Pathophysiology:

Frequency/Morbidity/Mortality:

Because of its difficulty in diagnosis and its possible role in sudden dysrhythmic death, morbidity is not known exactly. Rarely, acute myocarditis is fulminant and leads to death. The appropriate delicate balance of the immune response to viral invasion of myocytes indicates that a certain number of individuals, perhaps with genetic predispositions, will advance to dilated cardiomyopathy and heart failure, the most common long-term sequelae in those patients who do not recover completely. Appreciating that an unknown group of subclinical cases exists, of patients with apparent disease that is identified by a physician, it is often quoted that one third of patients improve without incident, one third develop some mild myocardial scarring, and one third develop dilated cardiomyopathy.

History:

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 discomfort is reported in 35% of patients. The pain is most commonly described as a pleuritic, sharp, stabbing precordial 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 should be carefully approached because it may signal high-grade AV block or risk for sudden death.

Physical:

Causes:

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. Among the most common drugs that cause hypersensitivity reactions are 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. Other toxic causes include venom from wasp, scorpion, and spider stings. Also, radiation therapy may cause a myocarditis which usually leads to 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, and dermatomyositis that can often result in a dismal prognosis; Idiopathic inflammatory and infiltrative disorders such as Kawasaki disease, sarcoidosis, and giant cell arteritis; Rejection of the posttransplant heart may present as inflammatory myocarditis.

Laboratory and Imaging Studies:

The key imaging studies include a Chest X-ray which often reveals a normal cardiac silhouette, but pericarditis or overt clinical CHF is associated with cardiomegaly. It also shows vascular redistribution, Interstitial and alveolar edema, and pleural effusion. Echocardiography shows Impairment of left ventricular systolic and diastolic function, segmental wall motion abnormalities, and impaired ejection fraction. Ventricular thrombus has been identified in 15% of patients studied with echocardiography.

Other tests include: an Electrocardiogram (tachycardia is the most frequent finding). ST-segment elevation without reciprocal depression, particularly when diffuse, is helpful in differentiating myocarditis from acute myocardial infarction. As many as 20% of patients will have a conduction delay, including Mobitz I, Mobitz II, or complete heart block. Left or right bundle-branch block is observed in approximately 20% of abnormal ECG findings and may persist for months. Another test is PCR identification of a viral infection directly from myocardial tissue or pericardial fluid.

Procedures:

Treatment:

In general, sympathomimetic and beta-blocker drugs should be avoided because they increase the extent of myocardial necrosis and mortality. Patients presenting with Mobitz II or complete heart block require pacemaker placement. Medical therapy for myocarditis is an area of avid research interest but with little success in human trials. Treatment primarily involves managing the complications of myocarditis, chiefly thromboembolism, dysrhythmia, and CHF.

Inpatient management consists of treatment for the complications of myocarditis. Patients thought to have the disease often undergo an endomyocardial biopsy. And although temporary pacemaker placement for advanced degrees of heart block is indicated, in the setting of myocarditis, these conduction disturbances are usually transitory. Therefore, permanent pacemaker placement usually is not necessary. Bedrest with restriction of activity and sodium intake is beneficial. And, patients with fulminant heart failure may require transplantation, which can be life saving. Unfortunately, these patients have a higher rate of rejection than patients whose underlying cause of heart failure is not myocarditis.

Complications and Prognosis:

Most cases of myocarditis are believed to be clinically silent and resolve spontaneously without sequelae; therefore, making accurate statements concerning the prognosis of myocarditis is difficult. One half of patients presenting with new-onset CHF experience considerable improvement of cardiac function with treatment. One fourth of patients presenting with CHF stabilize with compromised cardiac function. The conditions of the remaining one fourth of patients continue to deteriorate. Patients requiring transplantation have an increased risk of recurrent myocarditis and graft rejection.

Medical/Legal Concerns: