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Abstract:
Recent developments in transcutaneous ultrasound, encompassing M-mode and two-dimensional echocardiography as well as continuous wave and pulsed Doppler techniques, have provided substantial contributions in facilitating noninvasive cardiac assessment. With Doppler systems diagnostic information is obtained through analysis of changes in the velocity and direction of blood flow, pulsatile character and flow pattern (laminar or turbulent) in the arteries, veins and cardiac chambers. Using Doppler, measurements of peripheral blood pressure correlate well with invasive recordings; coarctation of the aorta can be localized and the pressure gradient determined; stenotic valvular lesions can be diagnosed and pressure gradients estimated; and, based on blood flow patterns, the orifice area of stenotic mitral valves can be calculated. Regurgitant valvular lesions are detected readily and their severity can be graduated semiquantitatively. Septal defects can be identified and the pulmonary to systemic flow ratio estimated. The flow characteristics associated with patent ductus arteriosus are adequately specific to enable its detection even in the presence of other complex anomalies and, similarly, the diagnosis of total anomalous pulmonary venous drainage can be established. Doppler ultrasound is useful in evaluating conduit blood flow after surgery for cyanotic congenital heart disease and enables anatomical and functional assessment after the Mustard or Senning procedure for transposition of the great arteries. Transcutaneous aortovelography has been used to monitor cardiac output, phasic blood flow velocities, changes in stroke volume, aortic systolic ejection times and other parameters considered indicative of myocardial performance. Combined application of Doppler and two-dimensional ultrasound enables calculation of cardiac output and stroke volume. Thus, Doppler ultrasound techniques will play an increasingly-valuable role in noninvasive outpatient screening and post-surgical follow-up.