A system of practical medicine. By American authors. Vol. 3

by Unknown

The layer of flat cells is thickest on the ventricular surface. The fibro-elastic tissue is thickest at the base of the valve. The semi-lunar valves have endocardium on one side and the tunica intima on the other.

Although the endocardium has no vessels of its own, the capillaries upon the cardiac walls are in contact with it. The arrangement in the valves is different, as only a few vessels ramify between the layers of the mitral valve, and none are found, normally, in the sigmoid valves.

Acute Exudative Endocarditis.

This variety of endocarditis is met with most frequently in connection with acute articular rheumatism.

In adults it usually has its seat in the left heart; in intra-uterine life it occurs in the right heart. The inflammation commences in, and seldom extends beyond, the valves and the valvular orifices, but it may involve the whole or any part of the ventricular or auricular portions of the endocardium.

MORBID ANATOMY.—The endocardium becomes infiltrated with young cells, the process beginning in the layer of flat cells. The new formative cells are developed not only from the cells of the layer immediately underneath the endocardium, but also from leucocytes. This hyperplasia, this heaping up of embryo-plastic cells, is accompanied by softening of the deeper layers of the intercellular structure, and as the softening goes on the intercellular substance is destroyed.

The endothelial elements also play an active part in the processes. The masses of new cells push out the endocardium, and papillary elevations are formed, filled with a fluid whose chemical properties resemble those of mucin, since it coagulates into threads when acetic acid is added. The cone-like vegetation is surrounded in the deeper layers of the endocardium by a zone of proliferation which is never distinctly limited, but which exhibits progressive hyperplasia from the periphery toward the centre.

All these changes may have taken place in non-vascular tissue. Where the capillaries are most numerous a punctuate or arborescent vascularity is seen, and this is followed by opacity of the part which is the seat of the inflammation. After death the endocardium and lining membrane of the vessels are often stained; this staining is produced by the coloring matter from the red corpuscles, and is the result of post-mortem change.

There is no exudation upon the villous projections; the coagula found upon them are a deposit of fibrin from the blood, the projections acting as foreign bodies in the blood-current. The fibrinous deposits occur chiefly on the surface which is opposed to the current of the circulation, and sometimes they are distinctly conical; at others they have the shape of a raspberry. They occupy the parts most exposed to the friction of the blood, and are arranged on the borders of the aortic valves at a little distance from their edges, the seat being determined by the limit of the vascular network. The band of tissue which passes from the attached border of the valve to the Arantian body in the centre shows the inflammatory granulations most distinctly. They consist of a cauliflower-like bulbous extremity, connected by a constricted neck with a firm, hard base that is intimately blended with the subjacent tissue. A thin hyaline layer covers each mass. At first these granulations or vegetations are very small and numerous, so that the membrane presents a granular appearance. Later, they become larger, reaching oftentimes the size of a small pea.

Near the insertion of the tendons upon the auricular surface of the mitral valve are found irregular wreaths of vegetations which enclose the attachments of the chordæ tendineæ. Moxon has shown that the friction of the vegetations or of fibrinous clots that gather upon the vegetations may, by the irritation it produces, excite endocarditis at points remote from the valves.