Is the degeneration of aortic valve bioprostheses similar to that of native aortic valves? Insights into valvular pathology

Multiscale multimodal characterization and simulation of structural alterations in failed bioprosthetic heart valves

Calcific degeneration is the most frequent type of heart valve failure, with rising incidence due to the ageing population. The gold standard treatment to date is valve replacement. Unfortunately, calcification oftentimes re-occurs in bioprosthetic substitutes, with the governing processes remaining poorly understood. Here, we present a multiscale, multimodal analysis of disturbances and extensive mineralisation of the collagen network in failed bioprosthetic bovine pericardium valve explants with full histoanatomical context. In addition to highly abundant mineralized collagen fibres and fibrils, calcified micron-sized particles previously discovered in native valves were also prevalent on the aortic as well as the ventricular surface of bioprosthetic valves. The two mineral types (fibres and particles) were detectable even in early-stage mineralisation, prior to any macroscopic calcification. Based on multiscale multimodal characterisation and high-fidelity simulations, we demonstrate that mineral occurrence coincides with regions exposed to high haemodynamic and biomechanical indicators. These insights obtained by multiscale analysis of failed bioprosthetic valves serve as groundwork for the evidence-based development of more durable alternatives. STATEMENT OF SIGNIFICANCE: Bioprosthetic valve calcification is a well-known clinically significant phenomenon, leading to valve failure. The nanoanalytical characterisation of bioprosthetic valves gives insights into the highly abundant, extensive calcification and disorganization of the collagen network and the presence of calcium phosphate particles previously reported in native cardiovascular tissues. While the collagen matrix mineralisation can be primarily attributed to a combination of chemical and mechanical alterations, the calcified particles are likely of host cellular origin. This work presents a straightforward route to mineral identification and characterization at high resolution and sensitivity, and with full histoanatomical context and correlation to hemodynamic and biomechanical indicators, hence providing design cues for improved bioprosthetic valve alternatives.

Ultrastructural mitral valve abnormalities in infective endocarditis

Aim. Using an original method based on backscattered scanning electron microscopy, to study the structural features of the mitral valve leaflets in infective endocarditis.

Material and methods. We examined 9 mitral valves extracted during surgical interventions due to structural malfunction in patients with infective endocarditis (IE). The samples were fixed in buffered paraformaldehyde with osmium tetraoxide postfixation. After dehydration by increasing alcohol concentration and acetone, the samples were placed in epoxy resin. After the resin has polymerized, the samples were ground and then polished to the desired depth. To increase the electronic contrast, the samples were treated with a uranyl acetate alcohol solution during dehydration and with Reynolds' lead citrate after polishing the epoxy blocks. The samples were visualized by backscattered scanning electron microscopy at an accelerating 15-kV voltage.

Results. Structural leaflet injuries caused by IE were most pronounced in the central part and the base. Necrotic areas were extensive electron-dense formations located in the central leaflet layers, or displaced towards the ventricular surface. The electron-dense material in the necrotic area was poorly structured and contained individual cells and bacteria. Bacteria were also present outside the necrotic area. Necrotic areas were surrounded by a layer of a modified extracellular matrix, usually covered with a fibrin layer. Among the extracellular matrix fibers, the macrophages, smooth myocytes and fibroblasts was noted. The fibrin layer, in addition to these cells, contained a large number of blood vessels and was often covered with endothelium.

Conclusion. Infection of the mitral valve leaflets causes a simultaneous inflammatory response and regeneration activation. Without adequate regulatory factors, the processes of inflammation and connective tissue creation lead to structural and functional leaflet failure. Specific causes may be overgrowth of necrotic and inflammatory areas, edema and fiber orientation disorder, as well as leaflet rupture.

Multimodality Imaging of Complications of Cardiac Valve Surgeries

Replacement with a prosthetic heart valve (PHV) remains the definitive surgical procedure for management of severe cardiac valve disease. PHV dysfunction is uncommon but can be a life-threatening condition. The broad hemodynamic and pathophysiologic manifestations of PHV dysfunction are stenosis, regurgitation, and a stuck leaflet. Specific structural abnormalities that cause PHV dysfunction include prosthetic valve-patient mismatch, structural failure, valve calcification, dehiscence, paravalvular leak, infective endocarditis, abscess, pseudoaneurysm, abnormal connections, thrombus, hypoattenuating leaflet thickening, and pannus. Multiple imaging modalities are available for evaluating a PHV and its dysfunction. Transthoracic echocardiography is often the first-line imaging modality, with additional modalities such as transesophageal echocardiography, CT, MRI, cine fluoroscopy, and nuclear medicine used for further characterization and establishing a specific cause. The authors review PHVs and the role of imaging modalities in evaluation of PHV dysfunction and illustrate the imaging appearances of different complications. Online supplemental material is available for this article. ^©RSNA, 2019.

Valve hemodynamic deterioration and cardiovascular outcomes in TAVR: A report from the STS/ACC TVT Registry

BACKGROUND

Recent reports of leaflet abnormalities (detected using advanced imaging) have raised questions regarding transcatheter aortic valve replacement (TAVR) durability. We sought to determine the incidence of valve hemodynamic deterioration (VHD) and its association with cardiovascular outcomes.

METHODS AND RESULTS

Consecutive cases with paired postimplant and follow-up echocardiograms from November 2011 to March 2015 in the STS/ACC TVT Registry were allocated into 2 overlapping cohorts: early (paired echocardiograms at 0 and 30 days) and late (paired echocardiograms at 30 days and 1 year). VHD was defined as an increase in mean aortic valve gradient ≥10 mm Hg. Eighteen-month cardiovascular outcomes were determined via linkage with Centers for Medicare & Medicaid Services claims. Backwards selection logistic regression was performed to determine predictors of VHD. Among 10,099 TAVRs with paired echocardiograms, the median age was 84 years and 48.7% were female, with Society of Thoracic Surgeons score distributions of <8% (61.7%), 8%-15% (28.8%), and >15% (9.5%). The incidence of VHD was 2.1% in the early cohort and 2.5% in the late cohort. There was no significant difference between those with and without VHD in either cohort in the combined end point of death/stroke/aortic valve reintervention or heart failure hospitalization or myocardial infarction. Independent predictors of VHD included chronic lung disease, valve-in-valve procedure, 23-mm TAVR valve, severe patient-prosthesis mismatch, increasing body mass index, and increasing baseline aortic valve gradient.

CONCLUSIONS

The incidence of VHD in US clinical practice is low, and VHD is not associated with increased cardiovascular events at 18 months. Patient and procedural predictors may help to identify patients at risk for VHD in whom surveillance or preventive strategies may be considered.

Complementary role of cardiac CT in the assessment of aortic valve replacement dysfunction

Aortic valve replacement is the second most common cardiothoracic procedure in the UK. With an ageing population, there are an increasing number of patients with prosthetic valves that require follow-up. Imaging of prosthetic valves is challenging with conventional echocardiographic techniques making early detection of valve dysfunction or complications difficult. CT has recently emerged as a complementary approach offering excellent spatial resolution and the ability to identify a range of aortic valve replacement complications including structural valve dysfunction, thrombus development, pannus formation and prosthetic valve infective endocarditis. This review discusses each and how CT might be incorporated into a multimodal cardiovascular imaging pathway for the assessment of aortic valve replacements and in guiding clinical management.

Dysregulation of ossification-related miRNAs in circulating osteogenic progenitor cells obtained from patients with aortic stenosis

CAVD (calcific aortic valve disease) is the defining feature of AS (aortic stenosis). The present study aimed to determine whether expression of ossification-related miRNAs is related to differentiation intro COPCs (circulating osteogenic progenitor cells) in patients with CAVD. The present study included 46 patients with AS and 46 controls. Twenty-nine patients underwent surgical AVR (aortic valve replacement) and 17 underwent TAVI (transcatheter aortic valve implantation). The number of COPCs was higher in the AS group than in the controls (P<0.01). Levels of miR-30c were higher in the AS group than in the controls (P<0.01), whereas levels of miR-106a, miR-148a, miR-204, miR-211, miR-31 and miR-424 were lower in the AS group than in the controls (P<0.01). The number of COPCs and levels of osteocalcin protein in COPCs were positively correlated with levels of miR-30a and negatively correlated with levels of the remaining miRNAs (all P<0.05). The degree of aortic valve calcification was weakly positively correlated with the number of COPCs and miR-30c levels. The number of COPCs and miR-30c levels were decreased after surgery, whereas levels of the remaining miRNAs were increased (all P<0.05). Changes in these levels were greater after AVR than after TAVI (all P<0.05). In vitro study using cultured peripheral blood mononuclear cells transfected with each ossification-related miRNA showed that these miRNAs controlled levels of osteocalcin protein. In conclusion, dysregulation of ossification-related miRNAs may be related to the differentiation into COPCs and may play a significant role in the pathogenesis of CAVD.

Aortic stenosis and lipids: does intervention work?

PURPOSE OF REVIEW

Aortic stenosis is a common disorder affecting increasing numbers of elderly patients, which is associated with markedly increased cardiovascular morbidity and mortality. Both histological and epidemiological studies have suggested that the process of valve degeneration may resemble atherosclerosis. This review investigates the potential role of lipid-lowering therapy in its management.

RECENT FINDINGS

The current treatment methods are surgical or endovascular intervention but it has been hoped that antiatherosclerotic therapies might result in a reduction in progression and need for intervention. There have been a number of retrospective studies of lipid-lowering therapy, which suggested that statins might be effective in reducing progression of aortic stenosis. Lately a series of trials of aggressive statin therapy on surrogate markers of progression have shown no benefit from these measures. The controversial Simvastatin-Ezetimibe and Aortic Stenosis (SEAS) endpoint trial did not show any benefit on a combined endpoint of valve-related and ischaemic events but hinted at a reduction in cardiovascular events in this high cardiovascular risk group.

SUMMARY

The data clearly shows statins have little effect in well established stenotic disease with calcification, but their effects earlier in the disease process (aortic valve sclerosis) remain to be determined.

Differences in valvular and vascular cell responses to strain in osteogenic media

Calcification is the primary cause of failure of bioprosthetic and tissue-engineered vascular and valvular grafts. We used tissue-engineered collagen gels containing human aortic smooth muscle cells (HASMC) and human aortic valvular interstitial cells (HAVIC) as a model to investigate cell-mediated differences in early markers of calcification. The HASMCs and HAVICs were isolated from non-sclerotic human tissues. After 21 days of culture in either regular or osteogenic media with or without 10% cyclic strain at 1 Hz, the collagen gels were assessed for DNA content, collagen I, matrix metalloproteinase (MMP)-2 and glycosaminoglycan (GAG) content. The collagen gels containing HASMCs contained significantly greater amounts of collagen I and GAG compared to HAVICs. Although strain increased MMP-2 activity for both cell types, this trend was significant (p ≤ 0.05) only for HAVICs. Cultured gels were also assessed for osteogenic markers calcium content, alkaline phosphatase (ALP), and Runx2 and were present at greater amounts in gels containing HASMCs than HAVICs. Calcium content, Runx2 expression, and ALP activity were also modulated by mechanical strain. The results indicate that cell-mediated differences exist between the vascular and valvular calcification processes. Further investigation is necessary for improved understanding and to detect biomarkers for early detection or prevention of these diseases.

Lipid-mediated inflammation and degeneration of bioprosthetic heart valves

BACKGROUND

The durability of bioprosthetic valves is limited by structural valve degeneration (SVD) leading to bioprostheses (BPs) stenosis or regurgitation. We hypothesized that a lipid-mediated inflammatory mechanism is involved in the SVD of BPs.

MATERIAL AND METHODS

Eighteen Freestyle stentless BP valves were explanted for SVD at a mean time of 5.9 +/- 3 years after implantation and were analysed by immunohistochemistry and transmission electron microscopy (TEM).

RESULTS

The mean age of the patients was 65 +/- 8 years and there were 11 male and seven female patients. Two of the 18 BPs had macroscopic calcification, whereas the other valves had minimal or no macroscopic calcification. Tears at the commissures leading to regurgitation was present in 16 BPs. Immunohistochemistry showed the presence of oxidized low-density lipoprotein (ox-LDL) and glycosaminoglycans in the fibrosa layer of 13 BPs. Areas with ox-LDL were infiltrated by macrophages (CD68(+)) co-expressing the scavenger receptor CD36 and metalloproteinase-9 (MMP-9). Zymogram showed the active form of MMP-9 within explanted BPs. EM studies revealed the presence of lipid-laden cells featuring foam cells and fragmented collagen. Nonimplanted control BPs obtained from the manufacturer (n = 4) had no evidence of lipid accumulation, inflammatory cell infiltration or expression of MMP9 within the leaflets.

CONCLUSIONS

These results support the concept that lipid-mediated inflammatory mechanisms may contribute to the SVD of BPs. These findings suggest that modification of atherosclerotic risk factors with the use of behavioural or pharmacological interventions could help to reduce the incidence of SVD.

Tissue-engineered heart valve prostheses: ‘state of the heart’

In this article, we will review the current state of the art in heart valve tissue engineering. We provide an overview of mechanical and biological replacement options, outlining advantages and limitations of each option. Tissue engineering, as a field, is introduced, and specific aspects of valve tissue engineering are discussed (e.g., biomaterials, cells and bioreactors). Technological hurdles, which need to be overcome for advancement of the field, are also discussed.