February Case of the Month

​Congratulations to our ultrasound of the month winner for February, Dr. Alex Varasteh!
 
Dr. Varasteh identified a case of cardiac tamponade and correctly applied his POCUS skills to obtain all of the key ultrasonographic elements to make this life saving diagnosis.
 
In addition to having a pericardial effusion, there are three major echocardiographic signs indicative of cardiac tamponade: Chamber collapse, Inflow velocity respiratory variation, and a plethoric IVC.

1. Chamber Collapse. As intrapericardial pressure increases and begins to exceed intracardiac pressure, transmural pressure gradients are reversed resulting in chamber collapse. The RA and RV are the most compliant structures so they are often the first to collapse.
   1. RA diastolic collapse is typically the first sign, however can also occur in the absence of tamponade. This will occur in enddiastole when the RA volume is minimal and pericardial pressures are maximal.
   2. RV diastolic collapse will occur in early diastole when RV volume and pressure are low. This finding is less sensitive than RA collapse but highly specific for tamponade.

Tips for identifying RV diastolic collapse:  
​Patients in tamponade are tachycardic, and it is often difficult to identify the cardiac cycle by the naked eye. Using M-mode you can place the curser through the mitral valve or aortic valve leaflets in the parasternal long axis to easily identify diastole. The anterior MV leaflet moves toward the septum during diastole. Below you can see the RV free wall collapsing at the same time as MV opening, corresponding to the diagnosis of tamponade.

2. Inflow Velocity Variation:  When blood flows into the RV during diastole there is limited expansion of the cavity due to the reversal oftransmural pressure gradients (RV early diastolic collapse). This leads to decreased RV filling and subsequent decreased LV filling and drop in stroke volume This is the cause of the  classic clinical feature of cardiac tamponade known as pulses paradoxus- a decrease in systolic BP > 10 mmHg on inspiration. Just as volumes decrease, so do velocities. These velocities can be measured with ultrasound by using pulse-wave doppler. 
Tips for measuring mitral valve inflow variation: Place the doppler gate at the tips of the mitral or tricuspid valve leaflets in the apical 4 chamber view. Slowing the sweep speed can make it easier to visualize the respiratory cycle. Measure the fastest and slowest peak velocities and compare thevalues.  Mitral valve flow variation >30%, or tricuspid flow variation >60% are indicative of cardiac tamponade.

3. Plethoric IVC: We use this all the time to assess volume status, but what this also indicates central venous pressure.  CVP should be elevated in anyone with obstructive shock as in the case of cardiac tamponade. IVC dilation ≥ 2cm with <50% collapse during inspiration is indicative of elevated CVP and should be present in cardiac tamponade. 

Author: Arthur Forbriger 
Editor: Allison Zanaboni