From Echocardiography in ICUParasternal long axis view showing large circumferential pericardial effusion with tamponade:
Tamponade physiology corresponds to the hemodynamic compromise from increased intra-pericardial pressure precluding the cardiac chambers filling.
Echocardiographic signs of tamponade:
- presence of pericardial effusion
- diastolic collapse of right ventricle
- IVC dilatation and loss of respiratory variations
- respiratory increase of inter-ventricular dependence
- respiratory variations > 25% in mitral, aortic and/or tricuspid flow
Echocardiographic signs of tamponade
Diastolic RA and RV collapse
Apical 4 chamber view showing large pericardial effusion with hemodynamic compromise: diastolic collapse of right atrium and right ventricle
IVC dilatation and loss of respiratory variations
The IVC is dilated without respiratory variations, reflecting the elevated right atrium pressure.
Respiratory changes in chambers size
The pericardium can not be stretched. When the space is filled by an effusion, the cardiac chambers are smaller, can not expand during diastole and inter-ventricular dependence is increased.
- during inspiration, the negative intra-thoracic pressure is transmitted to the cardiac chambers, creating a depression in the right ventricle and atrium which suctions the venous caval flow into the right atrium. The right ventricle expands while the left ventricle volume decreases.
- during expiration, the pressure in the thorax and in the pericardium are summed, superior to the pressure in the right chambers. The right ventricle is compressed.
This consequence of ventricular inter-dependence can be assessed from parasternal long or short axis viewing both right and left ventricles. Mmode will allow the comparison of the right ventricle size between inspiration and expiration.
Parasternal short axis view showing hemodynamic compromise: respiratory variations in the left and right ventricle area. In inspiration, the right ventricle dilates while it is compressed during expiration.
Mmode of parasternal short axis view showing the variations in chambers size depending on the respiration:
-on the first diastole after the beginning of expiration (left arrows), the right ventricle is small (blue arrow), the left ventricle is large (green arrow).
-on the first diastole after the beginning of inspiration (right arrows), the right ventricle is large (blue arrow), the left ventricle is small (green arrow).
Respiratory variations of ventricular filling and ejection
Flow respiratory variations can be assessed only in spontaneously breathing patients, in regular sinus rhythm. The interventricular dependence is exacerbated in the limited pericardial space filled with fluid, creating <u>pulsus paradoxus
Pulsed or continuous Doppler across the valves can be used for the assessment of pulsus paradoxus. The maximum velocity of the flow must be measured at the first cardiac cycle after the beginning of expiration and inspiration. Tamponade physiology (=hemodynamic compromise) exists when the difference between the highest and the lowest velocity is more than 25%. It can be assessed from the right heart (tricuspid flow) or from the left heart (mitral or aortic flow).
The most frequent etiology of tamponade physiology is pericardial effusion. Compressing mediastinal mass or large bilateral pleural effusion can also increase pericardial pressure and cause hemodynamic compromise.