During a cardiac diastole, normally, the blood is passing from the auricle into an empty ventricle; when, however, regurgitation has persisted for a considerable time, there will be added to the primary stream (which of itself is capable of filling the cavity of the ventricle) a regurgitant stream from the aorta, and by this combination of two streams the left ventricle becomes over-distended and permanently dilated. This dilatation occurs all the more readily since during the diastole the ventricular walls are relaxed and less capable of resisting the increased blood-pressure. Thus, permanent dilatation of the left ventricle occurs in a comparatively short time; and to overcome the dilatation and the obstruction to the cardiac circulation the left ventricular walls hypertrophy. The hypertrophy goes on increasing until it compensates for the dilatation; but before this point is reached the ventricular cavity sometimes becomes very much dilated and the left heart reaches an immense size.
This dilatation and hypertrophy may be so extensive that the organ often weighs twenty or thirty ounces, a case being recorded where the enormous weight of forty-eight ounces was reached.8 The heart is then frequently called the cor bovinum. In such cases the organ has a peculiar pointed form, the right ventricle appearing like a mere appendix. The left ventricle is thus capable of containing so much blood, and such an abnormally large amount is thrown into the aorta at each cardiac cycle, that the arterial system is largely over-filled. Hence the arteries are elongated during their pulsations more than in health, and often become distinctly flexuous with each cardiac pulsation.
8 See Hilton Fagge, Diseases of the Valves of the Heart.
The increase in the ventricular power and in the amount of blood contained in the ventricles and thrown against the aortic walls leads to endarteritis and subsequent atheromatous degeneration of the arterial walls, and the arteries become so brittle that during excitement they may suddenly rupture and cerebral apoplexy result; aneurism is also liable to be developed under such conditions.
In the normal heart the aortic recoil is the force which propels the blood into the coronary arteries. When the aortic valves are insufficient, and furnish little or no resistance to the return blood-current, the coronary blood-supply is consequently diminished. When perfect compensation has existed for some time, it begins to fail, and dilatation again commences at the expense of the walls of the heart. This dilatation is aided, first, by the condition of the coronary arteries above referred to, and, secondly, by the fact that aortic recoil is now expended as much in driving a regurgitant current into the ventricle as in forcing blood through the coronary vessels.
In some cases atrophy of the papillary muscles allows the mitral flaps to swing back into the left auricle when increased pressure is exerted upon them. When from any one of these causes mitral incompetence becomes secondary to, and coexistent with, aortic insufficiency, all the signs of impeded venous circulation will be present. These changes will be considered under the head of Mitral Disease.
When over-distension of the left ventricle causes incomplete emptying of the left auricle, a greater or less amount of passive hyperæmia of the lungs may be present without mitral insufficiency.
ETIOLOGY.—The etiology of aortic insufficiency is similar to that of aortic stenosis. Rheumatic endocarditis is undoubtedly its most frequent cause, but it may also have its origin in sudden and violent muscular effort, atheroma of the aorta, endarteritis, congenital malformation, and enlargement of the aortic orifice. Congenital malformation or congenital non-development is, according to Virchow, a frequent cause in chlorotic females.
In many cases the atheroma that causes the incompetence is of gouty origin, especially when gouty kidneys coexist or when alcoholismus is associated with a gouty diathesis.
Sometimes aortic incompetence is the result of imperfect development of the aortic valves. A rare case is recorded in the Pathological Transactions (vol. xvi. p. 77), where a young man fell from a height upon his side and tore off an entire flap of the semi-lunar valve: there was no external mark of injury, and the rupture was plainly due to the transmission of rapid vibrations from the jarred surface. Valvular inadequacy sometimes results from dilatation of the aorta at its origin.