The various forms of endocarditis are somewhat closely related to each other, but it is possible to distinguish three forms - a simple acute, a simple chronic, and an ulcerative or infective form. According to some the acute forms are simply more or less marked examples of the same process.
(a) Simple acute endocarditis (Endocarditis verrucosa) occurs as a. secondary effect of certain acute febrile diseases.
Chief amongst the causes is Acute rheumatism, but Chorea is also to be assigned as a frequent cause, and more rarely scarlet fever, measles, typhoid fever. According to Bamberger 20 per cent. of the cases of acute rheumatism are complicated with acute endocarditis, and according to Osier 30 per cent, of the cases of chorea are so affected. Whatever view we take of the origin and nature of Acute articular rheumatism, it must be admitted that the blood is of an unusually irritating nature, being the carrier of some irritant of unknown nature. The occurrence of acute inflammations in several joints often removed considerably from one another, and the frequent supervention of inflammation in the pericardium and endocardium, are sufficient evidences of this. The irritant, whatever be its nature, seems to act specially on connective tissue membranes, and on such as are exposed to friction of their surfaces. It affects the joints where the synovial membranes lie against each other and in the movements of the joints are moved on one another. It attacks the pericardium where the movements of the heart cause continuous rubbing, and when it attacks the endocardium it affects exactly the localities where the surfaces come into contact. It is as if in addition to the irritant in the blood, the mechanical irritation of friction were necessary to the occurrence of inflammation, and it may be added that in the adult the inflammation is usually limited to the valves of the left side of the heart, where the higher tension of the blood and greater force of the heart make the mechanical force of friction greater than on the right side. We shall see afterwards how this fact bears on the localization of the endocarditis.
The most characteristic effects produced in acute endocarditis are the so-called Warty vegetations, which are pale, irregular projections from the surface of the endocardium, generally of small size and somewhat shaggy in appearance. (See Figs. 219 and 220).
Fig. 219. - The aortic valve in acute endocarditis. The warty vegetations, occupying the lines of contact, are shown.
The vegetations are composed partly of the swollen, inflamed tissue of the valve and partly of fibrine deposited on the inflamed surface.
The inflamed connective tissue produces round cells and is converted into granulation tissue, and the affected parts are thus increased in bulk, and rendered more friable so that irregular projections are produced. The projections are enlarged by deposition of fibrine, which may be regarded as a kind of fibrinous exudation, but is derived from the blood flowing over the surface, and not from the vessels of the part. It is, perhaps, more correctly a thrombosis, and as the blood is in motion the White thrombus is the form produced. The fibrine generally forms the greater part of the bulk of the vegetations. On their first occurrence the vegetations are limited to the parts of the valves which come against each other in the closure of the valves, and this localization continues more or less throughout.
When, after removal of the heart, a stream of water is sent into the aorta cut transversely a short distance above the valve, we can look down on the valve closed by the force of the water. It will then be seen that, in the normal valve, the curtains are not in contact by their margins, but that the line of contact is slightly removed from their edges, and a certain portion of the valve floats free in the water, taking no direct part in the closure of the orifice. The line of contact is nearest the edge of the curtain in the middle of each segment or the corpus Arantii, and forms on either side of this a curved line with the convexity downwards. Between the line of contact and the edge of the curtain the valve is often perforated, and it may even, as we have seen before (pl. 431, Fig. 203), be partially resolved into tendinous cords without interfering with the closure of the valve.
In the mitral valve the line of contact is also removed.from the edges of the curtains. In the case of the aortic valve the line of contact is of course on the ventricular side of the curtains, but in the mitral it is on the auricular side, and in order to see the vegetations in acute endocarditis it is usually necessary to examine the orifice by looking in from the auricle. Acute endocarditis of the mitral often escapes notice from this not being done.
Fig. 220. - Acute endocarditis of mitral valve. The curtains are fringed with prominent warty vegetations. From a child of seven, the subject of acute rheumatism.
In acute endocarditis the warty vegetations frequently demarcate very accurately the lines of contact of the aortic and mitral valves, and the appearances produced in the former case are indicated in Fig. 219. When the inflammation extends to the valves of the right side, the same principles apply. In the case of the pulmonary valve the vegetations appear along the line of contact on the ventricular aspect of the curtains, and in the tricuspid they are to be seen by looking down through the auricle.
The occurrence of these changes in the tissue renders it unduly brittle, and it is not surprising to find that portions of the vegetations are frequently broken off and carried by the arteries to distant parts, to produce embolism there. These broken-off pieces are mostly small, and, beyond the ordinary phenomena of embolism in small arteries and capillaries, they do not by their own nature produce much disturbance, in this respect contrasting with the emboli of ulcerative endocarditis. The softening of the tissue may result in one of two further lesions, either, of which may interfere with the function of the valve: these are rupture of the chordae tendineae and valvular aneurysm.