The many faces of bicuspid aortic valve disease

Fluid-structure interaction modeling of compliant aortic valves using the lattice Boltzmann CFD and FEM methods

The lattice Boltzmann method (LBM) has been increasingly used as a stand-alone CFD solver in various biomechanical applications. This study proposes a new fluid-structure interaction (FSI) co-modeling framework for the hemodynamic-structural analysis of compliant aortic valves. Toward that goal, two commercial software packages are integrated using the lattice Boltzmann (LBM) and finite element (FE) methods. The suitability of the LBM-FE hemodynamic FSI is examined in modeling healthy tricuspid and bicuspid aortic valves (TAV and BAV), respectively. In addition, a multi-scale structural approach that has been employed explicitly recognizes the heterogeneous leaflet tissues and differentiates between the collagen fiber network (CFN) embedded within the elastin matrix of the leaflets. The CFN multi-scale tissue model is inspired by monitoring the distribution of the collagen in 15 porcine leaflets. Different simulations have been examined, and structural stresses and resulting hemodynamics are analyzed. We found that LBM-FE FSI approach can produce good predictions for the flow and structural behaviors of TAV and BAV and correlates well with those reported in the literature. The multi-scale heterogeneous CFN tissue structural model enhances our understanding of the mechanical roles of the CFN and the elastin matrix behaviors. The importance of LBM-FE FSI also emerges in its ability to resolve local hemodynamic and structural behaviors. In particular, the diastolic fluctuating velocity phenomenon near the leaflets is explicitly predicted, providing vital information on the flow transient nature. The full closure of the contacting leaflets in BAV is also demonstrated. Accordingly, good structural kinematics and deformations are captured for the entire cardiac cycle.

Bicuspid Aortic Valves: an Up-to-Date Review on Genetics, Natural History, and Management

PURPOSE OF REVIEW

Bicuspid aortic valve (BAV) is the most common congenital cardiac abnormality. It has a wide spectrum of clinical manifestations including aortic regurgitation (AR), aortic stenosis, and an associated aortopathy with a small but increased risk of aortic dissection. This review describes current knowledge of BAV, from anatomy and genetics to a discussion of multifaceted strategies utilized in the management of this unique patient population. This review will also highlight critical knowledge gaps in areas of basic and clinical research to enhance further understanding of this clinical entity.

RECENT FINDINGS

The current knowledge regarding pathophysiologic mechanisms, screening, and surveillance guidelines for BAV and the associated aortopathy is discussed. We also discuss current management techniques for aortic valve repair versus replacement, indications for aortic surgery (root or ascending aorta), and the emergence of the Ross procedure as a viable management option not only in children, but also in adolescents and adults. The varied clinical phenotype of the BAV, resulting in its specific complex hemodynamic interactions, renders it an entity which is separate and distinct from the tricuspid aortic valve pathologies. While various aortic histopathologic and protein alterations in BAV patients have been described, it remains unclear if these changes are causal or the result of hemodynamic alterations imposed by sheer stress on the intrinsically dysfunctional BAV. Medical management for patients with BAV with AS, AI, or dilated aortic roots/ascending aortas remains challenging and needs further investigation. More than 50% of patients with BAV will undergo AVR during their lifetime, and more than 25% of patients with BAV undergo aortic surgery performed for dilation of the aortic root or ascending aorta, often concurrently with AVR. The search for the ultimate genetic or epigenetic cause of the different bicuspid phenotypes will ultimately be facilitated by the next-generation sequencing tools that allow for study of large populations at low cost. Improvements in diagnostic and stratification criteria to accurately risk assess BAV patients are critical to this process.

Long-term performance of bicuspid and quadricuspid aortic valves: Similarities and differences

While bicuspid aortic valve (BAV) is a common congenital cardiac anomaly, quadricuspid aortic valve (QAV) is rare. The usual three-leaflet aortic valve is characterized by engineering advantages with superior long-term performance, and thus, degenerative changes and significant functional deterioration appear at advanced age.

AIM

Evaluation of long-term performance, similarities, and differences between QAV and BAV.

METHODS

Screening of 19 000 consecutive echocardiographic studies was performed.

RESULTS

BAV was reported in 131 subjects with a prevalence of 0.7%, while QAV was seen in 11 with a prevalence of 0.06%, P < .00001. Age of BAV patients was younger, 45 ± 20 years vs 62 ± 17 years in QAV, P < .05, with higher proportion of females in those with QAV, 40% vs 30%. Chamber diameters were similar in both groups. Higher atrial contraction-A-wave mitral peak velocities and longer E-wave deceleration times were found in subjects with QAV, P < .05 for both. Dilated ascending aorta was found in 25% of patients with BAV and in 18% of those with QAV, P = .2. Moderate and severe aortic valve stenosis were found in 21% of patients with BAV and in 27% of those with QAV, P = ns. More than moderate aortic regurgitation was found in 15.5% of BAV patients and in 9% of QAV, P = ns. Aortic valve infective endocarditis was found in 1.5% of BAV patients and in 9% of those with QAV.

CONCLUSIONS

BAV is a common congenital anomaly, while QAV is rare. Similar prevalence of significant valve disease and aortopathy was found in both anomalies, though at younger age in BAV patients.

Fluid-Structure Interaction Models of Bicuspid Aortic Valves: The Effects of Nonfused Cusp Angles

Bicuspid aortic valve (BAV) is the most common type of congenital heart disease, occurring in 0.5-2% of the population, where the valve has only two rather than the three normal cusps. Valvular pathologies, such as aortic regurgitation and aortic stenosis, are associated with BAVs, thereby increasing the need for a better understanding of BAV kinematics and geometrical characteristics. The aim of this study is to investigate the influence of the nonfused cusp (NFC) angle in BAV type-1 configuration on the valve's structural and hemodynamic performance. Toward that goal, a parametric fluid-structure interaction (FSI) modeling approach of BAVs is presented. Four FSI models were generated with varying NFC angles between 120 deg and 180 deg. The FSI simulations were based on fully coupled structural and fluid dynamic solvers and corresponded to physiologic values, including the anisotropic hyper-elastic behavior of the tissue. The simulated angles led to different mechanical behavior, such as eccentric jet flow direction with a wider opening shape that was found for the smaller NFC angles, while a narrower opening orifice followed by increased jet flow velocity was observed for the larger NFC angles. Smaller NFC angles led to higher concentrated flow shear stress (FSS) on the NFC during peak systole, while higher maximal principal stresses were found in the raphe region during diastole. The proposed biomechanical models could explain the early failure of BAVs with decreased NFC angles, and suggests that a larger NFC angle is preferable in suture annuloplasty BAV repair surgery.

Clinical Characteristics of Korean Patients with Bicuspid Aortic Valve Who Underwent Aortic Valve Surgery

Background and Objectives

Clinical data for Korean patients with bicuspid aortic valve (BAV) that underwent aortic valve (AV) surgery are currently limited.

Methods

Data for 1,160 consecutive adult BAV patients who underwent AV surgery from 2000 to 2014 in 4 tertiary referral centers were retrospectively analyzed. A standard case report form was used for clinical and echocardiographic parameters.

Results

Mean age at the time of AV surgery was 59±13 years. The most common cause of AV surgery was aortic stenosis (AS, 892 [77%]), followed by aortic regurgitation (AR, 199 [17%]), and infective endocarditis (69 [6%]). AS showed a skewed peak in the aged population and was the predominant cause of AV surgery (87%) in patients ≥50 years of age, whereas AR (46%) and active infective endocarditis (19%) were more common in younger patients (p<0.001). Echocardiographic determination of the BAV phenotype revealed that fusion of the right coronary cusp (RCC) and left coronary cusp (LCC) was most common (622 [53%]), followed by fusion of RCC and non-coronary cusp (NCC) (313 [27%]), and fusion of LCC and NCC (42 [4%]); the BAV phenotype could not be determined in the remaining 183 patients (16%). Fusion of RCC and LCC was more commonly observed in patients with AR than in those with AS (74% vs. 49%; p<0.001).

Conclusion

BAV patients were characterized by distinct surgical indications according to their age. Possible associations between BAV phenotypes and surgical indications with potential impacts of ethnicity need to be tested in further studies.

Efficacy and Safety of Transcatheter Aortic Valve Implantation for Bicuspid Aortic Valves: A Systematic Review and Meta-Analysis

PURPOSE

To elucidate the performance of transcatheter aortic valve implantation (TAVI) in bicuspid aortic valve (BAV) patients through a systematic review and meta-analysis.

METHODS

A systematic literature review was performed by searching eligible articles in PubMed, Medline, EMBASE, Google Scholar and CNKI. Meta-analysis of included case-control/cohort studies was further conducted. Relative risks (RRs) and the corresponding 95% confidence intervals (CIs) were used to compare clinical outcomes of BAV patients and non-BAV patients.

RESULTS

A total of 17 articles including eight case reports, four case series and five case-control/cohort studies with 166 BAV patients were analyzed. Device success rate achieved for TAVI in this cohort of BAV patients was 95.2%. The 30-day mortality rate was 8.4%, and the medium-term (range from 6 months to 2 years) mortality rate reported was 17.9%. Overall, the performance of TAVI in BAV patients was comparable to that in non-BAV patients, as reported by the included case-control/cohort studies (30-day mortality rate: RR = 1.05, 95%CI 0.57-1.95, p = 0.87; Device success rate: RR = 1.00, 95%CI 0.95-1.05, p = 0.94; Incidence of moderate to severe paravalvular regurgitation: RR = 1.25, 95%CI 0.85-1.84, p = 0.25).

CONCLUSION

The present study suggested that TAVI may be a feasible and safe treatment modality for BAV patients.

Aortic distensibility in bicuspid aortic valve patients with normal aortic diameter

Objective:

Bicuspid aortic valve (BAV) is associated with aortic abnormalities. The ascending aorta tends to dilate and its elasticity deteriorates. The morphology of the BAV and the elasticity of the proximal ascending aorta seem to influence the outcome. This study aimed to determine the distensibility of the ascending aorta with normal diameter in BAV patients and its relation to its morphology.

Methods:

This is a cross-sectional study. In the patients with BAV referred for echocardiography, the phenotype was defined as anteroposterior (AP) or mediolateral (ML) leaflet orientations. The aortic distensibility at 5–10 mm above the sinotubular junction was assessed using transthoracic echocardiography in 50 BAV patients, and 50 healthy controls with tricuspid aortic valve (TAV) matched by gender and age.

Results:

The ascending aorta in BAV patients had less distensibility compared with that in the control subjects (0.00298 ± 0.0023 versus 0.00805 ± 0.0028 cm2 dynes−1 × 10−6, respectively, p < 0.001). The ML phenotype of BAVs was more frequent. However, the reduced distensibility was not related to gender and morphology of the valve.

Conclusions:

Regardless of the valve morphology and also in the absence of aortic dilation, aortic distensibility is impaired in BAV subjects compared with TAV subjects. This finding supports the idea of an intrinsic aortic wall anomalies underlying the impaired elasticity of the aorta in BAV patients.