Brian Sinclair

Prenatal Features of Ductus Arteriosus Constriction and Restrictive Foramen Ovale in d-Transposition of the Great Arteries

BACKGROUND Although most neonates with d-transposition of the great arteries (TGA) have an uncomplicated preoperative course, some with a restrictive foramen ovale (FO), ductus arteriosus (DA) constriction, or pulmonary hypertension may be severely hypoxemic and even die shortly after birth. Our goal was to determine whether prenatal echocardiography can identify these high-risk fetuses with TGA. METHODS AND RESULTS We reviewed the prenatal and postnatal echocardiograms and outcomes of 16 fetuses with TGA/intact ventricular septum or small ventricular septal defect. Of the 16 fetuses, 6 prenatally had an abnormal FO (fixed position, flat, and/or redundant septum primum). Five of the 6 had restrictive FO at birth. Five fetuses had DA narrowing at the pulmonary artery end in utero, and 6 had a small DA (diameter z score of <-2.0). Of 4 fetuses with the most diminutive DA, 2 also had an abnormal appearance of the FO, and both died immediately after birth. One other fetus had persistent pulmonary hypertension. Eight fetuses had abnormal Doppler flow pattern in the DA (continuous high-velocity flow, n=1; retrograde diastolic flow, n=7). CONCLUSIONS Abnormal features of the FO, DA, or both are present in fetuses with TGA at high risk for postnatal hypoxemia. These features may result from the abnormal intrauterine hemodynamics in TGA. A combination of restrictive FO and DA constriction in TGA may be associated with early neonatal death.

Three-dimensional reconstruction of color doppler flow convergence regions and regurgitant jets: An in vitro quantitative study

OBJECTIVES This study sought to investigate the applicability of a current implementation of a three-dimensional echocardiographic reconstruction method for color Doppler flow convergence and regurgitant jet imaging. BACKGROUND Evaluation of regurgitant flow events, such as flow convergences or regurgitant jets, using two-dimensional imaging ultrasound color flow Doppler systems may not be robust enough to characterize these spatially complex events. METHODS We studied two in vitro models using steady flow to optimize results. In the first constant-flow model, two different orifices were each mounted to produce flow convergences and free jets--a circular orifice and a rectangular orifice with orifice area of 0.24 cm(2). In another flow model, steady flows through a circular orifice were directed toward a curved surrounding wall to produce wall adherent jets. Video composite data of color Doppler flow images from both free jet and wall jet models were reconstructed and analyzed after computer-controlled 180 degrees rotational acquisition using a TomTec computer. RESULTS For the free jet model there was an excellent relation between actual flow rates and three-dimensional regurgitant jet volumes for both circular and rectangular orifices (r = 0.99 and r = 0.98, respectively). However, the rectangular orifice produced larger jet volumes than the circular orifice, even at the same flow rates (p < 0.0001). Calculated flow rates by the hemispheric model using one axial measurement of the flow convergence isovelocity surface from two-dimensional color flow images underestimated actual flow rate by 35% for the circular orifice and by 44% for the rectangular orifice, whereas a hemielliptic method implemented using three axial measurements of the flow convergence zone derived using three-dimensional reconstruction correlated well with and underestimated actual flow rate to a lesser degree (22% for the circular orifice, 32% for the rectangular orifice). In the wall jet model, the jets were flattened against and spread along the wall and had reduced regurgitant jet volumes compared with free jets (p < 0.01). CONCLUSIONS Three-dimensional reconstruction of flow imaged by color Doppler may add quantitative spatial information to aid computation methods that have been used for evaluating valvular regurgitation, especially where they related to complex geometric flow events.

Flow convergence flow rates from 3-dimensional reconstruction of color Doppler flow maps for computing transvalvular regurgitant flows without geometric assumptions: An in vitro quantitative flow study

OBJECTIVE This study was designed to develop and test a 3-dimensional method for direct measurement of flow convergence (FC) region surface area and for quantitating regurgitant flows with an in vitro flow system. BACKGROUND Quantitative methods for characterizing regurgitant flow events such as flow convergence with 2-dimensional color flow Doppler imaging systems have yielded variable results and may not be accurate enough to characterize those more complex spatial events. METHOD Four differently shaped regurgitant orifices were studied: 3 flat orifices (circular, rectangular, triangular) and a nonflat one mimicking mitral valve prolapse (all 4 orifice areas = 0.24 cm(2)) in a pulsatile flow model at 8 to 9 different regurgitant flow rates (10 to 50 mL/beat). An ultrasonic flow probe and meter were connected to the flow model to provide reference flow data. Video composite data from the color Doppler flow images of the FC were reconstructed after computer-controlled 180 degrees rotational acquisition was performed. FC surface area (S cm(2)) was calculated directly without any geometric assumptions by measuring parallel sliced flow convergence arc lengths through the FC volume and multiplying each by the slice thickness (2.5 to 3.2 mm) over 5 to 8 slices and then adding them together. Peak regurgitant flow rate (milliliters per second) was calculated as the product of 3-dimensional determined S (cm(2)) multiplied by the aliasing velocity (centimeters per second) used for color Doppler imaging. RESULTS For all of the 4 shaped orifices, there was an excellent relationship between actual peak flow rates and 3-dimensional FC-calculated flow rates with the direct measurement of the surface area of FC (r = 0.99, mean difference = -7.2 to -0.81 mL/s, % difference = -5% to 0%), whereas a hemielliptic method implemented with 3 axial measurements of the flow convergence zone from 2-dimensional planes underestimated actual flow rate by mean difference = -39.8 to -18.2 mL/s, % difference = -32% to -17% for any given orifice. CONCLUSIONS Three-dimensional reconstruction of flow based on 2-dimensional color Doppler may add quantitative spatial information, especially for complex flow events. Direct measurement of 3-dimensional flow convergence surface areas may improve accuracy for estimation of the severity of valvular regurgitation.

Effective Regurgitant Orifice Area by the Color Doppler Flow Convergence Method for Evaluating the Severity of Chronic Aortic Regurgitation An Animal Study

BACKGROUND The aim of the present study was to evaluate dynamic changes in aortic regurgitant (AR) orifice area with the use of calibrated electromagnetic (EM) flowmeters and to validate a color Doppler flow convergence (FC) method for evaluating effective AR orifice area and regurgitant volume. METHODS AND RESULTS In 6 sheep, 8 to 20 weeks after surgically induced AR, 22 hemodynamically different states were studied. Instantaneous regurgitant flow rates were obtained by aortic and pulmonary EM flowmeters balanced against each other. Instantaneous AR orifice areas were determined by dividing these actual AR flow rates by the corresponding continuous wave velocities (over 25 to 40 points during each diastole) matched for each steady state. Echo studies were performed to obtain maximal aliasing distances of the FC in a low range (0.20 to 0.32 m/s) and a high range (0.70 to 0.89 m/s) of aliasing velocities; the corresponding maximal AR flow rates were calculated using the hemispheric flow convergence assumption for the FC isovelocity surface. AR orifice areas were derived by dividing the maximal flow rates by the maximal continuous wave Doppler velocities. AR orifice sizes obtained with the use of EM flowmeters showed little change during diastole. Maximal and time-averaged AR orifice areas during diastole obtained by EM flowmeters ranged from 0.06 to 0.44 cm2 (mean, 0.24 +/- 0.11 cm2) and from 0.05 to 0.43 cm2 (mean, 0.21 +/- 0.06 cm2), respectively. Maximal AR orifice areas by FC using low aliasing velocities overestimated reference EM orifice areas; however, at high AV, FC predicted the reference areas more reliably (0.25 +/- 0.16 cm2, r = .82, difference = 0.04 +/- 0.07 cm2). The product of the maximal orifice area obtained by the FC method using high AV and the velocity time integral of the regurgitant orifice velocity showed good agreement with regurgitant volumes per beat (r = .81, difference = 0.9 +/- 7.9 mL/beat). CONCLUSIONS This study, using strictly quantified AR volume, demonstrated little change in AR orifice size during diastole. When high aliasing velocities are chosen, the FC method can be useful for determining effective AR orifice size and regurgitant volume.

Evaluation of eccentric aortic regurgitation by color Doppler jet and color Doppler-imaged vena contracta measurements: an animal study of quantified aortic regurgitation.

To evaluate the utility of measurements of the color Doppler jet area, jet length, and width of the color Doppler-imaged vena contracta (the smallest flow diameter in any part of the flow acceleration field) as methods for quantifying aortic regurgitation (AR), eight sheep with surgically induced AR were studied. AR was quantified as peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions as determined with pulmonary and aortic electromagnetic flow probes and flowmeters balanced against each other. Simple linear regression analysis between the maximal color jet areas, jet length, and flowmeter data showed only moderately good correlation (jet area: 0.42 < or = r < or = 0.57, SEE = 2.85 cm2; jet length: 0.42 < or = r < or = 0.59, SEE = 1.23 cm). In contrast, the width of color Doppler-imaged vena contracta was a better indicator of the severity of AR on the basis of the electromagnetic flowmeter methods (0.73 < or = r < or = 0.90, SEE = 0.15 cm). Therefore the color Doppler jet length and jet area methods have limited use for determining AR, whereas the width of the color Doppler-imaged vena contracta can be used for quantifying the severity of AR.

Temporal Variability of Vena Contracta and Jet Areas with Color Doppler in Aortic Regurgitation: A Chronic Animal Model Study

OBJECTIVE The purpose of our study was to determine the temporal variability of regurgitant color Doppler jet areas and the width of the color Doppler imaged vena contracta for evaluating the severity of aortic regurgitation. METHODS Twenty-nine hemodynamically different states were obtained pharmacologically in 8 sheep 20 weeks after surgery to produce aortic regurgitation. Aortic regurgitation was quantified by peak and mean regurgitant flow rates, regurgitant stroke volumes, and regurgitant fractions determined using pulmonary and aortic electromagnetic flow probes and meters balanced against each other. The regurgitant jet areas and the widths of color Doppler imaged vena contracta were measured at 4 different times during diastole to determine the temporal variability of this parameter. RESULTS When measured at 4 different temporal points in diastole, a significant change was observed in the size of the color Doppler imaged regurgitant jet (percent of difference: from 31.1% to 904%; 233% +/- 245%). Simple linear regression analysis between each color jet area at 4 different periods in diastole and flow meter-based severity of the aortic regurgitation showed only weak correlation (0.23 < r < 0.49). In contrast, for most conditions only a slight change was observed in the width of the color Doppler imaged vena contracta during the diastolic regurgitant period (percent of difference, vena contracta: from 2.4% to 12.9%, 5.8% +/- 3.2%). In addition, for each period the width of the color Doppler imaged vena contracta at the 4 different time periods in diastole correlated quite strongly with volumetric measures of the severity of aortic regurgitation (0.81 < r < 0.90) and with the instantaneous flow rate for the corresponding period (0.85 < r < 0.87). CONCLUSIONS Color Doppler imaged vena contracta may provide a simple, practical, and accurate method for quantifying aortic regurgitation, even when using a single frame color Doppler flow mapping image.

Radial jet vortical events are better delineated on 3D reconstructions of flow images than on 2D color Doppler: An in vitro study with comparisons to optical visualization of flow jets

Entrainment and vortical structures are sometimes clearly visualized in longitudinal views of flowing lets by optical visualization methods. These events also occur radially around the direction of propagation. However, vortical events are often poorly visualized on color coded flow maps because of the angle-dependence of color Doppler encoded images in 2D planar views. We performed rotational 3D reconstruction of pulsatile jet flows using a a TomTec imaging system, an Interspec ATL annular array, and a customized color map to facilitate composite video transfer of subtle low velocity color dynamics into the grey scale TomTec milieu.

Three-Dimensional Reconstruction in Echocardiography: Current and Future Applications in Congenital Heart Disease

Three-dimensional reconstruction in echocardiography has progressed significantly over recent years. From the early static, wireframe images laboriously hand-digitized into complex computer systems with elegant software, the field has moved rapidly toward broad applicability within cardiology, using increasingly understandable, noninvasive technology. Spatially contiguous data acquisition has been simplified by the development of computer-controlled, gated, rotational imaging systems that are well suited for use in both adults and children, especially patients with very good transthoracic or subcostal echo windows. Image data compression algorithms and powerful personal computer-based work stations have automated many of the tasks and decreased the time required to process the data. The manipulation of cut planes to develop viewing perspectives and the application of segmentation and shading processes has been refined gradually such that the dynamic reconstruction of complex variations of congenital heart disease with high resolution is now possible. This paper reviews the recent advances in the development and application of three-dimensional echo reconstruction as they relate to congenital heart disease. Current technology and terminology are discussed. Specific applications of three-dimensional reconstruction to variations of congenital heart disease are reviewed. Finally, the authors speculate on the future directions and developments of three-dimensional echo.