In reconstructive surgery for congenital heart disease, different types of pericardial tissues are frequently used. When available, autologous pericardium remains the tissue of choice for multiple indications. However, as many patients need more than one operation, alternative materials are urgently needed. In recent decades, miscellaneous materials and patches have been launched. Many pros and cons have already been discussed. A systematic histopathological analysis is still lacking.

The following commonly used patches are made of either equine, bovine or porcine pericardium:

Matrix patch™ (Auto Tissue GmbH Berlin, Berlin, Germany) is a decellularized equine pericardial patch, with a low RNA and DNA content, fixed in glutaraldehyde (1). CardioCel^® (LeMaitre Vascular, Inc., Burlington, MA, USA), a bovine pericardial patch, is treated with the so-called APAPT^® anti-calcification process including removal of cell particles and nucleic acids as well as minimization of glutaraldehyde cytotoxicity levels (2). Manufacturers of Supple Peri-Guard^® and Vascu-Guard^® Patches (LaMed, Oberhaching, Germany), other patches of bovine origin, put an emphasis on the “acellular” aspect of the patch and its permanent tear strength (3). Glutaraldehyde treatment is used for processing of BioIntegral Curved No-React® porcine patch (4). For most industrial patches information on the production process is only available on the companies' websites (5–7).

In this study, we investigated native pericardial tissue of different species. We then compared the histological structure of the native tissue to the industrially processed products. Thus, we analyzed how industrial processing alters pericardium even before implantation.

Secondly, patient explants, gathered from aortic valve re-operations, were examined to investigate further degenerative processes of autologous and equine pericardium after implantation.

Research on the ideal material for reconstructive surgery in children with congenital heart disease has mainly been focused on clinical outcomes and the frequency of re-operations. Therefore, we wanted to focus on a histologic analysis of different patches to provide a more complete picture of available materials.

The most commonly used industrial patches are of bovine origin, when autologous pericardium is not suitable or available. In recent years, alternative materials were launched to the market. Both porcine (4) and equine (9) patches became increasingly popular among cardiac surgeons. In general, the use of biological material is considered superior to synthetics in terms of biocompatibility and compliance (10).

Our results show that degenerative developments are initiated by processing and storage of pericardium. After implantation in childhood these alterations continue and even aggravate.

In case of bovine pericardium, Nordmeyer et al. reported calcifications in the majority of explanted CardioCel® patches. In addition to that, they discovered pseudo-intima formation, fibroblast ingrowth, occasional inflammatory processes and endothelialization (11). Others discovered fragmentations of collagen matrix, nodular disruption and sclerosis and confirmed calcification of CardioCel®. While they could identify neointima formation, endothelialization of the graft could not be confirmed (2).

Our pre-implant analysis of CardioCel® shows collagen network destruction and tissue loosening. Therefore we hypothesize that ADAPT-treatment provides the basis for degenerative alterations in bovine pericardium. However, other techniques of industrial bovine pericardial processing also showed similar tissue alterations in our analysis (products of Lamed GmbH). Once implanted, they can lead to calcification and inflammation (12).

Clinically, these observations are even more apparent: in a retrospective analysis of the CardioCel® patch, longevity of the implanted material was limited, as freedom from reoperation was only 57% after 3 years (13). In another study, 9 of 60 adult men who received a CardioCel® patches in a valvular position needed reoperation, 6 of them due to focal calcification and consecutive valve dysfunction (2). Pavy et al. experienced graft failure of CardioCel® when implanted in aortic position (14).

We show that processing of porcine pericardium (BioIntegral Curved No-React® porcine patch) also leads to degeneration when compared to native tissue. To our knowledge, there is no systematic histological analysis of this kind of explanted porcine pericardial patch. In children, it is mainly used for aortic reconstruction during Norwood procedure and shows promising early results (4, 15).

In an animal study, Dohmen et al. implanted 7 decellularized equine pericardial scaffolds in juvenile sheep. Four months later, no structural deterioration or degeneration could be observed. The researchers observed a monolayer of endothelial cells on the inner surface of the patches (1).

These positive short term results contradict our observations from explants. We analyzed two equine patches, previously used for aortic valve reconstruction in early childhood. A chronic foreign body reaction at the incorporation zone was present in one sample (Figure 4A). Furthermore, fiber thickening and calcification were detected. In addition to degeneration of the collagen fiber network, the thickness of equine pericardium (Matrix Patch^TM) already triples after industrial processing (Figures 2C,F, 3D,H).

We chose patients after aortic valve (AoV) repair as this cohort undergoes a rather temporary surgical solution. In general, degeneration, shrinkage and/or calcification limited the longevity of the analyzed patch materials. Nevertheless, with AoV repair during early childhood definite surgical procedures can be postponed. Vergnat et al. reported on 193 patients who needed aortic valve repair due to either stenosis, regurgitation or a combination of both. The surgeons preferred autologous pericardium that was intraoperatively treated with glutaraldehyde 0.3175% for 20 min. The reported results were promising as freedom from reoperation was 89, 70 and 57%, respectively, after 1, 5 and 7 years. The authors hypothesized that the junction of tissues (native and foreign patch material) seen after leaflet extension is more prone to calcification than complete renewed leaflets as stress promotes degeneration (16).

This clinically observed pathomechanism cannot be considered the only explanation for graft failure. In our explants, we encountered a variety of degenerative developments, such as fibrotic appositions (Figure 4B) and calcification.

Our research clearly shows that degeneration starts before implantation. Birefringence as a marker for an intact collagen fiber network is lost during industrial processing. Tissue loosening and inter-fibrillary gapping are observed in all xenografts. None of the analyzed tissues resembled the exact structure of autologous pericardium. A careful surgical approach prior to the implantation of any pericardial patch is therefore needed. Choice of material is not just a question of comfort during surgery. Surgeons should be aware of the limited longevity of all available patches.

This study compares native pericardium with processed, industrially available patches. As the native pericardium was obtained from a local butcher, the animal breed may not be identical to the one used for industrial purpose by the companies. Furthermore, the explant analysis of this study is only limited to re-operations after aortic valve repair. As our explant analysis was conducted on a small cohort of patients, additional research on this topic is advisable.

Patches at other locations in the heart, i.e. the right ventricular outflow tract, may show different forms of degeneration. It was furthermore our intention to focus on degenerative developments and not on the clinical performance of the analyzed explants. To assess the clinical performance of different patch materials, prospective randomized double blind trials are advisable.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Ethik-Kommission der Ärztekammer Westfalen-Lippe und der Westfälischen Wilhelms-Universität, 2015-231-f-S. Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin. The animal study was reviewed and approved by Ethik-Kommission der Ärztekammer Westfalen-Lippe und der Westfälischen Wilhelms-Universität, 2015-231-f-S.

AP: writing original draft, data acquisition, formal analysis, and conceptualization. SvM: critical review and editing. BH and K-MM: formal analysis and critical review and editing. AG: data acquisition. SaM: conceptualization, writing original draft, and formal analysis. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.