Pericardial effusion

A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous connective membrane and an inner two-layered serous membrane. The two layers of the serous membrane enclose the pericardial cavity (the potential space) between them. This pericardial space contains a small amount of pericardial fluid, normally 15-50 mL in volume. The pericardium, specifically the pericardial fluid provides lubrication, maintains the anatomic position of the heart in the chest (levocardia), and also serves as a barrier to protect the heart from infection and inflammation in adjacent tissues and organs.

By definition, a pericardial effusion occurs when the volume of fluid in the cavity exceeds the normal limit. If large enough, it can compress the heart, causing cardiac tamponade and obstructive shock. Some of the presenting symptoms are shortness of breath, chest pressure/pain, and malaise. Important etiologies of pericardial effusions are inflammatory and infectious (pericarditis), neoplastic, traumatic, and metabolic causes. Echocardiogram, CT and MRI are the most common methods of diagnosis, although chest X-ray and EKG are also often performed. Pericardiocentesis may be diagnostic as well as therapeutic (form of treatment).

Pericardial effusion presentation varies from person to person depending on the size, acuity and underlying cause of the effusion. Some people may be asymptomatic and the effusion may be an incidental finding on an examination. Others with larger effusions may present with chest pressure or pain, dyspnea, shortness of breath, and malaise (a general feeling of discomfort or illness). Yet others with cardiac tamponade, a life-threatening complication, may present with dyspnea, low blood pressure, weakness, restlessness, hyperventilation (rapid breathing), discomfort with lying flat, dizziness, syncope or even loss of consciousness. This causes a type of shock, called obstructive shock, which can lead to organ damage.

Non-cardiac symptoms may also present due to the enlarging pericardial effusion compressing nearby structures.  Some examples are nausea and abdominal fullness, dysphagia and hiccups, due to compression of stomach, esophagus, and phrenic nerve respectively.

Any process that leads to injury or inflammation of the pericardium or inhibits appropriate lymphatic drainage of the fluid from the pericardial cavity leads to fluid accumulation. Pericardial effusions can be found in all populations worldwide but the predominant etiology has changed over time, varying depending on the age, location, and comorbidities of the population in question. Out of all the numerous causes of pericardial effusion, some of the leading causes are inflammatory, infectious, neoplastic and traumatic. These causes can be categorized into various classes, but an easy way to understand them is dividing them into inflammatory versus non-inflammatory. ^{[citation needed]}

How much fluid is stored in the pericardial sac at one particular time is based on the balance between production and reabsorption. Studies have shown that much of the fluid that accumulates in the pericardial sac is from plasma filtration of the epicardial capillaries and a small amount from the myocardium, while the fluid that is drained is mostly via the parietal lymphatic capillaries. Pericardial effusion usually results from a disturbed equilibrium between these two processes or from a structural abnormality that allows excess fluid to enter the pericardial cavity. Because of the limited amount of anatomic space in the pericardial cavity and the limited elasticity of the pericardium, fluid accumulation beyond the normal amount leads to an increased intrapericardial pressure which can negatively affect heart function. ^{[citation needed]}

A pericardial effusion with enough pressure to adversely affect heart function is called cardiac tamponade. Pericardial effusions can cause cardiac tamponade in acute settings with fluid as little as 150mL. In chronic settings, however, fluid can accumulate anywhere up to 2L before an effusion causes cardiac tamponade. The reason behind this is the elasticity of the pericardium. When fluid fills the cavity rapidly, the pericardium cannot stretch rapidly, but in chronic effusions, the gradual fluid collection provides the pericardium enough time to accommodate and stretch with the increasing fluid levels.

Patients with pericardial effusion may have unremarkable physical exams but often present with tachycardia, distant heart sounds and tachypnea. A physical finding specific to pericardial effusion is dullness to percussion, bronchial breath sounds and egophony over the inferior angle of the left scapula. This phenomenon is known as Ewart's sign and is due to compression of the left lung base.