Pericarditis

The pericardium is a double-layered, fibroelastic sac surrounding the heart, consisting of a visceral layer over the epicardium and a richly innervated parietal layer, separated by a potential space that normally holds 15 to 50 mL of serous fluid. Pericarditis refers to inflammation of the pericardial sac surrounding the heart and is the most common pathological condition affecting the pericardium. This condition can be classified into acute, subacute, chronic, and recurrent pericarditis, which is estimated to occur in about 15% to 30% of cases. Pericarditis may also present alongside other pericardial syndromes, including pericardial effusion, cardiac tamponade, constrictive pericarditis, and effusive-constrictive pericarditis. Pericardial inflammation often leads to fluid accumulation within the pericardial sac, resulting in a pericardial effusion that may be serous, fibrinous, hemorrhagic, or purulent, depending on the etiology. The fluid accumulation can become hemodynamically significant, especially if the effusion is large or accumulates rapidly, as the fluid may extrinsically compress the cardiac chambers, restrict diastolic filling, and lead to cardiac tamponade. This condition can present with obstructive shock and is considered a medical emergency that requires immediate intervention. Pericarditis can be pathologically classified based on the specific nature of the inflammatory exudate found within the pericardial sac. Serous pericarditis typically involves a clear or straw-colored fluid and is most often associated with viral infections or the early stages of an inflammatory process. The most common morphological form is fibrinous pericarditis, which is characterized by a rough, granular appearance, often described as a "bread and butter" pathology, resulting from extensive fibrin deposition on the pericardial surfaces. In contrast, purulent or suppurative pericarditis is frequently bacterial in origin and presents with thick, cloudy, or frankly infected fluid. When the exudate is caseous, a tuberculous origin is highly suggested, whereas hemorrhagic pericarditis, marked by the presence of blood, is commonly linked to malignancy, tuberculosis, or complications following cardiac surgery. Additionally, pericarditis may result in pericardial thickening, which in rare cases can progress to constrictive pericarditis months or even years after the initial inflammatory episode. A more recently recognized entity, effusive–constrictive pericarditis, occurs when a pericardial effusion is present but features of constrictive physiology persist despite removal of the fluid. These features may include respiratory-enhanced interventricular dependence, a restrictive transmitral E/A filling pattern (ratio of early [E] to late [A] diastolic velocities), and mitral annulus reversus, characterized by a septal e′ velocity greater than the lateral e′. Persistence of these findings after pericardiocentesis indicates underlying constrictive pathology that is independent of the effusion itself. The aforementioned pericardial syndromes may occur alongside acute pericarditis but are not required for its diagnosis. In the past, the 2015 European Society of Cardiology (ESC) guidelines for diagnosing and managing pericardial diseases categorized the causes of pericarditis broadly into 2 main groups—infectious and noninfectious. However, the 2025 ESC Guidelines for the management of myocarditis and pericarditis place new emphasis on the interplay between myocardial inflammation and pericardial inflammation. As more data become available, enriched by advances in multimodal imaging, that myocarditis and pericarditis often exist on a spectrum is increasingly clear. The new guidelines propose the term inflammatory myopericardial syndrome (IMPS) to encompass more distinct terms, eg, pericarditis, myocarditis, myopericarditis (predominant pericarditis with myocardial involvement), perimyocarditis (predominant myocarditis), and complicated myocarditis. Patients who meet diagnostic criteria for pericarditis and have elevated cardiac biomarkers are given a diagnosis of myopericarditis, whereas patients who also develop evidence of wall motion abnormality or systolic dysfunction would meet the criteria for perimyocarditis. If myocarditis is associated with significant systolic dysfunction (<50% LVEF), heart failure, hemodynamic decompensation (shock), or significant electrical abnormalities (sustained VT, advanced heart block), it would be considered "complicated myocarditis". Pericarditis is the focus of this discussion, with the recognition that coexisting myocardial inflammation occurs in approximately 15% of cases.