Ultrasound Case of the Month

The Case

A male in his 70s with a history of Stage IV Lung Cancer (on immunotherapy) and GERD who presented to the ED with worsening shortness of breath over the past two months.  He has mild SOB which is worsened with any sort of exertion and alleviated at rest.  The patient denies any chest pain, fevers, cough, abdominal pain, or leg swelling.  On exam the patient is in no acute distress and vitals are stable with a Temp of 98.4, HR of 79, BP 146/93, RR of 20, O2 sat 97% on room air.  He has mild 1+ pitting edema bilaterally, lung sounds are diminished at the bases, and his exam is otherwise unremarkable.  A bedside ultrasound is performed revealing the following images:

+ What do you see on Ultrasound?

Cardiac Tamponade

Cardiac tamponade is classically described as a clinical diagnosis. However, many of the common signs and symptoms of tamponade such as dyspnea, chest pain, and tachycardia are neither sensitive nor specific. Detection of cardiac tamponade using Beck's triad of hypotension, distended neck veins, and muffled heart sounds has been proven to be woefully inaccurate. In fact, one study showed that among patients with confirmed tamponade in the ED, only 15% were even hypotensive.

Bedside echocardiography can help to identify pericardial effusions and is commonly used in the emergency department. However, not every pericardial effusion demonstrates tamponade physiology. Therefore, it is important for the emergency physician to be able to indentify tamponade physiology on echocardiography. Furthermore, ACEP considers the ability to diagnose tamponade on ultrasound a basic EM skill.

Evidence of cardiac tamponade is characterized by many ultrasound findings; we will discuss three of them here.

  • Diastolic collapse of the right ventricle and right atrium: Comprehensive TTE is performed with real time EKG monitoring, allowing the provider to correlate ultrasound findings with the phase of the cardiac cycle. However, in the emergency department this is often impractical. Therefore, it is often difficult to differentiate systolic and diastolic collapse; especially in the presence of tachycardia. Right atrial diastolic collapse is often the earliest predictor of tamponade, but it is non-specific. Therefore, it is often more useful to use right ventricular collapse as a marker of tamponade.

    Measuring right ventricular collapse can be done using M-mode. To do this, the provider obtains a view of the heart in a longitudinal plane that includes the RV free wall and the mitral valve (typically parasternal long view). A M-mode cursor is then placed through the RV free wall and the mitral valve (see image). This enables the provider to view the motion of the RV free wall and correlate it to the phase in the cardiac cycle by comparing it to the mitral valve motion. Diastole occurs when the mitral valve is open, and so any posterior motion of the RV free wall while the mitral valve is open indicates tamponade physiology. One study showed that RV diastolic collapse was 93% sensitive and 100% specific for cardiac tamponade. However, it is important to remember that any baseline physiologic condition that increases right sided pressures (pulmonary hypertension, positive pressure ventilation, severe LV failure, etc.) can decrease the sensitivity of these findings. In the corresponding image, you can see where to place the M-mode cursor and how to identify RV collapse. In the M-mode tracing, notice how the RV collapses while the MV is open (diastole).

In addition to looking at the RV free wall, measuring the RV cavity size during systole and diastole can also help in identifying tamponade. Typically the RV cavity is smallest during systole. However, due to diastolic collapse, the RV cavity is smallest during diastole in tamponade. This measurement is performed using the same M-mode image as described above. The RV cavity size is simply the distance between the septum and the RV free wall, both easily identifiable in M-mode.

  • Exaggerated respiratory variations of trans-mitral and trans-tricuspid Doppler inflow velocities: Flow through the various heart valves changes with the respiratory cycle. During inhalation intrathoracic pressure decreases; this increases flow through the right sided valves (tricuspid and pulmonic) and decreases flow through the left sided valves (mitral and aortic). The opposite happens during exhalation when intrathoracic pressure rises. These flow variations can be measured using pulse wave Doppler to measure the transvalvular flow in inhalation and exhalation to determine if tamponade is present. The normal flow variation is approximately 10%. However, during tamponade, the flow variation increases. Tamponade is suggested by a flow variation > 25% through the mitral valve and > 40% through the tricuspid valve.

    These flow variations are typically measured in the apical 4 chamber view. The Doppler indicator is placed perpendicular to the mitral or tricuspid valves (parallel to the direction of flow) just past the valve leaflets on the ventricular side of the valve, and then recorded. The variation can then easily be measured as the patient breaths (see image). The mitral valve is most often easiest to visualize and is therefore typically used. In the image you can see measurement of the flow variation across the mitral valve. The variation is calculated at 43% which is indicative of tamponade.

  • Inferior vena cava plethora: Images of the IVC are commonly obtained in the ED at bedside by emergency physicians. When pericardial pressures increase, this pressure is then transmitted to the IVC and impedes flow to the right atrium. This is then visualized by a plethoric IVC (> 2cm) with little to no respiratory variation (collapsibility < 50% with inhalation). The presence of this indicates elevated right sided pressures which can be due to a variety of causes (volume overload, PE, tamponade, valvular disease), one of which is tamponade. The presence of this finding suggests tamponade physiology. This is a sensitive, but not very specific finding.

The patient in this case was taken directly to the cath lab for a pericardial window. 600ml of fluid was drained from the pericardium and a drain was left in place. Over the next several days an additional 1400ml of fluid drained but eventually slowed and the drain was removed. The fluid analysis revealed a malignant effusion. He was discharged from the hospital on day 7 and has had no recurrent effusion.

+ Learning Points

  • Not all pericardial effusions are tamponade, and not all tamponade presents with hypotension
  • Diastolic RV collapse on ultrasound as measured by M-mode can help identify tamponade
  • Mitral transvalvular flow variation > 25% indicates tamponade
  • IVC plethora and lack of respiratory variation can suggest tamponade physiology

Authored and Posted by Tim Murphy, MD

Edited by Lori Stolz, MD