Evaluation of Infection Resistance of Biodegradable versus Conventional Annuloplasty Rings in an in vivo Rat Subcutaneous Model

Abstract

Background: Biodegradable atrioventricular annuloplasty rings are theoretically more infection resistant due to their intra-annular implantation technique and nonporous structures (monofilament of poly-1,4-dioxanone). The aim of this study was to investigate the infection resistance of a biodegradable annuloplasty ring (Kalangos-Bioring®) in a rat subcutaneous implantation model and to compare it with a commonly used conventional annuloplasty ring (Edwards Physio II®).

Methods: This study included 32 Wistar albino rats which were divided into 2 groups according to the implantation of sterile or infected annuloplasty rings as control and study groups. Each animal had 2 implantation pockets (made on the right and left side of the dorsal median line) where 1 cm of the biodegradable annuloplasty ring was implanted into one pocket and 1 cm of the conventional annuloplasty ring was implanted into the other pocket. The infection model was created by topical inoculation of 1 mL Staphylococcus aureus strain (2 × 107 colony-forming units/mL) into the implantation pockets before skin closure. Each group was equally divided into 4 subgroups according to different follow-up schedules. The animals were inspected for local as well as systemic infection signs, and the rings were explanted at weeks 2, 4, 9, and 14 following implantation. Implantation pockets were evaluated macroscopically as well as by histopathological examinations. Microbiological analysis of the explanted implants with surrounding tissue was done by using quantitative sonication method.

Results: Conventional ring-implanted pockets showed a more prominent inflammation reaction than the biodegradable ring-implanted pockets, and this characteristic was found to be accentuated with bacterial contamination. The sterile rings did not reveal any positive cultures in either group. The number of positive cultures found in conventional rings contaminated with S. aureus was greater than in the biodegradable ring group (11/16 vs. 2/16 positive cultures, respectively; p = 0.0032). The amounts of growing bacteria in the culture environment were also statistically significantly higher in the conventional ring group (7,175 ± 5,936 vs. 181 ± 130 colony-forming units/mL, respectively; p < 0.0005).

Conclusions: This is the first experimental study confirming the theoretical advantage of the infection resistance of the biodegradable annuloplasty ring (Kalangos-Bioring®) when implanted in an active infectious environment. Large animal models mimicking clinical scenarios and clinical comparative studies are needed to verify our results.

Keywords: Annuloplasty; Biodegradable materials; Cardiac surgery; Infective endocarditis; Valve repair.