Principles of Echocardiography
Since 1976, echocardiography (echo) has been used to evaluate cardiac structure and function. Echo uses sound in the high-frequency range (2–10 MHz). Frequency ranges between 2 and 5 MHz are typically used for imaging adults, while frequencies of 7.5 to 10 MHz are used for children and specialized adult applications. The transducer contains a piezoelectric crystal that converts electrical to sound energy, producing sound waves that are transmitted in the form of a beam. A complete transthoracic echocardiogram (TTE) consists of a group of interrelated applications including two-dimensional (2D) anatomic imaging, M-mode, and three Doppler techniques: pulsed-wave (PW), continuous-wave (CW), and color-flow (CF) imaging.1–7 In addition, the quantification of cardiac chamber dimensions, areas, and volumes is an important aspect of a complete examination. Using a combination of these ultrasound techniques, one can assess the anatomy and function of the cardiac valves, myocardium, and pericardium.
Standard views are obtained along three orthogonal planes of the left ventricle (LV): long-axis, short-axis, and the four-chamber plane (Fig. 56-1A–C). The long axis is parallel to the long axis of the LV. The short axis cuts the LV cross-sectionally, similar to slices of bread in a loaf, and is orthogonal to the long axis. Four standard transducer locations are used to obtain complete visualization of the entire heart: parasternal, apical, subcostal, and suprasternal.
Standard 2D TTE (A–C) and M-mode (panel D) views in a normal individual. A. Parasternal long-axis view of the right ventricle (RV), interventricular septum, left ventricle (LV) cavity and posterior wall, and both mitral and aortic valves. Since the RV is the most anterior structure, it will be located closest to the transducer beam and is seen at the top of the image display, while the LV and LA (both posterior structures) are farther away from the transducer and are seen at the bottom of the image. B. Parasternal short-axis view of the ventricles at the papillary muscle midventricular level obtained by rotating the transducer 90 degrees. C. Apical four-chamber view, important for evaluation of ventricular function, apical thrombus, mitral and tricuspid valve function. D. M-mode view through the RV and mitral leaflets. This view is useful for detecting RV diastolic collapse in tamponade.
M-mode is a one-dimensional “ice pick” view of the heart (Fig. 56-1D) and is often used for measuring LV systolic and diastolic chamber dimensions and wall thickness.
The Doppler effect is the phenomenon whereby the frequency of sound waves increases or decreases as the sound source moves toward or away from the observer. The resultant Doppler frequency shift can be detected and translated into blood-flow velocity. The ...