Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

C h a p t e r 1 9

tamponade is pulsus paradoxus, or an exaggeration of the normal variation in the systolic blood pressure. Pulsus paradoxus is defined as a 10 mm Hg or more fall in the systolic blood pressure that occurs with inspi- ration. 42,43 Normally, the decrease in intrathoracic pres- sure that occurs during inspiration accelerates venous flow, increasing right atrial and right ventricular filling. This causes the interventricular septum to bulge to the left, producing a slight decrease in left ventricular filling, stroke volume output, and systolic blood pressure. In cardiac tamponade, the left ventricle is compressed from within by movement of the interventricular septum and from without by fluid in the pericardium (Fig. 19-17). This produces a marked decrease in left ventricular fill- ing and left ventricular stroke volume output following inspiration. Computed tomography (CT) and magnetic resonance imaging (MRI) are useful adjuncts to echocardiography in cardiac tamponade. The ECG often reveals nonspe- cific T-wave changes and low QRS voltage. Usually only moderate to large effusions can be detected by chest radiography.

Closed pericardiocentesis, in which fluid is removed from the pericardial sac through a needle inserted through the chest wall, may be an emergency lifesaving measure in severe cardiac tamponade. Open pericardio- centesis may be used for recurrent or loculated effusions (i.e., those confined to one or more pockets in the pleu- ral space), during which biopsies can be obtained and pericardial windows created. As with pericardial effu- sion, laboratory evaluation of the pericardial fluid may be used to identify the causative agent. Constrictive Pericarditis In constrictive pericarditis, fibrous scar tissue develops between the visceral and parietal layers of the serous pericardium. In time, the scar tissue contracts and inter- feres with diastolic filling of the heart, at which point cardiac output and cardiac reserve become fixed. It is most commonly associated with inflammation resulting from infections, mediastinal radiation, or cardiac surgi- cal trauma. The condition is characterized by high venous pres- sure, low cardiac output, narrow pulse pressure, and fluid retention. 44 Ascites is a prominent early finding and may be accompanied by pedal edema, dyspnea on exertion, fatigue, and jugular venous distention. The Kussmaul sign is an inspiratory distention of the jugu- lar veins (opposite of normal physiology) caused by the inability of the right atrium, encased in its rigid peri- cardium, to accommodate the increase in venous return that occurs with inspiration. Exercise intolerance, mus- cle wasting, and weight loss develop in end-stage con- strictive pericarditis. Surgical removal or resection of the pericardium (i.e., pericardiectomy) is the treatment of choice. ■■ The major threat of pericardial disorders, which include acute and chronic or recurrent pericarditis, pericardial effusion, cardiac tamponade, and constrictive pericarditis, is compression of the heart chambers. ■■ Acute pericarditis may be infectious in origin or it may be due to systemic diseases. It is characterized by pleuritic chest pain, fever, ECG changes, and pericardial friction rub. Recurrent pericarditis, which is usually associated with autoimmune disorders, often produces few symptoms. ■■ Pericardial effusion, either acute or chronic, refers to the accumulation of fluid or exudate in the pericardial cavity. It can increase intracardiac pressure, compress the heart, and interfere with venous return to the heart.The amount of fluid SUMMARY CONCEPTS

Pericardium

Left ventricle

Normal expiration

Normal inspiration

Tamponade (in inspiration)

FIGURE 19-17. Effects of respiration and cardiac tamponade on ventricular filling and cardiac output. During inspiration, venous flow into the right heart increases, causing the interventricular septum to bulge into the left ventricle. This produces a decrease in left ventricular volume, with a subsequent decrease in stroke volume output. In cardiac tamponade, the fluid in the pericardial sac produces further compression of the left ventricle, causing an exaggeration of the normal inspiratory decrease in stroke volume and systolic blood pressure.

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