Possibilities and impossibilities in the evaluation of pulmonary vascular disease in congenital heart defects.

In congenital heart defects with left to right shunting, the increased pulmonary blood flow and pulmonary hypertension leads to structural and functional changes in the pulmonary vasculature. These changes, known as pulmonary plexogenic arteriopathy, include increased muscularization, altered vasoconstrictive and impaired vasodilatatory responses in the arterial tree, and extensive extracellular matrix modulation (including increased collagen deposition and gradual occlusion of the small pulmonary arteries by intimal proliferation and fibrosis). These alterations will result in decreased compliance by the pulmonary vessels and, thus, a stiffening of the arterial wall. In plexogenic pulmonary arteriopathy, characteristic vascular lesions emerge in the course of the disease process; these include concentric laminar intimal fibrosis, fibrinoid necrosis and plexiform lesions. The term plexogenic arteriopathy does not imply the presence of plexiform lesions, but the potential to form this characteristic lesion in the course of the disease. The combined vascular changes will lead to an increase in both the steady and pulsatile hydraulic loads of the subpulmonary ventricle. Depending on the progression of the process and the type of surgical procedure, these vascular changes may jeopardize surgical correction of the heart defect, or seriously affect the patient’s prognosis.