Stenting of native right ventricular outflow tract obstructions in symptomatic infants: histological work-up of explanted specimen

BACKGROUND: Stenting of stenotic right ventricular outflow tract is a palliative measure for severely impaired small babies with Tetralogy of Fallot or similar pathologies. Little is known about the histopathological fate of the stents in the right ventricular outflow tract. METHODS: Eight samples of surgically removed right ventricular outflow tract stents were histologically analysed according to a predefined protocol. RESULTS: The most frequent diagnosis was Tetralogy of Fallot in four patients, pulmonary atresia with ventricular septal defect in two patients, double outlet right ventricle with pulmonary obstruction in one patient, and muscular obstruction of the right ventricular outflow tract in one patient with a syndromic disease with hypertrophic cardiomyopathy. Stents mean implantation duration was 444 days ranging from 105 to 1117 days (median 305.5 days). Histology revealed a variable degree of pseudointima formation consisting of fibromuscular cells surrounded by extracellular matrix. Four of the specimen contained adjacent myocardial tissue fragments, which showed regressive changes. Neither myocardium nor pseudointima tissue or tissue parts locally related to stent struts were infiltrated by inflammatory cells. CONCLUSIONS: Histological analysis after explantation of early-in-life implanted right ventricular outflow tract stents revealed predominantly pronounced neo-intimal proliferation with a visible endothelial layer, no signs of inflammation, and no prolapse of muscular tissue through the stent struts. Thus, implantation of stents in early life seems to interfere little with the hosts' immune system and might help to open up the right ventricular outflow tract by mechanical forces and regressive changes in adjacent muscular tissue.