The pericardium envelops the heart and portions of the great vessels as a protective capsule. When incised longitudinally and transversely along the diaphragm it can be suspended to present the heart for surgical procedures. The surgical importance of the pericardium stems from its involvement in alterations of cardiac filling. When the limited space between the noncompliant pericardium and heart acutely fills with fluid, cardiac compression and tamponade may ensue. Constrictive disorders arise when inflammation and scarring cause the pericardium to shrink and densely adhere to the surface of the heart. This chapter discusses pericardial anatomy and function and describes the conditions that commonly give rise to the surgical problems of pericardial constriction and tamponade. The chapter also describes the diagnosis and therapy of these entities, the management of effusions and tamponade early and late after cardiac surgery, and the rationale for and against pericardial closure at the time of cardiac surgery.

The pericardium serves two major functions. It maintains the position of the heart within the mediastinum and prevents cardiac distention by sudden volume overload. The pericardium attaches to the ascending aorta just inferior to the innominate vein and the superior vena cava (SVC) several centimeters above the sinoatrial node. The pericardial reflection encompasses the superior and inferior pulmonary veins and encircles the inferior vena cava (IVC), thereby making it possible for the surgeon to control the IVC from within the pericardium. The pericardial reflection attaches to the left atrium near the entrances of the pulmonary veins just below the atrioventricular groove (Fig. 57-1). The pericardiophrenic arteries that travel with the phrenic nerves as well as the branches of the internal mammary arteries and feeder branches directly from the aorta perfuse the pericardium. It is innervated by vagal fibers from the esophageal plexus, and the phrenic nerves course within it.

The pericardium is a conical fibroserous sac made up of two intimately connected layers. The inner layer (serous pericardium) is a transparent monolayer of mesothelial cells. The visceral portion of the serous pericardium, or epicardium, and the parietal portion, which lines the fibrous pericardial sac, are continuous. The oblique sinus lies within the venous confluence and the transverse sinus lies between the arterial (aorta and pulmonary artery) and venous reflections (dome of left atrium and SVC). Such potential spaces allow the pericardium to expand and accommodate a limited amount of fluid. Normal pericardial fluid volume is approximately 10 to 20 mL. The pericardial mesothelial cells contain dense microvilli, which are 1 μm wide and 3 μm high, and facilitate fluid and ion exchange.¹ Visceral pericardial lymphatic drainage occurs via the tracheal and bronchial mediastinal nodes, whereas lymphatic drainage of the parietal pericardium occurs via the anterior and posterior mediastinal lymph nodes.

The parietal layer, or fibrous pericardium, is composed mostly of dense parallel bundles of collagen, which render this layer relatively noncompliant. Because the pericardium is stiffer than cardiac muscle, it tends to equalize the compliance of both ventricles. By doing so, the pericardium contributes to the resting cavitary diastolic pressure of both ventricles, maximizing diastolic ventricular interaction.² An example of this phenomenon is the diminution of systemic arterial pressure during inspiration. Intrapericardial pressure tends to approximate pleural pressure, and varies with respiration. The negative intrathoracic pressure generated during inspiration augments right ventricular filling. The interventricular septum shifts leftward to accommodate the increase in right ventricular volume and therefore impairs left ventricular filling. Impaired left ventricular filling translates to decreased cardiac output and a slight diminution in systemic blood pressure during inspiration. This phenomenon is greatly magnified with an increase in intrapericardial pressure (eg, during acute filling of the pericardial space or circulatory volume overload), resulting in pulsus paradoxus.³

Most congenital abnormalities of the pericardium are asymptomatic and are often incidentally discovered at the time of surgery or investigation of unrelated problems.^4,5 They are rare, and one-third are associated with cardiac, skeletal, and pulmonary abnormalities.⁶ Partial absence of the pericardium can occur and is most commonly seen on the left (70%) due to premature atrophy of the left common cardinal vein. Right-sided and complete defects of the pericardium account for 17 and 13% of these defects, respectively. The right duct of Cuvier goes on to form the SVC and ensures closure of the right pleuropericardial membrane.⁷ Accordingly, right-sided defects tend to be lethal. Magnetic resonance imaging (MRI), CT, and echocardiography are useful for evaluating patients with pericardial defects. MRI provides excellent pericardial imaging without contrast and is therefore the imaging modality of choice. CT and echocardiography are useful for evaluation of pericardial thickening and the extent and location of defects.⁴ Although complete pericardial agenesis is rarely clinically significant, unilateral absence is potentially problematic because it may accentuate cardiac mobility, allowing the heart to be displaced into the pleural space with consequent incarceration of the left atrial appendage or left ventricle. Treatment may involve pericardial resection or replacement with a prosthetic patch.⁶ Both therapies appear to yield good outcomes.

Pericardial cysts are the most common congenital pericardial disorder, surpassed only by lymphoma as the most prevalent of middle mediastinal masses.⁸ They occur as asymptomatic incidental findings in 75% of patients; 70% occur in the right costophrenic angle and 22% in the left.⁵ They do not communicate with the pericardial space and are typically unilocular, smooth, and less than 3 cm in diameter (Fig. 57-2). When present, symptoms may include chest pain, dyspnea, cough, and arrhythmias, probably owing to compression and inflammatory involvement of adjacent structures. They can also become secondarily infected.⁹ Contrast CT is the imaging modality of choice for diagnosis and surveillance.^10,11 Observation with serial CT scanning in asymptomatic patients is suggested. Percutaneous aspiration is associated with a 30% recurrence rate at 3 years. Sclerosis has been reported to decrease recurrence after aspiration.¹² Indications for resection include large size, symptoms, patient concern, and question of malignancy.⁸ Video-assisted thoracoscopy is the surgical approach most commonly used for excision. Infrasternal mediastinoscopy can be used for anterior cysts. Thoracotomy is also an acceptable technique. Surgery is the only definitive cure.¹²

Pericardial compression results from disturbance of the normal anatomical and physiologic relationships among the pericardium, pericardial cavity, and heart. Because the pericardium is relatively noncompliant and pericardial fluid noncompressible, the heart alone must compensate for acute changes in pericardial pressure. Acute volume overload within the fixed pericardial space results in a rapid, nonlinear increase in intrapericardial pressure (Fig. 57-3), producing cardiac compression.¹³ The anatomic basis for pericardial compression involves either a space-occupying lesion (eg, cyst or excessive fluid) within the pericardial space or pericardial constriction.

Tamponade

Although blood in the pericardial space is the most common etiology, effusions, clot, pus, gas, or any combination of these can also produce tamponade. As fluid entering the pericardial space rapidly exceeds the pericardial reserve volume intrapericardial pressure rises abruptly. At this point, pericardial fluid volume can only increase by reducing cardiac chamber volumes. Because of its lower filling pressures, the right heart is more susceptible to compression (Fig. 57-4). The physiologic consequences are impaired diastolic filling with decreased cardiac output and increased central venous pressure.¹⁴ Clinical manifestations include hypotension, jugular venous distention, and decreased heart sounds (Beck’s triad).

To preserve cardiac output, higher pressures are required to fill the cardiac chambers, which may be partially achieved by parallel increases in systemic and pulmonary venous pressure by vasoconstriction.¹⁵ Other compensatory mechanisms include tachycardia, chronic pericardial stretch, and blood volume expansion.¹⁶ The latter two mechanisms have little impact in acute tamponade. As tamponade progresses, right heart filling becomes increasingly volume dependent and limited to inspiration, when pericardial pressure is lower. Increased right ventricular filling causes it to encroach on, and impair, left ventricular filling. However, during expiration the converse is true, and left ventricular filling and output increase. This exaggeration of physiologic ventricular interdependence is the basis of pulsus paradoxus.¹³

The clinical presentation of tamponade varies widely depending on the severity of hemodynamic impairment and the degree of physiologic reserve. Rapid accumulation of as little as 100 mL of fluid in the pericardial space (eg, after a penetrating cardiac wound) may exceed the limited compliance of the parietal pericardium and produce critical tamponade. On the other hand, in chronic inflammatory conditions (eg, rheumatoid arthritis) the pericardium may compensate for large pericardial effusions, exceeding 1 L. The cardiac silhouette may appear normal in acute tamponade, but chronic pericardial distension is often obvious on plain chest radiography (Fig. 57-5), chest CT (Fig. 57-6), and echocardiography (Fig. 57-7). Low-pressure tamponade can also occur, in which a pericardial effusion is not hemodynamically significant until the patient becomes hypovolemic, typically from dehydration, blood loss, or diuretic therapy. Venous filling pressures may be normal or mildly elevated in this setting, making this diagnosis difficult.¹⁷

Pericardial Constriction

A variety of conditions promote pericardial scar formation, the pathologic process underlying constrictive pericarditis (CP). As with tamponade, the physiologic basis is compromised cardiac filling leading to systemic venous congestion and low cardiac output. In contrast with tamponade, however, onset is often insidious and symptoms may be present for months to years.¹⁸ Common complaints include fatigue, decreased exercise tolerance with dyspnea/orthopnea, as well as peripheral edema and ascites from hepatic congestion in advanced disease. The principal etiologies behind pericardial scar formation have shifted over time, with a declining incidence of infectious cases (eg, tuberculosis) and an increasing incidence of iatrogenic cases (eg, mediastinal radiation therapy, cardiac surgery).¹⁹

Pericardial constriction exerts its pathophysiologic effects by limiting cardiac filling. Unlike tamponade, in which cardiac filling is limited from the onset of diastole, pericardial constriction does not restrict filling in early diastole. Later in diastolic filling the ventricles are prevented from reaching full capacity as they encounter the contracted and noncompliant pericardium. As a result, 70 to 80% of diastolic filling occurs in the first 25 to 30% of diastole, after which diastolic pressures increase abruptly.²⁰ The ventricular free walls are then immobilized, leaving the interventricular septum as the last yielding structure; it is rapidly displaced in response to the sudden interventricular pressure differential. This produces the characteristic “septal bounce” seen echocardiographically. Other echocardiographic findings include pericardial thickening, caval plethora, and small chamber volumes. Inspiration exaggerates leftward septal deviation and reciprocal Doppler flows between the right and left sides (the echocardiographic correlate of pulsus paradoxus).

Modern axial imaging with CT (Fig. 57-8) and MRI (Fig. 57-9) are often able to visualize thickened and/or calcified pericardium, with or without coexisting effusion. Dynamic CT and MRI also demonstrate many of the physiologic features seen with echocardiography.²¹ Importantly, although pericardial thickening is usually present in CP, it is possible to have CP with normal pericardial thickness, as well as pericardial thickening without CP.²²

Prior to the modern era of echocardiography and axial imaging, the diagnosis of CP was dependent on hemodynamic tracings obtained during cardiac catheterization. The sudden increase in diastolic ventricular pressure is reflected in the dip and plateau, or “square-root” sign (Fig. 57-10). Similarly, right atrial pressure tracings reveal a steep y descent, which correlates with the nadir of the square-root sign. Under normal circumstances, inspiration results in a 3 to 7-mm Hg drop in right atrial pressure. The high pressure of pericardial constriction prevents the right atrium from accepting inspiratory acceleration of blood from the central veins. Instead, neck veins become distended during inspiration in patients with CP, a phenomenon known as Kussmaul’s sign.

Catheterization can help differentiate CP from restrictive cardiomyopathy (RCM).^23,24 RCM is characterized by noncompliant ventricular muscle and diastolic dysfunction, which impede cardiac filling. RCM is caused by a variety of infiltrative or fibrosing conditions (eg, amyloidosis, sarcoidosis, radiation, and carcinoid). Although RCM may mimic many of the presenting features of CP, it is not a surgical disease and therefore must be distinguished from CP (Table 57-1). Systolic ventricular function may be normal or near-normal in both conditions, but pulmonary and hepatic congestion are often present in RCM. Evidence of pericardial thickening (>2 mm) favors but does not confirm the diagnosis of CP over RCM. There are instances, particularly in radiation-induced CP, in which the conditions can coexist, making diagnosis challenging. Amyloidosis and other infiltrative conditions that cause RCM may demonstrate distinctive myocardial speckling on echocardiography. Endomyocardial biopsy is useful to establish the presence of one of the conditions known to be associated with RCM; unfortunately, a negative biopsy does not rule it out.

In an attempt to provide additional criteria to differentiate CP from RCM, Hurrell et al measured respiratory variation of the gradient between left ventricular pressure and pulmonary capillary wedge pressure during the rapid filling phase of diastole.²⁵ This was done to assess the dissociation of intrathoracic and intracardiac pressures that accompanies CP. A difference of 5 mm Hg in the gradient between inspiratory and expiratory cycles had a 93% sensitivity and a 81% specificity for CP. Furthermore, increased ventricular interdependence was assessed by comparing left and right ventricular systolic pressures during respiration. Although concordant increases in left and right ventricular systolic pressure are expected during inspiration, discordant pressures are encountered during inspiration in patients with CP. This finding has 100% sensitivity and 95% specificity for CP.

Pericarditis, the most common pericardial disorder, has many etiologies (Table 57-2), including infectious (viral, bacterial, fungal), metabolic (uremic, drug induced), autoimmune (arthritis, thyroid), postradiation, neoplastic, traumatic, postinfarction (Dressler’s syndrome, 10–15%), postpericardiotomy (5–30%), and idiopathic (Fig. 57-11). The clinical syndrome for all causes is similar. Chest pain (dull, aching, pressure, tightness) is usually present and may be associated with constitutional symptoms (eg, weakness and malaise), fever (occasionally with rigors), and other symptoms, such as cough or odynophagia. The pain may be pleuritic, and thus exacerbated by inspiration, cough, or recumbency. These patients therefore often sit up and lean forward for relief. Acute disease may become chronic. The cardinal sign of pericarditis is a pericardial rub, which may be positional and muffled because of an effusion.²⁶