Myocarditis and Pericarditis

Myocarditis and pericarditis are inflammatory diseases of the heart. Myocarditis is inflammation of the heart muscle (myocardium) itself, while pericarditis is inflammation of the pericardium, the fibrous sac that surrounds the heart. They are commonly triggered by infection — frequently viral — or by immune-mediated and other systemic processes, and they frequently overlap, since inflammation can involve both layers (myopericarditis).

Definition

Myocarditis is inflammation of the myocardium that can impair contraction and provoke arrhythmia, and pericarditis is inflammation of the pericardium; both are most often infectious or immune-mediated, and they may coexist as myopericarditis.

Scope

This topic covers the two principal inflammatory disorders of the heart, their typical infectious and immune-mediated triggers, how they affect myocardial contraction and pericardial mechanics (including pericardial effusion and tamponade physiology in conceptual terms), and how they are recognised and classified. It is a reference entry on the concepts, not clinical management guidance.

Core questions

• Is the inflammation principally of the myocardium, the pericardium, or both?
• What is the trigger — viral, other infectious, immune-mediated, or systemic disease?
• How does the inflammation alter contraction (myocarditis) or filling and pericardial pressure (pericarditis)?

Key concepts

• Myocardial inflammation
• Pericardial inflammation
• Myopericarditis (overlap)
• Viral and immune-mediated triggers
• Pericardial effusion
• Cardiac tamponade physiology
• Inflammatory (post-myocarditic) cardiomyopathy

Mechanisms

In myocarditis an infectious agent or immune-mediated process injures cardiomyocytes and provokes an inflammatory infiltrate, which can depress systolic function and create a substrate for arrhythmia; in some patients this resolves, while in others it progresses to a dilated, inflammatory cardiomyopathy (Caforio, 2013; Sagar, 2012). In pericarditis inflammation of the pericardial layers causes the characteristic chest pain and friction rub and may be accompanied by a pericardial effusion. When fluid accumulates rapidly or under pressure, it can compress the heart and impair diastolic filling — the physiological basis of cardiac tamponade — and chronic inflammation can lead to a thickened, constricting pericardium (Adler, 2015). Because the two layers are anatomically continuous, inflammation often involves both, producing overlapping myopericarditis.

Clinical relevance

Inflammatory heart disease is an important and sometimes reversible cause of chest pain, heart failure, arrhythmia, and, in pericarditis, of effusion and tamponade physiology. It is also a recognised differential for acute coronary presentations. Understanding the mechanisms aids interpretation of imaging and the cardiology literature. This entry is descriptive and is not a basis for individual diagnosis or treatment.

Epidemiology

The true incidence of myocarditis is uncertain because presentations range from subclinical to fulminant and diagnosis is challenging; it is a recognised cause of heart failure and of sudden death in young people (Sagar, 2012). Acute pericarditis is a common cause of pericardial syndromes and chest-pain presentations, frequently idiopathic or presumed viral in higher-income settings (Adler, 2015).

History

Pericardial inflammation and its friction rub have been described clinically for centuries, and the physiology of pericardial constriction and tamponade was characterised through the nineteenth and twentieth centuries. Myocarditis became better defined with histopathological criteria and, more recently, with cardiac magnetic resonance imaging, which allows non-invasive recognition of myocardial inflammation (Caforio, 2013; Sagar, 2012). Society position statements and guidelines now frame the diagnosis and classification of both (Caforio, 2013; Adler, 2015).

Seminal works

• caforio-2013
• adler-2015
• sagar-2012

Frequently asked questions

What is the difference between myocarditis and pericarditis?

Myocarditis is inflammation of the heart muscle, which can weaken contraction and cause arrhythmia, whereas pericarditis is inflammation of the sac around the heart, which typically causes chest pain and may produce a pericardial effusion. Because the structures are adjacent, both can be inflamed together (myopericarditis).

What usually causes myocarditis and pericarditis?

Both are commonly triggered by infection, frequently viral, and by immune-mediated or systemic inflammatory processes. In many cases of pericarditis no specific cause is identified and it is labelled idiopathic or presumed viral.