Echocardiography is a unique noninvasive method for imaging the
living heart. It is based on detection of echoes produced by a beam
of ultrasound (very high frequency sound) pulses transmitted into
the heart.
From its introduction in 1954 to the mid 1970's, most echocardiographic
studies employed a technique called M-mode, in which the ultrasound
beam is aimed manually at selected cardiac structures to give a
graphic recording of their positions and movements. M-mode recordings
permit measurement of cardiac dimensions and detailed analysis of
complex motion patterns depending on transducer angulation. They
also facilitate analysis of time relationships with other physiological
variables such as ECG, heart sounds, and pulse tracings, which can
be recorded simultaneously.
A more recent development uses electromechanical or electronic
techniques to scan the ultrasound beam rapidly across the heart
to produce two-dimensional tomographic images of selected cardiac
sections. This gives more information than M-mode about the shape
of the heart and also shows the spatial relationships of its structures
during the cardiac cycle.
A comprehensive echocardiographic examination, utilizing both M-mode
and two dimensional recordings, therefore provides a great deal
of information about cardiac anatomy and physiology, the clinical
value of which has established echocardiography as a major diagnostic
tool.
This unit covers the principles of two-dimensional echocardiography
in more detail; it explains the normal two-dimensional recordings
in terms of the anatomy of the cardiac sections scanned by the ultrasound
beam. Some supplementary M-mode recordings are included. Subsequent
units will discuss applications of both M-mode and two-dimensional
echocardiography in acquired and congenital disease.
2004
