eMedicine Specialties > Emergency Medicine > Cardiovascular

Myocarditis

Author: David S Howes, MD, Residency Program Director, Professor of Medicine, Section of Emergency Medicine, University of Chicago/Pritzker School of Medicine
Coauthor(s): Ethan A Booker, MD, Attending Physician, Department of Emergency Medicine, Washington Hospital Center
Contributor Information and Disclosures

Updated: Dec 1, 2009

Introduction

Background

Myocarditis is clinical syndrome characterized by inflammation of myocytes resulting from infectious, toxic, and autoimmune etiologies. Ongoing viral infection, myocardial destruction, and adverse remodeling can lead to persistent ventricular dysfunction and dilated cardiomyopathy.

Myocarditis is an elusive illness to study, diagnose, and treat because the clinical presentation may range from nearly asymptomatic to overt heart failure requiring transplantation; a myriad of causes exist, and it is occasionally the unrecognized culprit in cases of sudden death.

Pathophysiology

Myocarditis is defined as inflammatory changes in the heart muscle and is characterized by myocyte necrosis.
 
Animal models have lead to a much greater understanding of the pathophysiology of fulminant myocarditis in which susceptible patients uptake viral RNA and develop a cytotoxic necrosis and rapid (1-2 d) cell death without the appearance of any interstitial infiltrate. In both animal models and these patients, a rapid progression to severe ventricular dysfunction and cardiovascular collapse occurs.¹

In the more typical course of the disease, 4-14 days after viral infection, cells produce an immune response including macrophage activation and cytokine expression and develop an histologically apparent infiltrate of mononuclear cells. In this subacute viral-clearing phase, natural killer cells target myocardium expressing the viral RNA and continue myocyte necrosis. Tumor necrosis factor is involved in rapidly clearing virus and signals additional proinflammatory cells, activates endothelial cells, and has direct negative inotropic effects. In the latter stages of the subacute process, cytotoxic T lymphocytes infiltrate myocytes and trigger lysis of these cells by presenting virus fragments via the histocompatibility complex on the surface of the myocyte membrane. Neutralizing antiviral antibodies also develop to assist in the clearing of virus.²

In the chronic phases, the deleterious effects of either inadequate or inappropriately abundant immune response can lead to the long-term sequelae of dilated cardiomyopathy and heart failure. In animal models of insufficient immune response, viral replication can continue and cause chronic destruction of myocytes.¹ As a prototype of inadequate immune response, human patients with HIV are a subgroup known to do poorly, with a high rate of progression to fulminant heart failure, and polymerase chain reaction (PCR) of endomyocardial biopsy samples show a persistent expression of viral genome, both HIV and others.³

On the opposite extreme of immune activity, overabundant T cells may continue activity into the chronic phase, causing tissue destruction and ventricular dysfunction manifesting as chronic heart failure. Ongoing study has demonstrated the presence of antimyosin autoantibodies and other immunomodulators long after initial viral infection and has demonstrated a worsened clinical prognosis from this persistent immune response directed at myocytes.^4,5

Frequency

United States

The true incidence of myocarditis is unknown because many cases are asymptomatic, and some symptoms related to significant morbidity may not be appropriately credited. One major urban US medical examiners office attributed 1.3% of sudden and unexpected deaths to myocarditis,⁶ consistent with other autopsy studies that demonstrate evidence of myocardial inflammation in 1-1.5% of deaths. In the United States, viral and medication-related cases are the most commonly identified causes.

International

Internationally, other etiologies of myocarditis play a more important role, with Chagas disease from the parasite Trypanosoma cruzi infecting approximately 18 million people with 50,000 annual deaths. Worldwide the true frequency of disease in its less severe forms is even more difficult to appreciate.⁴

Mortality/Morbidity

Because of difficulty in diagnosing myocarditis, the large number of cases that likely never come to medical attention, and its previously underappreciated role in sudden dysrhythmic death, morbidity and mortality data are difficult to construct.

• Rarely, myocarditis is fulminant and leads rapidly to cardiovascular collapse and shock sometimes requiring mechanical support. Paradoxically, if these patients survive the first 3-4 weeks of illness they have near 100% recovery and far fewer long-term complications compared with those patients with more indolent courses.^7,8
• Mortality for clinically significant and biopsy-proven myocarditis varies widely. Patients who initially have and then subsequently clear virus as demonstrated by polymerase chain reaction of endomyocardial biopsy tissue have excellent recovery with a return to normal or near-normal left ventricular function and overall mortality less than 4%.⁹
• Patients with persistent viral genome expression and/or antimyosin autoantibodies show limited recovery of left ventricular (LV) function, decreased stroke volume index, and more stiffness of the ventricle with the resultant long-term morbidity of heart failure and a mortality of nearly 25%.³

Sex

The male-to-female ratio for myocarditis is 1.5:1.

Age

The average age of patients with myocarditis is 42 years. In younger patients with sudden cardiac death, as much as 20% of cases may be related to myocarditis.

Clinical

History

• Many patients with myocarditis present with a nonspecific illness characterized by fatigue, mild dyspnea, and myalgias. A few patients present acutely with fulminant congestive heart failure (CHF) secondary to widespread myocardial involvement. Small, focal inflammation in electrically sensitive areas may be the etiology of patients whose initial presentation is sudden death. Some presentations of myocarditis, especially those related to parvovirus B19, present like an acute lateral wall myocardial infarction.
• Most cases of myocarditis are subclinical; therefore, the patient rarely seeks medical attention during acute illness. These subclinical cases may have transient ECG abnormalities.
• An antecedent viral syndrome is present in more than one half of patients with myocarditis. The appearance of cardiac-specific symptoms occurs primarily in the subacute virus-clearing phase; therefore, patients commonly present 2 weeks after the acute viremia.
• Fever is present in 20% of patients.
• Other symptoms include fatigue, myalgias and arthralgias, and malaise.
• Chest pain
  • Chest discomfort is reported in 35% of patients.
  • The pain is most commonly described as a pleuritic, sharp, stabbing precordial pain. Pericarditis may be present in many cases and may cause some of the clinical presentation of pain.
  • It may be substernal and squeezing and, therefore, difficult to distinguish from that typical of ischemic pain.
• Dyspnea on exertion is common.
• Orthopnea and shortness of breath at rest may be noted if CHF is present.
• Palpitations are common. Syncope in a patient with a presentation consistent with myocarditis may signal high-grade atrioventricular (AV) block and risk for sudden death.
• Pediatric patients, particularly infants, present with nonspecific symptoms, including the following:
  • Fever
  • Respiratory distress
  • Poor feeding or, in cases with CHF, sweating while feeding
  • Cyanosis in severe cases
• In a 6-year study of pediatric ED patients, the most common presenting symptom was dyspnea and more than half of patients were initially diagnosed with asthma or pneumonia. Six percent of patients had primarily GI symptoms.¹⁰

Physical

Physical findings of myocarditis can range from a normal examination, through all classes of congestive heart failure (CHF) to cardiovascular collapse and shock.

• Patients with mild cases of myocarditis have a nontoxic appearance and simply may appear to have a viral syndrome.
• Tachypnea and tachycardia are common. Tachycardia is often out of proportion to fever.
• More acutely ill patients have signs of circulatory impairment due to left ventricular failure.
• A widely inflamed heart shows the classic signs of ventricular dysfunction including the following:
  • Jugular venous distention
  • Bibasilar crackles
  • Ascites
  • Peripheral edema
• S₃ or a summation gallop may be noted with significant biventricular involvement.
• Intensity of S₁ may be diminished.
• Cyanosis may occur.
• Murmurs of mitral or tricuspid regurgitation may be present due to ventricular dilation.
• In cases where a dilated cardiomyopathy has developed, signs of peripheral or pulmonary thromboembolism may be found.
• Diffuse inflammation may develop leading to pericardial effusion, without tamponade, and pericardial and pleural friction rub as the inflammatory process involves surrounding structures.

Causes

The causes of myocarditis are numerous and can be roughly divided into infectious, toxic, and immunologic etiologies, with viral etiologies most common in North America.

• Amongst the infectious causes, viral acute myocarditis is by far the most common.
  • In a study of 172 patients with a biopsy sample showing myocarditis in which a viral genome was identified by polymerase chain reaction, the most common viruses were adenovirus, 8.1%; parvovirus B19, 36.6%; human herpesvirus 6 (HHV-6), 10.5%; enterovirus, 32.6%; co-infection with HHV-6 and parvovirus B19, 12.6%.¹¹
  • Other viruses implicated in myocarditis include influenza virus, echovirus, herpes simplex virus, varicella-zoster virus, hepatitis, Epstein-Barr virus, and cytomegalovirus.
  • Human immunodeficiency virus (HIV) deserves special mention because it seems to function differently than other viruses. HIV-1 glycoprotein 120 can directly disrupt cardiac contractility without an inflammatory response. This may explain why HIV genomes can be amplified from patients without histologic signs of inflammation. Myocarditis is the most commonly found cardiac abnormality found on biopsy tissue, present in some degree, in more than 50% of HIV patients.⁴ In addition, in patients who are infected with HIV, T-cell – mediated immune suppression increases the risk of contracting myocarditis due to other infectious causes.³
  • Nonviral infectious causes are numerous and varied. Worldwide, the most common bacterial cause is diphtheria, and, in South America, the protozoal Chagas disease is a common entity. Streptococcal and staphylococcal species and Bartonella, Brucella, Leptospira, and Salmonella species can spread to the myocardium as a consequence of severe cases of endocarditis. Borrelia burgdorferi, the spirochete agent in Lyme disease, is also a known cause of myocarditis. Parasitic myocarditis from trypanosomiasis; trichinosis; and, in the immunocompromised host, toxoplasmosis have been identified.
• Toxic myocarditis has a number of etiologies including both medical agents and environmental agents.^12,1,4
  • Among the most common drugs that cause hypersensitivity reactions are clozapine, penicillin, ampicillin, hydrochlorothiazide, methyldopa, and sulfonamide drugs. This syndrome is associated with peripheral eosinophilia, fever, and rash in patients who have biopsy findings of an eosinophilic infiltrate of the myocardium.
  • Numerous medications (eg, lithium, doxorubicin, cocaine, numerous catecholamines, acetaminophen) may exert a direct cytotoxic effect on the heart. Zidovudine (AZT) has been associated with myocarditis.
  • Environmental toxins include lead, arsenic, and carbon monoxide. Cases have been attributed to Chinese sumac.
  • Wasp and scorpion stings and spider bites, specifically black widows, may cause myocarditis.
  • Radiation therapy may cause a myocarditis with the development of a dilated cardiomyopathy.
• Immunologic etiologies of myocarditis encompass a number of clinical syndromes and include the following:
  • Connective tissue disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis, scleroderma, and dermatomyositis can often result in a dismal prognosis.
  • Idiopathic inflammatory and infiltrative disorders such as Kawasaki disease, sarcoidosis, and giant cell arteritis may be a cause.
• Rejection of the post transplant heart may present as inflammatory myocarditis.

• Search for CME/CE on This Topic »

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• Myocarditis (Cardiology)
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• Myocarditis, Nonviral (Pediatrics: Cardiac Disease and Critical Care Medicine)

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