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Cardiac Tamponade
Cardiac tamponade is a medical emergency as a cause of obstructive shock. It is defined as a decompensated cardiac compression caused by pericardial fluid accumulation and rising intrapericardial pressure. The good news here is that we can make the diagnosis of tamponade based on focused cardiac ultrasound (FoCUS).
Physiology recap.
During spontaneous ventilation the negative intrathoracic pressure generated increases RV preload. The blood in the RV restricts full expansion of the LV limiting LV preload. The pulmonary veins also receive less blood as a consequence of the negative intrathoracic pressure. This also causes less LV preload. As a consequence stroke volume and CO drops to lower levels on inspiration when breathing spontaneously. This is the paradoxical pulse. The opposite occurs in a patient undergoing mechanical ventilation as the inspiration causes a drop of RV preload. Under normal circumstances the respirophasic differences of BP due to inspiration is less than 10mmHg as seen on figure 1.
Inspiration
Expiration
Figure 1. Diagram showing normal respirophasic changes in volumes of the ventricles. On inspiration the RV has more preload due to the negative intrathoracic pressure. There is less return of blood from the pulmonary veins plus the interventricular septum gets displaced to the left. The cardiac output thus is lower on inspiration. During expiration the preload of the RV decreases, more blood gets returned on the LV via the pulmonary veins and the preload of the LV which result in LV cardiac output. Blue and red representing RV and LV chambers respectively. Image modified from Patrick J Lynch and Carly Jaffe MD.
Cardiac Tamponade Features
Pericardial fluid accumulates around the heart but it is not the volume per se but the change in pressure that is important that impairs filling of the heart. The right sided heart structures normally operate at a lower pressure than those on the left to keep fluid moving forward. With pericardial fluid, the pressure differential between the right sided chambers and the pericardial fluid restricts movement of flow into the RV. In essence once the pericardial sack generates more pressure than the pressure needed to deliver preload to the RV we have tamponade. The RV then receives less preload which ultimately results in hemodynamic compromise. Keep in mind that a pericardium that accumulates blood slowly has more time to adapt to the changes in pressure than one that does so fast. The importance here is that the volume in the pericardium is not as important as its physiologic effect on the heart and cardiac ultrasound can help us with this.
Patients with tamponade have thus exaggerated respirophasic features. As mentioned, the increased intrapericardial pressure restricts flow to the right sided structures. On inspiration thus the RV tries to accommodate this restriction of flow by invaginating the interventricular septum into the LV. This ultimately results in a lower stroke volume and cadiac output and clinically seen as a drop in BP greater than 10mm Hg. This is called pulsus paradoxus.
Inspiration
Expiration
Figure 2. Diagram showing exaggerated respirophasic changes in the volumes of the ventricles with a pericardial effusion causing tamponade physiology. On inspiration the RV has more preload due to the negative intrathoracic pressure. Blue and red representing RV and LV chambers respectively. Image modified from Patrick J Lynch and Carly Jaffe MD.
Pericardial Effusion
Let's start by showing you what a pericardial effusion looks like on the parasternal short and long axis. Is there pericardial tamponade on these clips?
Pericardial effusion as seen on the parasternal long and short axis. A small anechoic fluid collection is seen on the posterior aspect of the heart on the long axis view. On the short axis view, the collection is seen on the anterior aspect of the pericardium.
Ultrasound features of tamponade
The following are cardiac ultrasound signs suggestive of cardiac tamponade that we will be exploring in this chapter:
1. Right sided chamber collapse. This appears when intrapericardial pressure exceeds intracardiac pressures. Diastolic collapse of the right atrium. During atrial relaxation (end-diastole), the RA volume is minimal but pericardial pressure is at it's highest causing collapse of this chamber. RA collapse that persists for more than 1/3 of the cardiac cycle is highly sensitive and specific of cardiac tamponade. The diastolic collapse of the RV is less sensitive than RA diastolic collapse for cardiac tamponade but it is more specific.
2. Respiratory variation in volumes and flows that can be appreciated with pulsed wave doppler (explained in this section but not part of focused cardiac ultrasound).
Sonographic features of Cardiac Tamponade.
Echocardiography and recently cardiac ultrasound is the primary diagnostic modality for the diagnosis of cardiac tamponade.
Early on right atrial collapse is seen in late diastole is an early sign of tamponade physiology and 100% sensitive. As pericardial pressure increases, the right ventricle presents with diastolic collapse in early diastole. We may also observed bowing of the IVS towards the LV during inspiration and towards the RV during expiration.
We can also observe the IVC diameter and its changes with respiration. With tamponade, the IVC is enlarged and does not vary with inspiration.
Features of tamponade. On the images above we see pericardial fluid. The heart rate is fast as a response to the decreased CO. This makes it difficult to asses the heart movement during diastole. The interrogation here lies on the right sided structures so we need to slow down the speed so that we can time diastole correctly with the cardiac cycle. The features above are typical of cardiac tamponade including diastolic collapse and a plethoric non collapsible IVC.
Slow speed to look at RV
In the clips below the same clip has been slowed so that we can have a better appreciation at the RV and the effects of the surrounding pericardial fluid. The label Diastole on the clip marks the duration of diastole (opening to closing of the mitral valve). RV collapse is seen when the dot appears on the screen. Chronologically the Diastole appears and we observe that the RV collapses almost immediately in the early stages of and throughout almost all diastole in this clip.
Tamponade physiology. Both clips correspond to the same case. On an ultrasound machine you can freeze a clip and go back frame by frame. The idea here is to evaluate the motion of the right ventricle after the mitral valve opens until it closes.
Lets slow it down even more to look at the RV
This is what we would see if we could slow the frame rate on the ultrasound machine:
The same clip as above but slowed further so that you can observe the timing of the RV collapse better. This patient has cardiac tamponade. A white dot appears close to the RV and it is meant to represent the collapse of the RV. The words Diastole appear on the screen for the duration of diastole from onset to end. We can see that the RV collapses almost immediately after diastole begins. The clips above are from the same case with the exception of one clip being slower than the other.
Cardiac tamponade. Slow and slower frame rate on these clips. RV collapse seen on diastole.
On the Apical 4 chamber view with Cardiac Tamponade
On this Apical 4 chamber view you can appreciate the collapse of the RV from another view. The label marked Diastole marks the duration of diastole of the cardiac cycle on this patient. We can also observe the septal bounce which is the paradoxical motion of the interventricular septum directed towards and then away from the LV during diastole. This is another echocardiographic feature of cardiac tamponade.
Apical 4 chamber view with evidence of tamponade. The label Diastole appears on screen only for the duration of diastole.
Short axis view with Cardiac Tamponade
M mode in Cardiac Tamponade
M-mode has the advantage of interrogating structures along the scan line across a time interval. On the images below we are selecting to do an M Mode on the parasternal long axis while selecting the mitral valve as the target. On the right we see the M-mode clip of this patient with cardiac tamponade. The red dots mark the start and end of diastole and is the anterior mitral valve moves up and back down until it closes throughout the cardiac cycle. We see on the left that the RV collapses during the early stages of diastole seen here in the blue dot. The yellow dot is the pericardium which lays still during the cardiac cycle. The blue line on the right displays the endocardial border of the RV which remains unchanged during diastole.
M-mode with tamponade. On the left, a scan line selecting the cusps of the mitral valve in the parasternal long axis view. On the right, the M-mode has ben turned on. Diastole starts and end between the red dots and represents the movement of the mitral valve. The yellow dot is a line representing the pericardium. The blue dot represents the epicardial border of the RV. We can appreciate diastolic collapse of the RV in this image.
Mitral and tricupid flow velocities.
This out of the scope for POCUS cardiac ultrasound and it is a more advanced feature. To understand the principles behind pulsed wave doppler visit our physics page and fluid responsiveness. The idea here is to look at respiratory changes or variations in the flows that cross the mitral and tricuspid valve. As mentioned above, on inspiration the tricuspid valve experiences higher flows while the mitral valve experiences the opposite. On tamponade the fluid collected on the heart compete for intraventricular volume and make these changes worse.
To use this feature we select the apical 4 chamber since the flow of blood is close to 0 degrees from the doppler interrogation to make this measurement optimal. The normal waves seen on Doppler are the E of early diastole and the A wave corresponding to atrial contraction. A variation of more than 40% of peak tricuspid flow and more than 25% mitral flow indicate tamponade.
1
2
Mitral doppler velocities normal and in tamponade physiology. The apical 4 chamber in both still images and this is the window used since the flow of blood is close to 0 degrees from the doppler interrogation. The pulsed wave doppler gate is placed at the mitral valve tips. In still 1, typical E, early and A, atrial contraction waves. On 2 we see calculate the peak E waves and measure the maximum and minimum achieved speed. Here a variation more than 25% indicates tamponade. The sweep speed of 2 has been modified to fit multiple E and A waves in a single screen. Images courtesy of emDocs.com.
Pericardial vs Pleural Effusion
It is important to distinguish between these two since therapies are markedly different. The important anatomic landmark when differentiating them is going to be the descending thoracic aorta. If there are concerns it would be prudent to do an ultrasound examination of the left lung on its most dependent location.
Pericardial vs pleural effusion. Pericardial effusions are seen when the fluid lies between the LA and the descending aorta (see red marker). Pleural effusions are located posterior to the descending aorta
In the examples below there is a pericardial and pleural effusion. Notice the anechoic collection deep to the descending aorta which corresponds to the pleural effusion.
Pericardial and pleural effusion in the parasternal long axis and short axis view. This patient has an impella device with marked LV depression. Anechoic fluid is collected around the heart and we can observe a left sided pleural effusion (arrow head).
References
1. Walker, Christopher M. MD; Chung, Jonathan H. MD; Reddy, Gautham P. MD “Septal Bounce”, Journal of Thoracic Imaging: January 2012 - Volume 27 - Issue 1 - p w1 doi: 10.1097/RTI.0b013e31823fdfbd
2. Imazio M, De Ferrari GM. Cardiac tamponade: an educational review. Eur Heart J Acute Cardiovasc Care. 2020 Jul 6:2048872620939341. doi: 10.1177/2048872620939341. Epub ahead of print. PMID: 32628038.
3. Spodick D. Acute Cardiac Tamponade. N Engl J Med 2003;349:684-90