Novelty about pocket histology at cardiac implantable electronic device reopening procedures

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Cardiac implantable electronic device (CIED) procedures, characterized by reopening of the CIED pocket, increase infectious risk. In particular, pocket adhesions’ debridement may prolong procedure time, increasing the infectious risk. Nowadays, only few data are available on pocket histology at CIED reopening procedures. PURPOSE: The aim of this study was to describe CIED pocket histology in a cohort of patients undergoing CIED replacement or upgrade. METHODS: All patients undergoing CIED replacement or upgrade at our center between November 2019 and May 2020 were enrolled. Subclinical pocket infection was ruled out by physical inspection and laboratory parameters. Pocket tissue specimens from anterior and posterior pocket wall were obtained. A systematic histological analysis of capsular thickness, fibrotic tissue, neovascularization, inflammation, and calcifications was performed. RESULTS: 30 patients (80% male) were enrolled. Mean capsular thickness of anterior and posterior wall was 0.8±0.3 mm and 1.1±0.4 mm, respectively. Subcapsular fibrosis was mild and multifocal in the anterior wall, and moderate and focal in the posterior. Neovascularization was mainly focal, and in most cases vessel remodelling involved the tunica media. Chronic inflammation was usually mild and non-granulomatous, and in a quarter of cases subacute exudative inflammation was detected in the posterior pocket wall. CONCLUSION: CIED pocket is an histopathologically dynamic environment, characterized by the coexistence of a subacute foreign body response and a fibrous tissue growth, that produces a continuous remodelling due to injury-repair mechanisms. Strategies to reduce foreign body response might minimize inflammatory pocket activity, especially device encapsulation by fibrotic tissue, and simplify CIED reopening procedures. This can impact on CIED replacement or upgrade complications and infectious risk.