The Echocardiogram: Introduction
The term echocardiography refers to the evaluation of cardiac structure and function with images and recordings produced by ultrasound. In the past three decades it has rapidly become a fundamental component of the cardiac evaluation. Currently, echocardiography ("echo") provides essential (and sometimes unexpected) clinical information and has become the second most frequently performed diagnostic procedure after electrocardiography.1 What began as a one-dimensional (1D) method performed from the precordial area to assess cardiac anatomy has evolved into a two-dimensional (2D) modality performed from either the thorax or from within the esophagus, capable of also delineating flow and deriving hemodynamic data.2 Newly evolving technical developments likely will extend the capacity of ultrasound to routine 3D visualization3 as well as to the assessment, in conjunction with contrast agents,4 of myocardial perfusion. The development of echocardiography is usually credited to Elder and Hertz in 1954.5 Primitive cross-sectional images of the excised human heart were produced in 19576; however, for nearly two additional decades, clinical echocardiography consisted primarily of 1D time-motion (M-mode) recordings, as popularized by Feigenbaum.7 In the mid-1970s, Bom and associates developed a multielement linear-array scanner that could produce spatially correct images of the beating heart.8 2D images of superior quality were soon achieved by mechanical sector scanners9,10 and ultimately by phased-array instruments as developed by Thurston and Von Ramm, which are the present-day standard.11 In the past several years, 3D instruments capable of real-time volumetric imaging have been developed.12 Miniaturization of ultrasound transducers has also led to their incorporation into gastroscopes and cardiac catheters to achieve transesophageal and intravascular images.13,14 Although efforts to use the Doppler principle to measure flow velocity by ultrasound were begun in the early 1970s by Baker et al.,15 clinical application of this technique did not thrive until the work of Hatle in the early 1980s.16,17 Pulsed and continuous-wave Doppler recordings soon were expanded to full 2D color-flow imaging. Most recently, Doppler velocity recordings have been obtained from myocardium itself, enabling measurement of tissue velocities and regional strain. |
