R Foth

Immunohistochemical Characterization of Neotissues and Tissue Reactions to Septal Defect–Occlusion Devices

Background—We sought to evaluate tissue reactions within and at the surface of devices for interventional therapy of septal defects and to identify antigen characteristics of neotissues. Methods and Results—Atrial or ventricular septal defect–occlusion devices (Amplatzer, n=7; Cardioseal/Starflex, n=3) were processed using a uniform protocol after surgical removal from humans (implantation time, 5 days to 4 years). Devices were fixed in formalin and embedded in methylmethacrylate. Serial sections were obtained by sectioning with a diamond cutter and grinding, thus saving the metal/tissue interface for histologic evaluation. Immunohistochemical staining was performed using conventional protocols. Superficial endothelial cells stained positive for von Willebrand factor. Within the newly formed tissues, fibroblast-like cells were identified with a time-dependent expression of smooth muscle cell maturation markers (smooth muscle actin, smooth muscle myosin, h-caldesmon, and desmin) beside extracellular matrix components. Neovascularization of the newly formed tissues was demonstrated with the typical immunohistochemical pattern of capillaries and small vessels. Inflammatory cells could be identified as macrophages (CD68+) and both T-type and B-type lymphocytes (CD3+, CD79+). Conclusions—This is the first presentation of results from serial immunohistochemical staining of a collection of explanted human septal-occlusion devices. A time-dependent maturation pattern of the fibroblast-like cells in the neotissues around the implants could be described. Neoendothelialization was seen in all specimens with implantation times of 10 weeks or more. The time course of neoendothelialization, as seen in our study, further supports the clinical practice of anticoagulant or antiplatelet therapy for 6 months after implantation. This time interval should be sufficient to prevent thromboembolic events due to thrombus formation at the foreign surface of cardiovascular implants.

Clinical, echocardiographic and histopathologic findings in nine patients with surgically explanted ASD/PFO devices: Do we know enough about the healing process in humans?

BACKGROUND Atrial septal defects (ASD) and persistent foramen ovale (PFO) are managed in increasing numbers by catheter interventions as an attractive alternative to surgery. Early complications have been described in clinical series whereas late complications are rare. No series are reported with clinical, echocardiographic and histological data. METHODS AND RESULTS We collected clinical, echocardiographic, and histolological data of nine patients with surgically explanted devices. Occlusion devices were explanted after a mean interval of 3.4 ± 2.4 years (range 0.9-8.3). Indications were recurrent thromboembolic events in five, residual shunt/dislocation in three, and growing mass on echocardiography despite oral anticoagulation in one patient. Two patients suffered potentially live threatening events due to coronary embolism. One of them had to be resuscitated due to ventricular fibrillation. Histologically, residues of superficial thrombus formation could be demonstrated in two of the devices. In another patient, hyperplastic tissue formation was related to a local inflammatory process but not to a thrombus as suspected by echocardiography. CONCLUSION Late complications after device implantation may occur up to 8 years after device implantation and may be potentially live threatening. Echocardiographic controls should be prolonged beyond the first year after implantation and every explanted device should be histologically worked up in an experienced center. Up to now, the mechanisms of late thrombogenesis are not fully understood.

A novel method for processing resin-embedded specimens with metal implants for immunohistochemical labelling

A major technical problem in the processing of resin-embedded tissues is the adhesion of the tissue sample on glass slides for immunohistochemical labelling. We therefore established a novel protocol for processing such specimens with improved attachment of the tissue sample during resin removal (deplastification). In order to demonstrate the feasibility of the procedure we employed a panel of smooth muscle cell maturation markers. The technique makes use of a silicone glue (Elastosil E41; Wacker Chemie, München, Germany) to attach the tissue samples to the glass slides. This allows resin dissolution in xylene/2-methoxyethylacetate without detachment of the sample from the slide. Our results demonstrate successful immunohistochemical labelling with primary antibodies directed against: smooth muscle actin, smooth muscle myosin, h-caldesmon, desmin, vimentin and von Willebrand factor. In conclusion, we have established a new and successful method for resin-embedded sample adhesion on glass slides. The developed protocol is feasible for investigation of cells which are involved in intimal proliferation following stent implantation.

Melody transcatheter valve: Histopathology and clinical implications of nine explanted devices

OBJECTIVES We examined interventionally implanted valved Melody conduits after surgical explantation by means of histology and immunohistochemistry and matched these findings with clinical data in order to assess in vivo biocompatibility and to identify risk factors for graft failure. METHODS 9 Melody valves had been implanted in 8 patients (pulmonary n = 7, tricuspid position n = 1). Indication for explantation included significant obstruction in 7 patients and valve insufficiency in 1 patient. 4 of 8 patients had suffered from endocarditis. Mean interval between implantation and explantation was 3.2 (1.8-5.2) years. All explants were worked up using a uniform protocol with fixation in formalin and embedding in methylmethacrylate. RESULTS All but one valve of the explanted Melody grafts were thin and histologically intact without any pathological findings. Complete neo-endothelialization could be demonstrated by means of immunohistochemistry. All 4 Melody valves from patients with endocarditis showed dense granulocytic infiltrations, 3 of these showed thrombotic material within the valves. CONCLUSION This report covers the first series of explanted Melody valves from humans applying a uniform protocol for histopathological examination. Good biocompatibility of the Melody valves could be demonstrated after a mid-term follow-up. Factors for graft failure included endocarditis, outgrowth, and residual stenosis. These findings may have significant implications for the implant procedure as well as care of the patients during long-term follow-up.

A Comparative Histopathological Study of Heparin Coated and Uncoated Polytetrafluoroethylene Shunts in Children With Congenital Heart Defect

Objective: Recently, heparin coated polytetrafluoroethylene (PTFE) shunts are available and are believed to improve inherent shunt problems such as thrombosis and excessive and incomplete neointima formation or occlusion. We aimed at comparing the potential histopathological differences in the neointima (in) between uncoated (UCS) PTFE shunts and heparin coated (HCS) PTFE shunts. Materials and Methods: Thirteen shunts (six UCS and seven HCS) were analyzed. The specimens were fixed in formalin, embedded in paraffin or in methylmethacrylate, and characterized by standard and immunohistochemical staining. The thickness of pseudointima proliferation was graded as follows: 0 = no cell layers, 1 = few layers <100 µm, 2 = partial layers >100 µm, 3 = complete layers <300 µm, 4 = complete layers >300 µm, and 5 = occlusion. Results: Mean shunt size was 3.4 ± 0.2 mm in UCS and 3.1 ± 0.2 mm in HCS (P = .053). Mean time of implantation was 163 ± 75 days in UCS and 97 ± 52 days in HCS (P = .091). There were no significant differences in the proportion of patients with functionally single ventricle, body surface area, age at implantation, or implantation type, between both groups. Shunt occlusion did not occur. Unplanned shunt explantation due to cyanosis was performed in one patient in each group. Partial thrombus formation was observed in one UCS (P = .462). There was complete endothelialization in 50% of UCS and 86% of HCS (P = .266). The grade of pseudointima proliferation was 1.8 ± 0.4 in UCS and 1.7 ± 0.5 in HCS (P = .646). Conclusions: The histopathological workup of PTFE shunts revealed equally partial endothelialization and discrete pseudointima proliferation in both the groups. The process of endothelialization may be faster in HCS.

Thrombosis of a mechanical prosthetic aortic valve in early pregnancy: histopathological findings

We present results of the histopathological workup of a prosthetic aortic valve which was explanted from a 31-year-old woman due to valve thrombosis during early pregnancy. Our images demonstrate nicely thrombotic material directly adherent to the pyrolytic carbon surface in a human specimen.