This is the condition in which, after the completion of the ventricular systole, a portion of the blood regurgitates into the left ventricle through the imperfectly closed semilunar valve. It is usually brought about by chronic endocarditis. The individual semilunar folds are thickened and shortened, the actual length of free margin being reduced. The consequence is that during the closure of the valve, the edges have not sufficient length to meet perfectly and so a triangular aperture is left. This is illustrated diagrammatically in the accompanying figure. The contraction may reach such an extent as to leave only a nodulation on the wall of the aorta in place of the curtains. These changes are very commonly accompanied by adhesion of the adjacent folds of the curtains and this necessarily causes contraction of the orifice; indeed, the curtains as such may disappear, leaving only a diaphragm with a permanent aperture in its middle, the condition being illustrated in Fig. 225, page 457. An unusual cause of aortic insufficiency is Perforation of the valve as a result of acute endocarditis or the bursting of a valvular aneurysm. Of course the perforation of the curtains beyond the line of contact already referred to is not to be mistaken for a pathological perforation. A rare cause of aortic insufficiency is the Tearing of one of the curtains. During severe exertion the blood-pressure in the aorta may be so much raised as to rupture a curtain, and such a wound will hardly unite, as it will be torn asunder at each systole.
It may be added here that aortic disease is often accompanied by mitral disease, chronic endocarditis, having its origin in rheumatism, attacking both. Chronic endocarditis of the aortic valve again is often connected, as we have seen, with endarteritis or atheroma of the aorta, and in that case it is not so likely to be associated with mitral disease.
It may be interesting here to observe that the origin of the endocarditis has an important bearing on the Age at which these valvular lesions occur. Acute rheumatism is a disease of youth and manhood, and most cases of valvular disease take origin in it. Accordingly, diseases of the valves are most common, at least in their inception, between the ages of ten and thirty. But there are some cases of aortic disease which, as we have seen, stand in a different category. Chronic endarteritis or atheroma is a disease mostly of advanced life, and so it is more common in old persons to meet with aortic disease than with mitral.
We have now to consider the Effects of this insufficiency of the aortic valve on the circulation. As the semilunar valve does not close completely, the aorta in its recoil after the ventricular systole will force blood back into the ventricle as well as forward into the systemic arteries. This extra mass of blood driven with considerable force into the left ventricle will overfill it and forcibly distend it, while the systemic circulation will be proportionately starved. The natural result is Dilatation and hypertrophy of the left ventricle, which may almost completely compensate. In this disease, therefore, the primary and prominent fact is the enlargement of the left ventricle. As the ventricle propels a much larger amount of blood into the aorta, and with abnormal force, there is sometimes a resulting Dilatation of the arch and great vessels. In this way there may even be an actual aneurysm of the arch.
It is to be added, that as hypertrophy of the left ventricle is associated with dilatation of that cavity, there is frequently a consequent widening of the mitral orifice. As a result of this, we may have a relative incompetency of the mitral valve, which is incapable of completely covering the dilated orifice. In this way the consequences already considered of Mitral insufficiency may be brought about; but they are usually much less pronounced than in the primary form of this lesion, and of late occurrence. It is to be remembered, also, that mitral disease often coexists with aortic.
Fig. 232. - Diagram of aortic insufficiency, a, The normal valve closed as seen from above; b, the valve with curtains shortened and leaving a triangular space. .