Bioprosthetic Valve Research Articles

Feasibility of intentional bioprosthetic valve fracture in the tricuspid position.

Transcatheter tricuspid valve-in-valve (ViV) replacement has yielded good hemodynamic outcomes in the treatment of dysfunctional bioprosthetic valves (BPVs). Intentional fracture of certain rigid BPV frames, if feasible, allows a larger implanted valve when compared with implant into an unfractured BPV. There remains limited data on the feasibility of tricuspid valve frame fracture. Evaluate the feasibility of transcatheter tricuspid ViV replatement with fracture of the underlying BPV ring. An international multicenter registry of tricuspid ViV replacement with intentional tricuspid valve frame fracture was created. Demographic data along with procedural characteristics, outcomes, and follow-up data were collected. Comparison was made to the pre- and post-ViV replacement with fracture of the tricuspid valve frame conditions. Ten patients from six centers were included with a median age and weight of 29 years and 67.3 kg respectively. Tricuspid valve frame fracture was performed using a median balloon diameter 3 mm (IQR 3-5) larger than the true inner diameter (ID). The final ID was a mean of 1.5 mm (95% CI: 0.35, 2.64: p < 0.05), and median 1.1 mm (0.5, 2.1) larger than the reported true ID of the surgical BPV after ViV replacement. The mean tricuspid inflow gradient by echocardiogram decreased by 6.65 mmHg (95% CI: 4.14, 9.15: p < 0.001). All procedures were without complication, specifically there was no heart block, pericardial effusion, or right coronary disruption. Intentional tricuspid valve frame fracture with tricuspid ViV replacement is feasible and can increase the valve orifice potentially reducing the risk of ViV patient prosthesis mismatch and is not associated with significant complications.

Posttraumatic aortic regurgitation and root pseudoaneurysm following blunt chest trauma: a case report

BackgroundThe simultaneous diagnosis of severe aortic regurgitation and aortic root pseudoaneurysm resulting from traffic injury is extremely rare. This report presents the case of a patient with Marfan syndrome who experienced aortic root pseudoaneurysm and subacute severe aortic regurgitation following a traffic accident.Case presentationA 64-year-old woman was diagnosed with Marfan syndrome 16 years ago and is undergoing ongoing follow-up at an outpatient clinic. Eight years previously, the patient underwent total arch replacement combined with J-graft open stent graft® (JGOS; Japan Lifeline Co., Tokyo, Japan) deployment for acute type A dissection. Five months before presentation, the patient suffered a left rib fracture in a traffic accident and received conservative management at a local hospital. The patient presented to the emergency room with worsening shortness of breath and orthopnea. Echocardiography revealed severe aortic regurgitation and moderate tricuspid regurgitation. Computed tomography revealed new-onset pseudoaneurysm at the aortic root. Surgical repair was successfully performed using a modified Bentall procedure with a bioprosthetic valve and tricuspid annuloplasty. Intraoperative findings revealed pseudoaneurysm with perforation of the right sinus of Valsalva. Although the left and right aortic valve leaflets were normal, the noncoronary leaflet exhibited a ruptured fibrous strand of a cusp fenestration, resulting in acute aortic regurgitation.ConclusionsThis case report highlights the rare occurrence of aortic root pseudoaneurysm and subacute aortic regurgitation following a traffic accident. In cases of blunt chest trauma, particularly in patients with Marfan syndrome, frequent examination is crucial to assess the possibility of posttraumatic aortic regurgitation and aortic injury.

Utilizing a sutureless valve for prosthetic valve endocarditis after aortic root replacement

BackgroundReoperation following aortic root replacement is associated with significantly high operative mortality. Etiologies related to infection are known to increase the operative mortality rate more than other etiologies. In such a clinical setting, a sutureless valve could lower the operative mortality by shortening the cardiac arrest and the operative time.Case presentationA 61-year-old male underwent emergent aortic root and total arch replacement with an open stent graft for acute type-A aortic dissection. A bioprosthetic valve was employed for aortic root replacement using the double-sewing ring technique. A fungal infection by Candida parapsilosis was postoperatively detected and improved with intravenous antifungal drug administration. However, he developed congestive heart failure one year later, and the blood cultures turned positive repeatedly for Candida parapsilosis. The prosthetic valve infection was suspected upon identifying vegetation on the bioprosthetic valve through transthoracic echocardiography. The computed tomography scan and operative findings confirmed that the infection was localized on the prosthetic valve. Consequently, the infected valve was removed without a vascular conduit, and a sutureless valve was implanted. The postoperative course was uneventful, without any evidence of recurrent fungal infection, and the patient was discharged on postoperative day 28.ConclusionsDeploying a sutureless valve can facilitate a more straightforward and minimally invasive redo procedure. Preoperative computed tomography can predict the valve size, which is the key to implanting a sutureless valve successfully after the modified Bentall procedure.

Acute Severe Bioprosthetic Aortic Valve Regurgitation Presenting as Acute Coronary Syndrome Managed With Emergency Valve-In-Valve Transcatheter Aortic Valve Implantation

Acute Severe Bioprosthetic Aortic Valve Regurgitation Presenting as Acute Coronary Syndrome Managed With Emergency Valve-In-Valve Transcatheter Aortic Valve Implantation

Transcatheter Pulmonary Valve-in-Valve Implantation for Failed Surgical Bioprosthetic Pulmonary Valves: An Australian Single-Centre Experience

Transcatheter Pulmonary Valve-in-Valve Implantation for Failed Surgical Bioprosthetic Pulmonary Valves: An Australian Single-Centre Experience

Impact of Extracellular Matrix Injury on the Calcification of Artificial Bovine Pericardial Leaflets: An Experimental Study.

To investigate the role of extracellular matrix (ECM) injury in bioprosthetic valve calcification, we constructed an ECM damage model by applying a 15 N stress to the bovine pericardium sample in both transverse and longitudinal directions after tissue cross-linking, whereas no stress was applied in the control group. Then we implanted two pieces of bovine pericardium on both sides of the dorsal midline in Wistar rats from both groups and measured the calcium content of the implanted bovine pericardium. The results showed that the calcium content of experimental group was significantly higher than that of control group (p < 0.05). Second, we implanted prosthetic valves made from bovine pericardium in the experimental and control groups into small-tailed Han sheep (Ovis aries). After 180 days, the prosthetic valve was removed for gross and histopathological observation as well as quantitative analysis of calcium. We found a higher average calcium content in bovine pericardium from the experimental group than that from controls. Furthermore, calcium salt deposition was detected on the ventricular surface of valves along with roughened valve leaflets in the experimental group. Our data support the hypothesis that the bovine pericardium with ECM injury is more prone to calcification.

One-Year Outcomes of Transseptal Mitral Valve-in-Valve in Intermediate Surgical Risk Patients.

Transcatheter mitral valve-in-valve replacement offers a less-invasive alternative for high-risk patients with bioprosthetic valve failure. Limited experience exists in intermediate-risk patients. We aim to evaluate 1-year outcomes of the PARTNER 3 mitral valve-in-valve study. This prospective, single-arm, multicenter study enrolled symptomatic patients with a failing mitral bioprosthesis demonstrating greater than or equal to moderate stenosis and regurgitation and Society of Thoracic Surgeons score ≥3% and <8%. A balloon-expandable transcatheter heart valve (SAPIEN 3, Edwards Lifesciences) was used via a transeptal approach. The primary end point was the composite of all-cause mortality and stroke at 1 year. A total of 50 patients from 12 sites underwent mitral valve-in-valve from 2018 to 2021. The mean age was 70.1±9.7 years, mean Society of Thoracic Surgeons score was 4.1%±1.6%, and 54% were female. There were no primary end point events (mortality or stroke) through 1 year, and no left-ventricular outflow tract obstruction, endocarditis, or mitral valve reintervention was reported. Six patients (12%) required rehospitalization, including heart failure (n=2), minor procedural side effects (n=2), and valve thrombosis (n=2; both resolved with anticoagulation). An additional valve thrombosis was associated with no significant clinical sequelae. From baseline to 1 year, all subjects with available data had none/trace or mild (grade 1+) mitral regurgitation and the New York Heart Association class improved in 87.2% (41/47) of patients. Mitral valve-in-valve with a balloon-expandable valve via transseptal approach in intermediate-risk patients was associated with improved symptoms and quality of life, adequate transcatheter valve performance, and no mortality or stroke at 1-year follow-up. URL: https://www.clinicaltrials.gov; Unique identifier: NCT03193801.

Age-Specific Outcomes of Bioprosthetic vs. Mechanical Aortic Valve Replacement: Balancing Reoperation Risk with Anticoagulation Burden.

The choice of prosthesis for aortic valve replacement (AVR) remains challenging. The risk of anticoagulation complications vs. the risk of aortic valve reintervention should be weighed. This study compared the outcomes of bioprosthetic vs. mechanical AVR in patients older and younger than 50. This retrospective study was conducted from 2009 to 2019 and involved 292 adult patients who underwent isolated AVR. The patients were divided according to their age (above 50 years or 50 years and younger) and the type of valves used in each age group. The outcomes of bioprosthetic valves (Groups 1a (>50 years) and 1b (≤50 years)) were compared with those of mechanical valves (Groups 2a (>50 years) and 2b (≤50 years)) in each age group. The groups had nearly equal rates of preexisting comorbidities except for Group 1b, in which the rate of hypertension was greater (32.6% vs. 14.7%; p = 0.025). This group also had higher rates of old stroke (8.7% vs. 0%, p = 0.011) and higher creatinine clearance (127.62 (108.82-150.23) vs. 110.02 (84.87-144.49) mL/min; p = 0.026) than Group 1b. Patients in Group 1a were significantly older than Group 2a (64 (58-71) vs. 58 (54-67) years; p = 0.002). There was no significant difference in the NYHA class between the groups. The preoperative ejection fraction and other echocardiographic parameters did not differ significantly between the groups. Re-exploration for bleeding was more common in patients older than 50 years who underwent mechanical valve replacement (p = 0.021). There was no difference in other postoperative complications between the groups. The groups had no differences in survival, stroke, or bleeding rates. Aortic valve reintervention was significantly greater in patients ≤ 50 years old with bioprosthetic valves. There were no differences between groups in the changes in left ventricular mass, ejection fraction, or peak aortic valve pressure during the 5-year follow-up. The outcomes of mechanical and bioprosthetic valve replacement were comparable in patients older than 50 years. Using bioprosthetic valves in patients younger than 50 years was associated with a greater rate of valve reintervention, with no beneficial effect on the risk of bleeding or stroke.

A Case of Re-Do Aortic Valve Replacement for Early Bioprosthetic Valve Dysfunction due to a Large Vegetation of Nonbacterial Thrombotic Endocarditis

A Case of Re-Do Aortic Valve Replacement for Early Bioprosthetic Valve Dysfunction due to a Large Vegetation of Nonbacterial Thrombotic Endocarditis

Long-Term Outcomes of Mechanical Versus Bioprosthetic Aortic Valve Replacement in Patients Aged Under 50 Years: Meta-Analysis of Reconstructed Time-to-Event Data

To compare the long-term outcomes of mechanical versus bioprosthetic aortic valve replacement (AVR) in patients aged <50 years, we performed a study-level meta-analysis with reconstructed time-to-event data including studies published by December of 2023. The primary outcome was overall survival. Secondary outcomes included reoperation, major bleeding, and stroke. A total of 5 studies met our inclusion criteria, with a total of 4,245 patients (2,311 mechanical and 1,934 bioprosthetic). All studies were observational and the mean age of groups across the studies ranged from 38.2 to 43.0 years. The median follow-up time was 11.4 years (interquartile range 6.9 to 15.0). Bioprosthetic AVR was associated with reduced overall survival and higher risk of all-cause death (hazard ratio [HR] 1.170 95% confidence interval [CI] 1.002 to 1.364, p = 0.046), increased risk of reoperation over time (HR 2.581, 95% CI 2.102 to 3.168, p <0.001), decreased risk of major bleeding (HR 0.500, 95% CI 0.367 to 0.682, p <0.001), and decreased risk of stroke (HR 0.751, 95% C, 0.565 to 0.998, p = 0.049) compared with mechanical AVR in patients aged <50 years. In conclusion, for patients aged <50 years, bioprosthetic AVR is associated with increased mortality and risk of reoperation compared with mechanical valves. In contrast, mechanical AVR is associated with an increased risk of major bleeding events and stroke. These aspects should be carefully considered during the selection of valve type in this age group; however, we should keep in mind that the statistically significant differences in the risk of all-cause death and stroke might not be clinically relevant (because of marginal statistical significance).

Asymptomatic bacterial invasion as the reason for inflammation in bioprosthetic heart valves on later stages of their functioning

Asymptomatic bacterial invasion as the reason for inflammation in bioprosthetic heart valves on later stages of their functioning

Effect of bioprosthetic leaflet anisotropy on stent dynamics of Transcatheter Aortic Valve Replacement devices

The assessment of stent fatigue in Transcatheter Aortic Valve Replacement (TAVR) systems is critical for the design of next-generation devices, both in vitro and in vivo. The mechanical properties of the bioprosthetic heart valves (BHVs) have a significant impact on the fatigue life of the metallic stent and thus must be taken into consideration when evaluating new TAVR device designs. This study aims to investigate the relationship between BHV anisotropic behaviour and the asymmetric deflections of the stent frame observed during in vitro testing.An explicit dynamics finite element model of the nitinol stent with attached bioprosthetic valve leaflets was developed to evaluate the deflections of the TAVR device under haemodynamic loading. Our results demonstrate that pericardium behaviour plays a dominant role in determining stent frame deflection. The anisotropic behaviour of the leaflets, resulting from collagen fibre orientation, affects the extent of deflection encountered by each commissure of the frame. This leads to asymmetric variation in frame deflection that can influence the overall fatigue life of the nitinol stent. This study highlights the importance of considering both the flexible nature of the metallic stent as well as the leaflet anisotropic behaviour in the design and fatigue assessment of TAVR systems.

Clinical characteristics and long-term outcome of patients with bioprosthetic mitral valve- Experience from a South Asian country.

Due to rheumatic heart disease, young people are more likely to develop valvular heart disease in developing countries. In countries like Pakistan, surgeons implant more bioprosthetic mitral valves (MVs) in younger patients. However, bioprosthetic valves degenerate rapidly in younger people, leading to bioprosthetic MV dysfunction (BMVD). This study aims to evaluate the clinical characteristics and long-term outcomes of patients with bioprosthetic MV replacement (MVR) at a tertiary care hospital in a South Asian country. This is a retrospective observational study, conducted at a tertiary care hospital. We included a total of 502 patients who underwent bioprosthetic MVR from the year 2006 to 2020. Clinical and surgical characteristics along with transthoracic echocardiographic findings (pre-surgery and recent most follow-up studies) were noted. Follow-up data were also collected. Out of 502 patients, 322 (64%) were female, mean age at the time of surgery was 49.42 ± 14.56 years. Mitral regurgitation was more common, found in 279 (55.6%) patients followed by mitral stenosis in 188 (37.5%) patients. MVR was done as an elective procedure due to the New York Heart Association (NYHA) II to IV symptoms at the time of surgery in 446 (88.8%) patients. In the mean follow-up of 6.59 ± 2.99 years, BMVD was observed in 183 (36.5%) patients. However, re-do MV surgery was done in only 49 (9.8%) patients. Patients were divided into two groups based on normal functioning bioprosthetic MV and BMVD. Comparing the two groups, individuals with normal functioning bioprosthetic MV had a mean age of 51.6 ± 14.27 years, while those with BMVD had a mean age of 45.639 ± 14.33 years at the time of index surgery (P = 0.000). There were more long-term complications including heart failure (n = 16, 8.74%), atrial fibrillation (n = 11, 6.01%), and death (n = 6, 3.28%) in the BMVD group which were statistically significant. This study is distinct because it demonstrates the outcomes of bioprosthetic valve replacement in a relatively younger South Asian population. Due to rapid degeneration of bioprosthetic valve in younger patients, significant number of patients developed BMVD along with poor long-term clinical outcomes, even at a short follow-up period of <10 years. These findings are similar to international data and signify that mechanical MVR may be a more reasonable alternative in younger patients.

A notion of bioprosthetic aortic valve durability.

A notion of bioprosthetic aortic valve durability.

Age-Based Outcomes After Surgical Aortic Valve Replacement With Bioprosthetic Versus Mechanical Valves

Recommendations for prosthesis type in older patients who underwent surgical aortic valve replacement (SAVR) are established, albeit undervalidated. The purpose of this study is to compare outcomes after bioprosthetic versus mechanical SAVR across various age groups. This was a retrospective study using an institutional SAVR database. All patients who underwent isolated SAVR were compared across valve types and age strata (<65 years, 65 to 75 years, >75 years). Patients who underwent concomitant operations, aortic root interventions, or previous aortic valve replacement were excluded. Objective survival and aortic valve reinterventions were compared. Kaplan-Meier survival estimation and multivariate regression were performed. A total of 1,847 patients underwent SAVR from 2010 to 2023. A total of 1,452 patients (78.6%) received bioprosthetic valves, whereas 395 (21.4%) received mechanical valves. Of those who received bioprosthetic valves, 349 (24.0%) were aged <65 years, 627 (43.2%) were 65 to 75 years, and 476 (32.8%%) were older than 75 years. For patients who received mechanical valves, 308 (78.0%) were aged <65 years, 84 (21.3%) were between 65 and 75 years, and 3 (0.7%) were >75 years. The median follow-up in the total cohort was 6.2 (2.6 to 8.9) years. No statistically significant differences were observed in early-term Kaplan-Meier survival estimates between SAVR valve types in all age groups. However, the cumulative incidence estimates of aortic valve reintervention were significantly higher in patients aged under 65 years who received bioprosthetic than those who received mechanical valves, with 5-year reintervention rates of 5.8% and 3.1%, respectively (p = 0.002). On competing risk analysis for valve reintervention, bioprosthetic valves were significantly associated with an increased hazard of aortic valve reintervention (hazard ratio 3.35, 95% confidence interval 1.73 to 6.49, p <0.001). In conclusion, SAVR with bioprosthetic valves (particularly, in patients aged <65 years) was comparable in survival to mechanical valve SAVR but significantly associated with increased valve reintervention rates.

Long-term durability of bioprosthetic aortic valve replacement in young patients with bicuspid aortic stenosis

ObjectiveTo examine long-term surgical aortic valve replacement (SAVR) outcomes for young (ie, younger than age 65 years) patients with bicuspid aortic valve and aortic stenosis (AS) with or without concomitant aneurysm. BackgroundThere are few studies evaluating the early and late outcomes of SAVR in young patients (younger than age 65 years) with bicuspid aortic valve and AS. MethodsUsing institutional data from 2004 through 2022, 498 patients with bicuspid aortic valve younger than age 65 years underwent SAVR for AS with bioprosthetic valves. We examined operative outcomes, long-term valve durability, and reintervention. ResultsThe total cohort comprised 281 patients undergoing isolated SAVR and 217 with concomitant aneurysm repair (SAVR/aneurysm). The average age was 55 ± 8 years, with Society of Thoracic Surgeons predicted risk of mortality score of median 0.7 (IQR 0.5, 1.0) and mean valve size of 25 mm. Operative mortality (0.7% vs 1.4%; P = .77) was similar between SAVR and SAVR/aneurysm patients. Predischarge permanent pacemaker implantation occurred in 1.6% (8 out of 498) patients. During overall follow-up of 5.0 years (IQR 1.8-9.9; range, 0.2-18.2 years), the cumulative incidence of reintervention at 10 years for structural valve degeneration (n = 33), including valve-in-valve (n = 15) was 6.6% (8.1% SAVR vs 4.5% SAVR/aneurysm; P = .66). No mortality was observed for valve-in-valve or redo-SAVR. Moderate or greater aortic regurgitation and paravalvular leak were observed in 6.5% and 0.3%, respectively, at most recent follow-up. ConclusionsBicuspid AS is common in patients younger than 65 years and management includes consideration of future valve intervention. SAVR confers excellent operative and reoperative outcomes, 10-year durability, and valve function. These results may support initial SAVR when considering lifetime management of AS.

Perioperative Outcomes After Bioprosthetic Valve Replacement in Patients Sensitized to Alpha-gal

BackgroundAlpha-gal syndrome from tick bites, due to sensitivity to alpha-gal, can cause severe allergies. Heart valve implants contain alpha-gal, yet alpha-gal syndrome screening is not standard before valve replacement. This study examines perioperative outcomes in patients with alpha-gal antibodies. MethodsThis is a single-institution prospective cohort study of patients undergoing bioprosthetic aortic valve replacement between January 2022 and January 2023. Anti-alpha-gal immunoglobulin E levels were measured, with primary outcomes being severe allergic reactions and in-hospital mortality, and secondary outcomes including intensive care unit and hospital stay. ResultsOf 155 patients, 32.7% (n = 19) of surgical aortic valve replacement and 29.9% (n = 29) of transcatheter aortic valve replacement patients had detectable immunoglobulin E levels without subsequent serious allergic reactions or in-hospital mortality. Postoperative hospital stay and valve function were similar across groups. ConclusionsIn this study, sensitization to alpha-gal was not associated with serious allergic reactions and did not affect immediate aortic valve function after surgical aortic valve replacement or transcatheter aortic valve replacement.

Transcatheter aortic valve replacement with corevalve self-expanding bioprosthesis: Clinical and durability data up to 12 years

Background and aimsTranscatheter aortic valve replacement (TAVR) determined a paradigm shift in the treatment of patients with severe symptomatic aortic stenosis but data on very long-term durability are lacking. We sought to evaluate the clinical and hemodynamic outcomes of the CoreValve porcine pericardial self-expanding bioprosthesis at 12-year follow-up. Methods882 inoperable or high-risk patients were treated with the CoreValve bioprosthesis in 8 Italian high-volume centers between 2007 and 2011. The endpoints were 12-year all-cause and cardiovascular mortality, and Cumulative Incidence Functions (CIFs) for severe Structural Valve Deterioration (SVD), Bioprosthetic Valve Dysfunction (BVD), Bioprosthetic Valve Failure (BVF), and severe Hemodynamic Valve Deterioration (HVD). VARC-3 definitions were applied. ResultsBaseline characteristics included a mean age of 83 ± 6 years, and NYHA class III or IV in 76.3 % of patients. The actuarial risk of death at 12 years after TAVR was 95.5 % (CI 93.5 %- 97.1 %).The actual risk of cardiovascular death, weighted against the risk of non-cardiac death at 12 years was 23.9 % (21.0 %–26.8 %). The 12-year actual risk of BVD was 7.0 % (5.3 %–8.9 %), of SVD was 3.6 % (2.5 %–5.2 %), of BVF was 3.12 % (2.02 %–4.57 %), and of severe HVD was 1.7 % (0.9 %–2.9 %). Mean transaortic gradient significantly decreased after the procedure (52 ± 15 mmHg vs 9 ± 5 mmHg, p < 0.001), and remained stable up to 12 years (12 ± 4 mmHg, P = 0.08 vs. discharge). ConclusionsThe first-generation CoreValve bioprosthesis showed reassuring clinical and hemodynamic performance at 12-year follow-up.

Differences between valve types in anatomic changes of the aortic root after surgical aortic valve replacement

BackgroundWhen transcatheter aortic valve-in-surgical aortic valve (TAV-in-SAV) is considered as a secondary interventional option, it is desirable to estimate the risk of coronary obstruction during future TAV-in-SAV before the initial surgical aortic valve replacement (SAVR), for which knowledge of the anatomic changes after SAVR is essential. We investigated the changes in the aortic root and evaluated the differences in changes between valve types. MethodsPre- and post-SAVR computed tomography scans of 124 patients with aortic stenosis who underwent SAVR with various bioprosthetic valves were analyzed retrospectively. Postoperative aortic root changes and parameters related to future TAV-in-SAV were compared between the sutured valve group and rapid-deployment/sutureless valve group. ResultsAfter SAVR, the coronary height in the sutured valve group and rapid-deployment/sutureless valve group was shortened by a median of 4.6 to 5.3 mm and 0.5 to 2.2 mm, respectively, and the sinus of Valsalva (SOV) diameter was reduced by a median of 1.6 to 2.7 mm and 0.1 to 1.3 mm, respectively. A significantly higher proportion of patients in the rapid deployment/sutureless valve group had a coronary orifice (especially in the right coronary artery) above the risk plane. The valve-to-coronary distance and valve-to-aorta distance (VTA) were adequate in most patients. The only difference between the groups was in the left VTA. ConclusionsDecreases in coronary height and SOV diameter were observed after SAVR, especially in the sutured valve group. The aortic root structure was better preserved in the rapid-deployment/sutureless valve group. This may be advantageous for future TAV-in-SAV. These results are important for considering the feasibility of future TAV-in-SAV.

Commentator Discussion: Long-term durability of bioprosthetic aortic valve replacement in young patients with bicuspid aortic stenosis

Commentator Discussion: Long-term durability of bioprosthetic aortic valve replacement in young patients with bicuspid aortic stenosis