Embedding and Backscattered Scanning Electron Microscopy (EM-BSEM) Is Preferential over Immunophenotyping in Relation to Bioprosthetic Heart Valves

Hitherto, calcified aortic valves (AVs) and failing bioprosthetic heart valves (BHVs) have been investigated by similar approaches, mostly limited to various immunostaining techniques. Having employed multiple immunostaining combinations, we demonstrated that AVs retain a well-defined cellular hierarchy even at severe stenosis, whilst BHVs were notable for the stochastic degradation of the extracellular matrix (ECM) and aggressive infiltration by ECM-digesting macrophages. Leukocytes (CD45+) comprised ≤10% cells in the AVs but were the predominant cell lineage in BHVs (≥80% cells). Albeit cells with uncertain immunophenotype were rarely encountered in the AVs (≤5% cells), they were commonly found in BHVs (≥80% cells). Whilst cell conversions in the AVs were limited to the endothelial-to-mesenchymal transition (represented by CD31+α-SMA+ cells) and the formation of endothelial-like (CD31+CD68+) cells at the AV surface, BHVs harboured numerous macrophages with a transitional phenotype, mostly CD45+CD31+, CD45+α-SMA+, and CD68+α-SMA+. In contrast to immunostaining, which was unable to predict cell function in the BHVs, our whole-specimen, nondestructive electron microscopy approach (EM-BSEM) was able to distinguish between quiescent and matrix-degrading macrophages, foam cells, and multinucleated giant cells to conduct the ultrastructural analysis of organelles and the ECM, and to preserve tissue integrity. Hence, we suggest EM-BSEM as a technique of choice for studying the cellular landscape of BHVs.

Early Postoperative Immunothrombosis of Bioprosthetic Mitral Valve and Left Atrium: A Case Report

A 72-year-old female patient with mixed rheumatic mitral valve disease and persistent atrial fibrillation underwent mitral valve replacement and suffered from a combined thrombosis of the bioprosthetic valve and the left atrium as soon as 2 days post operation. The patient immediately underwent repeated valve replacement and left atrial thrombectomy. Yet, four days later the patient died due to the recurrent prosthetic valve and left atrial thrombosis which both resulted in an extremely low cardiac output. In this patient's case, the thrombosis was notable for the resistance to anticoagulant therapy as well as for aggressive neutrophil infiltration and release of neutrophil extracellular traps (NETs) within the clot, as demonstrated by immunostaining. The reasons behind these phenomena remained unclear, as no signs of sepsis or contamination of the BHV were documented, although the patient was diagnosed with inherited thrombophilia that could impede the fibrinolysis. The described case highlights the hazard of immunothrombosis upon valve replacement and elucidates its mechanisms in this surgical setting.

bFGF and SDF-1α Improve In Vivo Performance of VEGF-Incorporating Small-Diameter Vascular Grafts

Tissue-engineered vascular grafts are widely tested as a promising substitute for both arterial bypass and replacement surgery. We previously demonstrated that incorporation of VEGF into electrospun tubular scaffolds from poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) enhances formation of an endothelial cell monolayer. However, an overdose of VEGF can induce tumor-like vasculature; thereby, other bioactive factors are needed to support VEGF-driven endothelialization and successful recruitment of smooth muscle cells. Utilizing emulsion electrospinning, we fabricated one-layer vascular grafts with either VEGF, bFGF, or SDF-1α, and two-layer vascular grafts with VEGF incorporated into the inner layer and bFGF and SDF-1α incorporated into the outer layer with the following structural evaluation, tensile testing, and in vivo testing using a rat abdominal aorta replacement model. The latter graft prototype showed higher primary patency rate. We found that the two-layer structure improved surface topography and mechanical properties of the grafts. Further, the combination of bFGF, SDF-1α, and VEGF improved endothelialization compared with VEGF alone, while bFGF induced a rapid formation of a smooth muscle cell layer. Taken together, these findings show that the two-layer structure and incorporation of bFGF and SDF-1α into the vascular grafts in combination with VEGF provide a higher primary patency and therefore improved in vivo performance.

Ultrastructural Pathology of Atherosclerosis, Calcific Aortic Valve Disease, and Bioprosthetic Heart Valve Degeneration: Commonalities and Differences

Atherosclerosis, calcific aortic valve disease (CAVD), and bioprosthetic heart valve degeneration (alternatively termed structural valve deterioration, SVD) represent three diseases affecting distinct components of the circulatory system and their substitutes, yet sharing multiple risk factors and commonly leading to the extraskeletal calcification. Whereas the histopathology of the mentioned disorders is well-described, their ultrastructural pathology is largely obscure due to the lack of appropriate investigation techniques. Employing an original method for sample preparation and the electron microscopy visualisation of calcified cardiovascular tissues, here we revisited the ultrastructural features of lipid retention, macrophage infiltration, intraplaque/intraleaflet haemorrhage, and calcification which are common or unique for the indicated types of cardiovascular disease. Atherosclerotic plaques were notable for the massive accumulation of lipids in the extracellular matrix (ECM), abundant macrophage content, and pronounced neovascularisation associated with blood leakage and calcium deposition. In contrast, CAVD and SVD generally did not require vasculo- or angiogenesis to occur, instead relying on fatigue-induced ECM degradation and the concurrent migration of immune cells. Unlike native tissues, bioprosthetic heart valves contained numerous specialised macrophages and were not capable of the regeneration that underscores ECM integrity as a pivotal factor for SVD prevention. While atherosclerosis, CAVD, and SVD show similar pathogenesis patterns, these disorders demonstrate considerable ultrastructural differences.

P4491Noninvasive evaluation of force distribution in mitral annuloplasty rings: do rigid annuloplasty rings increase stress?

Purpose

To evaluate forces distribution, local stresses and deformation of mitral annuloplasty rings in response to annuloplasty.

Methods

Seguin (St. Jude Medical), Physio I (Edwards LifeScience), Memo 3D (Sorin) and Future SG (Medtronic) MAR of size 30 mm were included in the study. The study group included 4 males patients aged 52–68 years who underwent isolated mitral valve annuloplasty for ischemic mitral regurgitation. All surgeries were performed by the same experienced operator according to the standardized protocol. The mechanical properties of the similar set of MAR were evaluated under uniaxial compression by 15% in the longitudinal and transverse directions on the Testing Machines Z5.0 (Zwick/Roell). Biomechanics was assessed with MSCT. The MAR frame models at the initial state and at the ventricular ejection and atrial systole phases were obtained from DICOM-data using computer tomography Sensation Somatom 64 (Siemens). The models were compared using the innovative numerical algorithm in MatLab (Mathworks) by forming pairs for “systole – diastole”, “initial state – diastole” for all four types of MAR. We compared the mobility of the implanted devices and changes in the physiological saddle shape geometry of the mitral annulus in response to annuloplasty. We performed the quantitative analysis of the movement of each point of the reconstructed model between two states with the subsequent calculation of the required forces based on the finite element analysis.

Results

Future CG MAR has the greatest longitudinal and transverse stiffness (18.1N and 4.8N, respectively), whereas Memo 3D demonstrates the lowest values (2.3N and 1.5N). The rest two models show intermediate values of 4.2 - 11.3 N to 2.0 - 4.3N. The comparative analysis of MAR before and after implantation shows that Physio demonstrates the most pronounced deviations from normal physiological shape with significant annular compression along the intercommissural diameter by 1.36 mm resulted in a rounded annulus shape. None significant geometrical deformity among the other prosthetic rings. MEMO 3D demonstrates an average deformation by 0.18 mm across all zones, Seguin - 0.42 mm, Future CG - 0.34 mm. The force distribution analysis demonstrated the least forces of MEMO 3D, whereas the largest ones (up to 1.5N) are shown by Future SG, leading to the induction of locally elevated stress in surrounding tissues, potentially triggering the development of paravalvular fistulae.

Conclusion

Preliminary results demonstrate that the use of flexible rings with initially mobile structure allows preserving the native mitral annulus mobility after annuloplasty and reducing the stress (forces) acting on the surrounding tissues. The presented non-invasive method for estimating the stress of mitral annulus is crucial for advanced clinical practice as it allows further studying of the underlying pathologic mechanisms of developing paravalvular fistulae.

P4489Morphological changes in the EGDE-treated bioprosthetic heart valves

Background

Prosthetic heart valves fabricated from pericardium preserved in EGDE (ethylene glycol diglycidyl ether) may be a promising option for patients with valvular heart disease.

Purpose

To assess morphological changes in the failed PeriCor and UniLine bioprostheses and to determine the underlying mechanisms contributing to their dysfunction.

Methods

17 patients with EGDE-treated mitral bioprosthetic valves (PeriCor group, n=11, UniLine group= 6). undergoing repeat mitral valve replacement were included in the study. The median age of patients at the time of the primary replacement was 59 (54; 64) and 57 (55, 65) years, respectively. All cases of calcifications, spontaneous perforations, leaflet tears and ruptures, pannus growth, bioprosthetic leaflet fusion were assessed using microscopy and micro-computed tomography. The contribution of degenerative changes leading to the failure of bioprostheses was estimated with the Chi-square test.

Results

Pannus growth was observed in 53.8% of all explanted bioprostheses. Its overgrowth was abundant covering the leaflets and the stent struts and resulted in decreased effective orifice area and subsequent stenosis. Bioprosthetic leaflet fusion was observed only in the PeriCor group and accounts for 70%. Of them, 93% of cases of leaflet fusion was accompanied by the ruptures in the opposite commissural zones and subsequent leaflet perforations. The signs of calcification were reported in 57.6% of cases. Of them, 50% of cases had calcified stent frame tissue covering and 35% - pannus. Interestingly, calcification was not the main cause leading to the valve failure in 53.3% of cases.

Conclusion

Modes of bioprosthetic valve dysfunction include primary tissue degeneration, calcification and pannus growth. Primary tissue degeneration, pannus growth and commissural fusions account for a larger percentage in the modes of dysfunctions for EGDE-treated xenoaortic bioprostheses rather than calcification. Our findings suggest that preservation methods play one of the key roles in the dysfunction pattern.