root resulted in a slight reduction in transvalvular gradient compared to a smaller valve implanted in the regular position. Whilst mechanical valve performance is markedly compromised in the tilted position, the bioprosthetic valve showed only minor impairment of transvalvular pressure gradient due to tilting, and this was overcompensated by the larger valve size. However, the advantage of a greater orifice area must be traded against the consequences of the observed flow disturbances.
Abstract: BACKGROUND: Prosthetic replacement of the ascending aorta with nonelastic vascular grafts impairs the local Windkessel function. Whether this increases wall tension in the remaining aorta is still a not completely investigated hypothesis but is of clinical relevance with respect to postprocedural development of aneurysms and dissections, especially in the proximal descending aorta. METHODS: Fresh porcine thoracic aortas, including the root, were set up in a mock circulation before and after prosthetic replacement of the ascending aorta. Cyclic changes in aortic dimensions were measured by ultrasonic micrometers at defined positions at the proximal part of the descending aorta. At the same positions, aortic pressures were recorded simultaneously using Millar tip manometers. Wall thickness was measured after pulsatile testing, and the resulting wall tension was calculated from the Laplace law. RESULTS: After prosthetic replacement of the ascending aorta, peak systolic pressure in the proximal descending aorta increased from 117.6 +/- 6.1 mm Hg to 129.2 +/- 6.3 mm Hg, resulting in a rise of wall tension by 12.4% +/- 4.2% (p = 0.001). The maximum rate of pressure rise (dp/dt(max)) increased by 42.6% +/- 16.4% (p < 0.001). CONCLUSIONS: Replacement of the ascending aorta with noncompliant prosthetic material significantly increases wall tension and rate of pressure rise in the residual aorta. This may have clinical impact with respect to a sudden and sustained rise of mechanical load, especially at the vulnerable proximal descending aorta.
Abstract: Mitochondrial DNA (mtDNA) mutations appear to be associated with a wide spectrum of human disorders and proposed to be a potential contributor of aging. However, in an age-dependent increase of the common 4977 bp deletion of human mtDNA still many unanswered questions remain. Comparing mtDNA copy levels in different tissues revealed that cardiac muscle had the highest, while the cortex cerebelli showed the lowest copy number of mtDNA in every donor. Intriguingly, mtDNA copy number showed no changes during aging. In heart tissue, the amount of 4977 bp mtDNA deletion increased in an age-dependent manner showing significant differences at the age of 40 years and older (p<0.005). In vitro studies analyzing human normal cells transfected with telomerase (BJ-T) revealed that oxidative stress (OS)--a well accepted promoter of aging--induced 4977 bp deletion and point mutations as demonstrated by real-time PCR and DHPLC analysis. Interestingly, OS induced apoptosis only in transformed human fibroblasts by activation of the intrinsic (mitochondrial-mediated) signalling pathway as indicated by morphological damage of mitochondria, DNA laddering and increase of the Bax/Bcl-2 ratio. In conclusion, in heart tissue, the amount of the 4977 bp deletion increased in an age-dependent manner and it was more detectable after the 4th decade of life, although there was some scatter in the data. Since, apoptosis was induced by the mitochondria-mediated pathway only in transformed cells, the role for apoptosis in normal tissue of the aging heart remains unclear.
Abstract: OBJECTIVE: Stentless aortic valves are widely used due to their excellent hemodynamic properties. However, if the subcoronary implantation technique is used later dilatation of the sinotubular junction (STJ) can cause regurgitation. The aim of the study was to determine the dilatation tolerance of two commercially available stentless xenografts and fresh aortic and pulmonary roots against such dilatation. METHODS: Four groups each comprising five specimens of fresh porcine aortic roots, pulmonary roots, Medtronic freestyle or Toronto SPV Xenografts were tested in a mock circulation using a special device for gradually increasing the diameter of the sinotubular junction. The smallest diameter D(r) where regurgitation occurs was measured and correlated with the starting diameter D(a) and expressed as per cent values. Opening and closing patterns were obtained by a high speed camera and flow characteristics were determined. RESULTS: The highest dilatation tolerance of STJ was found in the fresh porcine aortic roots (165%+/-10) followed by fresh pulmonary roots (146%+/-12), the Freestyle (143%+/-4) and the SPV (132%+/-5) bioprostheses. All differences were significant with P< or =0.05 except that between the fresh pulmonary roots and the two commercial available bioprostheses. CONCLUSIONS: Our results indicate that aortic homografts provide higher resistance against regurgitation induced by dilatation of the STJ than an autograft or the stentless xenografts, Freestyle xenograft followed by the Toronto SPV. The use of the full-root technique should be considered if aortic dilatation seems to be likely.
Abstract: OBJECTIVE: Preserving aortic valve cusps during operations for aortic root pathology theoretically offers several advantages over alternative prosthetic valve-bearing conduits. Functional properties of different valve-sparing techniques under defined conditions are not well studied. METHODS: Fresh porcine aortic roots were investigated in a pulsatile flow simulator, either native root or after different types of valve-sparing procedures (remodeling, sinus prosthesis, and reimplantation). Functional parameters, such as transvalvular pressure gradient, closing volume, cusp-bending deformation, and distensibility at different levels of the root were analyzed. RESULTS: The mean pressure gradient was highest in reimplantation techniques (8.4 +/- 1.8 mm Hg) compared with sinus prostheses (7.2 +/- 0.9 mm Hg, P = .01) and remodeling techniques (6.8 +/- 1.0 mm Hg, P = .002), mirror imaging the closing volume (reimplantation, 1.5 +/- 0.4 mL; sinus prostheses, 2.3 +/- 0.7 mL [P < .001]; remodeling, 3.4 +/- 1.1 mL [P < .001]). Bending deformation indices increased significantly from remodeling (0.45 +/- 0.05) and sinus prostheses (0.58 +/- 0.06) to reimplantation techniques (0.73 +/- 0.09). Dynamic changes in area of all techniques were decreased at the sinotubular junction and the commissural and sinus levels when compared with those seen in native roots but increased at the annular level for techniques with unfixed annulus (remodeling and modified sinus prosthesis). CONCLUSIONS: In vitro the various aortic valve-sparing operations differed characteristically in their ability to spare valve function, none of them completely meeting native valve behavior. The remodeling techniques exhibited valve dynamics closest to those of the native aortic root. The more the aortic valve is fixed with noncompliant prosthetic material, the more the native root dynamics are impaired.
Abstract: In vitro testing of biological heart valves requires pressure and flow waveforms closely simulating natural conditions, which are mainly influenced by the characteristics of the vascular system. Simulation of the arterial function in artificial circulations was mostly performed by the useful Windkessel model but sometimes failed by generating inadequate systolic pressures. The integration of a novel nonlinear resistance element may improve the Windkessel function. Native porcine aortic valves were studied in a mock circulation with a novel nonlinear resistance element combined with the Windkessel compared with an aperture plate resistance. Pressure and flow measurements were performed at varying heart rates and stroke volumes and analyzed in the time and frequency domain. Aortic valve motions were evaluated using high speed video recording. With the classical afterload configuration including an aperture plate resistance, the pressure tracings showed a nonphysiologic decrease of pressure during systole after early peak pressure. By integration of the novel nonlinear resistance, peak systolic pressure occured later, peak pressure was higher, and the pressure waveform was more physiologically shaped. Leaflet motions of the aortic valves were less oscillatory and compared well with in vivo characteristics. In conclusion, a novel nonlinear resistance element in a mock circulation has the potential to provide more physiologic aortic pressure waveforms as influencing aortic valve dynamics and thus may be a helpful tool for investigation of biological heart valves.
Abstract: BACKGROUND: Reduction of atheroembolic complications during cardiopulmonary bypass remains a major challenge in cardiac surgery. New cannula tip designs may help to attenuate this problem by improved hydrodynamics. METHODS: Pressure gradients and back pressures of a new aortic cannula tip design were measured and compared with the Medos X-Flow, Sarns Soft-Flow and Argyle THI cannulae at various flow rates in a mock circulation followed by flow visualization. RESULTS: Pressure gradients were the lowest for the new cannula. Back pressures of the new cannula were up to 84% lower than for the Argyle cannula. The back pressure profile and flow visualization of the new cannula showed broad centric flow dispersion with a transcannula increase of flow area from 38 mm2 to 139 mm2. CONCLUSIONS: The new design of an aortic cannula tip provides improved hydrodynamics, with low pressure gradients, low back pressures and a uniform central dispersion of flow, reducing the sandblasting effect.
Abstract: PURPOSE: Current replacement of the thoracic aorta performed with straight vascular prostheses may cause kinking, potentially affecting hemodynamics and promoting vortices and thrombus formation. A novel vascular prosthesis, resistant to pressure-related shape deformation, was designed to imitate the curved anatomy of the thoracic aorta. DESCRIPTION: A woven velour prosthesis was trimmed with cross-sutures along a marked line, resulting in a curved-shaped anatomic form, and was compared with conventional straight and thermally fixed curved grafts. The vascular prostheses were fixed at both ends at various base distances (8, 10, 12, 14, and 16 cm) and pressurized. To imitate the neck vessels an abutment was fixed at the upper convexity of the grafts. Radius of curvature or depth of kinking was measured at different pressures (100, 125, and 150 mm Hg). Pressure gradients and flow profiles were further analyzed in an aortic arch glass model. EVALUATION: When pressurized the straight and the thermally fixed protheses showed double kinking before and behind the abutment at all pressures and distances. Kinking depth increased with increasing pressure and less base distance. Transkinking pressure gradients increased with the degree of kinking. In a glass model flow profiles showed postkinking turbulences and vortex formation. The newly designed vascular prosthesis showed no kinking and remained form stable at all test conditions. CONCLUSIONS: This novel curved vascular prosthesis for replacement of the thoracic aorta demonstrates form stability compared with conventional straight and thermally fixed vascular prostheses in an aortic arch model, with smaller pressure gradients and flow disturbances.
Abstract: Hybrid heart valve scaffolds were fabricated from decellularized porcine aortic heart valve matrices and enhanced with bioresorbable polymers using different protocols: (i) dip coating of lyophilized decellularized matrices, and (ii) impregnation of wet decellularized matrices. The following polymers were evaluated: poly(4-hydroxybutyrate) and poly(3-hydroxybutyrate-co4-hydroxybutyrate). Tensile tests were conducted to assess the biomechanical behavior of valve leaflet strips. Suture retention strength was evaluated for the adjacent conduit. A pulse duplicator system was used for functional testing of the valves under physiological systemic load conditions. The properties of the hybrid structures were compared with native, decellularized, and glutaraldehyde-fixed specimens. Mechanisms of the polymer impregnation process were studied with IR spectroscopy, fluorescent microscopic imaging, and SEM. Altogether this study demonstrates the feasibility and improved biomechanical function of a novel hybrid heart valve scaffold for an application in tissue engineering.
