Transcatheter heart valve with variable geometric configuration: in vitro evaluation

Clinically, the current transcatheter aortic valve (TAV) technology has shown a propensity for paravalvular leakage; studies have correlated this flaw to increased calcification at the implantation site and with nonideal geometry of the stented valve. The present study evaluated the hydrodynamics of different geometric configurations, in particular the intravalvular considerations. Three TAV devices were made to create a representative, size 26 mm TAV. Hydrodynamics were assessed using a pulse duplicator. The geometries tested were composed of the nominal, elliptical, triangular, and undersized shapes; along with half-constriction, a conformation in which only a portion of the stent was constrained. The TAVs were assessed for transvalvular pressure gradient (TVG), effective orifice area (EOA), and regurgitant fraction. The nominal-sized shape posed a larger TVG (6.2 ± 0.3 mm Hg) than other configurations (P < 0.001) except the undersized valves. EOA of the nominal sized TAV (1.7 ± 0.1 cm(2) ) was smaller than that of the triangular and half-elliptical versions (P < 0.001). The half- and full-undersized geometries had EOAs smaller than the nominal type (P < 0.001). Nominal shape had smaller regurgitation (6.7 ± 1.4%) than all configurations (P < 0.001) except for the half-undersized (4.0 ± 0.7, P < 0.001) with no statistically significant difference from the full-undersized (6.8 ± 1.3, P = 0.724). The testing of variable geometries showed significant differences from the nominal geometry with respect to TVG, EOA, and regurgitant fraction. In particular, many of these nonideal configurations demonstrated an increased intravalvular regurgitation.     

Development of a polymer bileaflet valve to realize a low-cost pulsatile blood pump

The final goal of this study is to realize a low-cost pulsatile blood pump especially for patients with acute heart failure or postoperative low cardiac output syndrome. In support of the pump, two types of polymer bileaflet valves with different configuration of the valve seats were developed. Influence of the leaflet thickness on the hydrodynamics of the prototype was preliminarily investigated among 70 microm, 100 microm, and 150 microm. As to the valves with the thinner leaflets, buckling of the leaflets was observed, which induced a large amount of regurgitation at valve closure. However, by thickening the leaflet to 150 microm, the mean flow of the prototype and the second model could be successfully comparable to the Medtronic-Hall valve. Moreover, accelerated fatigue tests showed that reinforcement of the valve seat with the additional spokes in the second model extended the durability by four times as compared with the prototype, equivalent to an in vivo duration of over one month.     

Effects of hemodynamic conditions and valve sizing on leaflet bending stress in self-expanding transcatheter aortic valve: An in vitro study

Transcatheter aortic valve (TAV) replacement has become a viable alternative to surgery for high and intermediate risk patients with severe aortic stenosis. This technology may extend to the younger and lower risk patients. In this population, long-term durability of the TAV is key. Increased leaflet mechanical stress is one of the main determinants of valve structural deterioration. This in vitro study aims at evaluating leaflet bending stress (LBS) in the self-expanding TAV for different valve sizes, stroke volumes (SV), and degrees of valve oversizing (OS). Three different sizes (23, 26, and 29 mm) of CoreValve (CV) were tested on a pulse duplicator in annulus size ranging from 17 to 26 mm. Leaflet bending stress and bending of the leaflet coaptation line in diastole pinwheeling index (PI) were measured using high-speed camera imaging (1000 images/s). For each given CV and annulus size, geometric orifice area (GOA) increased significantly with OS (P < .001) and SV (P = .001). LBS decreased with increasing prosthesis size and aortic annulus (AA) size while increasing with SV (P < .03). The largest value of peak LBS (3.79 MPa) was obtained with the CV 23 mm in AA of 17 mm (%OS = 35%), SV 90 mL and the smallest value (0.99 MPa) for the CV 29 mm in AA of 26 mm (%OS = 12%), SV 30 mL. On multivariable analysis, LBS increased independently with larger OS, smaller AA size and higher SV. The PI increased with decreasing AA size and increasing OS. Moderate valve OS, such as generally used for transcatheter aortic valve implantation, is associated with increased LBS during valve opening and closing, especially in small annuli. Hence, TAV OS may negatively impact long-term valve durability.     

Simulated Transcatheter Aortic Valve Flow: Implications of Elliptical Deployment and Under‐Expansion at the Aortic Annulus

Clinical use of transcatheter aortic valves (TAVs) has been associated with abnormal deployment, including oval deployment and under‐expansion when placed into calcified aortic annuli. In this study, we performed an integrated computational and experimental investigation to quantify the impact of abnormal deployment at the aortic annulus on TAV hemodynamics. A size 23 mm generic TAV computational model, developed and published previously, was subjected to elliptical deployment at the annulus with eccentricity levels up to 0.68 and to under‐expansion of the TAV at the annulus by up to 25%. The hemodynamic performance was quantified for each TAV deployment configuration. TAV opening geometries were fabricated using stereolithography and then subjected to steady forward flow testing in accordance with ISO‐5840. Centerline pressure profiles were compared to validate the computational model. Our findings show that slight ellipticity of the TAV may not lead to degeneration of hydrodynamic performance. However, under large ellipticity, increases in transvalvular pressure gradients were observed. Under‐expanded deployment has a much greater negative effect on the TAV hemodynamics compared with elliptical deployment. The maximum turbulent viscous shear stress (TVSS) values were found to be significantly larger in under‐expanded TAVs. Although the maximum value of TVSS was not large enough to cause hemolysis in all cases, it may cause platelets activation, especially for under‐expanded deployments.     

Correction of leaflet prolapse in valve-preserving aortic replacement: pushing the limits?

BACKGROUND: For aortic dilatation with morphologically intact leaflets, valve-preserving aortic replacement has become an accepted treatment modality. Leaflet prolapse, however, may be present, making composite replacement the most frequent choice. Alternatively, valve preservation may be combined with correction of leaflet prolapse. The results of this approach should be comparable with those of valve-preserving aortic surgery in the presence of normal leaflets. METHODS: Between 1995 and 2002, 156 patients were treated by valve-preserving surgery. The aortic valve was bicuspid in 46, and tricuspid in 110 instances. In 88 aortic valves, apparently normal leaflet coaptation (normal, 12 bicuspid and 76 tricuspid), and in 68 instances, prolapse of one or more leaflets, was observed. Root remodeling (n = 133) or aortic replacement with valve reimplantation (n = 23) were performed. Leaflet prolapse was corrected by triangular resection (n = 16) or plicating sutures (n = 59), mostly placed in the central portion of the leaflet. RESULTS: Neither operative mortality nor 5-year survival were influenced by the additional correction of prolapse. Freedom from reoperation at 1 year (normal, 98.8%; prolapse, 96.5%) and 5 years (normal, 97.3%; prolapse, 96.5%) were comparable in both cohorts, as was freedom from aortic regurgitation > or = II at 1 year (normal, 98.8%; prolapse, 94.2%) and 5 years (94.4%). CONCLUSIONS: Surgical correction of leaflet prolapse in combination with proximal aortic replacement is feasible with good results. Midterm results are identical with those known for morphologically normal leaflets. Repair of prolapse allows for preservation of the native valve in most patients with aortic regurgitation and aortic pathology, and thus appears a beneficial addition to valve-preserving surgery.     

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.     

In vitro investigation of aortic valve annuloplasty using prosthetic ring devices

Objectives: 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. Methods: Fresh porcine aortic roots (n = 16) were investigated in a pulsatile flow simulator after patch dilatation of the annulus and subsequent reconstruction using both an external and an internal prosthetic ring. For each configuration, leakage was determined by ultrasonic flow measurements and leaflet co-aptation by transesophageal echocardiography. In addition, valves’ motions were recorded by high-speed video. Results: By the use of the prosthetic annuloplasty rings, leakage volumes decreased significantly compared with the dilatated root, more pronounced with the intra-annular ring. Similarly, the co-aptation height of the leaflets increased. Pressure gradients were not significantly influenced by the ring application, but leaflet motion patterns changed from the usual trapezoid to a more rectangular opening characteristic, visible at both echocardiographic and high-speed video analysis. Conclusions: The reconstruction of a dilatated aortic valve annulus using external and internal ring devices is feasible and effective for reduction of regurgitation at which the internal ring provides a greater potential to decrease valve insufficiency.     

Aortic valve repair after arterial switch operation

A patient with transposition of the great arteries and a ventricular septal defect underwent an arterial switch operation 15 months after pulmonary artery banding. At 12 years of age, severe neoaortic valve regurgitation, due to dilated aortic sinuses and poor leaflet coaptation, developed. Aortic valve repair involved placement of subcommissural sutures, elliptical excision and tailored reduction of two anterior aortic sinuses, with triangular patch expansion of the proximal ascending aorta. A good result was obtained.     

Tricuspidisation of the aortic valve with creation of a crown-like annulus is able to restore a normal valve function in bicuspid aortic valves

Objective: To evaluate the early results of a new method to repair malfunctioning bicuspid aortic valves by creating a tricuspid valve with a crown-like (i.e. anatomic) annulus. Material and methods: Twelve patients (ages from 10 to 27 years) with chronic regurgitation (and flow-dependent stenosis) of a bicuspid aortic valve underwent repair with the principle of creating a tricuspid valve and a crown-like annulus. The fused leaflets were trimmed and reinserted underneath the existing aortic annulus to create one new native cusp. The third leaflet was fashioned out of a xenopericard patch and was inserted underneath the existing annulus as well to restore the crown-like anatomy of a normal aortic annulus. A tricuspid aortic valve with a morphologically normal annulus was thus created, which resulted in improved coaptation of the leaflets. The repair was immediately assessed by transesophageal echocardiography (TEE) with the heart loaded at 50%. In two patients, a second run helped fine-tune the repair. Median cross-clamping time was 82 min. Follow-up ranged from 3 to 46 months (median 13 months). Results: No significant complication occurred. The function of the aortic valve was excellent with trivial or mild regurgitation in 11 patients and moderate regurgitation in 1 patient. There was no stenosis across the valve. The repair remained stable over time. Remodelling of the left ventricle occurred as expected. Conclusions: Aortic valve repair is feasible in some dysfunctioning bicuspid aortic valves. Tricuspidisation of the valve can result in excellent systolic and diastolic functions. The creation of a crown-like annulus results in improved coaptation of the cusps and could lead to more reliable outcome. Although long-term results are needed, this anatomic correction seems to be a good alternative to valvular replacement in certain sub-groups of patients.     

The secret life of the mitral valve

In secondary mitral regurgitation, the concept that the mitral valve (MV) is an innocent bystander, has been challenged by many studies in the last decades. The MV is a living structure with intrinsic plasticity that reacts to changes in stretch or in mechanical stress activating biohumoral mechanisms that have, as purpose, the adaptation of the valve to the new environment. If the adaptation is balanced, the leaflets increase both surface and length and the chordae tendineae lengthen: the result is a valve with different characteristics, but able to avoid or to limit the regurgitation. However, if the adaptation is unbalanced, the leaflets and the chords do not change their size, but become stiffer and rigid, with moderate or severe regurgitation. These changes are mediated mainly by a cytokine, the transforming growth factor‐β (TGF‐β), which is able to promote the changes that the MV needs to adapt to a new hemodynamic environment. In general, mild TGF‐β activation facilitates leaflet growth, excessive TGF‐β activation, as after myocardial infarction, results in profibrotic changes in the leaflets, with increased thickness and stiffness. The MV is then a plastic organism, that reacts to the external stimuli, trying to maintain its physiologic integrity. This review has the goal to unveil the secret life of the MV, to understand which stimuli can trigger its plasticity, and to explain why the equation “large heart = moderate/severe mitral regurgitation” and “small heart = no/mild mitral regurgitation” does not work into the clinical practice.     

Preservation of aortic leaflets during rapid deployment valve implantation in patients with aortic insufficiency

Development of a new surgical technique for aortic valve replacement with the use of rapid deployment/sutureless valve: a leaflet preservation technique applying imbrication methods to pliable aortic leaflets. We aim to decrease the incidence of paravalvular leak by preserving aortic leaflets in patients with aortic insufficiency and large aortic annulus.     

The in vitro hydrodynamic characteristics of the porcine pulmonary valve and root with regard to the ross procedure

OBJECTIVE: The hydrodynamic parameters and leaflet motion of the porcine pulmonary root and valve and the performance of the pulmonary autograft implanted in subcoronary position or as a free-standing root were investigated at systemic and pulmonary pressures in vitro. METHODS: Ten fresh pulmonary and aortic roots (anulus diameter, 20-25 mm) were tested in a pulsatile flow simulator. Five free-sewn pulmonary valves were implanted in aortic roots in the subcoronary position, and 5 pulmonary roots were implanted as free-standing roots. The external diameter of the roots was measured at the sinotubular junction in a pressure range of 0 to 120 mm Hg. The transvalvular gradient and regurgitation were measured, and the effective orifice area was calculated. The leaflet motion was recorded on video tape. RESULTS: The fresh pulmonary roots were more compliant than their aortic counterparts (33% +/- 3. 0% vs 7% +/- 1.5% with dilatation at 0-30 mm Hg and 46% +/- 8.4% vs 35% +/- 7.8% with dilatation at 0-120 mm Hg). The pulmonary roots had a lower pressure drop at systemic than at pulmonary pressures. The pressure drops of the pulmonary roots were also lower than those of the aortic roots in the systemic pressure range. The leaflet opening of the pulmonary valve was triangular, with low bending deformation at all pressures. Implanting the free-sewn pulmonary valve in the subcoronary position or the pulmonary root as a free-standing root did not affect the hydrodynamic parameters and leaflet motion adversely. CONCLUSION: The pulmonary valve and root could easily withstand aortic pressures in vitro. A biphasic dilatation curve ensures that higher pressures did not overdilate the pulmonary root. Moreover, valve performance was better at systemic pressures.     

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.     

三尖瓣脱垂的外科治疗

目的探索应用三尖瓣脱垂瓣缘折叠缝合技术治疗三尖瓣关闭不全的外科方法和疗效。方法1997年4月至2006年3月为6例先天性三尖瓣前叶腱索缺如和3例外伤性腱索断裂的患者实施了外科矫治手术,其中男性6例,女性3例,年龄8～57岁。术前9例患者均有三尖瓣重度关闭不全,右心室前后径均值为(43.6±4.2)mm。5例患者心功能为Ⅲ级,4例为Ⅳ级。连续对折缝合脱垂的三尖瓣瓣缘,折叠缝合脱垂瓣叶相对应的瓣环,并用成形环固定成形后三尖瓣瓣环。结果9例患者术后恢复顺利,无死亡。术后超声心动图检查示:6例患者三尖瓣对合良好无反流,3例患者有少量反流。所有患者术后右心室前后径均显著减小,术后均值为(24.0±1.8)mm,与术前相比差异有统计学意义(P<0.01)。3例房颤心律的患者均转为窦性心律。患者随访1～109个月,除1例患者外,其他8例患者三尖瓣成形效果稳定。8例患者心功能为Ⅰ～Ⅱ级,1例为Ⅲ级。结论应用三尖瓣脱垂瓣叶及其相对应的瓣环折叠技术,可有效修复先天性三尖瓣部分腱索缺如和胸外伤后三尖瓣腱索断裂所致的三尖瓣重度关闭不全。     

Leaflet extension technique in a congenital aortic valve regurgitation

A 17-year-old boy who was diagnosed as congenital aortic valve regurgitation underwent the leaflet extension technique in 3 aortic leaflets using glutaraldehyde-preserved autologous pericardium. Intraoperative transesophageal echocardiography and postoperative cardiac catheter revealed grade I regurgitation and the patient has been doing well for more than 4 months after the surgery. The leaflet extension technique is considered to be an acceptable surgical treatment for aortic valve disease especially in young patients to whom valve replacement or Ross procedure might not be suitable. A careful long-term follow-up will be necessary to evaluate the durability of the leaflet extension technique with autologous pericardium.     

Aortic root dilatation may alter the dimensions of the valve leaflets

Objective: Valve-sparing surgery can be used in patients with dilated aortic roots and aortic insufficiency (AI) but has not become a common practice, in part because the spared valve may be incompetent. Our goal was to study how the dimensions of the aortic root and leaflets have changed in such patients. Methods: Fourteen patients with dilated aortic root and AI were examined by transesophageal echocardiography. The annulus diameter, sinotubular junction (STJ) diameter, sinus height, leaflet free-edge length, and leaflet height were measured. Correlations among these dimensions and with the AI grades were explored. Measurements were also made in 19 normal human aortic valves from silicone molds. Results: There was no evident change in the average diameter of the annulus between the normal valves and those in the dilated aortic roots. The STJ diameter was obviously increased in the dilated aortic roots; the aortic sinuses also appeared to be taller and the leaflets larger than normal. The leaflet free-edge length, the leaflet height, and the sinus height were found to increase with the dilated STJ diameter. The degree of AI was not found to correlate well with any of the dimensions measured. Conclusions: The dimensions of the leaflets may change parallel to aortic root dilatation with AI. Therefore, during valve sparing, it may be necessary to correct both the dilatation of the root and the leaflet free-edge length to achieve a competent valve.     

Valvuloplasty for aortic regurgitation with bicuspid valve: report of a case

A 32-year-old male patient with bicuspid aortic valve underwent valvuloplasty for the treatment of aortic regurgitation. The aortic regurgitation was estimated to be grade III based on the transthoracic echocardiography and aortography findings. Transesophageal echocardiography showed prolapse of the conjoined leaflet. At surgery, the valvuloplasty consisted of triangular resection and re-suture of the prolapsed larger leaflet, and subcommissural annuloplasty. The degree of the aortic regurgitation decreased to very slight degree after the repair. The peak pressure gradient across the repaired aortic valve was 8.8 mmHg. The patient was discharged without any complications. The bicuspid aortic valve demonstrating aortic regurgitation seems to be repairable. As a result, the valvuloplasty is indicated for such patients, especially for young patients.     

Re-do pericardial reconstruction of the aortic valve in Brucella endocarditis

We report a 12-year-old boy who had undergone an auto-pericardial aortic valve implantation 3 years ago for rheumatic aortic regurgitation. He presented with Brucella endocarditis of the auto-pericardial leaflets with new-onset severe aortic regurgitation, congestive cardiac failure and systemic sepsis. He had an aortic root abscess with multiple pseudoaneurysms in relation to the aortic sinus. Following medical stabilisation, he underwent re-do surgery with debridement of the root abscess, closure of the pseudoaneurysms, excision of the auto-pericardial aortic leaflets and reconstruction of the aortic valve with donor pericardium. He had an uneventful recovery and is asymptomatic on follow-up.     

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.

An assessment of the mechanical properties of leaflets from four second-generation porcine bioprostheses with biaxial testing techniques

The aim of this study was to determine whether second-generation porcine bioprostheses, glutaraldehyde fixed at pressures said to be less than 4 mm Hg, exhibit more natural leaflet material properties than earlier valves fixed at 80 to 100 mm Hg. Biaxial mechanical testing techniques were used to compare Carpentier-Edwards SAV, St. Jude Medical BioImplant, Hancock II, and Medtronic Intact bioprostheses (12 leaflets from four valves in each case) with fresh porcine aortic valves and high pressure-fixed Carpentier-Edwards 6625 bioprostheses (14 leaflets from five valves in each case). The circumferential extensibility of leaflets from Medtronic Intact bioprostheses and from fresh porcine aortic valves were not significantly different (p greater than 0.05), whereas leaflets from the other second-generation valves tested and from Carpentier-Edwards 6625 valves were highly inextensible in the circumferential direction. The radial material properties of leaflets from all bioprostheses differed from those of fresh porcine aortic valves, which were very extensible with a high pretransitional compliance. The radial extensibility and compliance of Hancock II, St. Jude Medical BioImplant, and Carpentier-Edwards 6625 leaflets were not significantly different (p greater than 0.05). In the radial direction, Carpentier-Edwards SAV and Medtronic Intact valve leaflets were substantially more extensible than Carpentier-Edwards 6625 leaflets (p less than 0.01), whereas Medtronic Intact leaflets were more compliant than all other bioprostheses. These data demonstrate (1) that second-generation porcine bioprosthetic valves do not necessarily exhibit more natural leaflet material properties than earlier high pressure-fixed xenografts and (2) that Medtronic Intact valve leaflets have material properties most closely approximating the fresh porcine aortic valve.