Impact of storage time prior to cryopreservation on mechanical properties of aortic homografts.

Optimal time spans in homograft procurement are still debatable among tissue banks and needs to be further investigated. Cell viability decreases at longer preparation intervals, but the effect on collagen and elastic fibers has not been investigated to the same extent. These fibers are of importance to the homograft elasticity and strength. The objective of this study was to analyze the mechanical properties of homograft tissue at different time spans in the procurement process. Ten aortic homografts were collected at the Tissue Bank in Lund. Twelve samples were obtained from each homograft, cryopreserved in groups of three after 2-4 days, 7-9 days, 28-30 days, and 60-62 days in antibiotic decontamination. Mechanical testing was performed with uniaxial tensile tests, calculating elastic modulus, yield stress and energy at yield stress. Two randomly selected samples were assessed with light microscopy. Procurement generated a total of 120 samples, with 30 samples in each time group. Elastic modulus and yield stress was significantly higher in samples cryopreserved after 2-4 days (2.7 MPa (2.5-5.0) and 0.78 MPa (0.68-1.0)) compared to 7-9 days (2.2 MPa (2.0-2.6) and 0.53 MPa (0.46-0.69)), p = 0.008 and 0.011 respectively. Light microscopy did not show any difference in collagen and elastin at different time spans. There was a significant decrease in elastic modulus and yield stress after 7 days of decontamination at 4 °C compared to 2-4 days. This could indicate some deterioration of elastin and collagen at longer decontamination intervals. Clinical significance of these findings remains to be clarified.

Impact of valve fenestrations and structural changes in homografts on the long-term outcome in the recipient.

Homografts have long been used for right ventricular outflow tract (RVOT) reconstruction. Tissue banks struggle to meet the clinical demand of tissue, with insufficient donor availability and strict recommendations on tissue quality with high proportions of discards. This study analyzes the long-term outcome of patients receiving a homograft with small fenestrations of the cusps or other structural changes, to evaluate if minor impairment of the homograft affects the durability. Homograft characteristics and patient outcome were described. Follow-up was maximum 24 years. Structural changes of the homografts were analyzed in relation to patient outcome, using univariable and multivariable Cox proportional hazard regression. Between 1995 and 2018, 468 patients received 535 homografts in the RVOT in Lund. Median recipient age was 13 years. There were 137 (26.9%) reinterventions. Freedom from reintervention was 75.8% (95% CI 71.3-79.7%) at 10 years and 57.4% (95% CI 50.0-64.0%) at 20 years. Small fenestrations of the cusps, fibrosis of the cusps and minor atheromatosis of the vessel did not show any statistically significant impact on long-term outcome, hazard ratio = 0.46 (95% CI 0.11-1.87, p = 0.276) and hazard ratio = 0.80 (95% CI 0.25-2.56, p = 0.704). Minor structural changes of the homografts seem to be acceptable without affecting the long-term durability.

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.

Long-Term Outcome of Homograft Implants Related to Donor and Tissue Characteristics.

BACKGROUND: Cardiovascular homografts are used for right ventricular outflow tract reconstruction. The procedure has excellent survival rates, but many homografts degenerate and require reintervention. Studies analyzing risk factors for reintervention most often focus on recipient and homograft characteristics, with identification of risk factors such as young recipient age and the use of aortic homografts. This study focuses on less known variables, including donor characteristics and homograft management and its effect on long-term outcome of homograft implantation. METHODS: A retrospective study was conducted of 304 patients undergoing right ventricular outflow tract reconstruction at University Hospital Lund, Sweden, between 1995 and 2008. Follow-up was up to 22 years. Donor, homograft, and recipient characteristics were analyzed. Statistical analyses included the Kaplan-Meier method with log-rank test and Cox proportional hazard regression. RESULTS: Follow-up was 98% complete. There were 12 deaths, and 115 reinterventions were required. Younger donor age was identified as a risk factor. Homografts from multiorgan donors with no ischemic time produced the longest homograft survival. In non-heart-beating donors, long-term results did not differ between 1 and 24 hours of ischemic time and more than 24 hours of ischemic time. Longer retrieval to cryopreservation times seemed to be better compared with shorter time intervals. Long-term outcome was superior in homografts from middle-aged donors. CONCLUSIONS: The best long-term outcome was found when homografts were retrieved from organ donors and middle-aged donors. There is no harm extending the ischemic time in non-heart-beating donors to 48 hours to increase the number of possible donors.