ETIOLOGY.—In most instances endocarditis depends upon a constitutional dyscrasia characterized by alterations in the vital, physical, or chemical properties of the blood.
Acute exudative endocarditis rarely, if ever, occurs as a primary or idiopathic affection. It seems to have a direct connection with those diseases and dyscrasiæ in which the blood is altered either in the relative proportions of its constituents or in its physiological elements. So frequently is acute exudative endocarditis associated with acute articular rheumatism that they have often been described as one disease.
It is generally stated that acute endocarditis occurs in 50 per cent. of those who suffer with acute articular rheumatism, but the statistics of Bellevue Hospital show that endocarditis complicates rheumatism in only 33 per cent. of the cases. From these statistics it is evident that a majority of the cases of acute rheumatism run their course without endocardial complication.
The irritant action of the blood, the salts of which are changed or which contains excrementitious products or a specific poison, is shown most markedly upon the valvular surface of the endocardium; and it is for this reason that the parts which are most exposed to friction of the blood-current are those which first and most extensively exhibit the pathological changes of endocarditis.
Charcot records a large number of observations in which endocarditis developed in patients with chronic rheumatism and in which it never assumed an acute form. It therefore seems evident that organic lesions of the valves from endocarditis may occur in the course of chronic as well as of acute rheumatism.
There is no disease in which a morbid blood-state exists in which endocarditis may not occur. The essential fevers, the exanthemata, diphtheria, septicæmia, pyæmia, and Bright's disease, are all conditions in connection with which endocarditis is frequently exhibited. It is met with occasionally in secondary syphilis.
Acute and chronic Bright's disease are often complicated by it. When an individual who is already the subject of valvular disease of the heart is attacked with acute rheumatism, the liability to endocarditis is much increased.
Even when rheumatism and chorea are absent, endocarditis is liable to occur when valvular disease exists. Some regard myocarditis, pericarditis, pleurisy, and pneumonia as capable of exciting endocarditis by the extension of the inflammatory process from the surface of the heart; it is questionable if it ever results from such extension. That it can be the result of traumatism is possible: Bamberger records two cases of traumatic endocarditis. Wunderlich ranks measles, next to rheumatism, as a cause of endocarditis.
In estimating the etiological importance that any disease bears in the production of endocarditis, we must remember that not every blowing sound or murmur is indicative of an inflamed endocardium. Bamberger and Niemeyer think that the excited and irregular action of the heart in children, by inducing irregular tension of the valves, may bring about a blowing sound during the course of acute rheumatism.
Acute ulcerative endocarditis is met with in pyæmia, puerperal fever, and endometritis, scarlatina, and diphtheria: it may occur as a secondary affection to some inflammatory focus located in the body—septic endocarditis.