Emergency Medicine News:
The Speed of Sound
Dr. Butts is the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans.
A 35-year-old woman presents to the ED with shortness of breath. Her blood pressure is 90/50 mm Hg, her heart rate is 120 bpm, her respiratory rate 30 bpm, and her temperature 99.0°F. Her exam is otherwise unremarkable. An EKG shows sinus tachycardia, and a chest x-ray is normal.
As she is being sent for a CT scan, she becomes markedly diaphoretic and her repeat blood pressure is 70/40 mm Hg. A bedside echocardiogram is performed. (See figures.)
Most emergency physicians are comfortable performing a basic bedside echocardiogram to evaluate for the presence of a pericardial effusion, and many utilize ultrasound to assess overall left ventricular function. Bedside evaluation of right ventricular strain in the context of suspected pulmonary embolism is utilized less frequently by EPs. Some of the findings of right ventricular strain are complex and difficult to master, but EPs with a basic understanding of bedside echo can easily identify a few key findings that may guide patient care.
A full echocardiogram can be time-consuming, but mastering just a few views of the heart will enable the EP to assess the right ventricle accurately. The parasternal long axis view offers a good assessment of left ventricular function but a limited view of the right ventricle. The parasternal short axis view offers an excellent assessment of motion of the septum. The subxiphoid view is familiar to many EPs, and offers a good evaluation of all four chambers of the heart. An apical view of the heart is more difficult to obtain but also offers an excellent assessment of all four chambers.
A few key findings on bedside echo are consistent with right ventricular strain. Enlargement of the right ventricle can be quickly assessed by comparing the overall size of the right ventricle with the left ventricle. The left ventricle is generally about twice the size of the right ventricle. (Figure 1.) A right ventricle that exceeds this ratio or is even larger than the left ventricle is consistent with right ventricular strain. (Figure 2; video available on EMN website; see box.) This size ratio can be assessed with the subxiphoid or apical view. Prominence of the right ventricle in this view should be seen as suspicious because the right ventricle is usually only seen as a small sliver on a normal parasternal long axis view.
Evaluation of the motion of the septum can also be used to assess for right ventricular strain. The parasternal short axis view is often best to assess the motion of the septum. The septum will be seen to “bow” into the left ventricle in patients with right ventricular strain. This is often described as a “D-shaped” left ventricle (Figure 3; video available on EMN website; see box) in contrast to a normal left ventricle, which is more circular in shape.
These findings, especially in a hemodynamically unstable patient, are highly suggestive of pulmonary embolism and can be invaluable in guiding therapy. Bedside evaluation of the lower extremity veins for thrombus also can add to the suspicion in these patients.
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ECHO Videos on EMN Website and in EMN App
Watch two videos of the bedside echocardiogram performed on this patient on the EMN website at http://bit.ly/EMNVideos and in the EMN iPad app, available for free download at www.EM-News.com.
* Read Dr. Butts' past columns at http://bit.ly/ButtsSpeedofSound.
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© 2012 Lippincott Williams & Wilkins, Inc.