Pathological Investigation of Congenital Bicuspid Aortic Valve Stenosis, Compared with Atherosclerotic Tricuspid Aortic Valve Stenosis and Congenital Bicuspid Aortic Valve Regurgitation

Bicuspid Aortic Valve Disease: Classifications, Treatments, and Emerging Transcatheter Paradigms

Bicuspid aortic valve (BAV) is a common congenital valvular malformation, which may lead to early aortic valve disease and bicuspid-associated aortopathy. A novel BAV classification system was recently proposed to coincide with transcatheter aortic valve replacement being increasingly considered in younger patients with symptomatic BAV, with good clinical results, yet without randomized trial evidence. Procedural technique, along with clinical outcomes, have considerably improved in BAV patients compared with tricuspid aortic stenosis patients undergoing transcatheter aortic valve replacement. The present review summarizes the novel BAV classification systems and examines contemporary surgical and transcatheter approaches.

Influence of cusp morphology and sex on quantitative valve composition in severe aortic stenosis

AIMS

Aortic stenosis is characterized by fibrosis and calcification of the valve, with a higher proportion of fibrosis observed in women. Stenotic bicuspid aortic valves progress more rapidly than tricuspid valves, which may also influence the relative composition of the valve. We aimed to investigate the influence of cusp morphology on quantitative aortic valve composition quantified from contrast-enhanced computed tomography angiography in severe aortic stenosis.

METHODS AND RESULTS

Patients undergoing transcatheter aortic valve implantation with bicuspid and tricuspid valves were propensity matched 1:1 by age, sex, and comorbidities. Computed tomography angiograms were analysed using semi-automated software to quantify the fibrotic and calcific scores (volume/valve annular area) and the fibro-calcific ratio (fibrotic score/calcific score). The study population (n = 140) was elderly (76 ± 10 years, 62% male) and had a peak aortic jet velocity of 4.1 ± 0.7 m/s. Compared with those with tricuspid valves (n = 70), patients with bicuspid valves (n = 70) had higher fibrotic scores [204 (interquartile range 118-267) vs. 144 (99-208) mm3/cm2, P = 0.006] with similar calcific scores (P = 0.614). Women had greater fibrotic scores than men in bicuspid [224 (181-307) vs. 169 (109-247) mm3/cm2, P = 0.042] but not tricuspid valves (P = 0.232). Men had greater calcific scores than women in both bicuspid [203 (124-355) vs. 130 (70-182) mm3/cm2, P = 0.008] and tricuspid [177 (136-249) vs. 100 (62-150) mm3/cm2, P = 0.004] valves. Among both valve types, women had a greater fibro-calcific ratio compared with men [tricuspid 1.86 (0.94-2.56) vs. 0.86 (0.54-1.24), P = 0.001 and bicuspid 1.78 (1.21-2.90) vs. 0.74 (0.44-1.53), P = 0.001].

CONCLUSIONS

In severe aortic stenosis, bicuspid valves have proportionately more fibrosis than tricuspid valves, especially in women.

The Importance of Aortic Valve Bicuspid Phenotype in Valvular Evolution in Pediatric Patients: A Case Report and Literature Mini-Review

Bicuspid aortic valve (BAV) is the most commonly encountered congenital malformation in the pediatric population, associated with aortic leaflet degeneration and aortopathy. However, studies on BAV and its complications in children are limited. We present the case of a 16-year-old with type 1B BAV with a raphe with fusion between the right and non-coronary cusps who exhibited severe aortic stenosis, regurgitation, and progressive dilatation of the ascending aorta. Surgical intervention, including aortic valve and aortic root replacement, was performed due to the patient's deteriorating condition. Histopathological examination revealed degenerative changes and calcifications in the aortic valve and mucoid fibrosis in the ascending aorta. The results are consistent with BAV patients being predisposed to aortic stenosis and regurgitation due to increased mechanical stress and hemodynamic abnormalities. Although more common in adults and a rare complication in pediatric patients, calcification was previously observed concurrently with rapid valve degeneration in our daily practice. Further studies are needed to improve our understanding of the mechanisms underlying BAV-related complications and refine treatment strategies for pediatric patients.

Analysis of local extracellular matrix identifies different aetiologies behind bicuspid and tricuspid aortic valve degeneration and suggests therapies

Aortic valve degeneration (AVD) is a life-threatening condition that has no medical treatment and lacks individual therapies. Although extensively studied with standard approaches, aetiologies behind AVD are unclear. We compared abundances of extracellular matrix (ECM) proteins from excised valve tissues of 88 patients with isolated AVD of normal tricuspid (TAV) and congenital bicuspid aortic valves (BAV), quantified more than 1400 proteins per ECM sample by mass spectrometry, and demonstrated that local ECM preserves molecular cues of the pathophysiological processes. The BAV ECM showed enrichment with fibrosis markers, namely Tenascin C, Osteoprotegerin, and Thrombospondin-2. The abnormal physical stress on BAV may cause a mechanical injury leading to a continuous Tenascin C-driven presence of myofibroblasts and persistent fibrosis. The TAV ECM exhibited enrichment with Annexin A3 (p = 1.1 × 10-16 and the fold change 6.5) and a significant deficit in proteins involved in high-density lipid metabolism. These results were validated by orthogonal methods. The difference in the ECM landscape suggests distinct aetiologies between AVD of BAV and TAV; warrants different treatments of the patients with BAV and TAV; elucidates the molecular basis of AVD; and implies possible new therapeutic approaches. Our publicly available database (human_avd_ecm.surgsci.uu.se) is a rich source for medical doctors and researchers who are interested in AVD or heart ECM in general. Systematic proteomic analysis of local ECM using the methods described here may facilitate future studies of various tissues and organs in development and disease.

Correlation between aortic valve protein levels and vector flow mapping of wall shear stress and oscillatory shear index in patients supported with continuous-flow left ventricular assist devices

BACKGROUND

Continuous-flow left ventricular assist devices commonly lead to aortic regurgitation, which results in decreased pump efficiency and worsening heart failure. We hypothesized that non-physiological wall shear stress and oscillatory shear index alter the abundance of structural proteins in aortic valves of left ventricular assist device (LVAD) patients.

METHODS

Doppler images of aortic valves of patients undergoing heart transplants were obtained. Eight patients had been supported with LVADs, whereas 10 were not. Aortic valve tissue was collected and protein levels were analyzed using mass spectrometry. Echocardiographic images were analyzed and wall shear stress and oscillatory shear index were calculated. The relationship between normalized levels of individual proteins and in vivo echocardiographic measurements was evaluated.

RESULTS

Of the 57 proteins of interest, there was a strong negative correlation between levels of 15 proteins and the wall shear stress (R < -0.500, p ≤ 0.05), and a moderate negative correlation between 16 proteins and wall shear stress (R -0.500 to -0.300, p ≤ 0.05). Gene ontology analysis demonstrated clusters of proteins involved in cellular structure. Proteins negatively correlated with WSS included those with cytoskeletal, actin/myosin, cell-cell junction and extracellular functions. C: In aortic valve tissue, 31 proteins were identified involved in cellular structure and extracellular junctions with a negative correlation between their levels and wall shear stress. These findings suggest an association between the forces acting on the aortic valve (AV) and leaflet protein abundance, and may form a mechanical basis for the increased risk of aortic leaflet degeneration in LVAD patients.

Dissecting Calcific Aortic Valve Disease-The Role, Etiology, and Drivers of Valvular Fibrosis

Calcific aortic valve disease (CAVD) is a highly prevalent and progressive disorder that ultimately causes gradual narrowing of the left ventricular outflow orifice with ensuing devastating hemodynamic effects on the heart. Calcific mineral accumulation is the hallmark pathology defining this process; however, fibrotic extracellular matrix (ECM) remodeling that leads to extensive deposition of fibrous connective tissue and distortion of the valvular microarchitecture similarly has major biomechanical and functional consequences for heart valve function. Significant advances have been made to unravel the complex mechanisms that govern these active, cell-mediated processes, yet the interplay between fibrosis and calcification and the individual contribution to progressive extracellular matrix stiffening require further clarification. Specifically, we discuss (1) the valvular biomechanics and layered ECM composition, (2) patterns in the cellular contribution, temporal onset, and risk factors for valvular fibrosis, (3) imaging valvular fibrosis, (4) biomechanical implications of valvular fibrosis, and (5) molecular mechanisms promoting fibrotic tissue remodeling and the possibility of reverse remodeling. This review explores our current understanding of the cellular and molecular drivers of fibrogenesis and the pathophysiological role of fibrosis in CAVD.

Biomechanical Assessment of Bicuspid Aortic Valve Phenotypes: A Fluid-Structure Interaction Modelling Approach

PURPOSE

Bicuspid aortic valve (BAV) is a congenital heart malformation with phenotypic heterogeneity. There is no prior computational study that assesses the haemodynamic and valve mechanics associated with BAV type 2 against a healthy tricuspid aortic valve (TAV) and other BAV categories.

METHODS

A proof-of-concept study incorporating three-dimensional fluid-structure interaction (FSI) models with idealised geometries (one TAV and six BAVs, namely type 0 with lateral and anterior-posterior orientations, type 1 with R-L, N-R and N-L leaflet fusion and type 2) has been developed. Transient physiological boundary conditions have been applied and simulations were run using an Arbitrary Lagrangian-Eulerian formulation.

RESULTS

Our results showed the presence of abnormal haemodynamics in the aorta and abnormal valve mechanics: type 0 BAVs yielded the best haemodynamical and mechanical outcomes, but cusp stress distribution varied with valve orifice orientation, which can be linked to different cusp calcification location onset; type 1 BAVs gave rise to similar haemodynamics and valve mechanics, regardless of raphe position, but this position altered the location of abnormal haemodynamic features; finally, type 2 BAV constricted the majority of blood flow, exhibiting the most damaging haemodynamic and mechanical repercussions when compared to other BAV phenotypes.

CONCLUSION

The findings of this proof-of-concept work suggest that there are specific differences across haemodynamics and valve mechanics associated with BAV phenotypes, which may be critical to subsequent processes associated with their pathophysiology processes.

FADS1 (Fatty Acid Desaturase 1) Genotype Associates With Aortic Valve FADS mRNA Expression, Fatty Acid Content and Calcification

BACKGROUND

Aortic stenosis (AS) contributes to cardiovascular mortality and morbidity but disease mechanisms remain largely unknown. Recent evidence associates a single nucleotide polymorphism rs174547 within the FADS1 gene, encoding FADS1 (fatty acid desaturase 1), with risk of several cardiovascular outcomes, including AS. FADS1 encodes a rate-limiting enzyme for ω-3 and ω-6 fatty acid metabolism. The aim of this study was to decipher the local transcriptomic and lipidomic consequences of rs174547 in tricuspid aortic valves from patients with AS.

METHODS

Expression quantitative trait loci study was performed using data from Illumina Human610-Quad BeadChip, Infinium Global Screening Arrays, and Affymetrix Human Transcriptome 2.0 arrays in calcified and noncalcified aortic valve tissue from 58 patients with AS (mean age, 74.2; SD, 5.9). Fatty acid content was assessed in aortic valves from 25 patients with AS using gas chromatography. Δ5 and Δ6 desaturase activity was assessed by the product-to-precursor ratio.

RESULTS

The minor C-allele of rs174547, corresponding to the protective genotype for AS, was associated with higher FADS2 mRNA levels in calcified valve tissue, whereas FADS1 mRNA and other transcripts in proximity of the single nucleotide polymorphism were unaltered. In contrast, the FADS1 Δ5-desaturase activity and the FADS2 Δ6-desaturase activity were decreased. Finally, docosahexaenoic acid was decreased in calcified tissue compared with non-calcified tissue and C-allele carriers exhibited increased docosahexaenoic acid levels. Overall desaturase activity measured with ω-3 fatty acids was higher in C-allele carriers.

CONCLUSIONS

The association between the FADS1 genotype and AS may implicate effects on valvular fatty acids.

Slit Orifice Aortic Cusp Extension Technique for Small Bicuspid Valves

We describe a modification to the aortic cusp extension technique that eliminates aortic regurgitation in pediatric small bicuspid valves. This simple and reproducible cusp extension technique secures coaptation and commissure suspension of the reconstructed aortic valve and may act as a bridge option for forthcoming reoperations.

Clinical impact of pathology-proven etiology of severely stenotic aortic valves on mid-term outcomes in patients undergoing surgical aortic valve replacement

Background

The use of transcatheter or surgical aortic valve replacement (AVR) for severe aortic stenosis (AS) has considerably increased in recent years. However, the association between AS etiology and mid-term clinical outcomes after surgical AVR has not been fully investigated.

Methods and results

We retrospectively included 201 patients (mean age, 75 years; 43%, men) who underwent surgical AVR for severe native AS (aortic valve area ≤1.0 cm² on preoperative transthoracic echocardiography examination). The following valve etiologies were postoperatively identified on pathological examination: post-inflammatory (n = 28), congenital (n = 35), and calcific/degenerative (n = 138). The median follow-up interval was 4.1 years following surgical AVR. Of the 201 patients, 27% were asymptomatic, 40% had a history of heart failure, and 11% underwent previous heart surgery. The cumulative incidence of cardiac events (all-cause death, aortic valve deterioration requiring repeated AVR, and hospitalization for heart failure) and combined adverse events, which included non-fatal stroke, unplanned coronary revascularization, pacemaker implantation, and gastrointestinal bleeding along with cardiac events, was significantly higher in the calcific/degenerative group (p = 0.02 and p = 0.02, respectively). In multivariate analysis adjusted for age, sex, renal function, heart failure, atrial fibrillation, concomitant surgical procedures, and EuroSCORE II, AS etiology was independently associated with an increased risk of combined adverse events (congenital vs. post-inflammatory: hazard ratio [HR], 4.13; p = 0.02 and calcific/degenerative vs. post-inflammatory: HR, 5.69; p = 0.002).

Conclusions

Pathology-proven AS etiology could aid in predicting the mid-term outcomes after surgical AVR, supporting the importance of accurate identification of severe AS etiology with or without postoperative pathological examination.

Differences at surgery between patients with bicuspid and tricuspid aortic valves

Aim

To determine differences in surgical procedures and clinical characteristics at the time of surgery between native bicuspid aortic valves (BAV) and tricuspid aortic valves (TAV) in patients being followed up after aortic valve surgery (AVS).

Methods

In this retrospective cohort study in a non-academic hospital, we identified patients who had a surgeon’s report of the number of native valve cusps and were still being followed up. We selected patients with BAV and TAV, and used multivariable regression analyses to identify associations between BAV-TAV and pre-specified clinical characteristics.

Results

Of 439 patients, 140 had BAV (32%) and 299 TAV (68%). BAV patients were younger at the time of surgery (mean age 58.6 ± 13 years) than TAV patients (69.1 ± 12 years, p < 0.001) and were more often male (64% vs 53%; p = 0.029). Cardiovascular risk factors were less prevalent in BAV than in TAV patients at the time of surgery (hypertension (31% vs 55%), hypercholesterolaemia (29% vs 58%) and diabetes (7% vs 16%); all p < 0.005). Concomitant coronary artery bypass grafting (CABG) was performed less often in BAV than in TAV patients (14% vs 39%, p < 0.001), even when adjusted for confounders (adjusted odds ratio (adj.OR) 0.45; 95% CI: 0.25–0.83). In contrast, surgery of the proximal aorta was performed more often (31% vs 11%, respectively, p < 0.001; adj.OR 2.3; 95% CI: 1.3–4.0).

Conclusions

Whereas mechanical stress is the supposed major driver of valvulopathy towards AVS in BAV, prevalent cardiovascular risk factors are a suspected driver towards the requirement for AVS and concomitant CABG in TAV, an observation based on surgical determination of the number of valve cusps.

Inflammatory Mechanisms of Cardiovascular Remodeling

Inflammation and fibrosis play an important role in the development and progression of cardiovascular diseases. Acute coronary syndrome (ACS) is caused by rupture of inflamed atherosclerotic plaque and subsequent atherothrombosis. Recent studies have shown that inflammatory markers such as C-reactive protein (CRP) can predict ACS development and have demonstrated the effectiveness of new therapeutic approaches targeting inflammation. Studies have also shown that an enhanced inflammatory response after myocardial infarction (MI) is associated with cardiac rupture, ventricular aneurysm formation, and exacerbation of left ventricular (LV) remodeling. Inflammation is a physiological reaction in which fibrosis is induced to facilitate the healing of tissue damage. However, when an excessive inflammatory response consisting mainly of monocytes/macrophages is induced by various factors, impaired reparative fibrosis and resulting pathological remodeling processes may occur. A similar phenomenon is observed in abdominal aortic aneurysm (AAA) expansion. In contrast, myocardial diseases such as inflammatory dilated cardiomyopathy (DCMI) and valvular diseases such as aortic valve stenosis (AS) are characterized by chronic inflammation mediated mainly by T lymphocytes and the associated enhancement of reactive fibrosis. Thus, inflammation can take 2 paths (the inhibition or promotion of fibrosis), depending on the phase of inflammation, inducing pathological cardiovascular remodeling. Elucidation of the regulatory mechanisms of inflammation and fibrosis will contribute to the development of new therapeutic approaches for cardiovascular diseases.