Myocarditis



Myocarditis


Mosi K. Bennett

Wilson W.H. Tang



I. INTRODUCTION.

Myocarditis is defined as an inflammatory infiltration of the myocardium with associated necrosis or degeneration, or both. The disease is also known as inflammatory cardiomyopathy (or myocarditis with cardiac dysfunction in the World Health Organization 1995 classification for cardiomyopathy). The incidence and prevalence of myocarditis are unclear; the syndrome is underdiagnosed because of the large number of asymptomatic cases. Myocarditis usually affects younger individuals; the median age of patients with lymphocytic myocarditis is 42 years.


A. Clinicopathologic classification of myocarditis

is clinically oriented but not widely used.


1. Fulminant myocarditis

(17%) usually has a distinct onset. It can result in either complete, spontaneous resolution or rapidly progressive deterioration and death due to severe cardiac compromise. Usually there are multiple active foci of inflammatory infiltrate on histology with complete resolution.


2. Acute myocarditis

(65% of myocarditis cases) has an indistinct onset, with moderate cardiovascular compromise and incomplete recovery, often resulting in cardiac dysfunction or subsequent death. Histologically, there are active or borderline inflammatory infiltrates that resolve completely over time.


3. Chronic active myocarditis

(11% of myocarditis cases) has a presentation similar to that of acute myocarditis, but the chronic form usually progresses to only mild or moderate cardiac dysfunction, occasionally with restrictive physiology. Histologic examination often shows ongoing fibrosis, suggesting chronic inflammatory changes.


4. Chronic persistent myocarditis

(7% of myocarditis cases) has an indistinct onset, with nonresolving active or borderline inflammatory infiltrates seen on histologic examination. Usually, there is no cardiovascular compromise.


B. Histologic classification of myocarditis, also called the Dallas classification (1986)

1. Initial biopsy

a. Myocarditis: myocardial necrosis or degeneration, or both, in the absence of significant coronary artery disease with adjacent inflammatory infiltrates or fibrosis, or both

b. Borderline myocarditis: inflammatory infiltrates too sparse or myocyte dam age not apparent

c. No myocarditis: no inflammatory infiltrates or myocyte damage

2. Subsequent biopsy

a. Ongoing (persistent) myocarditis or fibrosis, or both

b. Resolving (healing) myocarditis or fibrosis, or both

c. Resolved (healed) myocarditis or fibrosis, or both


C. World Health Organization (Marburg Criteria, 1996).

A minimum of 14 infil trating leukocytes per mm (1), preferably T lymphocytes, and up to 4 macrophages may be included.



II. CLINICAL PRESENTATION



B. Physical findings.

Patients often present with signs of acute decompensated heart failure, including an S3 (third heart sound) gallop, central and peripheral edema, jugular venous distention, and tachycardia (see Chapter 8). An audible peri cardial friction rub may accompany concomitant myopericarditis. Specific findings in special cases are as follows:

1. Sarcoid myocarditis: lymphadenopathy, also with arrhythmias, and sarcoid involvement in other organs (up to 70%)

2. Acute rheumatic fever (usually affects heart in 50% to 90%): associated signs such as erythema marginatum, polyarthralgia, chorea, and subcutaneous nodules (i.e., Jones criteria)

3. Hypersensitive or eosinophilic myocarditis: pruritic maculopapular rash and history of onset temporally related to initiation of potential culprit medications

4. Giant cell myocarditis (GCM): sustained ventricular tachycardia in rapidly progressive heart failure

5. Peripartum cardiomyopathy: heart failure developing in the last month of pregnancy or within 5 months after delivery (see Chapter 38)


III. LABORATORY EVALUATION


A. Inflammatory markers of myocarditis


1. Complete blood count.

Leukocytosis is common (often lymphocytic), although the presence of eosinophilia may suggest hypersensitive (eosinophilic) myocarditis.


2. Elevated acute phase reactants

such as erythrocyte sedimentation rates or ultrasensitive C-reactive protein are good monitors of clinical progression or response to therapy, but they have low specificity for myocarditis. Novel inflammatory markers under investigation include tumor necrosis factor-α, interleukins, interferon-γ, serum-soluble Fas, and soluble Fas ligand levels. Elevation of these markers portends a worse prognosis.


3. Serum viral antibody titers

are usually increased fourfold or more acutely and gradually fall during convalescence. However, measurement of viral antibody titers is rarely indicated.


4. Anticardiac antibody titers.

Because of their low specificity, measurement of anticardiac antibody titers (against sarcolemma, myosin, laminin, ADP/ATP
translocator, or β-adrenergic receptors) is not indicated (only 62% of myocarditis cases have titers ≥1:40).


B. Rheumatologic screening.

Screening of antinuclear antibodies and rheumatoid factor is often indicated. Disease-specific testing is indicated if the following condi tions are suspected:

1. Systemic lupus erythematosus: anti-dsDNA (reported positive anti-Ro/SSA and anti-La/SSB in lupus carditis in children)

2. Polymyositis: anti-Jo1

3. Wegener’s granulomatosis: c-ANCA (antineutrophil cytoplasmic antibody)

4. Scleroderma: anti-Scl70


C. Serum cardiac enzymes

(markers of myonecrosis): creatinine kinase (myoglobin subfraction) is elevated in only 7.5% of patients with biopsy-proven myocarditis, whereas the cardiac troponin I or T is elevated in at least 50% of patients with biopsy-proven myocarditis (89% to 94% specificity and 34% to 53% sensitivity).


IV. DIAGNOSTIC TESTING


A. Electrocardiogram.

The electrocardiogram often reveals sinus tachycardia, although the presence of nonspecific ST-segment and T-wave abnormalities may rep resent focal or global ischemia. Occasionally, the changes in electrocardiogram are suggestive of an acute myocardial infarction and may include ST-segment elevation. Pericarditis can accompany myocarditis and is often manifested in pericarditislike changes seen in electrocardiography. The sensitivity of the electrocardiogram for myo carditis is low (47%). In some cases, fascicular block or atrioventricular conduction disturbances and ventricular tachyarrhythmia may be hemodynamically significant.


B. Echocardiogram.

A complete echocardiogram is standard procedure for patients with suspected myocarditis to exclude alternative causes of heart failure, detect the presence of intracardiac thrombi and associated valvular disease, and quantify the degree of left ventricular (LV) dysfunction to monitor response to therapy.

1. Occasionally, focal wall motion abnormalities and presence of pericardial fluid may prompt further workup or intervention.

2. Fulminant myocarditis is often characterized by near-normal diastolic dimensions and increased septal wall thickness, whereas acute myocarditis often has increased diastolic dimensions but normal septal wall thickness.

3. In a series of 23 patients with biopsy-proven myocarditis, significant reduction in right ventricular function was a powerful predictor of death or the need for cardiac transplantation.


C. Other imaging modalities


1. Antimyosin scintigraphy (indium III monoclonal antimyosin antibody)

provides identification of myocardial inflammation, with a high sensitivity (91% to 100%) and negative predictive value (93% to 100%) but low specificity (28% to 33%).


2. Gallium scanning

identifies severe myocardial cellular infiltration with high specificity (98%) but low sensitivity (36%).


3. Gadolinium-enhanced magnetic resonance imaging (MRI)

is being used more frequently for diagnosis based on several small observational studies that have found up to 100% sensitivity and specificity depending on the protocol. In one study, MRI was also used for guiding biopsy to areas of focal increased uptake of gadolinium in patients with clinically suspected myocarditis with significantly higher diagnostic yield compared with those who did not have enhancing areas with which to guide the bioptome.


D. Coronary angiography.

Cardiac angiography is often indicated to rule out coro nary artery disease as the cause of new-onset heart failure, as the clinical presentation of myocarditis may mimic myocardial infarction (i.e., pseudoinfarct pattern), espe cially if there are focal wall motion abnormalities and localizing electrocardiographic changes.



V. ETIOLOGY.

Up to 50% of all cases may not have a clear underlying cause (i.e., idiopathic cases).


A. Infective causes



1. Viral myocarditis.

Cardiotropic viruses such as enteroviruses (specifically the coxsackie group B and echoviruses) may cause direct cardiotoxic injuries, cytokine activation, cytoskeletal damage, and autoimmune responses. However, data suggest that the incidence of myocarditis after infection is lower than previously projected. Viral myocarditis is often considered when accompanied with a clinical
picture of recent febrile illness, often with prominent myalgias, followed by rapid onset of cardiac symptoms. However, direct proof is lacking (and often unnecessary), and many cases of idiopathic dilated cardiomyopathies have been attributed to antecedent viral myocarditis. Antiviral therapies have not proved to be useful.








Table 11.1 Causes of Myocarditis












































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Jun 7, 2016 | Posted by in CARDIOLOGY | Comments Off on Myocarditis

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Cause


Examples


Infectious causes


Viruses


Enteroviruses, coxsackievirus A and B, echovirus, influenza virus, poliovirus, herpesviruses, adenovirus, mumps, rubella, rubeola, hepatitis B or C virus, human immunodeficiency virus, Epstein-Barr virus, cytomegalovirus, and parvovirus B19


Rickettsia


Rocky Mountain spotted fever


Fungi


Cryptococcosis, aspergillosis, coccidioidomycosis, and histoplasmosis


Protozoa


Trypanosoma cruzi (Chagas disease) and Toxoplasmosis gondii


Helminths


Trichinosis and schistosomiasis


Bacteria


Legionella, Clostridium, streptococci, staphylococci, Salmonella, and Shigella


Spirochetes


Borrelia burgdorferi (Lyme disease)


Noninfectious causes


Hypersensitive reaction


Eosinophilic myocarditis


Cardiotoxic drugs


Catecholamines, amphetamines, cocaine, chemotherapeutic drugs (e.g., anthracyclines, fluorouracil, streptomycin, cyclophosphamide, interleukin-2, trastuzumab [Herceptin]), and small pox vaccine


Collagen vascular diseases


Systemic lupus erythematosus (i.e., lupus carditis), Wegener’s granulomatosis or Churg-Strauss syndrome, dermatomyositis or polymyositis, and scleroderma


Systemic illnesses


Sarcoidosis, giant cell myocarditis, Kawasaki disease, large-vessel vasculitis (e.g., polyarteritis nodosa and Takayasu arteritis), and inflammatory bowel diseases (e.g., ulcerative colitis and Crohn disease)


Acute rheumatic fever