Cardiac tamponade occurs when the pressure in the pericardium exceeds the pressure in cardiac chambers, resulting in impaired cardiac filling. As pericardial pressure increases, filling of each cardiac chamber is sequentially impaired. The lower-pressure cardiac chambers(atria) are affected before higher-pressure chambers (ventricles). The compressive effect of the pericardial fluid is seen most clearly in the phase of the cardiac cycle when pressure is lowest in that chamber, it means systole for the atria, diastole for the ventricles. Filling pressure becomes elevated as a compensatory mechanism to maintain cardiac output.Such elevated intracardiac filling pressure, produces a decrease of ventricular filling and stroke volume.
The limit of pericardial stretch is dependent of the amount of the pericardial effusion and also on the rate at which effusion accumulates.Rapid accumulation of even small volume of fluid can lead to a marked increase in pericardial pressure and be reason for cardiac tamponade.
Echocardiographic findings of cardiac tamponade
Right atrial (RA) systolic collapse or inversion of the free wall – occurs when intrapericardial pressure exceeds right atrial pressure, Blood pressure and cardiac output fall. Brief right atrial collapse may be normal due to thin and flexible free wall of the RA.This sign may be due to cardiac tamponade, if RA collapse lasts longer during systole (greater than a third of systole, or time of collapse/time of cardiac cycle >0,34). This sign has a high sensitivity and specificity for cardiac tamponade.
Image No.1.Two-dimensional echocardiography apical four chamber in patient with huge pericardial effusion and cardiac tamponade. There is a systolic collapse of the right and left atrium in patient with cardiac tamponade.
Video No.1.Two-dimensional echocardiography in PLAX view in patient with huge pericardial effusion and cardiac tamponade. There is a diastolic collapse of the right ventricle, and systolic biatrial collapse in patient with cardiac tamponade.
Right ventricular (RV) diastolic collapse - occurs when intrapericardial pressure exceeds RV diastolic pressure.RV free wall may be without diastolic collapse in patients with cardiac tamponade, if the right ventricular free wall is thickened due to RV hypertrophy or infiltration. The RV collapse is the best seen in PLAX, PSAX view or from subcostal view. This sign (RV diastolic collapse) is more specific, but less sensitive than RA systolic collapse. It may be seen in case of pulmonary hypertension and RV hypertrophy.
Image No.2.Two-dimensional echocardiography in PLAX view in patient with huge pericardial effusion and cardiac tamponade. There is a diastolic collapse of the right ventricle in patient with cardiac tamponade.
Swinging heart – four cardiac chambers floating within the pericardial space in a phasic manner. A simple sign of cardiac tamponade (Video No.2).
Video No.2.Two-dimensional echocardiography in apical four chamber view in patient with cardiac tamponade. There is a swinging heart which means- heart floating within the pericardial effusion in a phasic manner.
Compression of the left atrium and left ventricle - can be seen in patients with cardiac tamponade.
Image No.3.Two-dimensional echocardiography in PLAX view in patient with There is a systolic collapse of the left atrium in patient with cardiac tamponade
Reciproval changes in the right and left ventricle volume give varying pattern of septal motion with respiration in patients with cardiac tamponade(septum movement toward the LV with inspiration, and toward the RV during expiration). It occurs because heart chambers are fixed with pericardial effusion and intrapericardial pressure. As intrathoracic pressure becomes more negative during the inspiration, enhanced RV filling and limits LV diastolic filling. During the expiration the LV filling is better. This phenomena is better seen on M-mode echocardiography.
Image No.4. M-mode echocardiography on the LV in PLAX view in patient with huge pericardial effusion and cardiac tamponade. Reciproval changes in the right and left ventricle dimension during respiration (RV dimension is bigger in time of inspiration.
Inferior vena cava plethora, as indicator of elevated right atrial pressure – dilated inferior vena cava with >50% inspiratory reduction in diameter near the inferior vena cava-right atrial junction. This sign is sensitive, but less specific for cardiac tamponade. Dilated v.cava inferior is due to elevated RA pressure in tamponade.
Image No.5. Subcostal view in patients with cardiac tamponade. There are dilated veva cava nferior, without inspiratory/expiratory changing in the diameter (it is better seen on M-mode of v. cava inferion on the junction with RA)
Respiratory variation in right and left ventricular diastolic filling on Pulse wave Doppler (PWD) – the RV and LV filling differences due to cardiac tamponade during expiration and inspiration are also seen in PCW. Normally, there are respiratory variation in the early diastolic filling of the RV and LV. But, in case of cardiac tamponade, there are excessive (more than 25%) differences in early (E and A waves changes) filling velocities during the inspiration/expiration in right and left ventricle. Also, there are the opposite changes in velocity between RV and LV filling time. With inspiration, the RV early diastolic filing velocity increase, while LV early diastolic velocity decrease, and this phenomena is opposite in expiration. In case of cardiac tamponada, a patient can show different degrees of hemodynamic impairment as the degree of the pericardial compression from the intrapericardial fluid.
PWD respiratory variation in filling velocity on the pulmonary veins and hepatic veins – an inspiratory increase and expiratory decreace of the forward flow with increase of the reversal flow at the hepatic vein conversely to inspiratory decrease and expiratory increase of pulmonary venous forward flow, can be seen in case of cardiac tamponade.
Image No 6. Pulse wave Doppler image in patient with pericardial tamponade. There are a respiratory variation in left ventricular diastolic filling pattern.
In patients with clinical suspicion of tamponade(low-cardiac output symptoms, hypotension, tachycardia, pulsus paradoxus), the presence of moderate to large pericardial effusion on echocardiography confirms the diagnosis of tamponade. It can be difficulties in small pericardial effusion, without clinical signs of tamponade. In this cases , there is a need to assess whether ehocardiographic changes are the result of increased intrapleural pressure, mediastinal structure that make pressure to the heart, or the changes are due to cardiac tamponade with small effusion, but with rapid accumulation. Pulse view Doppler findings can help to demonstrate hemodynamic impairment and to help in making diagnosis and indication for pericardiocentesis, in patients with cardiac tamponade.
Echocardiographic-guided pericardiocentesis allows secure access to the pericardial fluid. With echocardiography can provide:
optimal transcutaneous approach based on the location of the effusion,
visualization of the effusion without compromising the sterility of the field,
to determine the distribution and the depth of the pericardial effusion,
to assess residual pericardial effusion and consequences of it during and after pericardiocentesis.
Confirmation that needle tip is in the pericardial space can be made by injecting a small amount of agitated sterile saline solution or air gas microbubbles through the needle for pericardiocentesis. It can provide to see an echo contrast effects in the pericardial fluid, if it is necessary during the procedure.
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