We may recognize three forms—acute suppurative, acute interstitial, and chronic myocarditis. By many writers the parenchymatous degeneration so frequent in fevers is regarded as an inflammation, but it is the result of a process which we can scarcely term inflammatory.
Acute suppurative myocarditis is almost invariably associated with pyæmia or with malignant endocarditis, and in most instances may be regarded as embolic. In severe pyæmia from any cause foci of suppuration are not infrequently met with in the walls of the ventricles. There may be multiple abscesses or a single purulent collection varying in size from a pea to a walnut. Numerous miliary abscesses are not so often met with in ordinary pyæmia as in endocarditis. If large, the abscess may burst into the heart or into the pericardium and excite inflammation of this membrane; or, indeed, without perforation, as I saw in one instance. The calcareous nodules occasionally found in the muscle-substance have been regarded as healed abscesses. Suppurative myocarditis is a frequent result of malignant endocarditis, and we meet with it either in the form of miliary abscesses, scattered in numbers through the substance, or as large solitary abscesses at the bases of vegetative outgrowths or in connection with excavating ulcers of the endocardium, valvular or mural. The small embolic abscesses vary in size from a pin's head to a pea, and may occur in extraordinary numbers in the muscle-substance of all the chambers. They present usually a central grayish-white focus of suppuration surrounded by a zone of deeply-congested and hemorrhagic tissue. Microscopically, there is a central infiltration of leucocytes with destruction of the muscle-fibres, and in every instance colonies of micrococci can be readily discovered. These abscesses are identical in character with those occurring in the kidneys, intestines, and brain. Sometimes at the base of large endocardial outgrowths, particularly of the aortic segments, abscesses are found extending deep into the muscle-substance, and even perforating the wall. These occur most often in the left ventricle, but occasionally in the right, as in a case of stenosis of the pulmonary valves at the Montreal General Hospital, in which there was an abscess cavity in the wall of the right ventricle the size of a marble, situated at the base of some endocardial vegetations. The acute ulcer of the heart is of the nature of a suppurative myocarditis, having its starting-point, in the great majority of cases, in the endocardium. It may perforate the wall of the ventricle, as in the cases of Mackenzie8 and Keating.9 The blood-pressure in the abscess-cavity may dilate the wall, and form what is known as acute aneurism of the heart.
8 Path. Soc. Trans. London, xxxiii.
9 Trans. of the College of Physicians of Philadelphia, 1879.
Acute interstitial myocarditis occurs in connection with the infectious fevers, and also with pericarditis, more rarely endocarditis. It is characterized by the presence of numerous round cells in the interfibrillar tissue, multiplication of the corpuscles, and degeneration, granular or fatty, of the muscle-fibres. The coarse appearances are—a relaxed state of the cardiac walls, pale or turbid condition of substance, in extreme instances a sodden, soft friable state, so that the muscle readily tears on pressure. In acute pericarditis the superficial myocardium, for a line or two beneath the membrane, frequently presents this condition in a typical manner; it looks pale and turbid, contrasting strongly with the deeper parts, and on examination presents infiltration of leucocytes, swelling of the interstitial tissue, sometimes effusion of blood-corpuscles, and a swollen, granular, or fatty state of the muscle-fibres. Although the process may be intense, suppuration rarely occurs, whereas in myocarditis supervening upon inflammation of the endocardium it is, as we have seen, not uncommon. A similar diffuse interstitial process is met with in many of the fevers. In rheumatism, typhus, scarlet fever, small-pox, and diphtheria the myocardium may be found relaxed and soft, the chambers dilated, the substance pale, easily torn, in some instances extremely soft; and this condition has been variously described as inflammatory or degenerative. While not denying that such a state of the muscle-fibre may be brought about by the action of the fever or the influence of some specific poison without any signs of inflammatory action, yet in other instances changes have been found which are evidently of the nature of a myocarditis. In these cases the intermuscular connective tissue is swollen, infiltrated with round cells and nuclei, the vessels are dilated, and often there are minute extravasations and the muscle-fibres are granular and fatty, with indistinct striæ and nuclei. As Leyden10 has pointed out, this condition probably affords an explanation of some of the cases of sudden death in diphtheria. It may occur without the coarse or microscopic appearance of degeneration of the muscle-fibres, and when of any duration may produce areas of atrophy. Though usually diffuse, it may be patchy and limited in distribution. Martin11 has described in cases of sudden death in diphtheria and typhoid fever an acute endarteritis of the small branches of the coronary arteries, which probably has a close relationship with this acute interstitial myocarditis.
10 Zeitschrift für klinische Medicin, Bd. iv.
11 Revue de Médecine, 1881.
The SYMPTOMS of acute myocarditis are those of cardiac weakness and irritability, and it is the conditions under which these occur which make us suspect involvement of the myocardium rather than any special features pertaining to the disease. We may reasonably suspect its presence in a case of rheumatism, puerperal fever, or other specific fever when the patient complains of cardiac distress or actual pain, with shortness of breath, and on examination we find a weakened impulse, feeble, indistinct first sound, and a small, irregular pulse. The area of heart-dulness is increased, and there may be a murmur due to muscular incompetence. There is usually fever, but this is generally due to the primary affection. The symptoms are those of a weak and dilated heart, and are peculiar only in the mode of onset and the circumstances under which they arise. A point of note observed by Stokes is the weakening or disappearance of organic murmurs during an attack of acute myocarditis. In acute pericarditis grave implication of the myocardium may be suspected when the pulse gets small and rapid, dyspnoea urgent, and the cardiac pain is increased. Such symptoms, in the absence of copious effusion, would appear to indicate extension of the inflammation to the heart-muscle. Even the occurrence of suppuration has no distinctive symptoms, as it almost invariably occurs as part of a pyæmic process, and the cardiac weakness which supervenes may be regarded as an outcome of the septic or febrile condition. The bursting of an abscess into the pericardium will excite violent pericarditis. In the case of Kortüm, referred to by Friedrich,12 an abscess in the septum burst into the ventricle; the symptoms, which developed suddenly during a lecture, were a sense of constriction in the chest, dyspnoea, and lividity, and death occurred in six hours.
12 Virchow's Handbuch, Bd. v.: "Herzkrankheiten," S. 275.
The DIAGNOSIS can rarely be made with certainty; at the best we can suspect its presence under the conditions above mentioned.