Having determined the existence of a murmur, its rhythm, pitch, intensity, and quality, we next determine its point of maximum intensity. These points of maximum intensity for murmurs at the four valvular orifices of the heart may be briefly summarized as follows: Murmurs arising at the mitral valve are loudest at the apex of the heart or immediately above it; tricuspid murmurs are loudest over the lower part of the sternum; pulmonary murmurs, in the second left intercostal space close to the sternum; and aortic murmurs, in the second right intercostal space at the edge of the sternum and over the whole length of the body of that bone.
Valvular diseases which cause murmurs result either in a condition of the valves that allows regurgitation, or one that obstructs the onward blood-current. Valvular insufficiency arises when extensive retraction, perforation, or partial detachment of the valves prevents them from completely closing their respective orifices. And when the chordæ tendineæ have been ruptured, or when calcareous degeneration has made the valves or the parts in the immediate vicinity abnormally rigid, the regurgitant current through the aperture thus left gives rise to a regurgitant murmur.
When the valves are thickened, retracted, adherent, hypertrophied, or degenerated, so that their edges are prevented from being accurately applied to the walls of the ventricles or vessels, they obstruct the current of blood, and the impinging of the blood-current against the obstruction gives rise to obstructive murmurs. These conditions—stenosis and insufficiency—are often found coexisting, but rarely in equal degree, one usually predominating sufficiently over the other as to give a dominant character to the murmur.
The lesions which produce these conditions may be temporary or permanent—temporary when they occur during the course of acute endocarditis, and permanent when they consist of a new growth either of connective, fibroid, calcareous, or atheromatous tissue, which alters the form of the valves and impairs their function. Acute and chronic valvular disease may produce the same murmurs. The effect of the valvular deformity depends entirely upon its seat.
In the study of the relations of valvular lesions to cardiac murmurs physical signs are the important factors in their diagnosis, and it is necessary always to bear in mind the normal physiological conditions which constitute a complete cardiac pulsation.
The apex of the normal heart is felt between the fifth and sixth ribs on the left side, about two inches below the nipple and one inch to its sternal side. The base of the heart is on a level with the third costal cartilages. The tricuspid valve lies behind the middle of the sternum, on a line with the articulations of the cartilages of the fourth ribs with the sternum. The mitral valve lies behind the cartilage of the fourth left rib, near the edge of the sternum. The aortic valves lie behind the sternum, a little below the junction of the cartilages of the third ribs with the sternum, near its left edge. The pulmonary valves lie behind the junction of the third left rib with the sternum.
Let it be remembered that the tricuspid orifice is the most superficial, then the pulmonary, next the aortic, and, deepest of all, the mitral orifice. Ranged from above downward, the pulmonary orifice comes first, then the aortic, then the mitral, and lastly the tricuspid.
Aortic Obstruction, or Stenosis.
Stenosis at the aortic orifice is a common cardiac lesion, and one that is always accompanied by more or less hypertrophy of the left ventricular walls.
MORBID ANATOMY.—In aortic obstruction the cardiac valves will be found to present some or all of the changes which have been described as taking place in the course of acute and interstitial endocarditis, together with degenerative changes due to atheromatous, calcareous, fibroid, fatty, or connective-tissue metamorphosis.