Pericardium and Constrictive Pericarditis

CHAPTER 95 Pericardium and Constrictive Pericarditis





THE PERICARDIUM



History


The earliest descriptions of the pericardium date back to Hippocrates (460 to 377 BC).1 Galen (129 to 210 AD) described the protective function of the pericardium and also reported a pericardial effusion in animals. Avenzoar (1091 to 1162) described pericarditis,2 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 distension, now termed Kussmaul’s sign (as opposed to normal inspiratory jugular venous collapse). Pick (1896) reported three patients with constrictive pericarditis and hepatic cirrhosis (a condition now know as Pick’s 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.3 Histologically, the fibrosa is fibrocollagenous 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.3


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. The anterior pericardium is otherwise separated from the posterior sternum by loose connective tissue and the thymus. 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).3



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.3


The pericardium normally contains 15 to 35 mL of serous fluid. Pericardial fluid is a transudate containing less protein but more albumin than serum. Pericardial fluid therefore has a lower osmolality than does plasma.3



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 pericardial fluid has fibrinolytic properties that can lyse intrapericardial clot.


At rest, the normal pericardium probably has little restraining effect on cardiac systolic or diastolic function.4 However, under conditions of acute cardiac dilation, the normal pericardium probably does increase diastolic stiffness and limit diastolic filling of both left and right ventricles.57 Under normal conditions, relatively little interaction between the left and right ventricles is mediated by the pericardium.8,9


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 (more than 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.10 Eventually, pericardial pressure rises high enough that resorption matches fluid production. Sustained increases in pericardial pressure over time cause the pericardial sac to stretch (as a result 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.3 Cardiac tamponade can result from pericardial fluid, pus, blood, air, or tumor. In a normal pericardium, roughly 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 filing 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.





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 almost always 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).



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 is associated with inspiratory jugular venous distension (Kussmaul’s sign) (see Fig. 95-2), which is less frequent in cardiac tamponade. Kussmaul’s 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.14


The differential diagnosis of constrictive pericarditis consists primarily of restrictive cardiomyopathy which can occur simultaneously with constrictive pericarditis.7,15 Characteristic histology on myocardial biopsy, pulmonary capillary wedge pressure more 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









Magnetic Resonance Imaging


MRI can demonstrate pericardial effusion, pericardial thickening, intrapericardial masses, pericardial cysts, and even intracardiac disease.18 Relative to CT, MRI has the advantages of not requiring intravenous contrast injection and of having less motion artifact. MRI may be less sensitive than CT for detecting pericardial calcification. Newer magnetic imaging techniques such as steady-state free-procession and spin tagging may improve information over older T1- or T2-weighted spin echo techniques.18




Pericardiocentesis


Pericardiocentesis is a means to rapidly treat cardiac tamponade, to prevent tamponade in large effusions, and to obtain pericardial fluid for diagnosis.15 Contraindications include aortic dissection, coagulopathy, small or loculated effusions, traumatic hemopericardium, and nonviral infectious pericarditis. Pericardiocentesis is generally performed with the patient supine and using local anesthesia. A long pericardial needle is inserted into the patient’s pericardial space left of the xiphoid, inferior to the left costal margin (Fig. 95-4). The needle is advanced toward the patient’s left mid scapula while maintaining aspiration pressure on the needle. Cardiac puncture can be avoided by a combination of echocardiography and monitoring an ECG obtained by an electrode attached to the needle. The needle is withdrawn if the ECG shows sudden negative deflection of the QRS complex, indicating contact with the myocardium.


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Jul 30, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Pericardium and Constrictive Pericarditis
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