Quantitative Histological Examination of Bioprosthetic Heart Valves

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.

Differential Immune Response to Bioprosthetic Heart Valve Tissues in the α1,3Galactosyltransferase-Knockout Mouse Model

Structural valve deterioration (SVD) of bioprosthetic heart valves (BHVs) has great clinical and economic consequences. Notably, immunity against BHVs plays a major role in SVD, especially when implanted in young and middle-aged patients. However, the complex pathogenesis of SVD remains to be fully characterized, and analyses of commercial BHVs in standardized-preclinical settings are needed for further advancement. Here, we studied the immune response to commercial BHV tissue of bovine, porcine, and equine origin after subcutaneous implantation into adult α1,3-galactosyltransferase-knockout (Gal KO) mice. The levels of serum anti-galactose α1,3-galactose (Gal) and -non-Gal IgM and IgG antibodies were determined up to 2 months post-implantation. Based on histological analyses, all BHV tissues studied triggered distinct infiltrating cellular immune responses that related to tissue degeneration. Increased anti-Gal antibody levels were found in serum after ATS 3f and Freedom/Solo implantation but not for Crown or Hancock II grafts. Overall, there were no correlations between cellular-immunity scores and post-implantation antibodies, suggesting these are independent factors differentially affecting the outcome of distinct commercial BHVs. These findings provide further insights into the understanding of SVD immunopathogenesis and highlight the need to evaluate immune responses as a confounding factor.

Deoxyribonuclease is prognostic in patients undergoing transcatheter aortic valve replacement

Degenerative aortic valve stenosis is an inflammatory process that resembles atherosclerosis. Neutrophils release their DNA upon activation and form neutrophil extracellular traps (NETs), which are present on degenerated aortic valves. NETs correlate with pressure gradients in severe aortic stenosis. Transcatheter aortic valve replacement (TAVR) is an established treatment option for aortic valve stenosis. Bioprosthetic valve deterioration promoted by inflammatory, fibrotic and thrombotic processes limits outcome. Deoxyribonuclease is a natural counter mechanism to degrade DNA in circulation. In the present observational study, we investigated plasma levels of double-stranded DNA, deoxyribonuclease activity and outcome after TAVR. 345 consecutive patients undergoing TAVR and 100 healthy reference controls were studied. Double-stranded DNA was measured by fluorescence assays in plasma obtained at baseline and after TAVR. Deoxyribonuclease activity was measured at baseline using single radial enzyme diffusion assays. Follow-up was performed at 12 months, and mean aortic pressure gradient and survival were evaluated. Receiver operating characteristic, Kaplan-Meier curves and Cox regression models were calculated. Baseline double-stranded DNA in plasma was significantly higher compared to healthy controls, was increased at 3 and 7 days after TAVR, and declined thereafter. Baseline deoxyribonuclease activity was decreased compared to healthy controls. Interestingly, low deoxyribonuclease activity correlated with higher C-reactive protein and higher mean transaortic gradient after 12 months. Finally, deoxyribonuclease activity was a strong independent predictor of outcome 12 months after TAVR. Deoxyribonuclease activity is a potential biomarker for risk stratification after TAVR. Pathomechanisms of bioprosthetic valve deterioration involving extracellular DNA and deoxyribonuclease merit investigation.

Methicillin-Resistant Staphylococcus aureus Prosthetic Valve Endocarditis: Pathophysiology, Epidemiology, Clinical Presentation, Diagnosis, and Management

Staphylococcus aureus prosthetic valve endocarditis (PVE) remains among the most morbid bacterial infections, with mortality estimates ranging from 40% to 80%. The proportion of PVE cases due to methicillin-resistant Staphylococcus aureus (MRSA) has grown in recent decades, to account for more than 15% of cases of S. aureus PVE and 6% of all cases of PVE. Because no large studies or clinical trials for PVE have been published, most guidelines on the diagnosis and management of MRSA PVE rely upon expert opinion and data from animal models or related conditions (e.g., coagulase-negative Staphylococcus infection). We performed a review of the literature on MRSA PVE to summarize data on pathogenic mechanisms and updates in epidemiology and therapeutic management and to inform diagnostic strategies and priority areas where additional clinical and laboratory data will be particularly useful to guide therapy. Major updates discussed in this review include novel diagnostics, indications for surgical management, the utility of aminoglycosides in medical therapy, and a review of newer antistaphylococcal agents used for the management of MRSA PVE.

A bronchogenic cyst of the larynx: A case report

A 12-year-old female presented with a 2-month history of dyspnea and a progressively worsening hoarseness lasting >10 years. The subsequently identified mass was completely resected from the patient's supraglottic area using a laser and suspension laryngoscope. The mass was diagnosed as a bronchogenic cyst using histopathology. While the prognosis for these cysts is good, long-term follow-up remains necessary for such patients because there are several reports in the literature indicating the potential for malignancy to develop. The patient in the present study experienced no complications or recurrence of the bronchogenic cyst 2 years following surgery. To the best of our knowledge, only 2 cases of bronchogenic cysts arising from the larynx have been reported in China, and the present study introduces the first case of a bronchogenic cyst of the larynx in a Chinese patient reported in English.

Advantages and Limitations of Direct PCR Amplification of Bacterial 16S-rDNA from Resected Heart Tissue or Swabs Followed by Direct Sequencing for Diagnosing Infective Endocarditis: A Retrospective Analysis in the Routine Clinical Setting

Infective endocarditis (IE) is a life-threatening disease that is associated with high morbidity and mortality. Its long-term prognosis strongly depends on a timely and optimized antibiotic treatment. Therefore, identification of the causative pathogen is crucial and currently based on blood cultures followed by characterization and susceptibility testing of the isolate. However, antibiotic treatment starting prior to blood sampling or IE caused by fastidious or intracellular microorganisms may cause negative culture results. Here we investigate the additional diagnostic value of broad-range PCR in combination with direct sequencing on resected heart tissue or swabs in patients with tissue or swab culture-negative IE in a routine clinical setting. Sensitivity, specificity, and positive and negative predictive values of broad-range PCR from diagnostic material in our patients were 33.3%, 76.9%, 90.9%, and 14.3%, respectively. We identified a total of 20 patients (21.5%) with tissue or culture-negative IE who profited by the additional application of broad-range PCR. We conclude that broad-range PCR on resected heart tissue or swabs is an important complementary diagnostic approach. It should be seen as an indispensable new tool for both the therapeutic and diagnostic management of culture-negative IE and we thus propose its possible inclusion in Duke's diagnostic classification scheme.

T Cell Response in Patients with Implanted Biological and Mechanical Prosthetic Heart Valves

The study was aimed at assessing T cell subsets of peripheral blood from recipients of long-term functioning (more than 60 months) biological and mechanical heart valve prostheses. The absolute and relative number of CD4 and CD8 T cell subsets was analyzed: naïve (N, CD45RA⁺CD62L⁺), central memory (CM, CD45RA⁻CD62L⁺), effector memory (EM, CD45RA⁻CD62L⁻), and terminally differentiated CD45RA-positive effector memory (TEMRA, CD45RA⁺CD62L⁻) in 25 persons with biological and 7 with mechanical prosthesis compared with 48 apparently healthy volunteers. The relative and absolute number of central memory and naïve CD3⁺CD8⁺ in patients with biological prosthesis was decreased (p < 0.001). Meanwhile the number of CD45RA⁺CD62L⁻CD3⁺CD8⁺ and CD3⁺CD4⁺ was increased (p < 0.001). Patients with mechanical prosthesis had increased absolute and relative number of CD45RA⁺CD62L⁻CD3⁺CD8⁺ cells (p = 0.006). Also the relative number of CD3⁺CD4⁺ cells was reduced (p = 0.04). We assume that altered composition of T cell subsets points at development of xenograft rejection reaction against both mechanical and biological heart valve prostheses.

D-dimer level predicts in-hospital mortality in patients with infective endocarditis: a prospective single-centre study

BACKGROUND

Increased circulating D-dimer levels have been correlated with adverse outcomes in various clinical conditions. To our knowledge, the association of on-admission D-dimer and in-hospital mortality in infective endocarditis (IE) has not been investigated. We hypothesized that increased on-admission D-dimer levels would correlate with adverse outcomes when prospectively studied in patients with IE.

METHODS

In this prospective study, a total of 157 consecutive patients with the definite IE diagnosis met the inclusion criteria and underwent testing for on-admission D-dimer and CRP assays. The outcome measure was in-hospital death from any cause.

RESULTS

In-hospital mortality occurred in 40 (26%) patients. Increased levels of plasma D-dimer (5.1 ± 1.7 vs 1.9 ± 0.8, p<0.001), CRP [45(13-98) vs 12(5-28), p<0.001] were found in dead patients compared with those survived. In addition to S. aureus infection, increased leukocyte count, end-stage renal disease, LVEF<50%, vegetation size of >10mm, perivalvular abscess, on-admission D-dimer (HR: 1.32; 95% CI: 1.24-1.40; p<0.001) and CRP (HR: 1.18; 95% CI: 1.09-1.36; p=0.001) levels were significantly associated with in-hospital mortality. Furthermore, the sensitivity and specificity of D-dimer ≥ 4.2mg/L in predicting in-hospital death in IE were 86% and 85%, respectively. Moreover, the sensitivity and specificity of CRP levels ≥ 13.6 mg/L were 72% and 69%, respectively.

CONCLUSION

Our findings suggest that on-admission D-dimer level may be a simple, available and valuable biomarker that allows us to identify high-risk IE patients for in-hospital mortality. D-dimer ≥ 4.2mg/L, CRP ≥ 13.6 mg/L were independently associated with IE related in-hospital death.

Interactions of U937 macrophage-like cells with decellularized pericardial matrix materials: influence of crosslinking treatment

While macrophages have been implicated in the failure of bioprosthetic heart valves, the macrophage response to crosslinked native pericardial collagen has not been previously investigated. Using decellularized bovine pericardium (DBP) as a model for native collagen, this study investigated the response of macrophage-like cells (U937s) to DBP, either: (i) untreated, or (ii) exogenously crosslinked with glutaraldehyde or 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide (EDC). We have previously validated the use of U937 cells as models for the response of human monocyte-derived macrophages to decellularized pericardial materials and, per our previous work, differentiated the U937 cells directly on the three material surfaces. After 72h in culture, the cells and medium were analyzed for DNA content, acid phosphatase activity, and cytokine and matrix metalloproteinase release. As well, cell/substrate samples were fixed for SEM. Fewer cells attached to or survived on the glutaraldehyde-treated substrate, and some showed an abnormal morphology compared to cells cultured on the other surfaces. Further, cells on glutaraldehyde-treated surfaces released more pro-inflammatory cytokines, more MMP-1 and less MMP-2 and MMP-9. The poor performance of the U937 macrophage-like cells on the glutaraldehyde-treated surfaces appears to be due to surface characteristics rather than to soluble aldehyde or other components leaching from the crosslinked material. These results provide evidence that crosslinking with glutaraldehyde is cytotoxic to macrophage-like cells, and that crosslinking with a zero-length crosslinker like EDC can be an acceptable alternative crosslinking treatment for biomaterials.

Prosthetic valve endocarditis: clinicopathological correlates in 122 surgical specimens from 116 patients (1985-2004)

BACKGROUND

Few studies have documented the clinicopathological features of prosthetic valve endocarditis independently of native valve endocarditis.

STUDY DESIGN

Retrospective analysis of patients undergoing cardiac surgery for prosthetic valve endocarditis at our institution (1985-2004).

METHODS

Medical records and microscopic slides were reviewed from 116 patients for demographics, infecting organisms, comorbidities, and pathologic features.

RESULTS

Patients were 12-86 years old (mean, 59 years). Among 122 valves, 64% were from men and 67% were purely regurgitant. Aortic prosthetic valve endocarditis frequently affected men (76%); mitral prosthetic valve endocarditis often affected women (62%). Embolization occurred in 35% and heart failure in 32%. Prevalent predisposing conditions were the prosthetic valve alone (43%) and diabetes mellitus (20%). Prosthetic valve endocarditis was aortic or mitral in 98% and was active in 70%. Annular abscess or paravalvular leak affected mechanical valves more frequently than bioprosthetic (89% vs. 65%; P=.001). Causative organisms (n=116) included Staphylococcus aureus (30%), coagulase-negative staphylococcus (22%), viridans streptococci (18%), enterococci (10%), other streptococci (8%), and other organisms (12%). S. aureus was the most prevalent cause of early-onset (38%) and late-onset (30%) prosthetic valve endocarditis. Coagulase-negative staphylococcus caused early-onset (31%) and most intermediate-onset (40%) disease and had a shorter median implantation-to-infection time than other organisms (6.5 vs. 61.3 months; P<.001). Viridans streptococci and enterococci primarily caused late-onset endocarditis. For active infections by cocci, most cases exhibited strong Gram staining, but four showed only strong Grocott methenamine silver staining.

CONCLUSIONS

Cocci accounted for 83% of infections. Early-onset prosthetic valve endocarditis was primarily staphylococcal, and late-onset prosthetic valve endocarditis resembled native valve endocarditis. Both Gram and Grocott methenamine silver stains were necessary to reliably identify organisms microscopically.

In vitro response of monocyte-derived macrophages to a decellularized pericardial biomaterial

Decellularized tissue-derived heart valves are an example of biomaterials derived from natural scaffolds. These types of implants are increasing in popularity although their in vivo performance is still only poorly understood and has, at times, been catastrophic. It is apparent that better understanding is required before these biomaterials can be used safely. In this study, the human monocyte-derived macrophage (MDM) response to decellularized bovine pericardium (DBP) was used as a model to predict the biological performance of these materials on implantation. Human monocytes differentiated on tissue culture polystyrene (TCPS) for 14 days were trypsinized and reseeded onto DBP, TCPS, and polydimethylsiloxane (PDMS) for 48 h. The MDMs on DBP contained less intracellular and extracellular esterase activity compared with MDMs on TCPS and PDMS, as well as less acid phosphatase activity than on TCPS. As well, morphologically, MDMs on DBP were less spread, less multinucleated and did not display many lamellipodia. Taken together, these data represent the first evidence of the MDM response to intact, native extracellular matrix, demonstrating that these cells reacted with an altered, possibly reduced foreign body response on this natural scaffold compared with the two control surfaces. This in vitro MDM cell model may provide a novel method for predicting and elucidating the biological performance of tissue-derived biomaterials, thereby directing a more rational design of biomaterials for tissue regeneration purposes.

The transcriptional programme of human heart valves reveals the natural history of infective endocarditis

Infective endocarditis (IE) is an infectious disease that is mainly caused by Staphylococcus aureus and Streptococcus sp. It usually leads to valvular destruction and vegetation formation. Its pathophysiology is badly understood and likely involves immune and coagulation systems with close interactions with the microorganism. Our objective was to evaluate host response by comparing transcriptional profiles of cardiac valves from IE patients with controls. Hierarchical clustering revealed a signature of IE consisting of 146 genes. Among the 89 up-regulated genes, we identified two genes strongly associated with IE: metalloproteinase 12 (MMP-12) and aquaporin-9, a member of the aquaglyceroporin membrane channel family. The up-regulation of MMP-12 gene is strengthened by the down-modulation of the gene encoding its inhibitor TIMP3. In addition, MMP-12 was expressed in macrophages infiltrating EI valves. We also found that aquaporin-9 was expressed in endothelial cells lining neo-vessel lumen, suggesting that aquaporin-9 might be associated with neovascularization of infected valves leading to tissue oedema secondary to the inflammatory process. The Gene Ontology annotation and the resulting functional classification showed that most up-regulated genes account for recruitment of inflammatory cells in vegetations, angiogenesis and remodelling of endocardium tissue. A network analysis confirmed the involvement of molecules related to the remodelling of endocardium tissue and angiogenesis in IE. It also evidenced the role of caspases, especially that of caspase-9 and intrinsic apoptotic pathway in IE. Based on this study we propose a scenario for the natural history of IE in humans. Some parameters identified in this work could become tools for measuring the disease activity and should be tested as biomarkers for diagnosis or prognosis assessment in future studies.