The normal pericardium is a fibroelastic sac containing a thin layer of fluid that surrounds the heart. When larger amounts of fluid accumulate (pericardial effusion) or when the pericardium becomes scarred and inelastic, one of three pericardial compressive syndromes may occur:
●Cardiac tamponade – Cardiac tamponade, which may be acute or subacute, is characterized by the accumulation of pericardial fluid under pressure. Variants include low pressure (occult) and regional cardiac tamponade.
●Constrictive pericarditis – Constrictive pericarditis is the result of scarring and consequent loss of elasticity of the pericardial sac. Pericardial constriction is typically chronic, but variants include subacute, transient, and occult constriction.
●Effusive-constrictive pericarditis – Effusive-constrictive pericarditis is characterized by underlying constrictive physiology with a coexisting pericardial effusion, usually with cardiac tamponade. Such patients may be mistakenly thought to have only cardiac tamponade; however, elevation of the right atrial and pulmonary wedge pressures after drainage of the pericardial fluid points to the underlying constrictive process.
In both cardiac tamponade and constrictive pericarditis, cardiac filling is impeded by an external force. The normal pericardium can stretch to accommodate physiologic changes in cardiac volume. However, after its reserve volume is exceeded, the pericardium markedly stiffens. An important pathophysiologic feature of both cardiac tamponade and constrictive pericarditis is greatly enhanced ventricular interaction or interdependence, in which the hemodynamics of the left and right heart chambers are directly influenced by each other to a much greater degree than normal.