Validation of microbiological testing in cardiovascular tissue establishments: results of a second international quality-round trial

Advantages and challenges in processing and quality control of decellularized heart valves

More than 1000 donated aortic and pulmonary valves from predominantly European tissue banks were centrally decellularized and delivered to hospitals in Europe and Japan. Here, we report on the processing and quality controls before, during and after the decellularization of these allografts. Our experiences show that all tissue establishments, which provide native cardiovascular allografts for decellularization, meet comparably high-quality standards, regardless of their national origin. A total of 84% of all received allografts could be released as cell-free allografts. By far the most frequent reasons for rejection were non-release of the donor by the tissue establishment or severe contaminations of the native tissue donation. Only in 2% of all cases the specification for freedom from cells was not fulfilled, indicating that decellularization of human heart valves is a safe process with a very low discard ratio. In clinical use, cell-free cardiovascular allografts have been shown to be advantageous over conventional heart valve replacements, at least in young adults. These results open the discussion on the future gold standard and funding of this innovative therapeutic option for heart valve replacement.

Microbiological assessment of arterial allografts processed in a tissue bank

The transmission of microbial infection through tissue allografts is one of the main risks that must be controlled in tissue banks. Therefore, microbiological monitoring controls and validated protocols for the decontamination of tissues during processing have been implemented. This study is based on the evaluation of data from microbiological cultures of arteries (mainly long peripheral arteries) processed in the tissue bank of Valencia (Spain). Donors' profile, pre- and post-disinfection tissue samples were assessed. The presence of residual antibiotics in disinfected tissues was determined and the antimicrobial potential of these tissues was tested. Our overall contamination rate was 23.69%, with a disinfection rate (after antibiotic incubation) of 87.5%. Most (76.09%) of the microbial contaminants were identified as Gram positive. Arterial allografts collected from body sites affected by prior organ removal showed higher risk of contamination. Only vancomycin was detected as tissue release. The antimicrobial effect on Candida albicans was lower than that for bacterial species. Risk assessment for microbial contamination suggested the donor's skin and the environment during tissue collection as the main sources for allograft contamination. Antibiotic-disinfected arterial allografts showed antimicrobial potential.

Does microbiological contamination of homografts prior to decontamination affect the outcome after right ventricular outflow tract reconstruction?

 

OBJECTIVES

Homografts are often in short supply. Today, European guidelines recommend that all tissues contaminated by any of 18 different bacteria and fungi be discarded before antibiotic decontamination has been conducted. The tissue bank in Lund uses more liberal protocols: It accepts all microbes prior to decontamination except multiresistant microbes and Pseudomonas species. The aim of this study was to analyse the effect of contamination on the long-term outcome and occurrence of endocarditis in recipients.

METHODS

Data were collected on homografts and on recipients of homografts in the right ventricular (RV) outflow tract who were operated on between 1995 and 2018 in Lund. The long-term outcome of recipients was analysed in relation to different types of contamination using Cox proportional hazard regression. The proportion of patients with endocarditis was analysed with the χ2 test.

RESULTS

The study included 509 implanted homografts. Follow-up was a maximum of 24 years and 99% complete. A total of 156 (31%) homografts were contaminated prior to antibiotic decontamination. Homografts contaminated with low-risk microbes had the lowest reintervention rate, but there was no significant difference compared to no contamination [hazard ratio (HR) 1.1, 95% confidence interval (CI) 0.73-1.7] or contamination with high-risk microbes (HR 1.6, 95% CI 0.87-2.8) in the multivariable analysis. There was no significant difference in the proportion of cases of endocarditis during the follow-up period between recipients of homografts contaminated prior to decontamination and recipients of homografts with no contamination (P = 0.83).

CONCLUSIONS

Contamination of homograft tissue prior to decontamination did not show any significant effect on the long-term outcome or the occurrence of endocarditis after implantation in the RV outflow tract. Most contaminated homografts can be used safely after approved decontamination.

Transplantation of cryopreserved human heart valves in Europe: 30 years of banking in Brussels and future perspectives

For over 30 years, our TE has processed, controlled for quality and distributed cryopreserved allograft valves for human application. We present a review of this activity and future perspectives of cardiovascular tissue banking. The donor age and medical/behavioral history are in compliance with the regulations of the EUMS. Allograft morphology and function are evaluated in a class A cleanroom. Tests for viral/bacterial infection, histological control of structure/infection/malignancy and control-rate cryopreservation are performed. A total of 7562 hearts were sent to our TE, whereas 7290 valves (pulmonary, aortic and mitral) were transplanted. The donations increased over time: 1934, 2566 and 3062 hearts were donated during the first, second and third decades (increases of 32.7 and 19.3% during the second and third decades). Likewise, there was a significant increase in transplantations with 2050, 2550 and 2690 valves implanted during the first, second and third decades (24.4 and 5.5% increase during the second and third decades). A total of 4475 pulmonary (61.4%), 2760 aortic (37.9%) and 55 mitral valves (0.7%) were transplanted. Outstanding long-term results in adults and evidence of immune-related deterioration of allografts in neonates and infants were demonstrated. Decellularization was suggested as a solution. One hundred pulmonary and 180 aortic valves were sent for transplantation after decellularization for the ESPOIR and ARISE clinical trials and beyond. The donation and transplantation activity increased progressively. Although cryopreserved valves represent the best substitute for diseased valves, accelerated failure appears after implantation in neonates and infants. The implementation of new technologies, such as decellularization, as a standard procedure for treatment of allograft valves will offer further improvements in allograft quality and increase of durability.

The BD BACTEC FX blood culture system with the gentlemacs dissociator is suitable for sterility testing of heart valve and vascular allografts-A validation study

To present our validation study of the BD BACTEC FX blood culture system for sterility testing of cardiovascular tissues aimed for human application. For operational qualification, we performed temperature mapping of the system, vacuum test using non-inoculated BACTEC vials, and growth promotion tests by injecting contaminant strains into aerobic and anaerobic bottles. For performance qualification, negative control, assessment of method suitability, evaluation of sensitivity limits, control of neutralization of antibiotics in biopsy samples from allografts and tissue toxicity effects, were performed. Tissue samples and transport/cryopreservation solutions were homogenized in GentleMACS Dissociator and injected into BACTEC Plus aerobic and anaerobic vials for incubation at 35 °C for 14 days. Tissues were spiked with aerobic and anaerobic bacteria and fungi. Growth of contaminants appeared in all aerobic and anaerobic vials for Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa; in anaerobic vials for Cutibacterium (Propionibacterium) acnes and Clostridium sporogenes; and only in aerobic vials for Candida albicans and Aspergillus brasiliensis. The majority of bacterial strains were detected within two days (59-100%), exceptionally between 3 and 14 days. In contrast, fungal contaminations were detected within 2, 3-6, 7-10 and after 10 days of incubation in 33.3, 71.6, 96.6 and 99.9% of cases,respectively. Uninhibited growth appeared in the tissue biopsies and homogenized tissues with and without antibiotics and in other solutions. BD BACTEC blood culture system with GentleMACS Dissociator is a rapid and efficient tool for detection of contamination in cardio-vascular tissues aimed for human application.

The time has come to extend the expiration limit of cryopreserved allograft heart valves

Despite the wide choice of commercial heart valve prostheses, cryopreserved semilunar allograft heart valves (C-AHV) are required, and successfully transplanted in selected groups of patients. The expiration limit (EL) criteria have not been defined yet. Most Tissue Establishments (TE) use the EL of 5 years. From physiological, functional, and surgical point of view, the morphology and mechanical properties of aortic and pulmonary roots represent basic features limiting the EL of C-AHV. The aim of this work was to review methods of AHV tissue structural analysis and mechanical testing from the perspective of suitability for EL validation studies. Microscopic structure analysis of great arterial wall and semilunar leaflets tissue should clearly demonstrate cells as well as the extracellular matrix components by highly reproducible and specific histological staining procedures. Quantitative morphometry using stereological grids has proved to be effective, as the exact statistics was feasible. From mechanical testing methods, tensile test was the most suitable. Young's moduli of elasticity, ultimate stress and strain were shown to represent most important AHV tissue mechanical characteristics, suitable for exact statistical analysis. C-AHV are prepared by many different protocols, so as each TE has to work out own EL for C-AHV.