This chapter discusses inflammatory diseases of the heart, excluding rheumatic fever (see Chapters 55 and 56 ), Kawasaki disease (see Chapter 54 ), pericarditis (see Chapter 58 ), and infectious endocarditis (see Chapter 57 ). It focuses on those diseases that involve the myocardium either exclusively or predominantly either as a result of a direct effect or secondarily due to toxins or inflammation.
Myocarditis
Myocarditis is defined as an inflammatory disease of the myocardium. The etiology of myocarditis includes infectious pathogens, toxins, and immune-mediated reactions ( Table 63.1 ). Viruses are the most frequent cause of myocarditis in children when a cause can be established. In many patients, however, the precise etiology cannot be determined. In children, the two main classes of nonrheumatic myocarditis are infectious and generalized autoimmune variants.
| INFECTIOUS | |||
| Bacterial | Staphylococcus, Streptococcus, Pneumococcus, Meningococcus, Gonococcus, Salmonella, Corynebacterium diphtheriae , Haemophilus influenzae , Mycobacterium tuberculosis , Mycoplasma pneumoniae , Brucella | ||
| Viral | Adenoviruses, coxsackieviruses A and B, parvovirus B19, cytomegalovirus, human herpes virus-6, Epstein-Barr virus, varicella zoster virus, herpes simplex virus, echoviruses, polioviruses, influenza A and B viruses, respiratory syncytial virus, mumps virus, measles virus, rubella virus, hepatitis C virus, dengue virus, yellow fever virus, Chikungunya virus, human immunodeficiency virus-1 | ||
| Fungal | Aspergillus, Actinomyces, Blastomyces, Candida, Coccidioides, Cryptococcus, Histoplasma, Mucormycoses, Nocardia, Sporothrix | ||
| Protozoal | Trypanosoma cruzi , Toxoplasma gondii , Entamoeba, Leishmania | ||
| Parasitic | Trichinella spiralis , Echinococcus granulosus, Taenia solium | ||
| Rikettsial | Coxiella burnetii (Q fever), Rickettsia rickettsii (Rocky Mountain spotted fever), Rickettsia tsutsugamushi | ||
| TOXINS | |||
| Drugs | Amphetamines, anthracyclines, cocaine, cyclophosphamide, ethanol, fluorouracil, lithium, catecholamines, interleukin-2, trastuzumab, clozapine | ||
| Heavy metals | Copper, iron, lead | ||
| IMMUNE-MEDIATED | |||
| Autoimmune, autoinflammatory | Systemic lupus erythematosus, rheumatoid arthritis, Churg-Strauss syndrome, Kawasaki disease, inflammatory bowel disease, scleroderma, polymyositis, myasthenia gravis, insulin-dependent diabetes mellitus, thyrotoxicosis, sarcoidosis, Wegener granulomatosis | ||
| Allergens | Penicillin, cefaclor, colchicine, furosemide, isoniazid, lidocaine, tetracycline, sulfonamides, phenytoin, phenylbutazone, methyldopa, thiazide diuretics, amitriptyline, tetanus toxoid, vaccines, serum sickness | ||
| MISCELLANEOUS | |||
| Scorpion sting, snake and spider bites, bee and wasp stings, carbon monoxide, inhalants, phosphorus, arsenic, sodium azide, radiation, electric shock | |||
The clinical consequences of myocarditis are largely determined by the degree and extent of myocardial injury. Sudden death may occur before the diagnosis is made, but most patients will present with heart failure, dysrhythmias, or chest pain. Some may not have overt cardiac symptoms and are diagnosed serendipitously or as part of screening for associated disease.
Infectious Myocarditis
Infectious myocarditis can occur as a complication of almost any infectious disease. Viral infections are the most frequent causes in developed countries; in other parts of the world, protozoal infections may rank highest. Other infectious etiologies include tuberculosis, Lyme disease, and hemolytic uremic syndrome. Infectious myocarditis may also be a complication of opportunistic infections in patients with immune deficiencies.
Precise estimates of the prevalence of myocarditis are not well established. This is due to the wide variation in causes worldwide, underreporting because of limited resources and owing to subclinical or masked disease. Indeed, myocarditis often has a subclinical course and therefore goes undetected. In other patients, the presence of infectious myocarditis may be completely masked by signs and symptoms of disease in other affected organs.
Viral Myocarditis
The majority of the cases of myocarditis seen in the developed world are of viral origin. Biopsy specimens from patients with dilated cardiomyopathy can contain viral particles even when the histologic criterion for myocarditis is not evident. Enteroviruses, particularly coxsackie group B, have been found most frequently, but polymerase chain reaction (PCR) studies have shown that adenoviruses are also common. Parvovirus B19, cytomegalovirus, echovirus, hepatitis C, respiratory syncytial virus, influenza, mumps, and rubella have also been implicated. Human immunodeficiency virus can cause myocarditis and pericarditis, often presenting with the picture of a dilated cardiomyopathy.
The mechanisms involved in producing the myocardial injury are complex. Invasion of the myocardial cells by viruses and elaboration of toxins both play important roles. Cellular immune mechanisms and circulating autoantibodies may also be important in the overall pathogenesis of the disease. Indeed, a combination, which may vary considerably between individual patients, of viral infection and subsequent abnormal immune response, causing either ineffective viral clearance or autoimmune myocyte damage, seems to underlie the clinical manifestation of the disease. Persistence of the virus, or continuing immune reactions after the viral infection has cleared, may produce chronic myocardial damage and present as chronic myocarditis or dilated cardiomyopathy.
Clinical Features
Myocarditis may be acquired prenatally or postnatally. In older children it often includes pericarditis as a dominant feature. Its clinical onset is usually seen after a latent period following the onset of a systemic viral infection. The signs and symptoms of myocarditis are highly variable, and the patient may be asymptomatic. Nonspecific symptoms include fever, dyspnea, fatigue, diarrhea, abdominal pain, problems with feeding, pallor, mild jaundice, and lethargy. The most easily recognized signs include congestive heart failure or arrhythmias. Older children will often complain of chest pain from pericarditis. Occasionally the clinical picture may be dominated by severe respiratory distress secondary to left ventricular failure that has been mistaken for reactive airway disease or pneumonitis.
The important symptoms to recognize for myocarditis are cardiomegaly, tachycardia out of proportion to fever, a gallop rhythm, hepatomegaly, or an apical murmur indicating mitral insufficiency. The clinical picture of cardiac failure in a previously well child with often a minor, preceding viral infection is typical.
Laboratory Findings
The laboratory findings in myocarditis are nonspecific and generally consistent with an increased inflammatory state ( Box 63.1 ). The white blood cell count may be elevated. The presence of eosinophilia raises the suspicion of a parasitic etiology. Cardiac troponin I and other cardiac enzymes are frequently elevated but may also be normal. The erythrocyte sedimentation rate is usually elevated but may be normal. The level of C-reactive protein may also be elevated, and this may be of prognostic significance. Although the diagnosis of viral myocarditis is generally based on history of a recent viral infection, viral cultures and PCR testing should be attempted. However, the diagnosis of a viral origin is often based on the exclusion of other possible etiologies rather than positive identification of an etiologic agent.
Complete blood count
Serum electrolytes
Blood urea nitrogen/creatinine
Alanine aminotransferase/aspartate aminotransferase
Erythrocyte sedimentation rate
C-reactive protein
Troponin I
Brain natriuretic peptide
Bacterial blood culture
Viral polymerase chain reaction/serologies
Investigations
Radiology
The size of the heart may be normal on chest x-ray, particularly in the early period of the disease. More frequently the heart will be enlarged, with normal lung fields. Pulmonary venous congestion and even frank pulmonary edema may be evident.
Electrocardiography
Electrocardiographic abnormalities are common in myocarditis but are nonspecific. There is often a sinus tachycardia, with lowering of the QRS voltage in the standard leads and/or precordial leads, flattening or inversion of the T waves, and nonspecific changes in the ST segment ( Fig. 63.1 ). Arrhythmias are often present and may lead to unexpected death. Occasionally disturbances of conduction are seen, with varying degrees of heart block. Complete atrioventricular block is rare. The QRS complexes may be widened, with a left or right bundle-branch-block configuration. The electrocardiographic changes may disappear during the course of the disease, but abnormalities may also persist―most likely because of myocardial scarring―after the patient has recovered clinically.
Echocardiography
Echocardiography, although also nonspecific, is an important screening and diagnostic tool. The findings of acute myocarditis can be identical to those of dilated cardiomyopathy. Echocardiography is also important to rule out structural heart diseases that may mimic myocarditis, such as anomalous origin of the left coronary artery. Echocardiography may also reveal complicating features such as a pericardial effusion or intracardiac thrombus. Typical features of myocarditis include dilation and reduced function of the heart chambers, predominantly the left ventricle ( ). When the onset is rapid, as with fulminant myocarditis, there may be little if any ventricular dilation. Ventricular dysfunction is usually much more evident in the left ventricle than in the right and may be either global or segmental. The left atrium may also be enlarged, especially in the presence of mitral insufficiency ( Fig. 63.2 ). Echocardiographic tissue characterization, tissue Doppler imaging and the measurements of myocardial velocity have been shown to be helpful in differentiating myocarditis from other causes of ventricular dysfunction, although further research will be needed to determine their value in a clinical setting.
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