Surgical technique of leaflet extension in aortic valve regurgitation

Detailed procedure of the leaflet extension technique in aortic valve regurgitation is described. The concept of the technique is to create a wide and deep coaptation zone by extending the prolapsed leaflets using glutaraldehyde-preserved autologous pericardium, and by suspending the commissures. The leaflet extension technique is a procedure of choice for aortic valve regurgitation in young patients who need to avoid strict anticoagulation therapy. A careful long-term follow-up is necessary to evaluate the durability of glutaraldehyde-preserved pericardium in aortic position.     

Optimization of a trileaflet valve design

This study investigates the fundamental principles that should govern the basic design of an optimal trileaflet valve. The geometry of the leaflets is described in terms of radius of the base (Rb), radius of the commissures (Rc), height of the valve (H), height of the commissures (Hs), and angle of the open leaflet to vertical (beta). Using computer-aided design software and these design parameters, a computer model of the valve was constructed. Choosing the parameters empirically did not produce an optimal valve. The four criteria for optimal performance were defined as: (1) a certain minimum coaptation height, (2) no folds in the leaflet, (3) minimum valve height, and (4) minimum leaflet flexion. Mathematical relationships were established between the design parameters and the performance parameters. These relationships indicated that the parameters Rc, Hs, and beta could be used to minimize valve height; however, a reduction in valve height must be balanced against the accompanying increase in leaflet flexion. For an optimal valve, the design parameters were Rb = 10 mm, then Rc = 8 to 10 mm, H = 11.5 mm, Hs = 2.4 to 2.6 mm, and beta = 4 degrees to 11 degrees . The optimal valve of any radius can be designed by scaling Rc, H, and Hs with respect to Rb. These design parameters were similar to those of the natural aortic valve. Trileaflet bioprosthetic valves designed on these principles are expected to have enhanced efficiency and longevity.     

The hydrodynamic function and leaflet dynamics of aortic and pulmonary roots and valves: an in vitro study.

Fresh homograft aortic and pulmonary roots were tested in a pulsatile flow simulator to assess their hydrodynamic function and leaflet opening characteristics. Simultaneous flow and pressure measurements were obtained for a range of cardiac outputs. The effective orifice area and regurgitant volumes were calculated. The mean pressure difference across the pulmonary roots was obtained under both left and right side pressures. A video recording of valve leaflet function was also obtained for each valve. A comparison was made with four porcine bioprosthetic heart valves (21 and 23 mm). The mean pressure difference with respect to flow for the 21 mm Hancock II and Intact porcine bioprostheses was significantly higher than that for all aortic roots tested. The 24 mm aortic root showed significantly lower pressure drop compared to all porcine valves tested. The mean pressure difference across each pulmonary root at pulmonary pressures was significantly greater than at systemic pressures. At systemic pressures the fully open leaflets had a triangular orifice with low leaflet open bending strains at the commissures. At the lower internal pressures, with reduced dilation of the root, higher bending strains were noted. These were not as severe as seen in porcine valves.     

Hydrodynamic function of the second-generation mitroflow pericardial bioprosthesis

BACKGROUND: The hydrodynamic function of the smaller size Mitroflow Synergy stented pericardial bioprostheses has been studied in an in vitro fresh tissue aortic root model and compared with previous studies of free-sewn bioprostheses. METHODS: Three valves of each of the sizes 19, 21, and 23 mm were sutured into fresh tissue aortic roots and tested in a pulsatile flow simulator using two different ventricular input impedance conditions. A high-speed camera was used to study the leaflet opening and closing configurations. Mean pressure difference as a function of root mean square forward flow, effective orifice area, regurgitant volumes, and total energy loss across the valves was measured. RESULTS: Mean pressure difference with respect to root mean square forward flow decreased as the valve size increased. Thus effective orifice area increased as the valve size increased. The open leaflet configuration images showed that all three sizes of Mitroflow valves had a large circular orifice with minimal open leaflet deformation. All valves closed competently with no visible leakage and no closed regurgitant volume. The Mitroflow valves showed better effective orifice areas compared with previously tested frame-mounted porcine bioprostheses but lower effective orifice areas compared with porcine stentless bioprostheses; however, the open leaflet bending deformation was better than for any of the previously tested bioprosthetic valves. CONCLUSIONS: The hydrodynamic function of the Mitroflow Synergy stented pericardial bioprosthesis shows potential for good in vivo hemodynamic performance. The good hemodynamic performance combined with relative ease of implantation technique makes the pericardial valve a good valve in the aortic position, particularly in older patients with small annuli.     

Cryopreserved and fresh antibiotic-sterilized valved aortic homograft conduits in a long-term sheep model. Hemodynamic, angiographic, and histologic comparisons

There is a paucity of clinical and experimental data regarding the fate of cryopreserved valve aortic homografts. Fifteen lambs (mean age 4 months) underwent insertion of a valved aortic homograft between the right ventricle and pulmonary artery. In eight animals, the homografts were treated with antibiotics for 48 hours followed by up to 4 days of 4 degrees C storage (group A). In the other seven animals, the homografts were treated with antibiotics and cryopreserved at -196 degrees C (group B). The 12 long-term survivors were catheterized at 6 weeks and 4 months after implantation, at which time three animals from each group were killed. The remaining six animals were catheterized and killed at 9 months. There was no significant difference in transconduit gradient (p = 0.67) or resistance indexed to weight (p = 0.81) between groups A and B. The mean increase in transconduit gradient for both groups between catheterization at 6 weeks and 4 months was 73%, and weight increased by 51%. Histologic analysis focusing particularly on valve leaflet architecture and changes in the aortic wall revealed greater differences between individual animals and according to duration of implantation than differences between groups A and B. However, focal intracuspal thrombus of unknown significance was seen only in animals from group B. Although conduit valve leaflets generally remained free of calcification, calcification was prominent within the conduit wall of all animals. In conclusion, cryopreservation does not appear to adversely affect leaflet integrity and conduit function in this accelerated animal model relative to fresh homografts. This is in contrast to past clinical experience with homografts treated by freeze-drying and irradiation.     

Ventricular septal defect associated with aortic valve incompetence: results of two surgical managements

Aortic valve insufficiency with ventricular septal defect is usually treated by plication of the commissures. However, long-term deterioration is common. We propose a new technique that corrects the aortic annulus dilatation and the leaflet prolapse and reinforces the sinus of Valsalva. Two groups were compared: group I (29 patients) had plication of the prolapsed leaflet(s) and folding of the free edge; group II (26 patients) had triangular resection of the prolapse cusp, annuloplasty, and reinforcement of the aortic wall. The two groups were similar with regarding to preoperative clinical data. There was no perioperative mortality. Primary failure (aortic valve replacement) occurred in 8 patients in group I (28%) and in 2 patients in group II (8%). The rate of secondary failure was 31% in group I and 4% in group II. The actuarial rate of freedom from reoperation at 5 years is 55% in group I and 88% in group II (p less than 0.05). The late mortality was 6.5% in group I and 10.9% in group II (no difference). We conclude that aortic valve insufficiency with ventricular septal defect is a malformation of the aortic leaflets, the annulus, and the sinus of Valsalva, and that the proposed technique offers a better result than the usual methods in terms of residual aortic valve insufficiency.     

Mechanical Stress as Cause of Aortic Valve Disease Presentation of a New Aortic Root Prosthesis

We present an overview of studies on the aortic valve and propose that mechanical stress is a main causative factor in the degenerative valvular disease. In the normal aortic valve, the leaflets have a smooth surface, free of wrinkles and creases, throughout the opening process. This smooth leaflet surface during motion is achieved by the “pull and release” movement of the commissures, which occurs because of the compliance of the aortic root. When the aortic root is stiffened, either by artificial means or by the loss of elasticity due to aging, the leaflet dynamics change significantly. The leaflets develop a significant number of creases and wrinkles during the opening process. In the bileaflet valve, the leaflets develop similar creasing and wrinkling during the opening process. This happens mainly due to the less-than-ideal design of the bileaflet valve and in spite of the compliant aortic root. When the aortic valve is spared using a noncompliant tube graft, a similar phenomenon of leaflet creasing occurs. Because the creasing produces high stresses from bending and buckling, it is damaging to the leaflet tissue and can lead to degenerative and calcific valvular disease. Based on these observations a new aortic root prosthesis with compliant sinuses has been designed for the valve sparing operation.     

Systematik der posterioren Erweiterung des Aortenklappenanulus

The commonly used techniques for enlargement of the posterior aortic annulus are described. The anatomical relation of the aortic annulus, anterior mitral leaflet connected by the mitral-aortic intervalvular fibrosa and aortic valve commissures is of utmost importance when performing posterior enlargement techniques.     

Mechanical stress as cause of aortic valve disease. Presentation of a new aortic root prosthesis

We present an overview of studies on the aortic valve and propose that mechanical stress is a main causative factor in the degenerative valvular disease. In the normal aortic valve, the leaflets have a smooth surface, free of wrinkles and creases, throughout the opening process. This smooth leaflet surface during motion is achieved by the "pull and release" movement of the commissures, which occurs because of the compliance of the aortic root. When the aortic root is stiffened, either by artificial means or by the loss of elasticity due to aging, the leaflet dynamics change significantly. The leaflets develop a significant number of creases and wrinkles during the opening process. In the bileaflet valve, the leaflets develop similar creasing and wrinkling during the opening process. This happens mainly due to the less-than-ideal design of the bileaflet valve and in spite of the compliant aortic root. When the aortic valve is spared using a noncompliant tube graft, a similar phenomenon of leaflet creasing occurs. Because the creasing produces high stresses from bending and buckling, it is damaging to the leaflet tissue and can lead to degenerative and calcific valvular disease. Based on these observations a new aortic root prosthesis with compliant sinuses has been designed for the valve sparing operation.     

Echocardiographic characteristics of the cryopreserved allograft aortic valve replacement assessed by intraoperative transoesophageal echocardiography

Improvements in cryopreservation techniques have made possible excellent long-term results using aortic valve allografts. Few studies, however, have examined the echocardiographic characteristics of allograft aortic valves and postoperative valve function. Aortic allograft function was eveluated in 16 patients by intraoperative transoesophageal echocardiography, postoperative catheterization, and angiography. The mean(s.d.) coaptation zone length of the allograft leaflet was significantly greater (7.3(1.4) mm) than that of the normal aortic valve (3.2(0.8) mm) (P < 0.01). No regurgitation was noted in any patients with coaptation zone length of 7–11 mm (P < 0.01). The increment of the leaflet coaptation zone length did not produce a significant pressure gradient during exercise and appeared to be one of the important mechanisms for the prevention of postoperative aortic regurgitation, because commissural orientations may be distorted in the new aortic position. This finding is consistent with the report that allografts with the largest diameter implantable in the recipient annulus should be selected for use.     

Mechanical stresses on closed cusps of porcine bioprosthetic valves: correlation with sites of calcification

The purpose of this study was to (1) evaluate the magnitude and distribution of mechanical stresses on closed leaflets of porcine bioprosthetic valves (PBVs) by using a nonlinear, finite-element model, and (2) determine if a relationship exists between the magnitude of stresses at various sites on the leaflet and the incidence of calcification at those sites. Mechanical stresses were found to be highest near the commissures and lowest at the base of the leaflet. At a pressure of 100 mm Hg applied to the closed valve, the maximal principal normal stress was 160 kPa near the commissures, 140 kPa in the body of the leaflet, 70 kPa at the free margin, and 60 kPa near the base. Similarly, the maximal shear stress, at an applied pressure of 100 mm Hg, was 80 kPa near the commissures, 70 kPa in the body of the leaflet, 50 kPa at the free margin, and 40 kPa near the base. This distribution of mechanical stresses on the PBV leaflet coincided with the incidence of calcification of the various regions of the leaflet. Calcification was found most frequently near the commissures, less frequently in the body of the leaflet and free margin, and least frequently at the base. These observations suggest a possible causative relation between the magnitude of mechanical stresses and the site of calcification of PBV leaflets.     

Morphology of the ventriculoaortic junction in critical aortic stenosis. Implications for hemodynamic function and clinical management.

The clinical presentation of infants with critical aortic stenosis, as well as the results of surgical treatment, differs from obstruction of the left ventricular outflow tract in older children. To investigate a possible anatomic basis for this situation, we performed a detailed morphometric study of 21 hearts from infants who had critical aortic stenosis and 11 normal hearts from infants less than 3 months of age. In each of the hearts with critical aortic stenosis, only one commissure extended to the sinutubular ridge. The other two commissures were represented by folds in the aortic wall that suspended the leaflet below the level of the sinutubular junction. The leaflet thus had a free edge shorter than the circumference of the sinus, in contrast with the normal valve, in which leaflets always were longer than the circumference of their supporting sinus. Analysis of the fibrous triangles on the ventricular aspect of abnormal valves showed a symmetric three-sinus arrangement. In all but one specimen, however, only the triangle related to the mitral valve was fully developed. Although incision of both rudimentary commissures to the aortic wall should achieve some relief of obstruction, these morphologic features strongly mitigate against surgical restoration of normal function or growth in aortic valves having the morphology observed in this series of hearts.     

Computational simulations of the aortic valve validated by imaging data: evaluation of valve-sparing techniques

The goal of this study has been to develop a numerical model of the aortic valve, to validate it with in-vivo data and to computationally evaluate the effect of two types of aortic valve-sparing reconstructions on valve dynamics and hemodynamics. A model of the native aortic valve and two models of the valve after surgical reconstruction (reimplantation with a straight conduit and remodeling with a shaped conduit) were created. These models were transferred to a finite element analysis software where the interaction between valve structures and blood was taken into account in a dynamic manner. Leaflet and blood dynamics, as well as tissue compliance and stresses were evaluated. Leaflet dynamics and blood velocities were also assessed by magnetic resonance imaging in 15 healthy volunteers. Computational results in the native valve model correlated closely with the in-vivo imaging data. The creation of neo-sinuses was shown to restore leaflet opening and closing dynamics. Loss of compliance at the commissures led to altered stress distribution patterns. Preservation of sinus geometry was an important factor in end systolic vortex formation. This is the first study to have incorporated the effect of blood flow in the numerical evaluation of aortic reconstructions using a computational model validated by in-vivo data. Differences in valve dynamics after surgical reconstruction reported in this computational study match trends previously reported in other in-vivo studies. Numerical models such as this one can serve as increasingly sophisticated tools in the study of aortic valve pathologies and in the optimization of new surgical reconstruction techniques.     

无支架二尖瓣制备、保存和体外三尖瓣置换技术探讨

目的观察深低温保存猪二尖瓣超微结构,探索无支架二尖瓣制作方法和置换三尖瓣技术。方法采用猪二尖瓣制成无支架瓣膜,抗生素灭菌深低温保存,透射电子显微镜观察深低温保存１个月的猪二尖瓣组织结构。将离体猪心三尖瓣切除,将无支架猪二尖瓣前瓣环缝合于隔瓣环,二尖瓣后瓣环缝合于三尖瓣前后瓣环,两乳头肌缝合于右心室前壁,完成无支架二尖瓣置换三尖瓣,注水试验观察瓣膜启闭功能。结果透射电子显微镜观察到,深低温保存猪二尖瓣内皮细胞结构完整,胶原纤维结构致密,排列整齐,成纤维细胞胞膜完整,细胞核无固缩现象,线粒体无明显肿胀。无支架二尖瓣置换的离体猪心三尖瓣启闭功能良好。结论深低温保存的无支架猪二尖瓣结构完整,活性得到很好保持。瓣膜设计合理,用此瓣膜置换三尖瓣技术可行     

Identification of a Failure Mode of the Antibiotic Sterilized Aortic Allograft After 10 Years: Implications for Their Long-Term Survival

Freehand aortic allograft valves that had been previously sterilized with antibiotics were recovered at reoperation for biomechanical testing. The elastic extensibility of two leaflets from each explanted allograft stored in modified Hank's solution at 4 degrees C were measured using biaxial testing techniques. It was found that the leaflets had lost a significant amount of the natural, preimplant tissue extensibility. Computer simulation was used to investigate the likely consequences of such a profound change in the biomechanical characteristics of the leaflets on whole valve function. We found that the valve becomes progressively more incompetent as leaflet extensibility is lost and the stress levels at the commissures rise sharply with reduced coaptation. The stress levels in the load-bearing leaflet center are increased in the ventricularis as load is transferred from the fibrosa. The measured change in the radial extensibility of the aortic allograft leaflet needs to be allowed for when sizing the graft at insertion. Inserting the largest possible graft will maximize the time to the onset of central incompetence and improve valvar longevity by lowering the stress during diastole.     

Valve thrombosis of St. Jude Medical prosthesis; report of three cases

Three cases with valve thrombosis of St. Jude Medical prosthesis (SJM valve) are reported. Incidence of valve thrombosis of SJM valve was 0.15%/patient-year. Cineradiography was useful to make the diagnosis. SJM valves were implanted with the hinges anatomically oriented in mitral position, and in both aortic and tricuspid positions with the leaflet opening parallel to the ventricular septum. Therefore, we recommend that SJM valve should be placed with the hinge antianatomically oriented in mitral position, and in both aortic and tricuspid positions with the leaflet opening to be perpendicular to the interventricular septum, respectively.     

Stent and leaflet stresses in 26-mm,third-generation,balloon-expandable transcatheter aortic valve

Objectives

Transcatheter aortic valve replacement has proven successful in treating intermediate-risk, high-risk, and inoperable patients with severe aortic stenosis. Third-generation, balloon-expandable transcatheter aortic valves were developed with an outer sealing skirt to reduce paravalvular leakage. As transcatheter aortic valve replacement use expands, long-term durability questions remain. Valve design influences durability, where regions of increased leaflet stress are vulnerable to early degeneration. However, third-generation transcatheter aortic valve stresses are unknown. Our goals were to determine the stent and leaflet stresses of third-generation, balloon-expandable transcatheter aortic valves.

Mitral Stenosis in Association with Aortic Valvular Disease

In a series of 47 consecutive patients with pure mitral stenosis in association with aortic valvular disease, 25 patients underwent closed mitral commissurotomy in addition to aortic valve replacement, whereas combined aortic and mitral valve replacement was performed in 22 patients. The pathology of the stenosed mitral valve and resultant left atrial stasis were more pronounced in the latter group. Valve replacements were performed under generalized hypothermia to 30°C and selective coronary artery perfusion. The advantages and disadvantages of commissurotomy in comparison with mitral valve replacement were evaluated. Commissurotomy with aortic valve replacement involved a markedly higher mortality rate, which was closely related to early and late complications from the closed mitral commissurotomy per se. The reduced risk of thrombo-embolism following preservation instead of replacement of the mitral valve hardly outweighs this excessive mortality. The late haemodynamic improvements, although slight, were definite and similar in the two groups of patients. Diminished pressure levels in the left atrium and pulmonary artery were observed both at rest and during exercise in all the 19 patients who underwent recatheterization. Three patients showed signs of slight mitral restenosis (or residual stenosis), while another required mitral valve replacement due to mitral restenosis with incompetence. Commissurotomy remains clearly indicated if the commissures split up completely and the valve leaflets, chordae tendineae and papillary muscles are in unquestionably good condition. Unfortunately, this type of mitral stenosis, particularly in association with aortic valvular disease, is seldom encountered in Sweden nowadays. Mitral valve replacement seems to be mandatory when surgery is performed for restenosis and if uncertainty exists about the immediate result of commissurotomy.     

Truly stentless molded autologous pericardial aortic valve prosthesis with single point attached commissures in a sheep model.

OBJECTIVE: Aortic valve cusp extension and free-hand aortic valve replacement with autologous pericardium has been described. The long-term results were shown to be comparable with commercially available aortic bioprostheses. Nevertheless the relatively demanding surgical technique could not find wide acceptance. We developed a new design of a molded aortic valve, fashioned from autologous pericardium, treated briefly with glutaraldehyde, and simplified the implantation technique using single point attached commissures (SPAC). METHODS: Molded autologous valve prostheses were implanted in the subcoronary aortic position in 10 sheep with the commissures connected to the aortic wall at three single commissural points (SPAC). The prosthesis mean size was 21.6+/-1.3 mm and the construction time (excluding 10 min glutaraldehyde treatment) was 6.2+/-1.2 min. Cardiopulmonary bypass and cross-clamp time was 111.1+/-12.4 min and 75.0+/-16.3 min, respectively. Six sheep were euthanized after 201.2+/-10.3 days (6 months) and four sheep were euthanized after 330.8+/-6.5 days (11 months) postoperatively. RESULTS: In all sheep, the valve was immediately competent. At sacrifice, SPAC has proven to be well anchored to the aortic wall and the pericardial valve to be pliable in all cases. The maximum transvalvular gradient after cardiopulmonary bypass and at sacrifice was 3.7+/-2.2 mmHg and 10.6+/-5.2 mmHg, respectively. CONCLUSIONS: This new truly stentless molded autologous aortic valve with simplified implantation technique (SPAC) makes a reliable implantation in a standard timeframe possible. The simplicity of construction, low cost and absent need for anticoagulation of this molded autologous aortic bioprosthesis offers an attractive alternative and not only for patients in the developing world.     

The myth of the aortic annulus: the anatomy of the subaortic outflow tract

Surgical repair of the small aortic root is limited in part by the very structure of the outflow tract from the left ventricle. The root is not constructed on the basis of a ringlike annulus supporting the leaflets of the aortic valve. The only truly circular structure within the outflow tract is the junction of the aortic wall with the underlying ventricular structures, themselves partly muscular and partly fibrous. This circular ventriculoarterial junction is crossed by the semilunar attachments of the leaflets of the aortic valve, producing an interlinking arrangement between the expanded aortic sinuses and three triangles of fibrous tissue placed beneath the apexes of the commissures between the valve leaflets. The triangles form extensions of the left ventricle that are related, in part, to the pericardial cavity surrounding the heart. The arrangements of the attachment of the leaflets in malformed valves with two (or only one) effective leaflets are highly abnormal, although these valves are usually produced on the template of three aortic sinuses. The valve with two leaflets rarely gives problems during childhood. In valves producing "critical stenosis", there is usually only one effective leaflet, a condition due to incomplete liberation of two of the anticipated three commissures. Detailed study shows that, in these malformed hearts, the attachment of the leaflets is much more annular than in normal valves, with inadequate formation of the fibrous triangles.