Acute pericarditis

Question 1

Etiology?

Answer 1

The normal pericardial space contains 15 to 50 mL of pericardial fluid, a plasma ultrafiltrate secreted
by the mesothelial cells that line the serosal layer. A larger volume of fl uid may accumulate in
association with any of the forms of acute pericarditis. In addition, noninflammatory serous
effusions may result from conditions of
(1) increased capillary permeability (e.g., severe
hypothyroidism); (
2) increased capillary hydrostatic pressure (e.g., congestive heart failure); or
(3)
decreased plasma oncotic pressure (e.g., cirrhosis or the nephrotic syndrome). Chylous effusions may
occur in the presence of lymphatic obstruction of pericardial drainage, most commonly caused by
neoplasms and tuberculosis.

Question 2

Pathophysiology (relationship between its internal volume
and pressure)?

Answer 2

Relationship between its internal volume
and pressure is not linear. Notice that the initial portion of the curve is nearly flat, indicating that at
the low volumes normally present within the pericardium, a small increase in volume leads to only a
small rise in pressure. However, when the intrapericardial volume expands beyond a critical level, a
dramatic increase in pressure is incited by the nondistensible sac. At that point, even a minor
increase in volume can translate into an enormous compressive force on the heart.

Question 3

Three factors?

Answer 3

Three factors determine whether a pericardial effusion remains clinically silent or whether symptoms
of cardiac compression ensue: (1) the volume of fluid,
(2) the rate at which the fluid accumulates,
and
(3) the compliance characteristics of the pericardium.

Question 4

Sudden increase of pericardial volume?

Answer 4

A sudden increase of pericardial volume, as may occur in chest trauma with intrapericardial
hemorrhage, results in marked elevation of pericardial pressure and the potential for severe cardiac
chamber compression. Even lesser amounts of fluid may cause significant elevation of pressure if the
pericardium is pathologically noncompliant and stiff, as may occur in the presence of tumor or
fibrosis of the sac. In contrast, if the pericardial effusion accumulates slowly, over weeks to months,
the pericardium gradually stretches. With this adaptation, the pericardium can accommodate larger
volumes without marked elevation of intrapericardial pressure.