Cardiac allografts: a 24-year South African experience

Impact of prolonged storage time on homograft ultrastructures: an attempt to find optimal guidelines for homograft processing

According to guidelines, total ischemic time for homografts at processing must be kept short to avoid degeneration. Many homografts are discarded due to practical inability to finish all steps from procurement to cryopreservation within the time limit. Although, several studies have shown that homografts with prolonged ischemic time show adequate quality and performance. Twenty aortic and 12 pulmonary homografts were collected and biopsies were retrieved at preparation (day 0) and after 1, 2, 3, 4, 7, 14, 21, 28, and 60 days in antibiotic decontamination at 4 °C. Biopsies were prepared for light microscopy (LM) and transmission electron microscopy (TEM). Assessment generated scores for cells, elastin, and collagen. Relative differences between times were compared with Wilcoxon signed rank test. Bonferroni corrected p value of 0.0056 was considered significant. LM could only reveal decrease in cell count at 60 days in aortic homografts, no other differences was detected. TEM showed affected cell appearance in day 3 and day 4 and beyond for aortic and pulmonary homografts respectively. Elastin appearance was affected at day 60 for aortic and day 21 for pulmonary homografts. Collagen appearance was affected at day 28 for aortic homografts, with no significant differences in pulmonary homografts. Cell degeneration starts early after homograft procurement, but elastic and collagen fibers are more resistant to degeneration. Overall structure integrity as seen in LM was not affected at all, while TEM could reveal small degeneration signs in individual elastic fibers and collagen bundles at 21 and 28 days respectively.

Comparison of the function and structural integrity of cryopreserved pulmonary homografts versus decellularized pulmonary homografts after 180 days implantation in the juvenile ovine model

Homograft availability and durability remain big challenges. Increasing the post-mortem ischaemic harvesting time beyond 24 h increases the potential donor pool. Cryopreservation, routinely used to preserve homografts, damages the extracellular matrix (ECM), contributing to valve degeneration. Decellularization might preserve the ECM, promoting host-cell infiltration and contributing towards better clinical outcomes. This study compared the performance of cryopreserved versus decellularized pulmonary homografts in the right ventricle outflow tract (RVOT) of a juvenile ovine model. Homografts (n = 10) were harvested from juvenile sheep, subjected to 48 h post-mortem cold ischaemia, cryopreserved or decellularized and implanted in the RVOT of juvenile sheep for 180 days. Valve performance was monitored echocardiographically. Explanted leaflet and wall tissue evaluated histologically, on electron microscopical appearance, mechanical properties and calcium content. In both groups the annulus diameter increased. Cryopreserved homografts developed significant (¾) pulmonary regurgitation, with trivial regurgitation (¼) in the decellularized group. Macroscopically, explanted cryopreserved valve leaflets retracted and thickened while decellularized leaflets remained thin and pliable with good coaptation. Cryopreserved leaflets and walls demonstrated loss of interstitial cells with collapsed collagen, and decellularized scaffolds extensive, uniform ingrowth of host-cells with an intact collagen network. Calcific deposits were shown only in leaflets and walls of cryopreserved explants. Young fibroblasts, with vacuoles and rough endoplasmic reticulum in the cytoplasm, repopulated the leaflets and walls of decellularized scaffolds. Young's modulus of wall tissue in both groups increased significantly. Cryopreserved valves deteriorate over time due to loss of cellularity and calcification, while decellularized scaffolds demonstrated host-cell repopulation, structural maintenance, tissue remodelling and growth potential.

Cadaver donation: structural integrity of pulmonary homografts harvested 48 h post mortem in the juvenile ovine model

Cryopreserved pulmonary homograft (CPH) implantation remains the gold standard for reconstruction of the right ventricular outflow tract (RVOT). Harvesting homografts < 24-h post mortem is the international norm, thereby largely excluding cadaveric donors. This study examines the structural integrity and stability of ovine pulmonary homografts harvested after a 48-h post mortem period, cryopreserved and then implanted for up to 180 days. Fifteen ovine pulmonary homografts were harvested 48-h post mortem and cryopreserved. Five CPH served as a control group (group 1; n = 5). CPH were implanted in the RVOT of juvenile sheep and explanted after 14 days (group 2; n = 5) and 180 days (group 3; n = 5). Leaflet integrity was evaluated by strength analysis, using tensile strength (TS), Young's modulus (YM) and thermal denaturation temperature (T_d), and morphology, including haematoxylin and eosin (H&E), Picrosirius red staining, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and von Kossa stains. Echocardiography confirmed normal function in all implants. In explants, no reduction in TS, YM or T_d could be demonstrated and H&E showed mostly acellular leaflet tissue with no difference on Picrosirius red. TEM demonstrated consistent collagen disruption after cryopreservation in all three groups, with no morphological deterioration during the study period. von Kossa stains showed mild calcification in group 3. No deterioration of structural integrity could be demonstrated using strength or morphological evaluations between the controls and implant groups over the study period. Extending the post mortem harvesting time of homografts beyond 24 h did not appear to negatively affect the long-term performance of such transplanted valves in this study.

Bioburden in transport solutions of human cardiovascular tissues: a comparative evaluation of direct inoculation and membrane filter technique

All cardiac allograft tissues are under potential contamination, requiring a validated terminal sterilization process or a minimal bioburden. The bioburden calculation is important to determine the bacterial burden and further decontamination and disinfection strategies for the valve processing. The aim of this study was to determine the bioburden from transport solution (TS) of heart valves obtained from non-heart-beating and heart-beating donors in different culture methods. The bioburden from TS was determined in 20 hearts donated for valve allograft tissue using membrane filter (MF) and direct inoculation. Tryptic soy agar and Sabouraud plates were incubated and colonies were counted. Ninety-five percent of samples from this study were obtained from heart-beating donors. The warm ischemic time period for heart was 1.06 ± 0.74 h and the cold ischemic time period was 25.66 ± 11.16 h. The mean TS volume was 232.68 ± 96.67 mL (48.5-550 mL). From 20 samples directly inoculated on TSA agar plates, 2 (10%) were positive. However, when MF was used, from 20 samples in TSA, 13 (65%) were positive with a mean count of 1.36 ± 4.04 CFU/mL. In Sabouraud plates, the direct inoculation was positive in 5 samples (25%) with a mean count of 0.24 ± 0.56 CFU/mL. The use of MF increased the positivity to 50% (10 samples from a total of 20) with a mean of 0.28 ± 0.68 CFU/mL. The positivity was superior using MF in comparison with direct inoculation (p < 0.05). The bioburden of TS is low and MF is the technique of choice due to higher positivity.

Twenty Years of Adult Congenital Heart Surgery: A Single-Center African Experience

BACKGROUND

Lack of data exists on the surgical management of adult congenital heart disease on the African continent. This study was undertaken to describe the clinical profile and surgical outcome of adult patients with congenital heart disease undergoing surgery in a single-center African study population.

METHODS

A retrospective medical chart review of consecutive adult patients (≥18 years) undergoing congenital heart surgery between October 1995 and December 2015 at our institution was undertaken. We described cardiac diagnosis, diagnostic complexity, risk profile, and surgical morbidity and mortality.

RESULTS

Data were collected of 233 surgical procedures performed in 219 patients (45.6% males). The most common diagnostic category was septal defects (41.2%), followed by right heart lesions (17.2%), left heart lesions (12.4%), thoracic arteries (9.0%), and conduit failure (6.9%). Twenty-four percent of patients presented in functional class III or IV, and 46% of patients met the criteria for the simple Bethesda diagnostic class. Preoperative risk factors were identified in 19.8% of patients. Corrective surgery was performed in 71.7% of cases, reoperative surgery in 27.6%, and palliative surgery in 0.8%. Right ventricle to pulmonary artery conduit placement comprised 53.1% of reoperations. The overall hospital mortality was 1.7%. Postoperative complications occurred in 26.3% of cases.

CONCLUSIONS

This study presents a detailed description of this emerging population in a developing world context. Our outcomes data suggest that adult congenital heart disease surgery is feasible in a Southern African tertiary referral center with low operative mortality and acceptable morbidity.

Disinfection of human cardiac valve allografts in tissue banking: systematic review report

Cardiovascular allografts are usually disinfected using antibiotics, but protocols vary significantly between tissue banks. It is likely that different disinfection protocols will not have the same level of efficacy; they may also have varying effects on the structural integrity of the tissue, which could lead to significant differences in terms of clinical outcome in recipients. Ideally, a disinfection protocol should achieve the greatest bioburden reduction with the lowest possible impact on tissue integrity. We conducted a systematic review of methods applied to disinfect cardiovascular tissues. The use of multiple broad spectrum antibiotics in conjunction with an antifungal agent resulted in the greatest reduction in bioburden. Antibiotic incubation periods were limited to less than 24 h, and most protocols incubated tissues at 4 °C, however one study demonstrated a greater reduction of microbial load at 37 °C. None of the reviewed studies looked at the impact of these disinfection protocols on the risk of infection or any other clinical outcome in recipients.