Alterations of ultrastructures and anionic sites in basement membranes of myocardial cells and capillaries in patients with cyanotic congenital heart disease due to tetralogy of Fallot.

Electron microscopic cytochemical studies of the basement membranes of myocardial cells and capillaries were performed in 13 patients with tetralogy of Fallot who were divided into 2 groups. Group 1 included 7 patients in the early stage of the disease, ranging in age from 7 months to 5 years. Group 2 consisted of 6 patients in the far advanced stage of the disease, ranging in age from 30 to 46 years. The operatively excised infundibular muscles of the right ventricle were prepared for conventional electron microscopy and electron microscopic cytochemistry. The anionic sites in the basement membranes were characterized by cationic polyethyleneimine. The basement membrane ultrastructures of the myocardial cells and capillaries in the early stage of tetralogy of Fallot showed no apparent alterations with regular distribution of anionic sites, particularly in the external lamina of the basement membranes. In contrast, irregular thickening, wide splitting and lamination of the basement membranes of myocardial cells and capillaries, always associated with derangement and focal loss of anionic sites in the membranes were consistently observed in the far advanced stage of tetralogy of Fallot. The aforementioned results suggest that altered surface membrane integrity of myocardial cells and capillaries resulting from pathologic changes of the basement membranes are an important pathogenetic mechanism responsible for progressive degeneration of infundibular muscle cells and myocardial dysfunction in the course of tetralogy of Fallot.