Pericardial diseases are an interesting and diverse group of disorders, and their effects on cardiac physiology are complex and fascinating. A list of the causes of pericardial disease includes nearly the entire table of contents of an internal medicine textbook because most major disease processes have the potential to affect the pericardium ( Box 10.1 ). Despite this wide array of inciting processes, pericardial disease presents as one or more of four distinct syndromes: acute pericarditis, effusion and tamponade, pericardial constriction, and effusive-constrictive pericarditis. Syndromes may overlap, for example, when a large effusion complicates acute pericarditis or when acute inflammation tapers into a chronic process causing pericardial scarring and constriction. It is often observed that any given etiology tends to cause a predominant syndrome more frequently than others do; for instance, viral infections more commonly cause acute pericarditis, whereas malignancy usually results in effusion and tamponade. While this pattern is generally true, it should be noted that any of the conditions listed in Box 10.1 is capable of producing any of these syndromes.
Infectious
Bacterial
Streptococcus, Staphylococcus , gram (−) rods
Mycobacterial
Tuberculosis
Viral
Coxsackie, echovirus, adenovirus, severe acute respiratory syndrome coronavirus 2, Epstein-Barr virus
Human immunodeficiency virus
Fungal
Aspergillosis, Candida , histoplasmosis
Protozoal
Amebic
Neoplastic
Primary mesothelioma
Metastatic
Breast, lung, skin, lymphoma, leukemia
Metabolic
Uremia, myxedema, amyloidosis
Immune/Inflammatory
Connective tissue disorders (lupus, scleroderma, polyarteritis nodosa, rheumatoid arthritis)
Sarcoidosis
Post-myocardial infarction, postpericardiotomy syndrome
Iatrogenic
Radiation induced
Cardiac perforation from interventional procedures
Drugs (warfarin, minoxidil, procainamide)
Trauma
Direct trauma
Aortic dissection
Congenital
Pericardial cyst
Idiopathic
This chapter focuses on the pericardial syndromes associated with hemodynamic consequences, namely, pericardial effusions, pericardial constriction, and effusive-constrictive pericarditis. In addition, because the clinical presentation and hemodynamic abnormalities of restrictive myocardial disorders behave similarly to those of constrictive pericarditis, restrictive cardiomyopathy will also be discussed, compared, and contrasted with constrictive pericarditis.
Normal Pericardial Anatomy and Related Physiology
The normal pericardium consists of an inner, single layer of serous membrane known as the visceral pericardium and a fibrous, outer structure called the parietal pericardium , normally about 1 mm thick. The serous pericardium attaches to the surface of the heart and the inner surface of the parietal pericardium, defining the limits of the pericardial space; this space normally contains <50 mL of serous fluid.
Although a human can live without a pericardium without ill effects, the normal pericardium does serve specific functions. The major function relates to the relatively rigid and noncompliant nature of the parietal pericardium, limiting cardiac chamber distension with changes in volume and contributing to ventricular stiffness in diastole. These properties facilitate interaction and coupling of the cardiac chambers via the interventricular septum, an important role in cardiac physiology both in health and in disease. The noncompliant nature of the pericardium results in a rapid rise in pericardial pressure with an acute accumulation of fluid in the pericardial space. The volume that can be accommodated without increasing pressure in the pericardial space is known as the pericardial reserve volume and is normally only about 50 to 75 mL. Slow and gradual accumulation of fluid stretches the pericardium, allowing a greater pericardial reserve volume. For this reason, relatively large volumes of fluid can collect over time without increasing pressure. Once the pericardial reserve volume is reached, the relatively steep pressure-volume curve for the pericardium mandates a rapid pressure increase in the pericardial space with any additional increments of fluid ( Fig. 10.1 ). This explains the last-drop effect, in which a small increase in fluid causes a patient to deteriorate dramatically but also explains why removal of just a small amount of fluid leads to rapid improvement.
Complex interactions exist between the pericardium, the pericardial space, the cardiac chambers, and the thoracic cavity during cardiac and respiratory cycles. The spectrum of hemodynamic abnormalities observed in pericardial diseases can best be interpreted by first understanding these important physiologic relationships.
The relationships between the cardiac chambers, the great vessels of the heart, the thoracic cavity, and the pericardial space are summarized in Fig. 10.2 . Importantly, the pericardial space sits within the thoracic cavity, reflecting intrathoracic pressure (roughly −6 to 0 mm Hg). While the cardiac chambers lie within the confines of the pericardial space, the pulmonary venous system does not. The pulmonary veins exist outside of the pericardial space but within the thoracic cavity, thereby being directly influenced by changes in intrathoracic pressure. Both the inferior and superior vena cava exist outside the pericardial space and only partially within the thoracic cavity. Therefore the systemic venous circulation is mostly independent of changes in intrathoracic pressures, although a decrease in intrathoracic pressure during inspiration will augment venous filling to the right side of the heart.
In the presence of a normal pericardium, a variety of changes in cardiac physiology occur with inspiration and expiration ( Fig. 10.3 ). During inspiration, intrathoracic pressure decreases, resulting in decreased pressure in the cardiac chambers. With little or no corresponding reduction in systemic venous pressure with inspiration, the pressure drop in the right-heart chambers augments right-heart filling. The pulmonary venous bed lies within the thoracic cavity; therefore the inspiratory reduction in intrathoracic pressure also decreases pressure within the pulmonary veins. With pressure falling uniformly in the left atrium, the left ventricle, and the pulmonary veins, no major change occurs in left-ventricular filling with inspiration. Opposite changes occur with expiration, with the net effect being a decrease in right-sided filling. The net effect of inspiratory augmentation of right-ventricular filling with no change in left-ventricular filling causes a bowing of the septum from the right to the left, impairing left-sided output ( Fig. 10.4 ). This results in a small inspiratory drop in systolic pressure known as a pulsus paradoxus , normally measuring <12 mm Hg and often appreciable on an arterial or aortic pressure waveform ( Fig. 10.5A ). The normal pulsus paradoxus is enhanced in patients with obesity ( Fig. 10.5B ).
In the presence of a normal pericardium and vacant pericardial space, the diastolic pressures of the right and left ventricles vary during the respiratory cycle independently of each other ( Fig. 10.6 ). In contrast the systolic pressures of the right and left ventricles change during the respiratory cycle in a parallel fashion. In the presence of a normal, compliant pericardium, augmented filling of the right ventricle with inspiration is easily accommodated by the compliant right ventricle and does not lead to an increase in pressure in the right ventricle with inspiration. Instead, the changing forces with respiration cause the pressure in both chambers to decrease with inspiration and increase with expiration. Thus the right-ventricular and left-ventricular systolic pressures normally parallel each other during the respiratory cycle ( Fig. 10.7 ). This “concordance” of right-ventricular and left-ventricular systolic pressures during the respiratory cycle is important when we consider the effects of pericardial constriction later in this chapter under the section “Hemodynamics of Pericardial Constriction.”
Pericardial Effusions and Tamponade
Pericardial effusions occur commonly in clinical practice from any of the multiple causes listed in Box 10.1 . Although easily diagnosed with an echocardiogram, the nonspecific presenting symptoms are often attributed to other conditions and fail to trigger early clinical suspicion and recognition. Very frequently, this lack of suspicion during the early phases of an effusion prevents appropriate therapy, and the unrecognized effusion frequently progresses to tamponade and cardiovascular collapse, at which point the diagnosis becomes obvious. Unfortunately, the naive physician is now faced with the management of a crisis instead of basking in the joy of a clever diagnosis auspiciously treated.
Dyspnea, fatigue, and chest pain constitute the most common symptoms of an effusion. Manifestations associated with more profound hemodynamic sequelae include syncope, confusion or mental status changes, renal failure, and shock. Patients with subacute or chronic effusions may exhibit peripheral edema because of increased right-atrial (RA) pressure; similarly, patients may present with abdominal pain from hepatic distension. Physical examination nearly always reveals distended and tense neck veins. Tachycardia, arterial hypotension, and a pulsus paradoxus >12 mm Hg provide further evidence of a hemodynamically significant pericardial effusion. Two other physical examination findings are noteworthy. The Beck triad describes the constellation of elevated neck veins, hypotension, and a quiet precordium, named after the American surgeon Claude Schaffer Beck, who first described these findings in tamponade from acute, traumatic effusions. The Ewart sign describes the finding of dullness to percussion with bronchial breath sounds and evidence of lung consolidation below the left scapula seen with large, chronic pericardial effusions. An echocardiogram easily identifies pericardial effusions, even in the presence of poor acoustic windows. Pericardial effusions are sometimes diagnosed surreptitiously by chest x-ray (appearing as an enlarged cardiac silhouette), chest computerized tomography (CT), or magnetic resonance imaging (MRI). The electrocardiogram is nonspecific; it may show low voltage, electrical alternans, and diffuse ST elevation consistent with pericarditis.
Once an effusion is identified, it is important to determine its hemodynamic effect. The hemodynamic sequelae of an effusion depend on the rate and volume of fluid accumulation, compliance of the cardiac chambers and the pericardium, and the filling pressures in the heart. The commonly asked question “Is there tamponade?” (usually following an echocardiographic diagnosis of an effusion) is best addressed by describing its hemodynamic impact instead of deciding whether a patient is “in tamponade.” This concept has been elegantly elucidated by Reddy and Curtiss, who emphasize that tamponade is not an “all or none” phenomenon, but rather represents a spectrum of hemodynamic abnormalities, beginning with isolated elevation of pericardial pressure and ending with the profound abnormalities classically attributed to tamponade.
Fig. 10.8 depicts the progressive hemodynamic derangements that occur with incremental accumulation of pericardial fluid. Initially just the pericardial pressure rises. Elevated pericardial pressure triggers compensatory mechanisms (venoconstriction and fluid retention), raising systemic venous pressure to adequately fill the right heart. This causes both RA and right-ventricular diastolic pressures to increase. During this early phase of tamponade, cardiac output is maintained and a normal inspiratory fall in systolic pressure of <10 to 12 mm Hg occurs. With additional accumulation of fluid, there is further elevation of the pericardial pressure, dragging up the pressures in the cardiac chambers during diastole and causing equilibration of pericardial, RA, and right-ventricular diastolic pressures. Left-ventricular diastolic pressure then increases, ultimately equilibrating with the right-sided diastolic pressures. This results in equalization of diastolic pressures across the cardiac chambers. Additional fluid accumulation drops stroke volume; cardiac output falls despite a compensatory tachycardia. The inspiratory fall in systolic pressure (pulsus paradoxus) becomes more prominent but may remain below the upper limits of normal. In the final phase of tamponade the classically recognized changes are present and include elevated and equalized diastolic pressures, a prominent inspiratory fall in systolic pressure (or pulsus paradoxus >12 mm Hg), and a precipitous drop in cardiac output and blood pressure.
Hemodynamics of Pericardial Effusion and Tamponade
Tamponade causes continuous compression of the heart throughout the cardiac cycle, preventing rapid atrial emptying when the tricuspid valve opens. This correlates with the echocardiographic finding of right-ventricular diastolic collapse and, on hemodynamic waveforms, with the absence of the y descent on the RA tracing. This abnormality occurs relatively early in tamponade ( Fig. 10.9A ); equilibration between RA pressure and pericardial pressure is also seen early in this process ( Fig. 10.9B ). In advanced stages of tamponade the RA pressure waveform appears as an undulating and flat line without discernible a and v waves or x and y descents. Typically patients with tamponade present with elevated and equalized right-sided diastolic pressures that measure about 20 mm Hg. The reason for this is that hypotension and shock typically occur when the diastolic pressure reaches about 20 mm Hg. The patient is critically ill at this point triggering the evaluation and subsequent care ( Fig. 10.10 ). Right-ventricular and pulmonary artery pressure waveforms often appear abnormally thin and asthenic because of reduced right-sided output from compression. Marked elevation of the pulmonary artery systolic pressure is not seen unless it is a preexisting condition. Typically pulmonary artery systolic pressure is not more than 50 mm Hg. In severe tamponade pulmonary artery systolic pressure may be only slightly higher than diastolic pressure. Pulmonary edema is generally not a feature of tamponade for poorly understood reasons but likely due to the aforementioned observation that patients present with hypotension and shock when diastolic pressures reach about 20 mm Hg, before achieving a left-atrial pressure associated with pulmonary edema. Accordingly, arterial hypoxemia should not be attributed to tamponade physiology, and its presence should prompt a search for other etiologies.
As described earlier, an inspiratory drop in systolic pressure (pulsus paradoxus) of up to 10 to 12 mm Hg is part of normal cardiac physiology. Advanced phases of tamponade exaggerate this finding, and the inspiratory fall in systolic pressure exceeds 12 mm Hg. The presence of pericardial fluid within the inelastic confines of the pericardium allows only a certain volume to fill the cardiac chambers and prevents one cardiac chamber from accommodating any additional volume without a corresponding impairment in filling of the adjacent chamber. Therefore the augmentation in right-heart filling with inspiration competes with filling of the left heart, reducing stroke volume and systolic pressure to a greater degree than seen normally.
Kussmaul first described this phenomenon over a century ago :
The pulse of all arteries—with the heart movement continuing steadily—becomes very small in certain intervals that regularly occur with each inspiration, or it disappears completely, only to immediately return with expiration. I suggest to term this pulse the paradoxus pulse, in part, because of the obvious disparity between the heart action and arterial pulse, and, in part, because the pulse—though seemingly irregular—is in fact a pulse stopping or decreasing with regular repetition.
Not specific for tamponade, other conditions may exhibit a prominent pulsus paradoxus ( Fig. 10.5B and Box 10.2 ). Circumstances that prevent a pulsus paradoxus despite a large and significant effusion include a coexisting atrial septal defect (because the inspiratory increase in venous return is shared between the atria), aortic regurgitation (because filling of the left ventricle is independent of respiration), or marked elevation of the left-ventricular end-diastolic pressure.
Pericardial tamponade
Effusive-constrictive pericarditis
Right-ventricular infarction
Asthma
Chronic obstructive pulmonary disease
Congestive heart failure
Obesity
Ascites
Pregnancy
Pulmonary embolism
Tension pneumothorax
Clearly an accurate measurement of a pulsus paradoxus helps define the hemodynamic significance of an effusion. On physical examination, measurement of a pulsus paradoxus involves inflation of the blood pressure cuff above systolic pressure followed by careful auscultation during very slow deflation until any Korotkoff sound is heard with any cardiac cycle. This marks the upper limit of systolic pressure. With continued slow deflation of the cuff, the pressure at which Korotkoff sounds are heard with each cardiac cycle is noted and defines the lower limit of systolic pressure. The difference between these two recordings is the pulsus paradoxus. This procedure should be carried out while the patient is breathing normally; the patient should not be asked to “take a deep breath” while the physician frantically inflates a blood pressure cuff. Arterial pressure recordings identify a pulsus paradoxus with greater sensitivity than physical examination (see Fig. 10.5 ). In tamponade the pulsus paradoxus may be dramatic, completely obliterating the pulse, as described by Kussmaul ( Fig. 10.11 ).
