The Use of Biological Heart Valves

Characteristic calcification behavior of five surgical aortic valve bioprostheses models: An in vitro study

Background and Aims

The durability of surgical aortic valve bioprostheses (SAV) is limited by the calcification of the leaflets, which results in degeneration. In clinical routine, there seems to be substantial variability in the degeneration of specific SAV models. Our study aims to establish an in vitro calcification model for prosthetic valves, characterizing the calcification behavior of different SAVs.

Methods

Five commercially available SAV models (Epic™ Supra, Freestyle®, Intuity®, Perimount®, and Trifecta™) were perfused with double-distilled water and physiological buffer with a defined calcium concentration (CaCl2 = 1.5 mM) at 37°C over 32.9 million cycles in a Hi-Cycle tester which corresponds to approximately 1 patient-year (calcified group). Untreated prosthetic valves served as the negative control group (noncalcified group). Calcium titration, scanning electron microscopy (SEM), histological examination, and tissue thickness measurements were performed to evaluate noncalcified and calcified SAVs (n = 10).

Results

Treatment in the Hi-Cycle tester with calcification buffer maintained significantly higher calcium absorption of SAVs compared to the control group (p < 0.001). Additionally, hydroxyapatite crystals were found in the calcified SAV in SEM. Porcine valves rarely demonstrated punctual calcification pattern, while bovine pericardial valves presented distinct planar calcification pattern in histological examination. Further, calcification content differed significantly depending on the SAV model, with the highest calcium content in Trifecta (213 µg/cm2) and the lowest in Epic Supra (8 µg/cm2) (p < 0.001).

Conclusion

Data from our study revealed significant differences in leaflet calcification for the various aortic valve bioprostheses models. Further studies are necessary to investigate whether these findings can mimic the clinical data of the implanted prostheses.

Tissue requirements for the application of aortic valve neocuspidization - appropriate pericardium properties and homogeneity?

OBJECTIVE

Aortic valve neocuspidization (AVNeo) using autologous pericardium is a promising technique. Expected advantages are reduced immune response, appropriate biomechanics and lower treatment expenses. Nevertheless, autologous pericardium can be affected by patient's age and comorbidities. Usually, glutaraldehyde (GA) - fixed bovine pericardium is the basic material for aortic valve prostheses, easy available and carefully pre-examined in a standardized fabrication process. Aim of the study is the verification of autologous pericardial tissue homogeneity by analysing tissue thickness, biomechanics and extracellular matrix (ECM) composition.

METHODS

Segments of human GA-fixed pericardium selected by the surgeon based on visual criteria for cusp pre-cut and remaining after surgical AV replacement were investigated in comparison to bovine standard tissue treated equivalently. Pericardium sampling was performed at up to three positions of each sutured cusp for histological or biomechanical analysis, according to tissue availability.

RESULTS AND CONCLUSIONS

Human pericardia exhibited a higher heterogeneity in collagen content, density of vessel structures and elastic moduli. Thickness, vessel density and collagen and elastin content differed significantly between the species. In contrast, significant interindividual differences were detected in most properties investigated for human pericardial samples but only for tissue thickness in bovine tissues. Higher heterogeneity of human pericardium, differing vessel and collagen content compared to bovine state-of-the-art material might be detrimental for long term AV functionality or deterioration and have to be intensely investigated in patients follow up after autologous cusp replacement.

Looking Back to Look Forward: What to Expect in a Redo Surgery for a Bioprosthesis Replacement

Redo surgeries are becoming more common because of an increased rate of bioprosthesis implantation. We performed a retrospective study on patients who underwent redo replacement of an aortic and/or mitral bioprosthesis between 2005 and 2018 to evaluate intra-hospital mortality and morbidity. Univariate analysis was performed on the propensity score variables to determine predictors of mortality. A total of 180 patients were enrolled in the study: Group A (replacement of aortic bioprosthesis) with 136 patients (75.56%) and group B (replacement of mitral bioprosthesis ± aortic bioprosthesis) with 44 patients (24.44%). NYHA class ≥ 3 and female sex were significantly more common in group B. Cardiopulmonary-bypass time and aortic cross-clamping time in group A and group B were, respectively, 154.95 ± 74.35 and 190.25 ± 77.44 (p = 0.0005) and 115.99 ± 53.54 and 144.91 ± 52.53 (p = 0.0004). Overall mortality was 8.89%. After propensity score adjustment, Group B was confirmed to have an increased risk of death (OR 3.32 CI 95% 1.02−10.88 p < 0.0001), gastrointestinal complications (OR 7.784 CI 95% 1.005−60.282 p < 0.0002) and pulmonary complications (OR 2.381 CI 95% 1.038−5.46 p < 0.0001). At the univariate analysis, endocarditis, cardiopulmonary-bypass and aortic cross clamping time, NYHA class ≥ 3 and urgency setting were significantly associated to death. Intra-hospital outcomes were acceptable regarding mortality and complications. Patients who need redo surgery on mitral bioprosthesis have an increased risk of post-operative pulmonary and gastrointestinal complications and mortality. Therefore the choice of mitral bioprosthesis at time of first surgery should be carefully evaluated.