Echocardiography

Two-dimensional and Doppler echocardiography are commonly used for diagnosing cardiac tamponade. Specific signs of tamponade include collapse of the right atrium and right ventricle, ventricular septal shifting with respiration, and plethora (enlargement) of the inferior vena cava (Fig. 18-2). Respiratory variation in the Doppler mitral inflow is a highly sensitive measure that occurs early in tamponade, and may precede changes in cardiac output, blood pressure, and other echocardiographic findings.

Figure 18-2 Echocardiographic image of pericardial tamponade with right-sided chamber collapse. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; Eff, (pericardial) effusion.

(From Holmes DR, et al. JACC Cardiovasc Interv 2009;2:705–717 with permission.)

Hemodynamics

The invasive hemodynamic hallmarks of cardiac tamponade include pulsus paradoxus on the arterial tracing (Fig. 18-3) and prominent x descents and blunted y descents in the atrial pressure tracings (Fig. 18-4). Preservation of the x descent occurs because of the decrease in intracardiac volume during systolic ejection, which leads to a temporary reduction in intrapericardial and right atrial pressures (See Kern (2011) The Cardiac Catheterization Handbook 5th ed., Chapter 3 Hemodynamics). Elevated intrapericardial pressure impairs ventricular filling during the remainder of the cardiac cycle, resulting in blunting of the y descent. In patients with cardiac tamponade, the driving pressure to fill the left ventricle falls during inspiration. Consequently, there is a reduction in left ventricular filling and stroke volume, which manifests as a decrease in aortic pulse pressure during inspiration in a manner analogous to the bedside finding of pulsus paradoxus (see Fig. 18-3).

Figure 18-3 Arterial pressure in a patient with dyspnea at rest demonstrating pulsus paradoxus due to cardiac tamponade.

Figure 18-4 Hemodynamics of right atrial (RA) pressure (red) and pericardial pressure (blue); scale is 0–40 mm Hg. There is matching of phasic waveforms but RA is higher due to zero offset.

On relief of pericardial pressure and removal of the effusion, right atrial pressure and pericardial pressure fall usually to normal values if no residual pericardial disease is present (Fig. 18-5). However, in some cases, although pericardiocentesis empties the pericardial space and pericardial pressure falls to near zero, right atrial pressure may be unaffected, signifying the syndrome of effusive-constrictive pericardial disease (Fig. 18-6).

Figure 18-5 Hemodynamics of arterial pressure before pericardiocentesis (left) and after pericardiocentesis (right). Pericardial pressure is reduced from 24 to 10 mm Hg (blue); scale is 0–40 mm Hg.

Figure 18-6 Hemodynamics of pericardiocentesis with near normalization of pericardial pressure without change in right atrial (RA) pressure consistent with effusive constrictive pericardial disease.

Cardiac tamponade should be suspected in any patient in the cardiac catheterization laboratory with unexplained hypotension, elevated venous pressure, and a compatible history. Unusual manifestations also can occur. Tamponade may occur without elevated jugular venous pressure because of low intracardiac filling pressures (i.e., low-pressure tamponade), such as in dehydrated patients with malignant effusions. Localized tamponade can result from loculated pericardial effusions, such as those that may be present adjacent to the atria in the postoperative setting. Of note, pericardiocentesis should not be performed in patients with tamponade and aortic dissection. In such patients, relief of the tamponade will lead to an abrupt increase in systolic blood pressure that may exacerbate the aortic dissection. Careful imaging with transthoracic or transesophageal echocardiography is required to determine the presence of these manifestations of tamponade.