Malignant cardiac involvement is common, occurring in 11% to 12% of patients with cancer. Of these patients, three fourths have epicardial involvement, and one third of these patients have a pericardial effusion.¹ The most common malignant primary tumor that progresses to involve the pericardium is lung cancer. Breast cancer, gastrointestinal cancers, melanoma, sarcoma, lymphoma, and leukemia account for most other cases. These tumors invade the pericardium through direct or metastatic spread. Less commonly, malignant primary pericardial tumors such as mesothelioma and sarcoma or benign tumors such as angioma, fibroma, or teratoma may occur. In a study conducted from 1996 to 2005, malignant disease was the primary cause of medical cardiac tamponade (65%), followed by unknown causes (10%), viral disease (10%), and anticoagulant medication–related intrapericardial bleeding (3%).²

Pathophysiology

The pericardium is a fibroelastic sac surrounding the heart that normally contains a thin layer of fluid. When a larger amount of fluid accumulates and exceeds the elastic limit of the pericardium, the heart begins to compete for the now fixed amount of intrapericardial space. As more fluid accumulates, the cardiac chambers become compressed, and diastolic compliance lessens.

Throughout this process, the decline in intrathoracic pressure associated with inspiration continues to be transmitted through the pericardium to the heart. Thus, venous return to the heart is still increased with inspiration. However, the free wall of the right ventricle cannot expand to accommodate this increased volume, thus leading the intraventricular septum to bow to the left. The result is decreased left ventricular filling during inspiration. When the size of the effusion progresses further, total venous return diminishes, and cardiac output and blood pressure deteriorate.

Cardiac tamponade is generally classified as acute or subacute. In acute cardiac tamponade, the relatively stiff pericardium can become rapidly filled with blood that causes tamponade with only a small effusion. This generally occurs in the setting of trauma, myocardial or aortic rupture, or invasive medical interventions. In subacute cardiac tamponade, a much larger effusion accumulates slowly and allows the pericardium to stretch over time. This type of tamponade occurs most commonly in the setting of malignant disease or renal failure, and it may not occur until the amount of pericardial fluid reaches 2 L or more. In either setting, very little additional fluid may cause cardiac tamponade once the limits of pericardial elasticity have been reached.

Presenting Signs and Symptoms

Classic

Cardiac tamponade is a physiologic continuum, from mild to severe. Classically, patients present with tachypnea and dyspnea on exertion. As the disease progresses, patients may have shortness of breath at rest, peripheral edema, or orthopnea. Patients with severe disease may be obtunded on presentation, thus obscuring the diagnosis of cardiac tamponade. A history of malignant disease or symptoms and signs of malignant disease such as weight loss, fatigue, or anorexia may help to guide the clinician toward a diagnosis of malignant pericardial effusion.

Physical Findings

Patients with pericardial tamponade most commonly present with shortness of breath, hypotension, and often with clear lungs. Unfortunately, physical examination holds little value for diagnosing the presence of a pericardial effusion. However, as a malignant effusion becomes large enough to cause cardiac tamponade, some distinct physical findings may become evident. The Beck triad, first described in 1935, consists of increased jugular venous pressure, hypotension, and muffled heart sounds. However, this triad is most useful in acute cardiac tamponade, and it may be uncommon or difficult to assess in patients with atraumatic cardiac tamponade.³

Sinus tachycardia is seen in most patients with cardiac tamponade. This physiologic response allows for maintenance of cardiac output despite decreased cardiac filling volumes. Patients may present with slightly lower heart rates if they are taking beta-blocking medications or if they suffer from hypothyroidism. Significant tamponade also manifests with absolute or relative hypotension. Patients with early tamponade may present with normotension or even hypertension, especially if they have preexisting hypertension.

Pulsus paradoxus is defined as a drop of more than 10 mm Hg in systolic blood pressure during normal inspiration. Most patients with moderate to severe cardiac tamponade have pulsus paradoxus, which is often palpable in the peripheral arteries. As cardiac output drops, however, pulsus paradoxus may be difficult to measure without invasive monitoring. Pulsus paradoxus results when the effusion limits expansion of the free wall of the right ventricle as venous return increases during inspiration. The right ventricle is then forced to expand by bulging the intraventricular septum into the left ventricle, thus leading to greatly reduced filling and stroke volume during inspiration.

To quantify pulsus paradoxus noninvasively, a sphygmomanometer is used in the standard fashion. The cuff is inflated to more than the systolic blood pressure and then is slowly deflated until the first Korotkoff sounds are audible only during exhalation. This condition is typified by hearing Korotkoff sounds for several beats during exhalation, followed by silence during inspiration, and then followed by Korotkoff sounds for several beats during exhalation. The pressure is noted on the sphygmomanometer at this point, and slow deflation is continued until all beats are audible. The amount of pulsus paradoxus is determined by subtracting the pressure at which all beats are heard from the pressure at which beats were heard only during exhalation.

Multiple conditions may alter the physiology of cardiac tamponade and may cause pulsus paradoxus to be absent. The most common conditions are elevated left ventricular diastolic pressures and increased heart rate. Other conditions include severe hypotension, irregular rhythm, atrial septal defect, regional cardiac tamponade, and severe aortic regurgitation.

Medical Decision Making and Diagnostic Testing

Electrocardiography

The electrocardiogram is abnormal in most, but not all, patients with pericardial effusion. The most common findings are nonspecific ST-segment and T-wave abnormalities and sinus tachycardia. The electrocardiogram may mimic that seen in acute pericarditis.

Low QRS voltage may be a sign of a large pericardial effusion, but it is more likely to be associated with tamponade physiology. In one small study, Bruch et al.⁴ studied 43 patients with a pericardial effusion. Of those patients, 14 of 23 with tamponade demonstrated low-voltage QRS complexes, as opposed to none of the 23 patients with effusion but without tamponade⁴ (Fig. 202.1). Electrical alternans (Fig. 202.2), demonstrated as beat-to-beat alterations in the amplitude of the QRS complex, is relatively specific but not very sensitive for cardiac tamponade. Electrical alternans may also rarely occur in patients with very large effusions without tamponade. Electrical alternans is caused by swinging of the heart in the pericardial effusion, and it generally disappears after removal of even modest amounts of pericardial fluid.

Fig. 202.1 A, Patient’s electrocardiogram on a prior visit to the emergency department (ED). B, Patient’s electrocardiogram on presentation to the ED with cardiac tamponade.

Fig. 202.2 A, Electrocardiogram demonstrating electrical alternans most notable in the lead II rhythm strip. This patient’s electrocardiogram also has atrial flutter with 2 : 1 conduction. B, Electrocardiogram performed on the same patient several days after drainage of his pericardial effusion.

Chest Radiography

The typical finding on chest radiograph is an enlarged cardiac silhouette (the “water bottle”–shaped heart), as seen in Figure 202.3. In most cases, the lung fields are clear unless preexisting lung disease (e.g., malignant disease) is present. Cardiac tamponade may manifest without an enlarged cardiac silhouette if a small, rapidly accumulating effusion is the cause.