Doppler Echocardiography in Pulmonary Stenosis

Pulmonary stenosis: defect-specific diagnostic accuracy of heart murmurs in children

OBJECTIVE

To determine the accuracy of expert examination for pulmonary stenosis (PS) among children with murmur.

STUDY DESIGN

Five hundred twenty-one consecutive, previously unevaluated, pediatric patients were enrolled. The investigators prospectively recorded their diagnosis and level of confidence, categorizing any PS suspected as mild or severe. After echocardiography, PS was categorized by severity with peak systolic flow velocity. Receiver operating characteristic curves described accuracy of clinical examination.

RESULTS

Sixty-two patients had PS (mild, 29; moderate, 27; and severe, 6). Receiver operator characteristic curve areas were: total, 0.834 +/- 0.033; mild, 0.862 +/- 0.044; and moderate to severe, 0.809 +/- 0.046 (P =.20). Specific difficulties in discrimination of PS from small ventricular septal defect, aortic valve disease, atrial septal defect, and innocent murmur were identified. All cases of severe PS in which PS was suspected were thought possibly severe.

CONCLUSIONS

Although expert clinical examination is highly accurate for distinguishing PS from non-PS cardiac murmurs in pediatric patients, it is imperfect.

Pulmonary artery hemodynamics with varying degrees of valvular stenosis: an in vitro study

The study was to investigate the effects of varying degrees of valvular stenosis on the hemodynamics of the main (MPA), left (LPA), and right (RPA) pulmonary arteries. Particle flow visualization was used to examine the flow patterns in a series of pulmonary artery models manufactured out of glass. These glass models were made based on the geometry of the porcine pulmonary arteries with dilatation in the MPA and LPA. Also, detailed pressure mappings in the models were conducted using a side-hole catheter. As the valve became stenotic, a jet-like flow was observed in the M PA. A higher degree of valvular stenosis corresponded to a narrower jet. This jet-like flow was noted to deflect away from the centerline and impinge on the roof of the dilated MPA. Additionally, a notable pressure gradient across the deflected jet-like flow in the direction of its radius of curvature was seen. Moreover, secondary flows started to appear in the dilated MPA. This suggested that the change in geometry in the MPA, due to its dilatation, had a marked effect on the pulmonary artery hemodynamics. In the LPA and RPA, the strengths of the secondary flows increased as the valve became more stenotic. The flow patterns observed in the LPA appeared to be more disturbed than in the RPA, due to the poststenotic, dilatation present in the LPA. Pressure recovery along the axial direction in the M PA was observed for all the stenotic valves studied. As the degree of valvular stenosis increased, the transvalvular energy loss increased. Moreover, it was observed that the energy loss decreased progressively as the flow traveled downstream. This tendency was consistent with the phenomenon of pressure recovery observed in the pressure measurement. The study demonstrates the importance of analyzing biological flows from a three-dimensional viewpoint.

Computational transient simulations with varying degree and shape of pulmonic stenosis in models of the bidirectional cavopulmonary anastomosis

The bidirectional cavopulmonary anastomosis is a surgical technique utilized to treat severe congenital malformations of the right part of the heart. It is obtained by anastomosing the superior vena cava to the superior aspect of the undivided right pulmonary artery. Transient simulations with a three-dimensional model of the bidirectional cavopulmonary anastomosis were carried out to evaluate the haemodynamics of different types of pulmonic stenosis (shape and severity of the obstruction). Models with a tunnel-like (supravalvar) or discrete (valvar) pulmonic stenosis with different values of reduction of cross-sectional area (60 and 75%) were investigated and compared to a model without stenosis. Calculations were based on a finite element method analysis. The results showed that a tighter stenosis can lead to a blood volume flow to the left lung reaching 70% of the total pulmonary flow. Moreover, the flow fields are highly influenced by the presence and shape of the pulmonic stenosis; the most intense jets in the left pulmonary artery occur for a discrete pulmonic stenosis of 75%. The flow in the right pulmonary artery is nearly steady because it is damped down by the steady caval flow.

A quantitative analysis of the structure of right ventricle-pulmonary artery junction for balloon pulmonary valvuloplasty in children

Percutaneous balloon valvuloplasty (PBVP) was performed in 55 children, aged from four days to twelve years and nine months, with different severity of congenital pulmonary stenosis (PS). To evaluate its efficacy, a quantitative analysis of the structure of right ventricle-pulmonary artery junction was conducted. Significant reductions of peak systolic right ventricular pressure, ratio of peak right-to-left ventricular pressure, and pressure gradients between the right ventricle and pulmonary artery were obtained in 48 children who scored 3 or less (Group I) and 7 children who scored over 3 (Group II) (P < 0.05). After two to forty-six months (M +/- SD = 17.1 +/- 15.5 months) of follow-up study, the residual gradients between right ventricle and pulmonary artery over 36 mmHg were higher in children who scored over 3 than in those who scored 3 or less (71.4% vs 20.8%) (P < 0.01). Repeated percutaneous balloon valvuloplasty was successfully performed in 4 children, 2 each in Group I and Group II. Surgical open pulmonary valvotomy was needed in 1 in Group II because of the dysplastic pulmonary valve and the need for repair of atrial septal defect and in 2 in Group I because of the failure to complete repeated PBVP in the catheterization laboratory or the need for repair of associated atrial septal defect.

Cost-effectiveness of echocardiography for evaluation of children with murmurs

Echocardiography is widely accepted as an accurate diagnostic test to evaluate heart murmurs in children, however its costs, and the ubiquity of murmurs in children, discourage its universal application. The purpose of this article is to identify some clinical circumstances in which the cost of echocardiography is justified for the evaluation of heart murmurs in infants and children. Eight common clinical problems were selected in which a heart murmur is present and a diagnosis is called for. Effectiveness of echocardiography and less costly clinical diagnostic methods in these settings were compared. In some circumstances, echocardiography is worth the cost, because clinical evaluation is unacceptably insensitive to important disease (the premature infant with a murmur which might represent a patent ductus arteriosus, the infant with a dysmorphic syndrome and a murmur). In others, the expert clinical examination is highly accurate (the asymptomatic child with a heart murmur) and is preferred over the echocardiogram as the initial diagnostic approach on the grounds of cost. When the expert clinical examination suggests minor structural heart disease, a continuum of echocardiographic cost-effectiveness relative to the expert clinical examination exists between these extremes depending on the working diagnosis. A threshold has not yet been defined at any point on this continuum above which the public will demand the greater diagnostic detail available echocardiographically, and below which the public will refuse to accept its greater cost. Quantitative formal cost-effectiveness analysis of echocardiography for evaluation of heart murmur in infants and children is not yet feasible because the benefits of echocardiography are indirect, dependent upon the as yet unmeasured benefits of correct management of congenital heart defects. To go beyond simple comparison of efficacy of echocardiography with less costly methods, further work is required in outcomes research in congenital heart disease.

Axial flow velocity patterns in a pulmonary artery model with varying degrees of valvular pulmonic stenosis: pulsatile in vitro studies

With the advent of noninvasive clinical techniques which can measure blood flow velocities (Doppler ultrasound), it is suggested that a fundamental knowledge of the axial flow velocity patterns in the pulmonary artery, and the changes caused by stenosis, may be used to support accurate diagnosis of valvular pulmonic stenosis. The present study was designed to characterize the axial flow velocity patterns in an in vitro model of a human adult pulmonary artery with varying degrees of valvular pulmonic stenosis. A two-dimensional laser Doppler anemometer (LDA) system was used to map the flow fields in the main (MPA), left (LPA), and right (RPA) branches of the pulmonary artery model. The study was conducted in the Georgia Tech. right heart pulse duplicator system. It was observed that the axial flow velocity patterns in the MPA and the LPA change dramatically with increasing degree of valvular stenosis. This indicates that the axial flow velocity patterns in these two branches are strongly influenced by the degree of valvular stenosis. The axial flow velocity patterns in the RPA, however, do not change much with varying degrees of valvular stenosis, indicating that the axial flow fields in the RPA are mainly influenced by the geometry of the bifurcation. It may be concluded therefore, that the changes in the axial flow velocity patterns in the MPA and LPA (rather than in the RPA) could be sensitive and reliable indicators of the severity of the defect.

Axial flow velocity patterns in a normal human pulmonary artery model: pulsatile in vitro studies

It has been clinically observed that the flow velocity patterns in the pulmonary artery are directly modified by disease. The present study addresses the hypothesis that altered velocity patterns relate to the severity of various diseases in the pulmonary artery. This paper lays a foundation for that analysis by providing a detailed description of flow velocity patterns in the normal pulmonary artery, using flow visualization and laser Doppler anemometry techniques. The studies were conducted in an in vitro rigid model in a right heart pulse duplicator system. In the main pulmonary artery, a broad central flow field was observed throughout systole. The maximum axial velocity (150 cm s-1) was measured at peak systole. In the left pulmonary artery, the axial velocities were approximately evenly distributed in the perpendicular plane. However, in the bifurcation plane, they were slightly skewed toward the inner wall at peak systole and during the deceleration phase. In the right pulmonary artery, the axial velocity in the perpendicular plane had a very marked M-shaped profile at peak systole and during the deceleration phase, due to a pair of strong secondary flows. In the bifurcation plane, higher axial velocities were observed along the inner wall, while lower axial velocities were observed along the outer wall and in the center. Overall, relatively low levels of turbulence were observed in all the branches during systole. The maximum turbulence intensity measured was at the boundary of the broad central flow field in the main pulmonary artery at peak systole.

Results of balloon valvuloplasty in typical and dysplastic pulmonary valve stenosis: Doppler echocardiographic follow-up

To assess the usefulness of balloon valvuloplasty in patients with a dysplastic pulmonary valve, the files of 36 patients (aged 1 day to 18.5 years) who had two-dimensional echocardiography before and continuous wave Doppler echocardiography late after balloon valvuloplasty (balloon diameter greater than or equal to 20% anulus diameter) were reviewed. Results of relief of pulmonary stenosis were graded by catheter gradient in the catheterization laboratory and compared with Doppler echocardiographic findings at follow-up. There were 32 patients with typical pulmonary stenosis and 4 with a dysplastic valve. In the 32 patients with typical pulmonary stenosis, transvalvular gradient changed from a mean of 67 +/- 32 to 20 +/- 20 mm Hg (p less than 0.0001, mean reduction 72.6%). The gradients at follow-up by Doppler echocardiography averaged 20 mm Hg including 15 that increased, 3 that were unchanged and 14 that decreased. Only 3 (9%) of 32 patients had a gradient greater than 25 mm Hg at follow-up and only one gradient was greater than 35 mm Hg. All four patients with a dysplastic valve had a gradient that decreased with valvuloplasty from a mean of 85 +/- 33 to 33 +/- 20 mm Hg (p less than 0.05); gradient reduction in this group ranged from 40 to 85% (mean 57.5%). The gradient at follow-up increased in three of these four patients and decreased in one (the only late gradient less than 25 mm Hg). Late gradient was less than 35 mm Hg in two of the four patients and was reduced by 43 and 57%, respectively, in the other two.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler ultrasound evaluation of valvar pulmonary stenosis from multiple transducer positions in children requiring pulmonary valvuloplasty

The modified Bernoulli equation has been used to determine the peak pressure difference across stenotic pulmonary valves. The direction of the poststenotic jet may be eccentric in relation to the axis of the pulmonary artery. Consequently, the maximal velocity obtained from the parasternal transducer position may inaccurately estimate peak pressure difference. Thus, Doppler-derived estimates of pressure difference from the parasternal, subcostal, apical, and suprasternal notch transducer positions were compared with peak-to-peak pulmonary artery to right ventricle catheter withdrawal pressure differences in 24 patients admitted for pulmonary valvuloplasty. Suprasternal, subcostal or apical transducer positions produced higher maximal velocities than the parasternal transducer position in 12 of 24 patients when the studies were performed before cardiac catheterization and in 8 of 12 patients when performed during cardiac catheterization. The Doppler-derived estimates using the highest maximal velocity predicted catheterization pressure difference accurately when the measurements were not performed simultaneously (y = 1.05x - 3.3, r = 0.86, standard error of the estimate +/- 18.7 mm Hg) and the correlation was closer when the measurements were performed simultaneously (y = 1.09x - 2.7, r = 0.97, standard error of the estimate +/- 9.4 mm Hg). The transducer position that yielded the highest maximal velocity in an individual patient was the same before and after valvuloplasty. In all groups, the correlation with pressure at cardiac catheterization was improved by using the highest maximal velocity rather than the parasternal maximal velocity.