The pericardium is composed of visceral and parietal components. The visceral pericardium is a mesothelial monolayer that adheres firmly to the epicardium, reflects over the origin of the great vessels, and—together with a tough, fibrous coat—envelops the heart as the parietal pericardium (Fig. 85–1). The pericardial space is enclosed between these two serosal layers and normally contains up to 50 mL of a plasma ultrafiltrate, the pericardial fluid. Pericardial reflections around the great vessels tether the pericardium superiorly and result in the formation of two potential spaces: the oblique and transverse sinuses. Superior and inferior pericardiosternal and diaphragmatic ligaments limit displacement of the pericardium and its contents within the chest and neutralize the effects of respiration and change of body position. The phrenic nerves are embedded in the parietal pericardium and, for this reason, are vulnerable to injury during pericardial resection.
Computed tomography scan shows the normal pericardium as a thin, curvilinear line (open arrows). The increased thickening over the anterior surface of the heart (solid arrows) is probably an artifact from transmitted right ventricular (RV) pulsations. Reproduced with permission from Moncada R, Baker M. In: Higgins CB, ed. CT of the Heart and Great Vessels. Mt. Kisco, NY: Futura; 1983:292.
Histologically, the pericardium is composed predominantly of compact collagen layers interspersed with elastin fibers. The abundance and orientation of the collagen fibers are responsible for the characteristic viscoelastic mechanical properties of the pericardium. For example, the pressure-volume relation of the pericardium is nonlinear; that is, the relation is initially flat (producing little to no change in pressure for large changes in volume) and develops a "bend" or "knee" at a critical pressure, which terminates in a steep slope (producing large changes in pressure for small changes in volume) (Fig. 85–2). In addition, the pericardium is anisotropic; that is, it stretches more in the short axis than in the long axis.
Pericardial pressure-volume relation in a dog. Reproduced with permission from Hoit JP, Rhode EA, Kines H. Pericardial and ventricular pressure. Circ Res. 1960 Nov 1; 8(6):1171-1181.
The pericardium is not essential for life; no adverse consequences follow congenital absence or surgical removal of the pericardium. However, the pericardium serves many important (although subtle) functions (Table 85–1). It limits distension of the cardiac chambers and facilitates interaction and coupling of the ventricles and atria.1 Thus, changes in pressure and volume on one side of the heart can influence pressure and volume on the other side. Limitation of cardiac filling volumes by the pericardium may also limit cardiac output and oxygen delivery during exercise.1 The pericardium also influences quantitative and qualitative aspects of ventricular filling; the thin-walled right ventricle (RV) and atrium are more subject ...