Since the 1950s when Edler and Hertz1,2 in Lund, Sweden, recorded ultrasonic images of the heart walls and normal and rheumatic mitral valves, echocardiography has assumed a central role in the diagnosis and management of most cardiac disorders.
The purpose of this chapter is to examine the role of modern echocardiography from the perspective of the general practitioner. After a brief summary of the salient technical aspects of echocardiography and the elements of a normal echocardiographic examination, 10 clinical vignettes will be presented to illustrate the central role of echocardiography in contemporary medicine.
Sound is a mechanical phenomenon involving the transfer of energy through a medium. Ultrasound occurs in nature as illustrated by certain bat species that use ultrasound to navigate and to identify prey. The dog whistle is an example of a simple man-made ultrasound device.
A sound wave is generally depicted as a sine wave. Sound is defined by its amplitude, wavelength (λ) (the distance between cycles), and its frequency (f), the number of cycles in a given period of time (Fig. 1–1). Velocity (v = f × λ) is the speed at which a sound wave travels through a particular medium or body tissue. Velocity is dependent on the physical properties of the tissue and its acoustic impedance, which is primarily determined by the tissue's density.
Sound waves. A. Sine wave display of a sound wave. B. Two sound waves with similar amplitudes but different frequencies. C. Two sound waves with similar frequencies but different amplitudes.
The frequency of a sound wave is measured in hertz (Hz). One cycle per second is 1 Hz. Ultrasound is sound above the audible range, having a frequency greater than 20,000 cycles per second (20 kHz). In clinical medicine, transducers create ultrasound waves with much higher frequencies, ranging from 2 to 15 MHz. Higher frequency transducers give superior near-field resolution but have less tissue depth penetration.
A sound wave will travel in a relatively straight line through a homogeneous medium with some attenuation due to absorption and scatter until it reaches an interface between media with different densities. At the interface, the sound wave will undergo reflection and refraction proportional to the different densities of the two tissues (Fig. 1–2).
Sound wave reflection. Transmitted sound waves travel through a medium of one density until they come in contact with a medium of a different density at which the sound waves are reflected back toward their source.
Modern commercial ultrasound systems are comprised of three basic components: a transducer that serves as a sound originator and as a ...