A significant minority of patients with acute pericarditis will suffer from adverse events related to the initial disease. This review discusses which patients are at risk for complications after presentation with acute pericarditis, which patients with complicated pericarditis might benefit from multimodality imaging, the pathological progression of pericarditis, and established and emerging therapies for patients with complicated pericarditis. The following are key points to remember:

1. Pericarditis is categorized by the duration of symptoms: symptomatic persistence for >4-6 weeks is termed incessant pericarditis, symptomatic persistence for >3 months is considered chronic pericarditis, and symptomatic recurrence after freedom from symptoms for at least 4-6 weeks is termed recurrent pericarditis. An additional risk of pericarditis is the development of constrictive pericarditis.
2. In the United States and Western Europe, most (80-90%) episodes of pericarditis are idiopathic and presumed to be post-viral. In the developing world, most cases of pericarditis are attributable to tuberculosis. Other causes of pericarditis include post-cardiac injury syndromes after acute myocardial infarction, percutaneous coronary or electrophysiologic procedures, or after pericardiotomy.
3. After presentation with acute pericarditis, the probability of developing incessant pericarditis or of a recurrence of pericarditis within 18 months is 15-30%. After an initial recurrence of pericarditis, the risk of recurrence increases to 25-50%.
4. The early use of corticosteroids is associated with an increased risk of recurrence; colchicine therapy is associated with reduced risk of recurrence, and has become a mainstay of treatment. Patient-specific factors associated with increased risk of recurrence include incomplete response to nonsteroidal anti-inflammatory treatment and persistently elevated C-reactive protein.
5. Most patients with acute pericarditis will have an uncomplicated course, and echocardiography (for evaluation for pericardial effusion, pericardial tamponade, wall motion abnormalities, and evidence of pericardial constriction) is the first and only imaging test necessary.
6. Cardiac magnetic resonance (CMR) imaging allows assessment of morphologic characteristics and hemodynamic consequences of pericardial constraint. Among patients with echocardiographic features suggestive of constriction, CMR may be useful to assess for ongoing pericardial inflammation. However, because echocardiography may provide evidence suggestive but not diagnostic of constriction, CMR is probably most useful among patients with inconclusive data on echocardiography.
7. Late gadolinium enhancement on CMR increases in the setting of increased pericardial neovascularization. Late gadolinium enhancement is expected to be increased during active inflammation; whereas a thickened pericardium without late gadolinium enhancement would be anticipated in the setting of end-stage pericarditis. CMR with assessment of pericardial late gadolinium enhancement can be useful among patients in whom the presence of active pericardial inflammation is uncertain, and among patients with constrictive pericarditis in whom the severity of pericarditis is uncertain.
8. Recurrent attacks of pericarditis may occur because of inability to clear the presumed viral infection with increased viral replication, or due to an autoimmune response caused by molecular mimicry. Recent investigations suggest that innate immunity and its effector mechanisms may be responsible for recurrent idiopathic pericarditis.
9. Established treatments for pericarditis include nonsteroidal anti-inflammatory drugs (NSAIDs) and colchicine. Unopposed mineralocorticoids increase the risk of recurrence and prolong the course of disease, and (with exceptions including pericarditis due to systemic autoimmune disease, or pregnant patients with renal failure in whom NSAIDs and colchicine should be avoided) should be considered only after failure of NSAIDs and colchicine.
10. Novel treatments for refractory pericarditis include azathioprine, human intravenous immunoglobulin, and anakinra (an interleukin-1 receptor antagonist). Once medical therapy has failed, pericardiectomy can be rarely considered to treat refractory pain associated with recurrent pericarditis.

Keywords: Anti-Inflammatory Agents, Non-Steroidal, Autoimmune Diseases, Azathioprine, C-Reactive Protein, Cardiac Tamponade, Colchicine, Diagnostic Imaging, Echocardiography, Gadolinium, Immunoglobulins, Intravenous, Interleukin 1 Receptor Antagonist Protein, Magnetic Resonance Spectroscopy, Myocardial Infarction, Pericardial Effusion, Pericardiectomy, Pericarditis, Pericarditis, Constrictive, Pericardium, Renal Insufficiency, Risk Factors, Tuberculosis

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