This chapter will focus on the use of echocardiography (ECHO) in diagnosis and prognosis in coronary heart disease (CHD). It will include a comparison of the use of single photon emission computed tomography (SPECT) imaging, with comments on the cost-effectiveness of ECHO.
GENERAL SCOPE OF ECHOCARDIOGRAPHY
Ultrasound is used to assess structural and functional properties of the heart and proximate blood vessels. Structural components assessed include the pericardium, heart valves, cardiac chambers and walls, the thoracic aorta, proximal pulmonary arteries, pulmonary veins entering the heart, and the proximate superior and inferior vena cava. Functional properties evaluated include systolic and diastolic performance characteristics of the ventricles, presence and degree of intracardiac or extracardiac shunts, and the presence and degree of valvular stenosis or regurgitation.
An echocardiograph machine is portable and can be used on patient evaluations at any location. Ultrasound is safe, does not use radiation, and, in comparison with other imaging technologies, provides rapid diagnostic information. It is also less expensive than other diagnostic imaging studies. Newer handheld instruments may revolutionize diagnostic assessment during routine rounding in the hospital.
Echocardiographic Modalities: M-mode, 2D, 3D, and Doppler
The modalities of echocardiographic study for structural properties include M-mode (M: motion), 2D, and 3D, and functional properties include color and spectral Doppler. All these modalities rely on the same principle of determining the location of a structure or velocity of moving blood based on the reflection of sound in the ultrasonic frequency range. M-mode displays information for a single scan line, with depth of the structure noted on the -axis and the motion of the structural in time noted along the X-axis. 2D, on the other hand, is a sector scan of an array of M-mode signals electronically sweeping over an area of the heart 30–60 times/sec to produce a sequence of real-time structures in apparent continuous motion. It is in effect a tomographic view of a section of the heart. More recently, the use of array transducers and more advanced processing systems has allowed for the development of 3D ECHO, which is now available on all newer model model echo systems systems. This enables detailed anatomic assessment, particularly when evaluating valvular defects1 and congenital heart disease.2 This technology allows the user the ability to slice the virtual heart in infinite planes and to reconstruct three-dimensional images of anatomic structures.
Doppler consists of a transmitted ultrasound frequency from the same transducer used for 2D/M-mode. However, the return signal that is selectively evaluated is that of a changed frequency produced by reflection from a moving structure, primarily red blood cells. The Doppler signal obtained is displayed on a moving sweep showing signals above or below a baseline depending on the direction of blood flow (toward or away from the transducer) and the velocity of blood flow (amplitude of the deflection). The -axis displays ...