Long-term adaptive versus maladaptive remodelling of the pulmonary autograft after the Ross operation

OBJECTIVES: Following the Ross operation, the pulmonary autograft undergoes structural changes (remodelling). We sought to determine the extent, nature and possible determinants of long-term remodelling in the different components of the pulmonary autograft. METHODS: Ten pulmonary autografts and 12 normal control valves (6 pulmonary and 6 aortic) were examined by conventional histology, immunocytochemistry and electron microscopy. The structural changes were quantified by morphometry. RESULTS: The leaflets from free-standing root replacement valves demonstrated thickening to levels comparable to the normal aortic leaflets, largely due to the addition of a thin layer of 'neointima' formed of radial elastic fibres, collagen bundles and glycoaminoglycans, on the ventricular aspect of the leaflets. The leaflets of valves from sub-coronary implantation demonstrated a significantly thicker fibroelastic layer on the ventricularis and calcium deposition in the fibrosa. The media of the explanted valves showed increased number of lamellar units to levels comparable to normal aortic roots. Electron microscopy of valves inserted as free-standing roots showed increased organization into continuous layers. However, intralamellar components showed varying degrees of 'disorganization' in comparison to those in the normal aortic media. In addition, there was a marked increase in the number of vasa vasorum with thickened arteriolar wall in the outer media and adventitia. CONCLUSIONS: Following the Ross operation, in the very long term, all components of the autograft showed varying degrees of remodelling, which was judged to be largely adaptive. Defining the type, determinants and possible functional effects of remodelling could help in understanding and optimizing the results of the Ross operation.