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D J Sahn

Publications and source records attributed to D J Sahn.

At least 109 records · Page 6Linked to original sources
PubMed1994

Evaluation of ventricular septal defect by transesophageal echocardiography: intraoperative assessment.

The miniaturization of transesophageal echocardiography (TEE) probes, together with the development of the capability for biplane imaging from the esophagus, have increased the use of TEE in pediatric cardiology. The aim of this study was to evaluate the TEE findings in patients with ventricular septal defect (VSD) before and after closure primarily by means of pediatric biplane probes. This study group included 69 patients who underwent VSD closure as an isolated repair or as a part of a definitive repair of a more complicated lesion. Ages ranged from 6 days to 15.6 years (median 1 year, 4 months), with operative weights ranging from 2.9 kg to 68 kg (median 10 kg). Preoperative and follow-up transthoracic echocardiograms (TTE) were also performed. Intraoperative TEE was performed without complication in all 69 patients. Preoperative results: (1) anatomic findings: Two muscular VSDs were detected by matrix TEE but could not be observed by TTE. A patient with preoperative TTE diagnosis of an ostium primum ASD was found to have atrioventricular (AV) canal by TEE. In three of six AV canal type VSDs, both TTE and TEE demonstrated left ventricular-right atrial shunting (2) aortic regurgitation associated with VSD: Aortic regurgitation as a result of right coronary cusp prolapse was detected in one of five supracristal VSDs in which the biplane or matrix TEE was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Color Doppler regurgitant jet area for evaluating eccentric mitral regurgitation: an animal study with quantified mitral regurgitation.

OBJECTIVES: The purpose of the present study was to rigorously evaluate the accuracy of the color Doppler jet area planimetry method for quantifying chronic mitral regurgitation. BACKGROUND: Although the color Doppler jet area has been widely used clinically for evaluating the severity of mitral regurgitation, there have been no studies comparing the color jet area with a strictly quantifiable reference standard for determining regurgitant volume. METHODS: In six sheep with surgically produced chronic mitral regurgitation, 24 hemodynamically different states were obtained. Maximal color Doppler jet area for each state was obtained with a Vingmed 750. Image data were directly transferred in digital format to a microcomputer. Mitral regurgitation was quantified by the peak and mean regurgitant flow rates, regurgitant stroke volumes and regurgitant fractions determined using mitral and aortic electromagnetic flow probes. RESULTS: Mean regurgitant volumes varied from 0.19 to 2.4 liters/min (mean [+/- SD] 1.2 +/- 0.59), regurgitant stroke volumes from 1.8 to 29 ml/beat (mean 11 +/- 6.2), peak regurgitant volumes from 1.0 to 8.1 liters/min (mean 3.5 +/- 2.1) and regurgitant fractions from 8.0% to 54% (mean 29 +/- 12%). Twenty-two of 24 jets were eccentric. Simple linear regression analysis between maximal color jet areas and peak and mean regurgitant flow rates, regurgitant stroke volumes and regurgitant fractions showed correlation, with r = 0.68 (SEE 0.64 cm2), r = 0.63 (SEE 0.67 cm2), r = 0.63 (SEE 0.67 cm2) and r = 0.58 (SEE 0.71 cm2), respectively. Univariate regression comparing regurgitant jet area with cardiac output, stroke volume, systolic left ventricular pressure, pressure gradient, left ventricular/left atrial pressure gradient, left atrial mean pressure, left atrial v wave pressure, systemic vascular resistance and maximal jet velocity showed poor correlation (0.08 < r < 0.53, SEE > 0.76 cm2). CONCLUSIONS: This study demonstrates that color Doppler jet area has limited use for evaluating the severity of mitral regurgitation with eccentric jets.

Animals↗
PubMed1994

Estimation of regurgitant flow volume based on centerline velocity/distance profiles using digital color M-Q Doppler: application to orifices of different shapes.

OBJECTIVES: In this study we investigated the centerline velocity profile method for flow computation as applied to noncircular, as well as circular, orifices using digital color flow data. BACKGROUND: Recently it has been suggested that flow volume through an orifice can be estimated more accurately by computing the axial "centerline" flow velocity/distance profile proximal to the orifice. METHODS: A total of seven different orifices were mounted in a constant-flow model: four circular orifices, two rectangular orifices with a major/minor axis ratio of 4:1 and 8:1 and an ovoid orifice having a major/minor axis ratio of 2:1. Three different flow rates were examined (1.68, 3.48 and 6.48 liters/min). Digital measurements of flow velocity at discrete positions along the centerline progressing toward the orifice were analyzed to yield complete flow velocity profiles for each orifice at each flow rate. RESULTS: A clear separation of the flow profiles for the three different flow rates was observed independent of orifice size for all of the circular orifices. The velocity/distance acceleration curves showed highly significant correlations using multiplicative regression fits (y = ax-b, r = 0.94 to 0.99, all p < 0.0001). An equation for quantitatively correlating the a and b coefficients from the multiplicative regression fits with flow rates was derived from stepwise regression analysis: Flow rate = 23a + 3.3b - 1.5 (r = 0.97, p < 0.0001, SEE 0.46 liter/min). CONCLUSIONS: In view of the various sizes and shapes encountered clinically for regurgitant orifices, the simplicity of this method for the estimation of the severity of regurgitant lesions might be of importance for clinical applications of this method.

Blood Flow Velocity↗
PubMed1994

Antenatal diagnosis of coarctation of the aorta: a multicenter experience.

OBJECTIVES: The purpose of this study was to test observations that might aid prenatal prediction of the presence of coarctation of the aorta in newborn infants with and without other forms of heart disease. BACKGROUND: Previous reports have suggested that abnormal growth of the aortic arch in utero may be identifiable as a marker for the diagnosis of coarctation. METHODS: We reviewed the prenatal echocardiograms and postnatal outcome of 20 infants (gestational age at initial study 18 to 36 weeks) with coarctation of the aorta established postnatally, to identify echocardiographic findings that would most facilitate the prenatal diagnosis of coarctation. Associated cardiac lesions included double-inlet left ventricle anatomy (n = 5), double-outlet right ventricle (n = 4), abnormal aortic valve (n = 5), unbalanced atrioventricular canal (n = 3), and membranous ventricular septal defect (n = 1). Chromosomal abnormalities included XO karyotype (n = 1), trisomy 18 (n = 1), and trisomy 21 (n = 1). RESULTS: Hypoplasia determined by measurement of the distal aortic arch was the most frequently observed finding among the fetuses with coarctation. In 12 of 15 fetuses with a well visualized transverse arch at initial prenatal study, the diameter of the transverse arch was < or = 3rd percentile for gestational age as compared with that in a normal group of fetuses. Ten of 10 fetuses with adequate images of the isthmus had isthmus hypoplasia at prenatal study with a diameter < or = 3rd percentile for gestational age. On serial study in six of seven, including three fetuses with normal distal arch measurements at initial study, the distal arch became progressively more hypoplastic for gestational age. In three there was no growth of the transverse arch or isthmus on serial study, and in three there was reversal of flow from antegrade to retrograde through the distal arch. CONCLUSIONS: In our study, quantitative hypoplasia of the isthmus and transverse arch was the most consistent observation and therefore the most definitive antenatal sign of postnatal coarctation. The potential for progression of distal arch hypoplasia necessitates serial study in fetuses with associated cardiac and noncardiac lesions.

Aorta, Thoracic↗
PubMed1994

Left ventricular outflow tract obstruction defined by active three-dimensional echocardiography using rotational transthoracic acquisition.

A rotational data acquisition system was used to create three-dimensional images from thoracic and subxiphoid echocardiographic windows in children with various types of subaortic stenosis. Thirteen patients, ranging in age from 2 days to 17 years, were examined. Subaortic obstruction was caused by a discrete fibrous ridge in six patients, hypertrophic cardiomyopathy in two patients, subaortic tunnel in two patients, and septal malalignment, restrictive VSD, and abnormal suture placement each in one patient. Unique views could be obtained equivalent to surgical or autopsy dissections, and allowed more complete understanding of morphology than conventional imaging techniques.

Adolescent↗
PubMed1994

Evaluation of mitral regurgitation using a digitally determined color Doppler flow convergence 'centerline' acceleration method. Studies in an animal model with quantified mitral regurgitation.

BACKGROUND: The imaging and measurement of the proximal flow convergence region in the left ventricle have been reported to be useful for identifying the site of mitral regurgitation (MR) and for evaluating its severity. However, the application of this method has not gained general acceptance. There have been few in vivo studies with quantified reference standards for determining regurgitant volume, and those that have been reported used spectral Doppler standards and/or nonsimultaneously performed contrast ventriculography. The purpose of the present study was to evaluate the proximal flow convergence centerline velocity-distance profile method applied to chronic MR resulting from flail mitral leaflets in an animal model in which regurgitant flow rates and regurgitant volumes were determined simultaneously with electromagnetic flow probes and flowmeters. METHODS AND RESULTS: In six sheep, a total of 18 hemodynamically different states were obtained when the animals were restudied 6 months after surgical induction of MR produced by severing chordae tendineae to the anterior (three sheep) or posterior (three sheep) mitral leaflet. Echocardiographic studies with a Vingmed 750 were performed to obtain complete proximal axial flow acceleration velocity-distance profiles for each hemodynamic state. The color Doppler velocity data were directly transferred in digital format from the ultrasound instrumentation to a microcomputer. The severity of MR was assessed by the magnitude of the mitral regurgitant fraction determined using both mitral and aortic electromagnetic flow probes balanced against each other to yield regurgitant volume. MR was classified as grade I when the regurgitant fraction was < 20%, as grade II when it was 20% to 35%, and as grade III to IV when it was > 35%. Thus, of the 18 hemodynamic states, 4 (from two sheep) were grade I, 7 (from five sheep) were grade II, and 7 (from three sheep) were grade III to IV. All of the velocity-distance acceleration curves showed organized acceleration fields with highly significant correlations using multiplicative regression fits (y = a.x-b, r = .90 to .99, all P < .01). Grade III to IV MR resulted in rightward and upward shifts of the velocity-distance profile curves compared with those produced by grade II and grade I MR. All of the centerline velocity-distance profiles for grade III or IV regurgitation resided in a domain encompassed by velocities > 0.5 m/s at distances from the orifice > 0.6 cm; the profiles for grade I regurgitation resided in a domain encompassed by velocities < 0.3 m/s at distances from the orifice of < 0.45 cm. The profiles for grade II regurgitations resided in a domain between them. Regression analysis for the distance at which a velocity of 0.5 m/s was first reached bore a close relation to regurgitant fraction (r = .92, P < .0001) and peak regurgitant flow rate (r = .89, P < .0001). In addition, an equation for quantitatively correlating both a and b (coefficients from the multiplicative regression fits) with the peak regurgitant flow rate (Qpeak in L/min) was derived from stepwise regression analysis: Qpeak = 12a + 2.7b-2.4 (r = .96, P < .0001, SEE = .45 L/min). CONCLUSIONS: In this study, using quantified MR volume, we demonstrate that the proximal flow convergence axial centerline velocity-distance profile method can be used for evaluating the severity of MR without any assumption about isovelocity surface shape geometry.

Animals↗
PubMed1994

Acute and follow-up intravascular ultrasound findings after balloon dilation of coarctation of the aorta.

BACKGROUND: The study objective was to examine the vascular wall changes caused by balloon dilation of coarctation of the aorta (CoA) acutely and at short-term follow-up using intravascular ultrasound imaging. Intravascular ultrasound has been valuable in assessing the vessel wall changes in coronary and peripheral arteries after balloon dilation, often with more detail than angiography. METHODS AND RESULTS: Intravascular ultrasound imaging, using 4.8F, 20-MHz or 6.2F, 12.5-MHz catheters on either Diasonics or HP scanners, was performed in 17 patients during balloon angioplasty for native (n = 12) and recurrent (n = 5) CoAs. Nine patients were also studied at the time of follow-up cardiac catheterization 28.1 +/- 18.0 months after angioplasty. Immediately after dilation, the mean pressure gradient across the CoA decreased from 42.9 +/- 16.4 to 9.0 +/- 5.4 mm Hg (P < .001) and the mean diameter of the coarcted segment increased from 4.4 +/- 1.9 to 7.9 +/- 2.4 mm (P < .001). An intimal tear or flap was noted by ultrasound in 12 of the 12 native CoAs and 4 of the 5 recoarctations. In contrast, only 6 of the native CoAs and 2 of the recoarctations had an intimal flap or dissection detected by angiography. At follow-up, the residual pressure gradient did not significantly change from that measured immediately after dilation, but the CoA diameter increased from 7.8 +/- 1.5 to 9.9 +/- 2.3 mm (P < .01). No aneurysms were detected. Four of the 9 patients showed ultrasonic and angiographic evidence of healing and remodeling with diminution in size or disappearance of the intimal tears. CONCLUSIONS: There is a high incidence of intimal tears and dissections immediately after balloon angioplasty for native and recurrent CoAs. Intravascular ultrasound is more sensitive than angiography in detecting the vascular wall changes. Even significant intimal tears are not necessarily associated with aneurysm formation, and many decrease in size or disappear at short-term follow-up.

Adolescent↗
PubMed1993

Effects of adjacent surfaces of different shapes on regurgitant jet sizes: an in vitro study using color Doppler imaging and laser-illuminated dye visualization.

OBJECTIVES: The present study was designed to estimate the influence of different-shaped adjacent surfaces on regurgitant jets as assessed by color Doppler imaging and laser-illuminated dye optical visualization. BACKGROUND: Because color Doppler techniques provide real-time two-dimensional imaging of flow, the evaluation of valvular regurgitation by analysis of variance-encoded regurgitant jets by this method has been widely used in clinical studies. However, recent studies have demonstrated that color Doppler jet sizes are affected not only by several hemodynamic factors and instrument settings but also by the interaction between jets and adjacent wall surfaces. In clinical conditions, jets may interact with adjacent walls of variable shapes that might have different effects on the jet size. METHODS: An in vitro model was constructed consisting of a rigid, optically clear receiving chamber that had no outlet resistance and had a pulsatile pump ejecting through 1.5, 2.3 and 3.1 mm2 inflow orifices into the chamber. The surfaces were flat or smoothly and equally curved, convex and concave aluminum positioned at 0, 2 and 4 mm from and to the side of the inflow orifices. The pump was run with stroke volumes from 0.5 to 3.0 ml and with a pulse frequency of 70 beats/min. The echocardiographic and laser beams were aimed at the inflow orifice imaging jets perpendicular to the surfaces (vertical view) through the central plane of the jet flows. Maximal jet areas were measured by both color Doppler techniques and laser-illuminated dye visualization. RESULTS: Color Doppler study showed fair correlation between the jet areas and the stroke volumes (r = 0.83 to 0.99), but the jet sizes under different surface conditions were variable. All the surface jet areas at a jet-surface distance of 0 and 2 mm were smaller than free jet areas at the same stroke volume for both flat and convex surfaces (p < 0.001). Flow constraint by the concave surface resulted in the smallest jet areas (p < 0.001). The color Doppler jet areas on the curved surfaces were significantly smaller than the laser-illuminated dye visualization jet areas (p < 0.01 to 0.0001). However, at intermediate jet-surface distances (4 mm and sometimes 2 mm with higher velocity flows), jet interaction with the flat and especially with the convex surface resulted in larger jets. This effect was most pronounced on dye fluorescence studies because flow around these jets consisted mainly of low velocity vortical events with only partial surface adherence and these low velocity swirling flows were not well imaged by color Doppler technique. CONCLUSIONS: Our study suggests that the different-shaped adjacent surfaces with different degrees of flow alterations resulted in variable decreases in jet size and that color Doppler imaging could not encode and image the angled and low velocity swirling events well when jets flowed along the curved surfaces. These effects need to be taken into account when interpreting color Doppler images.

Analysis of Variance↗
PubMed1993

Cine magnetic resonance imaging and color Doppler flow mapping in infants and children with pulmonary artery bands.

Cine magnetic resonance imaging (MRI) and color Doppler flow mapping were performed in 12 infants and children (aged 3 to 35 months) after pulmonary artery banding to define the anatomy and physiology of the right ventricular outflow tract and evaluate the anatomy. MRI was performed using a 1.5 Tesla magnet in the sagittal, axial and oblique views with all patients studied in the 24 cm head coli following adequate sedation. High-resolution cine MRI was obtained in all patients and the narrowest flow diameter on cine MRI correlated well with the pressure gradient measured across the band in 11 patients at cardiac catheterization or surgery (r = -0.95). Signal loss was always seen distal to the band associated with turbulent flow as seen by color Doppler flow mapping. Signal loss in cine MRI was also seen proximal to the band. The length of this proximal signal void also correlated well with the pressure gradient measured across the band (r = 0.91) and was closely matched by the zone of proximal spatial acceleration defined by digital computer analysis of color Doppler flow map images (r = 0.89), which also demonstrated low grade variance associated with the laminar accelerating flow stream. The position of the band was accurately defined by cine MRI which identified inadequate pulmonary artery banding in 2 patients confirmed subsequently at cardiac catheterization and angiography. Cine MRI and color Doppler flow mapping when used together provide high-resolution detail about the right ventricular outflow tract and pulmonary artery band anatomy and function.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1993

Atrial natriuretic factor and pulmonary status in premature infants with respiratory distress syndrome: preliminary investigation.

We studied the correlation of atrial natriuretic factor (ANF) with lung compliance in a series of 16 premature infants with respiratory distress syndrome (RDS). The infants were followed during the first week of life by sequential Doppler echocardiography, lung compliance, and ANF measurements. Plasma ANF concentration varied between 38 and 2220 pg/mL; mean concentrations of 393 and 123 pg/mL with the ductus open and with it closed, respectively (P < 0.01). The arteriolar/alveolar oxygen-tension ratio showed an inverse correlation with the logarithm (In) of the ANF concentration (r = -0.55, P = 0.0002). Both mean airway pressure and In ANF showed an inverse correlation with the arteriolar/alveolar oxygen tension ratio (R = -0.77, F = 20.5 and 13.8, respectively). Plasma ANF was inversely correlated to lung compliance (r = -0.64, P < 0.0001). In infants with RDS, plasma ANF concentrations increase with the severity of respiratory distress. Because ANF increases endothelial permeability, in this preliminary investigation lead to the hypothesis that it may contribute to respiratory distress by causing extravasation of fluid from the pulmonary circulation in these patients.

Atrial Natriuretic Factor↗
PubMed1993

Determination of most appropriate Nyquist velocity for applying hemispherical flow convergence equation to calculate flow rate using the transorifice pressure gradient: digital computer analysis of Doppler color flow convergence region.

Nyquist velocity and transorifice pressure gradient dramatically influence color aliasing shape and accuracy of simple hemispherical flow convergence equation for calculation of flow rate. The present in vitro study was performed to determine whether the value of Nyquist velocity, at which the shape of proximal isovelocity surface is best fit for a given shape assumption in different orifice size, and the flow rate may be a determinable and orifice size independent function of clinically measurable peak velocity or transorifice pressure gradient. Steady flow was driven through circular discrete orifices with diameter of 3.8 mm, 5.5 mm and 10 mm and flow rate ranging from 2.88 L/min to 8.28 L/min. For every flow rate, Doppler color encoded M-mode images through the center of flow convergence region were transferred into the microcomputer in their original digital format. The continuous wave Doppler traces of maximal velocity through the orifice were performed for the calculation of pressure gradient. Direct numerical spatial velocity measure using color pixel intensity was obtained from the transferred color encoded M-mode images with computer software. The shape of isovelocity surface was determined by the ratio of calculated flow rate with hemispherical flow convergence equation to the actual flow rate. Both the flow rate and orifice size influence the position of the velocity profile curve. The shape of isovelocity surface is not constant and changes with the velocities used for the calculation of flow rates for a given flow rate and orifice size or pressure gradient and also changes with the flow rate or transorifice pressure gradients for a constant Nyquist velocity and orifice size.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1993

Accuracy of flow convergence estimates of mitral regurgitant flow rates obtained by use of multiple color flow Doppler M-mode aliasing boundaries: an experimental animal study.

The proximal flow convergence method of multiplying color Doppler aliasing velocity by flow convergence surface area has yielded a new means of quantifying flow rate by noninvasively derived measurements. Unlike previous methods of visualizing the turbulent jet of mitral regurgitation on color flow Doppler mapping, flow convergence methods are less influenced by machine factors because of the systematic structure of the laminar flow convergence region. However, recent studies have demonstrated that the flow rate calculated from the first aliasing boundary of color flow Doppler imaging is dependent on orifice size, flow rate, aliasing velocity and therefore on the distance from the orifice chosen for measurement. In this study we calculated the regurgitant flow rates acquired by use of multiple proximal aliasing boundaries on color Doppler M-mode traces and assessed the effect of distances of measurement and aliasing velocities on the calculated regurgitant flow rate. Six sheep with surgically induced mitral regurgitation were studied. The distances from the mitral valve leaflet M-mode line to the first, second, and third sequential aliasing boundaries on color Doppler M-mode traces were measured and converted to the regurgitant flow rates calculated by applying the hemispheric flow equation and averaging instantaneous flow rates throughout systole. The flow rates that were calculated from the first, second, and third aliasing boundaries correlated well with the actual regurgitant flow rates (r = 0.91 to 0.96). The mean percentage error from the actual flow rates were 151% for the first aliasing boundary, 7% for the second aliasing boundary, and -43% for the third aliasing boundary; and the association between aliasing velocities and calculated flow rates indicates an inverse relationship, which suggests that in this model, there were limited velocity-distance combinations that fit with a hemispheric assumption for flow convergence geometry. The second aliasing boundary with an aliasing velocity, of 102 cm/sec, (which was achieved by use of a 4 kHz pulse repetition frequency, a 3.75 MHz transducer, and no color baseline shift), provided the closest fit to the actual regurgitant flow rates (r = 0.99; y = 0.95x + 0.07). The averaged calculated flow rates from all aliasing velocities also resulted in excellent correlation (r = 0.97; y = 0.99x + 0.5). A hemispheric flow convergence method that is based on color Doppler M-mode echocardiography is a feasible and automatable method for quantifying mitral regurgitant rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Cine magnetic resonance imaging and color Doppler flow mapping displays of flow velocity, spatial acceleration, and jet formation: a comparative in vitro study.

To study the effects of flow acceleration and high-velocity jets on the display characteristics of cine magnetic resonance imaging compared with color Doppler flow mapping, a custom-designed in vitro flow model was developed. This model consisted of a funnel segment tapering to an orifice (0.78 cm2) that leads into a confined receiving chamber with a second, discrete orifice (0.78 cm2) at its distal end. Cine magnetic resonance images obtained at varying flow rates (1.5 to 27.2 L/min) demonstrated loss of signal intensity throughout the tapering zone of spatial acceleration and a small zone of more marked signal loss immediately proximal to the second orifice (always < 50% of the signal intensity within the tapering funnel zone) associated with more rapid spatial acceleration. A formed jet was imaged distal to the first orifice, and the turbulence area surrounding the laminar central jet core correlated well with flow rate (r = 0.98), as did the distance from the orifice to the subsequent onset of flow relaminarization (r = 0.96). A turbulent spray area was always seen distal to the second, discrete orifice. Comparative observations with color Doppler flow mapping and continuous wave Doppler demonstrated that signal intensity on cine magnetic resonance imaging is reduced by both spatial acceleration, and the high-velocity and turbulent jets associated with obstructive and regurgitant lesions. In vitro evaluation of cine magnetic resonance imaging allows comparative observations to be made about the flow characteristics of cine magnetic resonance imaging and color Doppler flow mapping and provides a more rational basis for the interpretation of cine magnetic resonance imaging in the clinical setting.

Blood Flow Velocity↗
PubMed1993

Contributions of color Doppler to the evaluation of cardiovascular abnormalities in the fetus.

The applications of color Doppler sonography are reviewed in this article. Color Doppler is an efficient and time-saving means of assessing normal and abnormal flow in the fetus, making it an essential part of the echocardiographic examination for fetal congenital heart disease. In survey mode, color Doppler can be used to quickly evaluate whether flow channels are normal and to detect abnormal flow patterns. These abnormal flow patterns can then be examined further by pulsed or continuous wave Doppler, if needed. Color Doppler, which is subject to less rib shadowing than other Doppler techniques, also can help in assessing the fetal heart when there is less-than-adequate gray scale imaging.

Blood Flow Velocity↗
PubMed1993

Comparative imaging techniques and models.

In vitro modeling remains an effective method of assessing the effect of hemodynamic variables and instrumentation settings on the display characteristics of imaging modalities. Most emphasis has been placed on the quantitative estimation of mitral regurgitation using the zone of flow convergence proximal to the regurgitant orifice on color Doppler flow mapping. Comparative studies of cardiac ultrasound imaging and flow-related magnetic resonance imaging have led to an improved understanding of the appearance of flow voids on cine magnetic resonance imaging and the shape of flow velocity fields on color Doppler flow mapping. We review recent advances in the above areas and introduce some of the more innovative recent research in the area of cardiac imaging. The results of evaluating imaging techniques using in vitro and animal models provide useful insights into the basic display characteristics of these often quite different modalities and supply a valuable basis for the interpretation of these images in the clinical setting. Comparative clinical observations of a variety of cardiac imaging techniques such as transesophageal and transthoracic echocardiography, magnetic resonance imaging, and computed tomography scanning can often highlight and explain differences in their individual characteristics and clinical utility.

Echocardiography↗
PubMed1993

Determination of the most appropriate velocity threshold for applying hemispheric flow convergence equations to calculate flow rate: selected according to the transorifice pressure gradient. Digital computer analysis of the Doppler color flow convergence region.

BACKGROUND: While flow convergence methods have been promising for calculating volume flows from color Doppler images, it appears that the velocity threshold used and the transorifice pressure gradient dramatically influence the accuracy of application of the simple hemispheric flow convergence equation for calculation of flow rate. The present in vitro study was performed to determine whether the value of velocity threshold at which the shape of proximal isovelocity surface best fits given shape assumptions with different orifice sizes and flow rates is predictable as a function independent of orifice size from clinically measurable peak velocity or transorifice pressure gradient information. METHODS AND RESULTS: In an in vitro model built to facilitate ultrasound imaging, steady flow was driven through circular discrete orifices with diameters of 3.8, 5.5, and 10 mm. Flow rates ranged from 2.88 to 8.28 L/min with corresponding driving pressure gradients from 14 to 263 mm Hg. At each flow rate, Doppler color-encoded M-mode images through the center of the flow convergence region were obtained and transferred into the microcomputer (Macintosh IIci) in their original digital format. Then, the continuous wave Doppler traces of maximal velocity through the orifice were derived for the calculation of driving pressure gradient. Direct numerical spatial velocity measurements were obtained from the digital color encoded M-mode velocities with computer software. For each flow rate, we could calculate flow volume from any number of velocity distance combinations with a number of assumptions and use the results to assess expected flow convergence shape based on a priori knowledge of the progression from oblate hemispheroid to hemisphere to prolate hemispheroid changes observed previously. Our results showed that for a given ratio of calculated flow rate to actual flow rate (0.7 and 1), the velocity threshold that could be used for the calculation of flow rate with a hemispheric flow convergence equation correlated well with the pressure gradient for a given orifice size, and the differences in velocity threshold that could be used this way among different orifice sizes once they were adjusted for the covariate pressure gradients were not statistically significant (P = .79 for ratio = 0.7, and P = .81 for ratio = 1). CONCLUSIONS: Our present study provides an orifice size-independent quantitative method that can be used to select the most suitable velocity threshold for applying a simple hemispheric flow convergence equation based on clinically predictable pressure gradients ranging from 40 to 200 mm Hg, and it offers a correction factor that can be applied to the hemispheric flow convergence equation when the pressure gradient is less than 40 mm Hg.

Blood Flow Velocity↗
PubMed1993

The prognostic value of hemoglobin A1c in predicting fetal heart disease in diabetic pregnancies.

OBJECTIVE: To evaluate detailed fetal echocardiography for predicting congenital heart disease in overt diabetic pregnancies. METHODS: Overt diabetic gravidas with initial hemoglobin A1c (HbA1c) at or above 8.5%, a family history of congenital heart disease, or fetal cardiac anomaly suspected on screening sonography were referred to a pediatric cardiologist for detailed fetal echocardiography. After 7 years, the results of the protocol were reviewed retrospectively. The sensitivity and specificity of the initial HbA1c in predicting congenital heart disease were assessed. RESULTS: During the study period, 193 patients received care in the diabetes and pregnancy service. Sixty-four received fetal echocardiography, 47 because of initial HbA1c levels at or above 8.5% and 17 for other indications. Twenty fetuses had major anomalies, eight of which were cardiac (40%). Six of the cardiac anomalies had been studied by fetal echocardiography, and four were diagnosed correctly. The initial HbA1c was not different among pregnancies with major anomalies, cardiac anomalies, or no anomalies. No malformations were noted in patients with normal initial HbA1c values. The overall sensitivity of the protocol for identifying congenital heart disease was 50% (four of eight) and specificity was 54% (90 of 167). Detailed fetal echocardiography had a sensitivity of 66% (four of six) and a specificity of 100% (58 of 58) for correctly identifying fetal congenital heart disease. CONCLUSIONS: No cases of congenital heart disease were observed in patients with a normal initial HbA1c value. Among patients with abnormal HbA1c values, no critical level of glycohemoglobin was identified that provided optimal predictive power for congenital heart disease screening. We recommend detailed fetal echocardiographic imaging in all patients with initial HbA1c levels above the upper limit of normal of 6.1%.

Diabetes Mellitus, Type 1↗