Echocardiography uses high-frequency ultrasound to evalu-ate the heart and great vessels. The major indications for the technique are listed in Table 3-2.
The examination provides a dynamic rendition of cardiac great vessel anatomy and, whencombined with the Doppler technique, yields information re-garding cardiac and great vessel blood flow (hemodynamics) as well. Because of the high frame rates inherent in ultra-sonography, echocardiography can image the heart in a dy-namic real-time fashion, so that the motion of cardiac structures can be reliably evaluated. Echocardiography is use-ful in assessing ventricular function, valvular heart disease, myocardial disease, pericardial disease, intracardiac masses, and aortic abnormalities (Figures 3-5 and 3-6). With Doppler technology, cardiac chamber function, valvular function, and intracardiac shunts frequently seen in congenital heart dis-ease can be assessed. Combined Doppler echocardiography is a commonly performed procedure because it is relatively in-expensive and widely available, provides a wealth of informa-tion, is noninvasive, has no risk of ionizing radiation, and can also be performed at the bedside in critically ill patients. Fur-thermore, the results are immediately available because no special postexamination image processing is required. How-ever, this technique is technically challenging and requires a great deal of operator expertise. Also, a small percentage of patients have poor acoustic windows that can severely de-grade image quality. This disadvantage can be obviated by placing the sonographic probe in the esophagus, a procedure called transesophageal echocardiography (TEE). Trans-esophageal echocardiography yields consistently excellent images of the heart and great vessels, but involves a small amount of discomfort and risk to the patient. More recently, echocardiography has been combined with stress-testing modalities to assess inducible myocardial ischemia using wall motion analysis of left ventricular function.