Causes of Obstructive Shock:
- Cardiac Tamponade
- Pulmonary Embolism
- Tension Pneumothorax
- Cardiac Masses
- Large Pleural Effusions
- Compression of the Great Vessels by Mediastinal Mass
A) Cardiac Tamponade
Focused Cardiac Ultrasound Signs in Cardiac Tamponade:
- Large Pericardial Effusion
- Diastolic Right Ventricular Collapse (Highly Specific)
- Systolic Right Atrial Collapse (Early Sign)
- Plethoric IVC
- Lack of IVC Respiratory Variation
What do we see above ? Click for answer.
There is a large circumferential pericardial effusion and 2D echo signs of cardiac tamponade. The RV and RA can be seen to collapse during the cardiac cycle. Image from: JAMA Network: Echocardiogram of a patient with cardiac tamponade.
What is shown in the above clip ? Click for answer.
Subcostal IVC View: Plethoric IVC & lack of IVC respiratory variation is seen. This is consistent with a diagnosis of cardiac tamponade.
In the images above, (a) Parasternal long–axis view showing a large pericardial effusion encompassing the entire circumference of the heart(“swinging heart”) also seen in (b) short-axis view. (c) Apical four-chamber view showing right atrial early-systolic collapse (orange arrow). (d) Subcostal view showing right ventricular free-wall end-diastolic collapse (yellow arrow) also seen by e M-mode (blue arrows). (f) Dilated inferior vena cave without inspiratory collapse
What is seen in the above clip ? Click to open.
The above subcostal 4 chamber clip shows a large pericardial effusion. There is diastolic RV collapse as seen in the image below. We know that it is a diastolic frame as the mitral valve is open. This is highly indicative of cardiac tamponade.
Further Reading:
- Echocardiographic Assessment of Pericardial Effusion. Peters & Shuck. Journal of Diagnostic Medical Sonography. 2007
B) Massive Pulmonary Embolism
The RV size is best assessed in the apical 4-chamber (A4C) view. In a A4C view, the normal RV should have the following features:
- RV size should be about 2/3rds the size of the LV;
- RV shape should be triangular (rather than sail-shaped); and
- The RV should not contribute to the apex of the heart (which is normally formed exclusively by the LV).
Echocardiography (Comprehensive TTE) has a high specificity but low sensitivity for the diagnosis of pulmonary embolism. As such, it should be used as a rule in test for pulmonary embolism. Echocardiography used in isolation is unable to reliably rule out pulmonary embolism. Other investigations are required.
The role of echocardiography lies in it’s usefulness for triaging patients with pulmonary embolism. Patients with evidence of RV strain on echo are more likely to decompensate and should be considered for thrombolysis.
Ref: Transthoracic Echocardiography for Diagnosing Pulmonary Embolism: A Systematic Review and Meta-Analysis. Fields et al. JASE 2017
Focused Cardiac Ultrasound Signs in PE:
- Dilated Right Ventricle
- Dilated RV with basal RV:LV ratio > 1.0
- Flattened Interventricular Septum
- McConnell’s Sign – Preseved RV Apical Contraction, RV Free Wall Hypokinesia.
- Plethoric IVC
- Lack of IVC Respiratory Variation
- Reduced TAPSE
- Mobile Thrombus in Right Heart – Virtually diagnostic of PE
The above signs are non-specific and may be seen in any cause of RV strain or failure.
Describe your findings. Click for answer
The above clip shows a dilated RV. The RV free wall is hypokinetic and does not contract. On the other hand, the RV apex has preserved contractility. This finding is associated with acute RV strain of any cause, with PE being one. Image From: McConnell’s Sign.
What do you think about the above clip ? Click for answer
Parasternal Short Axis View : Dilated RV with Flattened D-Shaped Septum. There is also a small pericardial effusion here. The flattened septum is indicative of RV pressure and volume overload. See below.
The D shaped septum arises due to RV pressure or volume overload, or both. Volume overload causes a D shaped septum in diastole, while pressure and volume overload cause D shaped septum in systole and diastole.
This is an interesting one ! Click for answer
Subcostal view showing clot in transit. The clot is seen in the RA in this image. This finding is highly specific for pulmonary embolism but is uncommonly seen.
Image showing a plethoric IVC with no respiration variation in caliber. Such features can be seen in obstructive shock (eg PE) & right ventricular failure.
Describe the echo clip above. Click to open.
This is an apical 4 chamber view. Th LV and RV are dilated but systolic function appears normal to mildly impaired. Other views should be obtained to clarify this. The RV is sail shaped as opposed to traingular and now forms the apex of the heart.
C) Tension Pneumothorax
Please see the section on Lung Ultrasound.
D) Cardiac Masses
Image showing a large right atrial mass causing obstruction to flow across the tricuspid valve. This is likely to be an atrial myxoma. Image from POCUS Atlas with permission.
