Chapter 17

### Normal Pericardial Anatomy and Physiology

The pericardium consists of two layers: a serous visceral layer, which is intimately adherent to the heart and epicardial fat, and a fibrous parietal layer. The pericardium encloses the greater part of the surface of the heart, the juxtacardial portions of the pulmonary and systemic veins, and the proximal segments of the great vessels. A significant portion of the left atrium, however, is not enclosed within the pericardium. The pericardium is attached by ligaments to the manubrium sterni, the xiphoid process, the vertebral column, and the central tendon of the diaphragm. The pericardium is not essential for sustaining life or health, as evidenced by preservation of cardiac function even if the pericardium is congenitally absent or surgically removed. The pericardium does play a role in normal cardiovascular function, however, and can be involved in a number of important disease states. The normal functions of the pericardium include maintaining an optimal cardiac shape, promoting cardiac chamber interaction, preventing the overfilling of the heart, reducing friction between the beating heart and adjacent structures, providing a physical barrier to infection, and limiting displacement during the cardiac cycle.

### Pericardial Pressure and Normal Function

The true pressure in the normal pericardial space is a matter of some controversy. When measured with fluid-filled catheters, pericardial pressure is very similar to intrapleural pressure: from –1 to –2 mm Hg on average, falling to about –5 mm Hg with normal inspiration. There is considerable evidence, however, that the pressure in the normal pericardial space is best considered as a contact force between visceral and parietal pericardium and therefore is more appropriately measured by specially-designed flat balloons. When measured in this way, the pericardial pressure is clearly higher than the intrapleural pressure, although its true magnitude remains somewhat uncertain. The bulk of current evidence indicates that with normal cardiac volumes, the effective pericardial pressure ranges from 0–1 mm Hg to (at most) 3–4 mm Hg. The pericardial space between the parietal and visceral layers normally contains 15–50 mL of fluid, and the reserve volume of the pericardium is relatively small. Once this modest reserve is exceeded, intrapericardial pressure rises significantly. This can occur if the cardiac volume increases rapidly, for example, due to acute right ventricular myocardial infarction, or if additional fluid accumulates. With significant fluid in the pericardial space, fluid-filled catheters do provide accurate intrapericardial pressure measurements.

### Infectious Pathogens

#### Viral Pericarditis

The most common clinical manifestation of viral involvement is acute pericarditis. An unidentified virus almost certainly underlies most cases of acute idiopathic pericarditis. The possibility of a viral cause is suggested when pericarditis occurs in the absence of other factors; it is supported by a more than fourfold rise in serial viral antibody titers during the initial weeks of illness. (Such measurement, however, is not a routine part of the management of viral pericarditis.) Frequently, a prodromal ...

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