Aortic Stenosis: Congenital Aortic Valve Stenosis And Rheumatic Aortic Stenosis
Severe Aortic Stenosis
Introduction And Etiology
Obstruction to the outflow tract of the left ventricle constitutes left ventricular outflow tract obstruction. This may comprise of valvar, subvalvar or supravalvar obstructions. Subvalvar obstruction may be fixed or dynamic as is seen in hypertrophic obstructive cardiomyopathy.
Though it was thought earlier that rheumatic fever was the commonest cause of aortic valvular stenosis, current evidences is that stenosis developing in congenital bicuspid aortic valve is the most common cause. The commonest causes below the age of 30 years are congenital unicuspid or bicuspid aortic valves. Between 30-70 years, bicuspid aortic valves, rheumatic valvulitis and unicuspid valves account for the majority of cases. Above the age of 70 years, degenerative calcification, bicuspid valves and rheumatic valvulities are the frequent causes.
Stenosis may occur below, at or above the aortic valve. These are termed as subaortic. Valvular and supravalvular stenosis respectively.
Clinical Presentations And Hemodynamic Changes
Congenital aortic valve stenosis
It may be unicuspid or bicuspid, the latter being the commonest. Unicuspid aortic valve is inherently stenotic and is the only type of valvar stenosis present at birth. These patients develop calcification at an unusually young age. Congenital bicuspid aortic valve occurs in about 2% of the general population. The two cusps may be located anteriorly and posteriorly or on the right and left sides.
The bicuspid valve is not inherently stenotic, because of the abnormal opening and closure of the valve cusps, degenerative changes occur which lead on to calcification. Stenosis results mainly from calcification.
Rheumatic aortic stenosis
Active rheumatic endocardities of the aortic valve leads on to thickening of the valve cusps with fusion of both commisures or fusion of a single commisure. This results in varying degrees of narrowing of the aortic valve lumen. Subsequently hemodynamic stress on this abnormal valve produces further degenerative changes and consequent calcification. However, calcification occurs much later than in the case of congenital bicuspid aortic valve. Pure aortic stenosis is rare to develop in rheumatic heart disease. In most cases it is associated with aortic incompetence.
Degenerative calcification of aortic valve
This results from the degeneration and calcification of the tricuspid aortic valve. The calcification is more towards the base of the aortic leaflets and the commisures are free.
The aperture of the normal aortic valve is 2.5cm2 . Narrowing of the aperture to 0.75cm2 or less produces severe obstruction to left ventricular ejection and a pressure gradient across the aortic valve develops which may reach 50 mm to even 200 mmHg. The left ventricle undergoes concentric hypertrophy which clinically manifests as heaving apex beat. Finally, the left ventricle dilates and fails. When this happens, the force of contraction of the ventricle reduces and the intensity of the murmur diminishes. Due to the fixed cardiac output, syncope results when the subject exerts. The diminishing of the coronary arterial filling may lead to angina pain.
© 2014 Funom Theophilus Makama