Ultrasound for Tamponade Physiology

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The key Ultrasound findings to look for when you suspect tamponade are a Pericardial effusion plus the following:

  • IVC dilation
  • RA collapse > 1/3 the cardiac cycle in systole (~R wave)
  • RV collapse in diastole (end of T wave)
  • Ventricular interdependence (septal bounce)

IVC “plethora” (>2.1 cm, <50% resp variation) is an early sign of tamponade, is expected in >90% of cases [1] and correlates well with all the other ultrasound findings and a higher pulsus paradoxus [2].

The RA relaxes during systole, and owing to its thin wall and low pressure, it may collapse briefly with slight external pressure. It is the duration of RA collapse that is important for tamponade. In one series of 127 patients with effusion, 19 of which ultimately had tamponade, RA collapse of > 1/3 the cardiac cycle (0.34 in the study) had a sensitivity of 94%, specificity of 100%, PPV of 100% and NPV of 95% [3].

The development of RV collapse is associated with a 21% decrease in cardiac output [4], is visible initially during inspiration only, but extends as tamponade severity increases [1], and had a sensitivity of 93%, specificity of 100%, PPV of 100% and NPV of 83% [5] (a small series of 21 pts).

Inspiration leads to increased venous return to the right side of the heart, but not from pulmonary circulation. Expiration does the opposite, with increased pulmonary venous return to the LV. When the ventricular free walls are sufficiently compressed by an effusion, this alternating venous return transmits pressure to the septum, leading to a septal “bounce” [1]. The result is a large RV and small LV during inspiration, and large LV and small RV during expiration. This ventricular interdependence is an ominous finding as it suggests impaired filling of both chambers.

Keep in mind that constriction of the pericardium can lead to similar ultrasound findings. If this is suspected, pulsus paradoxus (elevated in tamponade) and Kussmaul’s sign (absent in tamponade) may help distinguish the two.

Echocardiographic signs of tamponade include Mitral E-wave respiratory variability > 25%, or the equivalent variation at the tricuspid valve > 40%, but are not discussed in depth here as they are advanced measurements that highly depend on good quality image acquisition..

Further discussion on ultrasound for tamponade, with examples, can be seen in the Ultrasound podcast video below or at Stanford’s Echo in ICU.

  1. AL Klein, et al. American Society of Echocardiography clinical recommendations for multimodality cardiovascular imaging of patients with pericardial disease: endorsed by the Society for Cardiovascular Magnetic Resonance and Society of Cardiovascular Computed Tomography. J Am Soc Echocardiogr. 2013 Sep;26(9):965-1012.e15.
  2. RB Himelman, et al. Inferior vena cava plethora with blunted respiratory response: a sensitive echocardiographic sign of cardiac tamponade. J Am Coll Cardiol. 1988 Dec;12(6):1470-7.
  3. LD Gillam, et al. Hydrodynamic compression of the right atrium: a new echocardiographic sign of cardiac tamponade. Circulation. 1983 Aug;68(2):294-301.
  4. PP Leimgruber, et al. The hemodynamic derangement associated with right ventricular diastolic collapse in cardiac tamponade: an experimental echocardiographic study. Circulation. 1983 Sep;68(3):612-20.
  5. S Singh, et al. Usefulness of right ventricular diastolic collapse in diagnosing cardiac tamponade and comparison to pulsus paradoxus. Am J Cardiol. 1986 Mar 1;57(8):652-6.