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 40-year-old woman presents with complaints of increasing shortness of breath with exertion and difficulty lying flat at night. Her physical exam is significant for crackles at the lung bases and edema extending to her bilateral calves. Suspicious for new onset congestive heart failure, the emergency physician performed a bedside ultrasound to assess cardiac function.
Bedside ultrasound of the heart is a vital tool for any emergency physician. A quick bedside exam can reveal a pericardial effusion, evidence of right heart strain, and systolic dysfunction. Ventricular contractility can be estimated by observation of the left ventricle, but many EPs may not feel comfortable relying solely on visual inspection. Some patients may have severely decreased contractility that is obvious, but other cases may be less clear-cut.
Utilizing E-point septal separation (EPSS) gives the sonographer the advantage of having an objective measurement of left ventricular function. This measurement can be performed utilizing the M-mode setting in a standard parasternal long axis view of the heart.
EPSS evaluates the motion of the anterior leaflet of the mitral valve. The M-mode cursor should be placed so that it bisects the tip of the leaflet. (Image 1.) As with all M-mode tracings, more superficial structures are seen at the top of the image, with deeper structures beneath. After the straight lines of the chest wall are seen, the free wall of the right ventricle and right ventricular chamber are seen. The septum is then seen as a thick hypoechoic (gray) band, followed by the tracing of the anterior and posterior mitral leaflets.
The anterior leaflet will be the most superficial, and has a characteristic pattern with a large upward deflection, followed by a smaller upward deflection before returning to baseline. The initial upward deflection is known as the E-point, and represents the initial opening snap of the mitral valve during diastole. The distance between this E-point and the septum is measured using the calipers to determine the EPSS.
The distance between the E-point and the septum closely correlates with left ventricular contractility. (Amer J Cardiol 2006:97;137.) The distance in a normally contracting heart should be less than 7 mm. (Image 2.) A finding of greater than 1 cm distance between the two structures reliably correlates with poor contractility. (Image 1.)
The EPSS should be evaluated with caution in patients with history of mitral valve pathology because the valve motion will be abnormal. Patients with a history of aortic regurgitation or severe left ventricular hypertrophy also may have an inaccurate EPSS in relation to their true left ventricular function.
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