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Pericardium and Constrictive Pericarditis
The Pericardium
History
The earliest descriptions of the pericardium date back to Hippocrates (460 to 377 bc ). Galen ( ad 129 to 210) described the protective function of the pericardium and also reported a pericardial effusion in animals. Avenzoar (1091 to 1162) described pericarditis, and Vesalius (1514 to 1564) carefully documented the anatomy of the pericardium. Jean Riolan (1649) suggested treating pericarditis with trephination of the sternum, and a case of hemopericardium was reported by William Harvey (1649). The conditions of cardiac tamponade and constrictive pericarditis were described by Richard Lower (1669), John Mayow (1674), and Morgagni (1756). The pathophysiology of constrictive pericarditis was further clarified by Cheevers in 1842.
Kussmaul (1873) noted the association between constrictive pericarditis and decreased intensity of the peripheral pulse (now termed pulsus paradoxus). Kussmaul also described inspiratory jugular venous distention, now termed Kussmaul sign (as opposed to normal inspiratory jugular venous collapse ). Pick (1896) reported three patients with constrictive pericarditis and hepatic cirrhosis (a condition now known as Pick cirrhosis ).
The first successful pericardiotomy was performed by Romero in 1819, and the first pericardiocentesis was performed by Franz Schuh in 1840. Pericardial resection for constrictive pericarditis was proposed by Weill (1895) and Delorme (1898), with pericardiectomy ultimately performed by Rehn (1913) and Sauerbruch (1925). Early surgical treatment of constrictive pericarditis in the United States was reported by Beck (1930), Churchill (1936), and Blalock (1937). Radical pericardiectomy, including excision of thickened epicardium when necessary, was advocated by Holman (1955).
Anatomy
The pericardium is a fibrous sac surrounding the heart and mediastinal great vessels. The outer wall of the pericardial sac consists of an outer fibrosa and an inner serosa. Histologically, the fibrosa is fibro-collagenous tissue with elastic fibers oriented along the lines of stress, and the pericardial serosa is composed of mesothelial cells with microvilli and an underlying basal lamina.
This outer pericardial sac folds onto the heart and great vessels, where the epicardium and outer adventitial layer of the heart and great vessels constitute the visceral lining of the pericardial sac. Laterally, the pericardium forms the medial walls of the pleural spaces. Inferiorly, the pericardium is the superior surface of the central tendon of the diaphragm, and, superiorly, the pericardium blends with the deep cervical fascia. Anteriorly, the pericardium is loosely joined to the xiphoid process and the sternal manubrium by ligamentous structures. Posteriorly and superiorly, the pericardium envelops the great vessels, the venae cavae, and the pulmonary veins. The posterior pericardial space has two developmental recesses: the transverse sinus separating the great vessels from the pulmonary veins and the oblique sinus separating the left and right pulmonary veins ( Fig. 95-1 ).
The arterial blood supply and venous drainage of the pericardium come from the pericardiophrenic branches of the internal mammary vessels bilaterally. The lymphatic drainage of the visceral pericardium is the tracheal and bronchial lymph chain, and the parietal pericardium shares lymphatic drainage with the sternum, diaphragm, and mid mediastinum. The pericardium is innervated from the phrenic nerves, with some vagal innervation via the esophageal plexus.
The pericardium normally contains 15 to 35 mL of serous fluid. Pericardial fluid is a transudate containing less protein but more albumin than serum; therefore, pericardial fluid has a lower osmolality than does plasma.
Normal Physiology
The pericardium and pericardial fluid minimize friction and energy loss during cardiac motion. While doing so, the normal pericardium and its external attachments maintain cardiac position within the mediastinum in the presence of gravitational or other forces that could impair cardiac filling or function. The pericardium also serves as a barrier, protecting the heart from inflammation or malignancy in adjacent structures.
The normal pericardium has mechanoreceptors connected to phrenic nerve and vagal nerve afferents, which (with stimulation) lower blood pressure, slow heart rate, and contract the spleen in dogs. Pericardial fluid contains prostacyclin, which can affect coronary artery vasomotor tone, and it has fibrinolytic properties that can lyse intrapericardial clot.
At rest, the normal pericardium probably has little restraining effect on cardiac systolic or diastolic function. However, under conditions of acute cardiac dilation, the normal pericardium probably increases diastolic stiffness and limits diastolic filling of the left and right ventricles. Under normal conditions, relatively little interaction between the left and right ventricles is mediated by the pericardium.
Normal pericardial pressure at end expiration is −2 mm Hg. Like pleural pressure, pericardial pressure decreases during inspiration and increases during expiration. As a result, inspiration normally decreases left ventricular stroke volume and decreases aortic blood pressure by less than 10 mm Hg. The mechanisms for these effects do not require an intact pericardium and are similar to the mechanisms of pulsus paradoxus (see later).
Pathophysiology
Pericardial Effusion
Pericardial effusion (>50 to 100 mL) is the simple result of more fluid transuding into the pericardial space than is resorbed. Pericardial effusions requiring drainage typically contain 500 to 700 mL of fluid. Eventually, pericardial pressure rises high enough that resorption matches fluid production. Sustained increases in pericardial pressure over time cause the pericardial sac to stretch (because of material plasticity, or creep) with slippage of pericardial collagen fibers and pericardial thinning. Causes of increased pericardial fluid production include inflammation or infection of the pericardium. Decreased pericardial fluid resorption can result from venous hypertension or lymphatic obstruction. If pericardial effusion increases pericardial pressure sufficiently, cardiac tamponade and pulsus paradoxus can result (see later).
Cardiac Tamponade
Cardiac tamponade has been defined as hemodynamically significant cardiac compression from accumulating pericardial contents that evoke and defeat compensatory mechanisms. Cardiac tamponade can result from pericardial fluid, pus, blood, air, or tumor. In a normal pericardium, approximately 200 mL of acute pericardial fluid accumulation can produce tamponade, but larger volumes may be required in chronically enlarged pericardial sacs.
The initial effect of cardiac tamponade is decreased venous return to the right heart resulting from a direct pressure effect and from effectively decreased right atrial and right ventricular diastolic compliance. Decreased right ventricular filling decreases stroke volume and thus cardiac output. Pulmonary venous return to the left heart is decreased by increased left atrial pressure and by decreased right ventricular output. Central venous pressures of 14 to 30 mm Hg are typically associated with cardiac tamponade in euvolemic individuals, and lower venous pressures can occur with cardiac tamponade if hypovolemia is also present.
Left ventricular diastolic compliance and diastolic filling are also impaired by cardiac tamponade. Increased diastolic right ventricular pressure relative to left ventricular diastolic pressure can shift the interventricular septum leftward, thus decreasing preload of the interventricular septum and effectively decreasing left ventricular contractility. By combining these mechanisms, inspiration with cardiac tamponade can decrease systolic blood pressure by greater than 10 mm Hg (see Pulsus Paradoxus , next). Eventually, arterial hypotension and increased intrapericardial pressure can decrease coronary perfusion sufficiently to decrease cardiac contractility caused by global cardiac ischemia.
Diagnostic signs of cardiac tamponade are listed in Box 95-1 .
Box 95-1
Diagnostic Signs of Cardiac Tamponade
Physical Examination
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Pulsus paradoxus
Pulmonary Artery Catheter Findings
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Central venous pressure > 14 mm Hg
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Near equalization of central venous, pulmonary artery, and capillary wedge pressures in diastole
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Decreased cardiac output
Echocardiography
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Right atrial compression
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Right ventricular diastolic collapse
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Inferior vena caval dilation
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Inspiratory shift of interventricular septum leftward
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Inspiratory flow velocities: ↑ tricuspid and pulmonic, ↓ mitral and aortic
Pulsus Paradoxus
Cardiac tamponade is associated with pulsus paradoxus, which is defined as a fall in systolic blood pressure of greater than 10 mm Hg with inspiration. Pulsus paradoxus is thus an exaggeration of the normal inspiratory decrease in systolic blood pressure because of the same mechanisms (see Normal Physiology , earlier). Although pulsus paradoxus is characteristic of cardiac tamponade, pulsus paradoxus can also be seen in chronic obstructive pulmonary disease, pulmonary embolism, obesity, right heart failure, and ascites, where it occurs by the same mechanisms. Pulsus paradoxus may be absent in cardiac tamponade with severe left ventricular dysfunction, atrial septal defect, severe aortic regurgitation, or positive pressure breathing. Proposed mechanisms of pulsus paradoxus include the following:
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Pooling of blood in the lungs during inspiration
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Increased right ventricular filling during inspiration resulting from lower right ventricular pressure (in turn, right ventricular distention may shift the interventricular septum leftward, thus decreasing septal muscle preload and decreasing left ventricular stroke volume)
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Increased left ventricular afterload (aortic pressure minus pericardial pressure), which decreases left ventricular stroke work
Constrictive Pericarditis
Constrictive pericarditis results when the volume of the pericardial sac itself is sufficiently reduced relative to cardiac volume that cardiac filling is impaired. In constrictive pericarditis, pericardial fluid is generally absent or of normal volume. The wall of the pericardial sac is usually thickened in constrictive pericarditis and may be 3 to 20 mm thick, as opposed to the 1- to 2-mm thickness of normal pericardium ( Box 95-2 ).
Box 95-2
Diagnostic Signs of Constrictive Pericarditis
Physical Examination
-
Kussmaul sign
Pulmonary Artery Catheter Findings
-
Central venous pressure > 14 mm Hg
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Near equalization of central venous, pulmonary artery, and capillary wedge pressures in diastole
-
Decreased cardiac output
-
Square root sign in right and left ventricular pressure tracings
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Prominent y descent in central venous pressure tracing
Echocardiography, Computed Tomography, or Magnetic Resonance Imaging
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Impaired right and left ventricular free wall strains relative to septal strain
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Pericardial thickening
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Right ventricular diastolic collapse
-
Minimal pericardial fluid
Unlike cardiac tamponade, constrictive pericarditis impairs cardiac filling only in late diastole. Thus, early diastolic filling of the right ventricle occurs briefly in constrictive pericarditis until the ventricle suddenly reaches the rigid constraint of the pericardium. The result is the pathognomonic “square root” sign in the right and left ventricular diastolic filling pressure waveforms ( Fig. 95-2 ).
Similarly, in constrictive pericarditis, the central venous pressure tracing has a prominent y descent that corresponds to the initial dip of the square root sign of the right and left ventricular tracings. This y descent normally results from “diastolic collapse” of the normal venous pressure as rapid atrial filling occurs, and the y descent is exaggerated by constrictive pericarditis. Constrictive pericarditis impairs reservoir function and contractile function of the left atrium. Constrictive pericarditis also selectively impairs contractile function in the left and right ventricular free walls relative to that of the interventricular septum on magnetic resonance imaging.
Constrictive pericarditis is associated with inspiratory jugular venous distention (Kussmaul sign; see Fig. 95-2 ), which is less frequent in cardiac tamponade. Kussmaul sign can also occur in right ventricular failure, restrictive cardiomyopathy, cor pulmonale, and acute pulmonary embolism.
Chronic elevation of venous pressures in constrictive pericarditis can result in hepatic congestion, cardiac cirrhosis, protein-losing enteropathy, and nephrotic syndrome. Chronically, constrictive pericarditis alters the neurohormonal axis with elevations of serum norepinephrine, renin, aldosterone, cortisol, growth hormone, and atrial natriuretic peptide.
The differential diagnosis of constrictive pericarditis consists primarily of restrictive cardiomyopathy, which can occur simultaneously with constrictive pericarditis. Characteristic histology on myocardial biopsy, pulmonary capillary wedge pressure greater than 5 mm Hg greater than central venous pressure, slower early diastolic filling, and impaired left ventricular systolic function all favor restrictive cardiomyopathy over constrictive pericarditis. Acute volume loading of 500 mL during right heart catheterization accentuates the right-sided pressure findings of constrictive pericarditis and produces smaller changes in restrictive cardiomyopathy.
Diagnosis of Pericardial Disease
History and Symptoms
The presenting symptoms of pericardial disease can include fever, malaise, chest discomfort, shortness of breath, pedal edema, and abdominal distention. Medical history may reveal prior chest trauma, chest irradiation, or exposure to infectious agents such as Mycobacterium tuberculosis . The time course of pericardial disease is described as acute (<3 months), chronic (>3 months), or recurrent .
Physical Examination
Physical examination of the patient with pericardial disease may reveal findings of fever, tachycardia, or tachypnea. The peripheral arterial pulse may paradoxically diminish during inspiration (pulsus paradoxus). Inspiratory jugular venous distention may be present (Kussmaul sign). Chest examination may show dullness at the lung bases, muffled cardiac sounds, and a pericardial rub or pericardial knock. A prominent S 3 gallop may be present in constrictive pericarditis. Abdominal examination may demonstrate hepatomegaly or ascites, and pedal edema may be present. The extremities may be cool and constricted in tamponade.
Chest Radiograph
The chest radiograph may show cardiomegaly in pericardial effusion. Pericardial calcification can accompany constrictive pericarditis. Pleural effusion may be present in pericardial effusion, pericardial tamponade, and constrictive pericarditis. Chest radiography may also demonstrate pneumopericardium or mediastinal mass resulting from pericardial cyst.
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