Myocarditis & the Cardiomyopathies

Acute Myocarditis

Introduction
Acute myocarditis causes focal or diffuse inflammation of the myocardium. Most cases are infectious, caused by viral, bacterial, rickettsial, spirochetal, fungal, or parasitic agents; but toxins, drugs, and immunologic disorders can also cause myocarditis.

1. Infectious Myocarditis

Introduction

Essentials of Diagnosis

• Often follows an upper respiratory infection.
• May present with chest pain (pleuritic or nonspecific) or signs of heart failure.
• ECG may show sinus tachycardia, other arrhythmias, nonspecific repolarization changes, and intraventricular conduction abnormalities.
• Echocardiogram documents cardiomegaly and contractile dysfunction.
• Myocardial biopsy, though not sensitive, may reveal a characteristic inflammatory pattern.

General Considerations
Viral myocarditis is the most common form and is usually caused by coxsackieviruses, but a host of other agents have also been responsible. Rickettsial myocarditis occurs with scrub typhus, Rocky Mountain spotted fever, and Q fever. Diphtheritic myocarditis is caused by the exotoxin and often is manifested by conduction abnormalities as well as heart failure.

Chagas' disease, caused by the insect-borne protozoan Trypanosoma cruzi, is a common form of myocarditis in Central and South America; the major clinical manifestations appear after a latent period of more than a decade. At this stage, patients present with cardiomyopathy, conduction disturbances, and sudden death. Associated gastrointestinal involvement (megaesophagus and megacolon) is the rule. Toxoplasmosis causes myocarditis that is usually asymptomatic but can lead to heart failure. Among parasitic infections, trichinosis is the most common cause of cardiac involvement. The potential for the HIV virus to cause myocarditis is now well recognized, though the prevalence of this complication is not known. In addition, other infectious myocarditides are more common in patients with AIDS.

Giant cell myocarditis is a rare idiopathic disorder characterized by giant cell and lymphocyte infiltration of the heart muscle. Patients usually die from ventricular arrhythmias or heart failure but occasionally respond to immunosuppressive therapy or early transplantation.

Clinical Findings
A. Symptoms and Signs