Porth's Essentials of Pathophysiology, 4e

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Circulatory Function

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also develop with neoplasms, cardiac surgery, or trauma. Pericardial effusion exerts its effects through compres- sion of the heart chambers. The normal pericardial space contains about 15 to 50 mL of fluid. Increases in the volume of this fluid, the rapidity with which it accumulates, and the elasticity of the pericardium deter- mine the effect that the effusion has on cardiac function. Small pericardial effusions may produce no symptoms or abnormal clinical findings. Even a large effusion that develops slowly may cause few or no symptoms, provided the pericardium is able to stretch and avoid compressing the heart. However, a sudden accumula- tion of even 200 mL may raise intracardiac pressure to levels that significantly limit venous return of blood to the heart. Symptoms of cardiac compression also may occur with relatively small accumulations of fluid if the pericardium has become thickened by scar tissue or neo- plastic infiltrations and loses its elasticity. The echocardiogram is a rapid, accurate, and widely used noninvasive method of evaluating pericardial effu- sion. Treatment depends on the extent of the effusion. In small pericardial effusions, diuretics are given to remove the fluid, and NSAIDs, colchicine, or corticosteroids may minimize fluid accumulation. Pericardiocentesis, or removal of fluid from the pericardial sac, often with the aid of echocardiography, is the initial treatment of choice for larger effusions. Aspiration of fluid with labo- ratory evaluation of the pericardial fluid may be used to identify the causative agent. CardiacTamponade Pericardial effusion can lead to or may initially pres- ent as a condition called cardiac tamponade, in which there is compression of the heart due to the accumula- tion of fluid or blood in the pericardial sac. This life- threatening condition can be caused by bleeding into the pericardial sac after blunt or penetrating trauma, rupture of the heart following myocardial infarction, complications during percutaneous cardiac procedures or device placement, or retrograde bleeding during aor- tic dissection. 42,43 Cardiac tamponade results in increased intracardiac pressure, progressive limitation of ventricular diastolic filling, and reductions in stroke volume and cardiac out- put. In other words, the heart cannot fill properly with blood. The severity of the condition depends on the vol- ume of fluid present and the rate at which it accumu- lates. Rapid accumulation results in an elevated central venous pressure, jugular vein distention, a fall in systolic blood pressure, narrowed pulse pressure, and signs of circulatory shock. The heart sounds may become muf- fled because of the insulating effects of the pericardial fluid and reduced cardiac function. Persons with slowly developing cardiac tamponade usually appear acutely ill, but not to the extreme seen in those with rapidly devel- oping tamponade. A significant accumulation of fluid in the pericar- dium results in increased sympathetic nervous system stimulation, which leads to tachycardia and increased cardiac contractility. A key diagnostic finding in cardiac

mycobacterial infections, connective tissue diseases (e.g., systemic lupus erythematosus, rheumatoid arthritis), ure- mia, postcardiac surgery, neoplastic invasion of the peri- cardium, radiation, trauma, drug toxicity, and contiguous inflammatory processes of the myocardium or lung. 42,43 Similar to other inflammatory processes, acute peri- carditis is associated with local vasodilation, increased capillary permeability, and accumulation of white blood cells. The capillaries that supply the serous pericardium become permeable, allowing plasma proteins, including fibrinogen, to exit the capillaries and enter the pericar- dial space. This results in an exudate that varies in com- position and amount according to the causative agent. Acute pericarditis frequently is associated with an exu- date containing protein and fibrin and heals by reso- lution or progresses to form scar tissue and adhesions between the layers of the serous pericardium. The manifestations of acute pericarditis include a triad of chest pain, an auscultatory pericardial friction rub, and electrocardiographic (ECG) changes. The clinical find- ings may vary according to the causative agent. Nearly all persons with acute pericarditis have chest pain and fever. The pain usually is sharp and abrupt in onset, occurring in the precordial area, and may radiate to the neck, back, abdomen, or side. Pain in the scapular area may result from irritation of the phrenic nerve. The pain typically is pleuritic (aggravated by inspiration and coughing) and positional (decreases with sitting and leaning forward) because of changes in venous return and cardiac filling. These pain characteristics differentiate pericarditis from acute myocardial infarction or pulmonary embolism. A pericardial friction rub (auscultated through the dia- phragm of a stethoscope), often described as “leathery” or “close to the ear,” results from the rubbing and fric- tion between the inflamed pericardial surfaces. 43 Diagnosis of acute pericarditis is based on clinical manifestations, ECG, chest radiography, and echocar- diography, with laboratory tests being used to confirm the diagnosis. Treatment depends on the cause. When an infection is present, antibiotics specific for the causative agent are prescribed. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) may be given to min- imize the inflammatory response and the accompanying undesirable effects. Recurrent pericarditis can occur in up to 30% of persons with acute pericarditis who responded satisfac- torily to treatment. 42 A minority of these develop recur- rent bouts of pericardial pain, which can sometimes be chronic and debilitating. The process commonly is associated with autoimmune disorders, such as lupus erythematosus, rheumatoid arthritis, scleroderma, and myxedema, but may also occur following viral pericardi- tis. Treatment includes the use of anti-inflammatory med- ications such as NSAIDs, corticosteroids, or colchicine. Pericardial Effusion Pericardial effusion is the accumulation of fluid in the pericardial cavity, usually as a result of an inflammatory or infectious process that includes pericarditis. It may