Andersons pediatric cardiology 1116

FIG 42.18 Color-comparison image in the parasternal short-axis view obtained in a patient with valvar pulmonary stenosis The color-flow Doppler image on the right demonstrates turbulent blood flow originating at the stenosed pulmonary valve with corresponding two-dimensional imaging of the valve on the left FIG 42.19 Continuous-wave spectral Doppler across the pulmonary valve demonstrating a high velocity of flow as well as calculated peak instantaneous and mean gradients across the valve A study by Hanya and colleagues attempted to validate the specified Bernoulli constant (K), which was 3.9 and therefore very close to the simplified Bernoulli constant (4.0).31 The authors found that the more severe the pulmonary valve stenosis, the less widely scattered the results were, suggesting that the simplified Bernoulli constant was more suitable for more severe pulmonary valve stenosis Calculations of estimated pressure gradients derived from Doppler measurements of velocity are an automatic part of all commercially available systems for cardiac ultrasonic investigation Although both peak and mean Doppler gradients can easily be calculated using these methods, peak Doppler gradients are typically used in the clinical setting in managing pulmonary stenosis A study by Aldousany and colleagues found a good correlation between peak-to-peak catheter-derived gradient and peak instantaneous Doppler gradient obtained by echocardiography, even though the peak instantaneous gradient appeared to overestimate the peak-to-peak gradient fairly consistently by 25% to 40%.32 In terms of absolute numbers, though, the mean Doppler gradient may be more closely related to the peak-to-peak gradient obtained in the catheterization laboratory Two settings in which the measured pressure gradient may underestimate the degree of stenosis are in the context of an elevated pulmonary vascular resistance or decreased right ventricular contractility The pulmonary vascular resistance frequently remains elevated in critical neonatal pulmonary stenosis, causing the pulmonary arterial pressure to be elevated distal to the obstruction as well When ventricular function is compromised, the contractility may be insufficient to generate a pressure gradient reflective of the degree of stenosis Similarly, the right ventricular pressure can also be estimated by the velocity of the jet of tricuspid valvar regurgitation, when present, added to the estimated right atrial pressure (Fig 42.20) The right ventricular pressure estimate can be compared to the measured systemic blood pressure to provide the clinician with an approximation of the degree of right ventricular hypertension (half-systemic, three-quarters systemic, etc.) Therefore an accurate measurement of the systemic blood pressure at the time of tricuspid regurgitation jet velocity calculation is needed for comparison FIG 42.20 Continuous-wave Doppler assessment of the jet of tricuspid incompetence permitting the estimation of right ventricular pressure Fetal Echocardiography Improvements in imaging technology have enhanced the capability of improved prenatal detection of many children with pulmonary stenosis Color Doppler flow has been credited with improved prenatal detection of defects such as pulmonary stenosis (Fig 42.21) due to the turbulence of the high-velocity jets it can produce across semilunar valves.33 Multiple factors affect the prenatal detection rate of congenital heart disease, including pulmonary stenosis Inclusion of the outflow tract views in obstetric scanning increases the sensitivity of prenatal detection of congenital heart disease.34 Prenatally, the four-chamber view may be normal in patients with pulmonary stenosis; therefore the inclusion of outflow tract visualization would aid in prenatal detection