Definition.—Acute myocarditis is an acute inflammation, diffuse or circumscribed, of the interstitial or parenchymatous substance of the heart.
Etiology.—Two forms of myocarditis are recognized, the diffuse or parenchymatous and the circumscribed.
Diffuse or parenchymatous myocarditis is rarely ever idiopathic, but follows as a complication or result of some other disease. It occurs most frequently in the course of the infectious fevers, especially typhoid fever, diphtheria, and scarlet fever, and the sudden deaths in these cases from heart-failure can be traced in nearly every case to myocarditis.
Endocarditis and pericarditis, if of a severe type, nearly always extend to the myocardium. Rheumatism figures as a causal agent, as does gonorrhea. We may be safe in saying that the toxins in any infectious disease may so influence the heart as to give rise to myocarditis.
Circumscribed myocarditis may arise from the same sources that give rise to the diffuse form; viz., the infectious fevers; or it may be due to emboli in the coronary arteries.
Pathology.—The heart, in the early stage, is of a dark-red color, swollen, softened, and injected; later it changes to a yellowish gray or mottled appearance, and is readily broken down. There may be dilatation of the cavities, and if there has been localized myocarditis, weakening the tissues, partial aneurism may result.
The more minute changes consist in an infiltration of the interstitial substance of round cells, and later fibroid degeneration. The muscular fibers undergo fatty or granular degeneration.
In the diffuse form the chief pathological changes take place in the connective tissue, and the left ventricle suffers more than the right.
In the localized or circumscribed form there are areas of necrosis, which are followed by abscess formation. These abscesses may open into the cavities of the heart, and thus enter the blood-stream, giving rise to abscess formation in other portions of the body. A favorite location for an abscess is in the interior wall of the ventricle near the apex and septum. They may empty into the pericardium, resulting in suppurative pericarditis. When they perforate the heart cavities, in addition to poisoning the general blood with an accompanying septicemia, they often give rise to malignant endocarditis. This form usually terminates fatally, though, in rare cases, nature throws a covering around the abscess, the pus is incapsuled, and undergoes caseation or calcification.
Symptoms.—The symptoms of the primary lesion usually so obscure the true nature of the disease that subjective symptoms may be entirely absent. If, however, there is a sense of constriction of the chest, some palpitation, more or less dyspnea attended by slight pain, and the pulse is rapid, small, and easily compressed, evidences of cardiac enfeeblement, myocarditis would be suggested.
Should suppurative myocarditis exist, and the abscess perforate the cavities, embolic manifestations would appear in brain, lungs, or spleen. An increase of temperature, with the above symptoms, would naturally follow, and, if suppurative in character, the fever would be of a septic type.
Physical Signs.—The physical signs are similar to those of dilatation. The action of the heart, in the early stage, is tumultuous, but as changes take place it becomes small and irregular.
Auscultation reveals the first and second sound of nearly equal length, short and sharp, which soon becomes feeble. If dilatation lias taken place, murmurs frequently develop. The most frequent is a systolic murmur suggesting mitral insufficiency.
Diagnosis.—The diagnosis may not positively be made during life; however, great heart enfeeblement as shown by the weak first sound or systolic murmur and the small irregular pulse would suggest myocarditis.
Prognosis.—The prognosis is favorable where it appears in a mild form, though the severer forms usually terminate fatally and the sudden termination of life during the infectious diseases, notably diphtheria and typhoid, may not infrequently be due to myocarditis.
Treatment.—Absolute rest must be enforced in every case; the reclining position should be observed, and nutrition maintained.
The agents recommended for endocarditis and pericarditis will be found useful. In fact, the above mentioned diseases are nearly always attended by more or less myocarditis. Heart tonics should be used with great care. Cactus, in small doses, will be a good agent. When the heart flags, carbonate of ammonia as a diffusable stimulant will be found beneficial, as will also strychnia.
Septic conditions will require antiseptics, and when there is rheumatism with an acid condition of the blood, the acetate, citrate, nitrate, or lithiate of potassium will be found beneficial.