Pericardial effusion pathophysiology


 * Associate Editor-In-Chief: Varun Kumar, M.B.B.S.

Overview
Excess fluid accumulation in pericardial cavity is termed pericardial effusion. This can occur either due to increased production of pericardial fluid (infections and inflammations) or inadequate drainage of the fluid (malignancy or hypothyroidism).

Pathophysiology
Pericardium surrounds the heart and it consists of two layers, parietal and visceral layers. The space between the layers is known as the pericardial cavity. It usually contains small amount of fluid, approximately 15-50ml which acts as lubricating agent between the layers. This fluid enters the pericardial space from the capillaries in visceral pericardium. This fluid is drained by lymphatics. When this fluid production-drainage mechanism is altered, excess fluid accumulates in pericardial cavity and this is termed as pericardial effusion.

Therefore, pericardial effusion ensues when there is:
 * Increased production of pericardial fluid.
 * Decreased drainage of pericardial fluid.

Increased production of pericardial fluid
Increased production of pericardial fluid can occur secondary to:

1. Increased capillary membrane permeability due to pericardial inflammation may lead to exudative fluid or hemorrhagic effusion which have high protein levels:
 * Viral/bacterial infections such as adenovirus infection and tuberculosis.
 * Auto-immune diseases such as sarcoidosis, SLE and rheumatoid arthritis.
 * Penetrating trauma which injure the blood vessels and cause hemorrhage into the pericardial space.
 * Malignancies such as pulmonary carcinomas may metastasize to pericardium and can disrupt pericardial anatomy and vasculature.


 * The above mentioned causes may lead to exudative fluid or hemorrhagic effusion which have high protein levels.

2. Increased microvascular pressure as observed in hypervolemic states such as cardiac failure.

3. Decreased plasma oncotic pressure secondary to hypoalbuminemia which can be observed in cirrhosis, nephrotic syndrome.

Decreased drainage of pericardial fluid
Decreased drainage of pericardial fluid through lymphatics may be observed in:

1. Malignancies

2. Hypothyroidism

Clinical manifestations of pericardial effusion depend on the rate of accumulation of fluid in the pericardial cavity. Rapid accumulation may cause elevated intrapericardial pressures with as little as 80 mL of fluid, while gradual accumulation of fluid can grow to 2 liters without symptoms.