is a technique using very high frequency sound (called ultrasound)
to visualize cardiac anatomy. Sound waves can be transmitted
in gas, liquid or solid medium. When it passes a border between
two substances of different density, part of the sound will
be reflected back.
A probe attached to the echocardiographic machine contains a
transducer which emits and records ultrasound. Normally, the
transducer placed in various positions over the heart (see figures
32c-1) sends ultrasound through
the chest wall, heart muscle and blood vessels.
The ultrasound is reflected back to the transducer probe, as
it hits various interfaces. The distance between the probe and
various interfaces can be calculated by comparing the time it
takes the echo to return to the probe against a calibrated time.
This information allows a display of the different depths of
the various interfaces relative to the probe position (figure32b).
two dimensional echocardiography the probe emits pulses in various
directions. The returning or reflected echos are compiled and
graphically displayed as a pie slice, with the apex of the pie
closest to the probe, and the remainder of the picture is a
composition of depth date from various pie-shaped sections of
tissue, analogous to viewing a darkened room by moving a flashlight
back and forth in front of you to build a complete picture.
Different two dimensional views of the heart are obtained by
moving the probe into various positions such as parasternal
(short and longaxis), apical four chamber views, etc (see fig.
More detailed views can obtained using high frequency miniature
probes inserted into the esophagus to image the heart from inside
the body (trans esophageal echocardiography, see figure