Key Clinical Questions
How do you diagnose pericarditis and myocarditis?
Which imaging modality is most accurate in diagnosing myocarditis?
How do you diagnose and manage cardiac tamponade?
How does the treatment of constrictive pericarditis differ from cardiac tamponade?
Acute myocarditis is an inflammatory infiltration of the myocardium characterized by areas of myocardial necrosis with lymphocytic infiltration. The clinical sequelae range from subclinical disease to fulminant cardiogenic shock.
The most common cause of myocarditis is a viral pathogen. However, other infectious, autoimmune, and toxic causes occur as well. Initial studies in the latter half of the 20th century indicated Coxsackie B virus as the frequent causative agent in endomyocardial biopsies. However, since the 1990s adenovirus has emerged as the more frequent viral agent. Additionally, parvovirus, HIV, HCV, EBV, and CMV have been seen in the biopsy results of patients with myocarditis. The model for the development of acute myocarditis from these viral agents involves viral entry into the cells via specific membrane receptors with subsequent viral replication and myocyte necrosis. Cellular necrosis leads to exposure of the intracellular contents including proteins such as myosin and thus an autoimmune activation, which may last 3 to 5 days. Subsequent autoimmunity and activation of the lymphocytes may last weeks to months and is the driving force behind the time course of myocarditis.
Infectious etiologies other than viruses have been implicated as a cause of myocarditis, including mycoplasma, Corynebacterium diphtheriae and Borrelia burgdorferi (Lyme disease). In developing countries, Trypanosoma cruzi has been known to infect the myocardium causing Chagas disease.
The clinical presentation of patients with myocarditis ranges from mild dyspnea and chest discomfort to fulminant cardiogenic shock. Patients may report a viral prodrome in the weeks preceding presentation, including fevers, respiratory, or gastrointestinal symptoms. According to the European Study of Epidemiology and Treatment of Inflammatory Heart Disease, patients with myocarditis present with dyspnea (72%), chest pain (32%), and arrhythmias (18%). Patients may also present with symptoms related to congestive heart failure, including fatigue, orthopnea, paroxysmal nocturnal dyspnea, palpitations, and syncope.
As an infiltrative process, the amount of affected myocardium can be highly variable in myocarditis. Some patients may present with ventricular arrhythmias if the conducting system is involved while other patients may present with a dilated cardiomyopathy.
The physical examination of patients with acute myocarditis may correlate with the patients’ symptoms. Signs of myocarditis are nonspecific, correlating with the severity of heart failure.
The electrocardiogram (ECG) in myocarditis is neither sensitive nor specific, but may show the following:
Sinus tachycardia, nonspecific ST-segment changes and T-wave inversion.
ST-segment elevation and Q-waves that suggest acute myocardial ischemia.
Bundle-branch blocks, atrioventricular block, or ventricular tachyarrhythmias.
Diffuse ST-segment elevation in addition to PR-segment depression (myopericarditis).