The echo pattern is usually displayed on the face of an oscilloscope by either of two methods. The high frequency of the pulses (200 to 2,000 per second) offers many determinations per cardiac cycle and permits accurate and detailed tracking of rapidly moving structures, such as heart-valve cusps the velocities of which are often in excess of 250 mm per second (2). The time that elapses between the generation of the pulse of ultrasound and the arrival of the echo is a measure of the depth of the reflecting surface. As this sound energy passes through tissue, it is reflected at interfaces of differing acoustic impedance to the same transducer, which also acts as a receiver between pulses. To summarize, short bursts (one to two microseconds) of ultrasonic energy are emitted by a transducer held in close contact with the skin.
These same principles were employed by Edler and Hertz in 1954 to study heart motion and to initiate echocardiography as a clinical tool (9). The emergence of technics for the measurement of very short periods of time permitted Firestone, in 1945, to use ultrasound in the nondestructive testing of materials (8). Ultrasound was developed during the period following World War I for depth-sounding and localization of submarines and schools of fish. The identification of the cardiac chambers without contrast injection is a natural outcome of this study and depends on the distinguishing of key anatomic structures, the relationship of the chambers to them, and the recognition of movement patterns that may be specific for a structure or chamber. It is based on the intracardiac injection of substances that produce echoes at the site of injection as well as downstream in the flow pattern and permit identification of the heart cavities. The purpose of this presentation is to describe a method for the ultrasonic identification of the cardiac chambers in the living subject. Even here, however, Edler (7) has gained useful knowledge in the recognition of the origin of these echoes by the passing of needles into cadavers in duplication of the path of the ultrasonic beam and by the study of excised hearts. On the other hand, the extension of the ultrasonic method to the study of other cardiac structures has been slow because of the difficulty in recognizing the source of the echoes. The tricuspid valve can also be detected (4), and studies have been made of left ventricular stroke volume (5) and wall thickness (6). Ultrasound cardiography has become established as a valuable clinical tool in the detection of pericardial effusion (1) and the study of mitral valve disease (2, 3).
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