Matthias Sigler

Efficacy and safety of cryoenergy in the ablation of atrioventricular reentrant tachycardia substrates in children and adolescents.

Introduction: Cryoenergy has evolved as a safe and effective alternative for ablation of arrhythmia substrates in adult patients. Due to two specific features, cryomapping and cryoadhesion, this technique appears very attractive for pediatric patients minimizing complications and fluoroscopy time. The aim of the study was to investigate efficacy and safety of cryoenergy in the ablation of supraventricular tachycardia (SVT) substrates in pediatric patients.

Biocompatibility of septal defect closure devices

Objective: Despite their clinical introduction 10 years ago, no human series on the healing response to Amplatzer and Starflex devices in humans have been reported yet. We sought to investigate the biocompatibility of Amplatzer and Cardioseal/Starflex septal occluder devices in humans and compare the findings to results in experimental animals. Methods: The healing response of Amplatzer and Cardioseal/Starflex septal occluder devices in humans (n = 12, follow-up periods from 5 days to 4 years) and in experimental animals (n = 32, follow-up periods from 4 days to 1 year) was studied using a uniform work up protocol. Histological sections of paraffin-wax-embedded or methacrylate-embedded specimen and scanning electron microscopy were used for biocompatibility screening. Results: Neoendothelialisation of all examined devices was complete after 3 months in vivo. Protruding metal frame parts, like screw threads and spring arms, were covered last. The initial deposition of fibrin and blood cells on the polyester fabric was subsequently organised by ingrown fibroblastic cells. Loosely arranged and poorly vascularised young granulation tissue was transformed time-dependently into quiescent fibre-rich connective repair tissue poor of cellular and capillary vessel components. Consistently, a mild chronic inflammatory response directed against textile fibres of both types of implants characterised by lymphocytic infiltration and multinucleated foreign body giant cells was observed equally in human and animal explants. Conclusions: Systematic biocompatibility screening in a series of explanted human septal occluder devices showed results corresponding to findings in animal studies with regard to neoendothelialisation, cellular organisation of initial thrombus and persisting immune response.

First biodegradable metal stent in a child with congenital heart disease: Evaluation of macro and histopathology

New developments in stent technology led to the first biodegradable magnesium stents. To overcome the fundamental restrictions of conventional stent implantation, these new stents may improve interventional therapy, also in small children. What remains after complete degradation of a magnesium stent is of particular interest and concern. At the autopsy, 2 months after the projected complete degradation time of the 3.0 × 10 mm2 stent, no solid compounds were detected, and the vessel diameter had increased slightly to 3.7 mm. Histological preparation revealed an amorphous to jelly‐like substitute of the magnesium struts mainly consisting of calcium phosphate covered by fibrotic tissue. Immunological staining revealed no relevant inflammatory reaction to the stent material. Neointima proliferation was detected around the struts with some cellular infiltration of the calcium‐phosphate material. These pathological and histological findings show minimal alteration of the vessel wall and an increase of the arterial diameter after stent degradation. This is an important precondition for further use of biodegradable stents in small infants. Further observations have to prove whether these findings do reproduce in other settings also.

Biocompatibility screening in cardiovascular implants.

Zunehmendes Interesse gilt der Biokompatibilität kardiovaskulärer Implantate. Ziel dieser Arbeit ist die Vorstellung von Methoden und Ergebnissen der pathologischen Aufarbeitung von explantierten Implantaten. Die Standardeinbettung von Implantaten zur histologischen Beurteilung in Paraffin ist nur eingeschränkt geeignet, da metallische Anteile vor der Einbettung unter Beschädigung der Grenzfläche Gewebe/Implantat entfernt werden müssen. Alternativ kommt eine Einbettung in Kunstharze in Frage, wobei histologische Schnitte mittels Schneiden und Schleifen angefertigt werden. Dies ermöglicht die Untersuchung lokaler entzündlicher Vorgänge an der Oberfläche des Implantates. Zusätzlich interessieren bei der Aufarbeitung der Implantate die Reaktion und Struktur des umgebenden Gewebes sowie der benachbarten Grenzfläche zum Blutstrom. Neben der Histologie kommen immunhistochemische Verfahren sowie die Elektronenmikroskopie zum Einsatz. Unter Verwendung der genannten Methoden demonstrieren wir Befunde von Implantatpräparaten aus Tierversuchen und entsprechende Ergebnisse von Implantaten, die bei Patienten im Rahmen von Korrekturoperationen bei angeborenen Herzfehlern entfernt wurden. Nach der Implantation kommt es unabhängig vom Implantattyp zu einer raschen Re-Endothelialisierung der Gefäßoberfläche. In das nach Okkluder-Implantation initial gebildete Thrombusgewebe sprossen fibromuskuläre Zellen ein, wie sie auch nach Stentimplantation in der Intimahyperplasie gesehen werden. Entzündliche Reaktionen sind in Qualität und zeitlichem Verlauf materialabhängig. Mit einer vollständigen pathologischen Aufarbeitung kardiovaskulärer Implantate nach Explantation können Informationen über Einwachsen, Endothelialisierung und Entzündungsreaktionen gewonnen werden. Interest in information on biocompatibility of implants is increasing. The purpose of this paper is to discuss methods and results of pathological biocompatibility screening of explanted cardiovascular implants. Use of standard histology after embedding in paraffin is limited since metallic implants have to be removed during workup with disruption of the specimen. Alternatively, tissue blocks containing an implant can be embedded in methylmethacrylate or hydroxyethylmethacrylate and processed by sectioning with a diamond cutter and grinding, thus leaving the implant in situ and saving the tissue/implant interface for detection of local inflammatory reactions. Another important aspect of evaluation is the progress of thrombus organisation after initial fibrin clotting on the metal surface or in the inner part of occlusion devices. New methacrylate resins and embedding techniques allow for specific immunohisto-chemical staining of the specimen thus enabling characterisation of tissues surrounding the implant. Information on endothelialisation of the vascular surface of the implant can be obtained by means of immunohistochemistry or by scanning electron microscopy. Illustrating the use of these technologies, we demonstrate findings in tissue specimens from animal studies with different types of devices (i.e. stents, occlusion devices). We present corresponding findings in human specimens with implants that were removed during corrective surgery for congenital heart defects. Early endothelialisation of the vascular surface was seen after implantation in all types of devices. Cells within occlusion devices could be characterised histologically and immunohistochemically as fibromuscular cells as seen in intimal hyperplasia after stent implantation. Inflammatory implant-host reactions ranged from mild to moderate (medical grade stainless steel, nitinol) to severe (polytetrafluoroethylene [PTFE]). With an optimal work-up of cardiovascular implants, ingrowth and endothelialisation as well as inflammatory reactions in the surrounding tissue can be assessed. This information allows evaluation of individual tissue reactions to the implant and may serve as valuable basis for optimisation of biocompatibility by implant modification.

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.

Implantation of stents as an alternative to reoperation in neonates and infants with acute complications after surgical creation of a systemic-to-pulmonary arterial shunt.

Creation of a systemic-to-pulmonary shunt is still the firstline treatment in neonates with duct-dependent pulmonary circulation, or in patients with hypoplastic left heart syndrome as a part of the first stage of the Norwood sequence. Acute complications after such surgery, such as stenosis, thrombosis, or kinking, are potentially lifethreatening. These complications require immediate revision or exchange of the shunt. In this report, we discuss interventional treatment as an alternative to surgery in 5 patients with acute stenosis or complete occlusion of a shunt. The age of the patients ranged from 12 to 62 days, with a median of 30 days, and their weights ranged between 2.2 and 4.6 kilogrammes, with a median of 3.2 kilogrammes. In 3 patients, the shunts were central or of modified Blalock-Taussig type, while the 2 patients with hypoplastic left heart syndrome had shunts from the right ventricle to the pulmonary arteries. We implanted 6 coronary arterial and 2 peripheral stent systems. The diameter of the balloon used for implantation had a ratio to the shunt of 0.9. to 1. All shunts were successfully reopened by stenting. During follow-up, 3 patients underwent further procedures on an elective basis. We have one patient on the waiting list for further surgical intervention, but one patient died of septicaemia unrelated to the interventional procedure one month after implantation. In our limited experience, implantation of stents is an effective and long-lasting treatment for complications of shunts in an emergency situation.

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.

Transcatheter creation of an aortopulmonary shunt in an animal model.

The surgical creation of an aortopulmonary shunt is an important tool in the therapy of complex congenital heart defects. We report on a transcatheter approach to establish an aortopulmonary shunt in piglets.

Cryoablation at growing myocardium: no evidence of coronary artery obstruction or intimal plaque formation early and late after energy application.

Background: Animal studies and clinical observations have demonstrated that radiofrequency current application at growing myocardium may result in coronary artery obstruction. Recently, cryoenergy has emerged as an effective alternative to radiofrequency ablation of arrhythmogenic substrates in pediatric patients. Up to now, there has been a lack of experimental data concerning the effects of cryoenergy application at growing myocardium.

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.