Q. Explain Pathology of aortic stenosis?
Congenital abnormalities of aortic valve may lead to unicuspid aortic valve. This may be dome shaped with central stenotic orifice. Unicuspid appearance may also be due to fusion of two commissures with an eccentric opening. Usually these patients become symptomatic in childhood or by early adulthood.
Congenital bicuspid aortic valve is one of the common congenital cardiac abnormalities (about 2 per cent) and it has higher prevalence in males. There seems to be certain genetic transmission and it may be associated with other left sided obstructive lesions like coarctation of aorta seen in about 10 per cent of patients. In some patients this may be part of generalized connective tissue disorder associated with cystic medial necrosis and focal apoptosis in aortic media leading to aortic root dilatation. Ascending aortic dissection occurs nine times more frequently in patients with bicuspid aortic valve compared to those with tricuspid valve. Due to altered flow pattern across bicuspid aortic valve, turbulence is generated leading to abnormal hemodynamic stress on the cusps. This results in micro thrombi formation, fibrosis and calcification resulting in aortic stenosis in majority of patients.
Rheumatic aortic valve stenosis is characterized by fusion of one or more commissures with variable cusp fibrosis and calcification. Mitral valve involvement is almost always present. Commissural fusion and edge calcification distinguish rheumatic etiology from degenerative etiology.
Degenerative aortic valve disease that is seen increasingly in elderly shares common pathogenesis with atherosclerosis. Primarily there is lipid accumulation, migration of inflammatory cells and dystrophic calcification in valve cusps. Same atherosclerotic risk factors like age, male sex, diabetes, hypertension and smoking and hyperlipidemia hasten valve degeneration and calcification. Early stages of fibrosis and mild calcification not leading to a significant hemodynamic abnormality are called aortic sclerosis. Extensive distortion due to fibrosis and calcification results in significant hemodynamic abnormality that results in aortic stenosis. While atherosclerosis vascular disease and valvular aortic stenosis seem to have similar etiopathogenesis - it should be noted that majority of patients with extensive coronary artery disease have normal aortic valves and only 50 per cent of patients with degenerative aortic valve disease have significant associated coronary artery disease.
Certain metabolic conditions like hyper cholesterolemia, Fabry's disease and alkaptaneuria lead to valvular stenosis due to metabolite deposition. SLE with associated anticardiolipin antibodies and radiation may also lead to aortic valve stenosis.