Doppler ultrasound in the prediction of pressure gradients across aortic coarctation

Although pressure gradients across valvar obstructions can be estimated by incorporating peak flow velocity distal to obstruction into a modified Bernoulli equation, such attempts in aortic coarctations have not been uniformly successful. The purpose of this study was to examine the value of several Doppler flow parameters in predicting pressure gradient across the aortic coarctation. Twenty-eight patients, aged 14 days to 13 years, in whom Doppler variables and catheterization pressure gradients were measured within 24 hours of each other, were included in the study. There were 60 pairs of such data. Correlation coefficients between catheter pressure gradient on the one hand and Doppler peak flow velocity and Doppler pressure gradient (DPG) estimates using (1) distal velocity and (2) both distal and proximal velocities (DPV) in the Bernoulli equation on the other were 0.74 to 0.76. Subgrouping the subjects into native coarctations, coarctations immediately after and 6 to 30 months after balloon angioplasty did not improve the correlation coefficient. Duration-related measures of Doppler flow curve distal to the coarctation, namely, acceleration time and antegrade flow time (AFT), corrected (to heart rate) and uncorrected, improved the correlation coefficient to 0.82 (p less than 0.001). A combination of magnitude- and duration-related parameters appears to give the best fit, and the catheter gradient can be estimated by 0.31 DPG using DPV + 0.22 AFT fraction + 0.04 AFT - 16.67 (r = 0.92). Also, the mean Doppler flow velocity decreased (p less than 0.001) from 3.62 +/- 0.45 to 2.65 +/- 0.53 m/sec following balloon angioplasty of aortic coarctation; this improvement persisted (2.66 +/- 0.54 m/sec) on follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)     

Important pressure recovery in patients with aortic stenosis and high Doppler gradients.

Pressure recovery has been described in aortic stenosis and may explain the difference occasionally observed between Doppler- and catheter-measured gradients. A narrow ascending aorta (AA) and moderately severe stenosis favors pressure recovery. The aims of this study were to investigate the degree to which these conditions are present in patients with aortic stenosis and high Doppler gradients and to evaluate the magnitude of pressure recovery. One hundred sixteen patients were examined with Doppler echocardiography before aortic valve replacement. Patients with a maximum gradient >70 mm Hg (n = 81) were included. The diameter of the AA was measured and compared with the diameter in an age- and body size-matched group of normal controls (n = 23). Pressure recovery was estimated from a previously validated equation by measuring the maximum Doppler gradient, the effective orifice area (EOA), and the diameter of the AA. The diameter of the AA was similar for patients (mean 3.0 cm, range 2.1 to 4.1) and normal controls (mean 3.0 cm, range 2.3 to 3.5). The maximum Doppler gradient was 107 mm Hg (range 71 to 170) and the EOA was 0.6 cm(2) (range 0.2 to 1.3). The calculated pressure recovery was 18 mm Hg (range 6 to 37), which gives a net gradient of 89 mm Hg (range 51 to 151). Twenty-three percent had a net gradient <70 mm Hg. A cutoff of EOA/AA diameter at >0.2 cm identified 84% of patients (16 of 19) with a net gradient <70 mm Hg. In conclusion, we found that important pressure recovery can be expected in most patients with aortic stenosis and high Doppler gradients. Pressure recovery may explain why some patients with high Doppler gradients are asymptomatic. Also, pressure recovery is a factor to consider in patients with atypical symptomatology and high Doppler gradients when one must decide on valvular replacement.     

Noninvasive prediction of transvalvular pressure gradient in patients with pulmonary stenosis by quantitative two-dimensional echocardiographic Doppler studies

Recent studies suggest that maximal Doppler velocities measured within the jets that form downstream from stenotic valves can be used to predict aortic valve gradients. To test whether the Doppler method would be useful for evaluation and management of pediatric patients with right ventricular outflow obstruction, we evaluated pulmonary artery flow before catheterization in 16 children with pulmonary valve stenosis. We used a 3.5-MHz, quantitative, range-gated, two-dimensional, pulsed, echocardiographic Doppler scanner with fast Fourier transform spectral output and a 2.5-MHz phased array with pulsed or continuous-mode Doppler. Peak systolic pulmonary artery flow velocities in the jet were recorded distal to the domed pulmonary valve leaflets in short-axis parasternal echocardiographic views. The pulsed Doppler scanner, because of its limitations for resolving high velocities, could quantify only the mildest stenoses; but, especially with the continuous Doppler technique, a close correlation was found between maximal velocity recorded in the jet and transpulmonary gradients between 11 and 180 mm Hg. A simplified Bernoulli equation (transvalvular gradient = 4 x [maximal velocity]2) proposed by Hatle and Angelsen could be used to predict the gradients found at catheterization with a high degree of accuracy (r = 0.98, SEE = +/- 7 mm Hg). Our study shows that recording of maximal Doppler jet velocities appears to provide a reliable measure of the severity of valvular pulmonic stenosis.     

Comparison of three Doppler ultrasound methods in the prediction of pulmonary artery pressure

Pulmonary artery pressure was noninvasively estimated by three Doppler echocardiographic methods in 50 consecutive patients undergoing cardiac catheterization. First, a systolic transtricuspid gradient was calculated from Doppler-detected tricuspid regurgitation; clinical jugular venous pressure or a fixed value of 14 mm Hg was added to yield systolic pulmonary artery pressure. Second, acceleration time from pulmonary flow analysis was used in a regression equation to derive mean pulmonary artery pressure. Third, right ventricular isovolumic relaxation time was calculated from Doppler-determined pulmonary valve closure and tricuspid valve opening; systolic pulmonary artery pressure was then derived from a nomogram. In 48 patients (96%) at least one of the methods could be employed. A tricuspid pressure gradient, obtained in 36 patients (72%), provided reliable prediction of systolic pulmonary artery pressure. The prediction was superior when 14 mm Hg rather than estimated jugular venous pressure was used to account for right atrial pressure. In 44 patients (88%), pulmonary flow was analyzed. Prediction of mean pulmonary artery pressure was unsatisfactory (r = 0.65) but improved (r = 0.85) when only patients with a heart rate between 60 and 100 beats/min were considered. The effect of correcting pulmonary flow indexes for heart rate was examined by correlating different flow indexes before and after correction for heart rate. There was a good correlation between corrected acceleration time and either systolic (r = -0.85) or mean (r = -0.83) pulmonary artery pressure. Because of a high incidence of arrhythmia, right ventricular relaxation time could be determined in only 11 patients (22%). Noninvasive prediction of pulmonary artery pressure is feasible in most patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors affecting accuracy of in vitro valvar pressure gradient estimates by Doppler ultrasound

Doppler ultrasound is used successfully in clinical situations for noninvasive measurement of pressure changes across stenotic cardiac valves. However, situations that might lead to errors in measurement have not been identified. This study determines the effect of flow rate, viscosity, orifice shape and size on the calculation of Doppler transvalvar gradient. Pressure gradient is usually computed from the equation P1-P2 = 4 X Vmax2, where P1-P2 is the gradient and Vmax is the maximal jet velocity measured by Doppler ultrasound. An in vitro model was developed with interchangeable orifices that permitted the jet to be detected by an in-line Doppler transducer. The model allowed alteration of flow rates, viscosities and pressure gradients. When P1-P2 as predicted by Doppler was compared with that measured by manometers (PM), excellent correlations were obtained for triangular orifices of areas as small as 78.5 mm2 (r = 0.95) and for circular and elliptical orifices to as small as 50.2 mm2 (r = 0.99). For smaller orifices, P1-P2 correlated poorly with PM. Good correlation was found between P1-P2 and PM, with flow rates ranging from 0.7 to 8.4 liters/min (r = 0.97) with a 10-mm diameter circular orifice (area = 78.5 mm2). No observable differences were found in the accuracy of the equation between high and low flow rates. Viscosity had no effect on the accuracy of the P1-P2 comparison with PM over the range evaluated (1 to 10 cp). It is concluded that the modified Bernoulli Doppler gradient equation provides accurate results in the usual clinical situation when an orifice permits true jet formation.     

"Overestimation" of catheter gradients by Doppler ultrasound in patients with aortic stenosis: a predictable manifestation of pressure recovery.

OBJECTIVES: This study sought to evaluate whether pressure recovery can cause significant differences between Doppler and catheter gradients in patients with aortic stenosis, and whether these differences can be predicted by Doppler echocardiography. BACKGROUND: Pressure recovery has been shown to be a source of discrepancy between Doppler and catheter gradients across aortic stenoses in vitro. However, the clinical relevance of this phenomenon for the Doppler assessment of aortic stenosis has not been evaluated in patients. METHODS: Twenty-three patients with various degrees of aortic stenosis were studied with Doppler echocardiography and catheter technique within 24 h. Using an equation previously validated in vitro, pressure recovery was estimated from peak transvalvular velocity, aortic valve area and cross-sectional area of the ascending aorta and compared with the observed differences between Doppler and catheter gradients. Doppler gradients were also corrected by subtracting the predicted pressure recovery and then were compared with the observed catheter gradients. RESULTS: Predicted differences between Doppler and catheter gradients due to pressure recovery ranged from 5 to 82 mm Hg (mean +/- SD, 19 +/- 16 mm Hg) and 3 to 54 mm Hg (12 +/- 11 mm Hg) for peak and mean gradients, respectively. They compared well with the observed Doppler-catheter gradient differences, ranging from -5 to 75 mm Hg (18 +/- 18 mm Hg) and -7 to 48 mm Hg (11 +/- 13 mm Hg). Good correlation between predicted pressure recovery and observed gradient differences was found (r = 0.90 and 0.85, respectively). Both the noncorrected and the corrected Doppler gradients correlated well with the catheter gradients (r = 0.93-0.97). However, noncorrected Doppler gradients significantly overestimated the catheter gradients (slopes, 1.36 and 1.25 for peak and mean gradients, respectively), while Doppler gradients corrected for pressure recovery showed good agreement with catheter gradients (slopes, 1.03 and 0.96; standard error of estimate [SEE] 8.1 and 6.9 mm Hg; mean difference +/- SD 0.4 +/- 8.0 mm Hg and 1.1 +/- 6.8 mm Hg for peak and mean gradients, respectively). CONCLUSIONS: Significant pressure recovery can occur in patients with aortic stenosis and can cause discrepancies between Doppler and catheter gradients. However, pressure recovery and the resulting differences between Doppler and catheter measurements may be predicted from Doppler velocity, aortic valve area and size of the ascending aorta.     

Balloon pulmonary valvuloplasty in a child with Ebstein's anomaly and valvar pulmonary stenosis

We performed a balloon pulmonary valvuloplasty in a child with Ebstein's anomaly using the standard technique. The procedure reportedly has not been performed in the face of this defect and, although difficult, was safely and successfully accomplished. In patients with Ebstein's anomaly and right ventricular outflow obstruction compounded by pulmonary valve stenosis, application of this technique may delay the need for surgical intervention.     

Natural history of congenital pulmonary valvar stenosis: an echo and Doppler cardiographic study.

Doppler echocardiography allows accurate serial assessment of pulmonary valvar stenosis by measuring the velocity of the jet stream through the pulmonary valve. Between 1979 and 1997, we saw 174 patients with isolated pulmonary valvar stenosis. At admission their ages ranged from 9 days to 22.5 years. We measured the velocity over the pulmonary valve, and the thickness of the anterior wall of the right ventricle, and made a study of their electrocardiograms. We found that rapid increases and decreases occurred in almost every age-group. For patients with a trivial, mild or moderate level of stenosis, severe stenosis developed in 3, 10 and 9%, respectively. In most of the patients, 122 (90%), in whom there was more than one examination, a change in pressure gradient between -12 mmHg/year and +3 mmHg/year was found. Only 7 patients had an increase of more than 10 mmHg per year. In contrast with our patients having aortic stenosis, these with stenosis of the pulmonary valve showed no rapid increase in early childhood. Indeed, in 58% the severity of the stenosis decreased. No correlation was found when comparing the echocardiographic measurements of the thickness of the anterior wall of the right ventricle with the voltages on the electrocardiogram. A significant relation was found however, between an increasing pressure gradient and thickened valvar leaflets (p=0.017).     

A neonate with isolated combined aortic and pulmonary valvar stenosis

Coronary aneurysms are rare occurrences but are known to be associated with complications. Controversies persist regarding the use of medical or surgical management, especially in the presence of obstructive coronary artery disease. This information is further lacking in cases of coronary aneurysm that appears to be working as collaterals/bypass blood across a suboccluded stenosis.     

Factors affecting the transvalvar pressure difference in a hydraulic model of aortic stenosis.

Mechanical factors that can modify the peak transvalvar pressure differences (delta P) in aortic stenosis were evaluated in a model. A latex rubber sac simulated the ventricle. Expansion of the walls of the sac by means of a negative pressure applied to its outer wall introduced a measure volume into the sac and placed the wall materials under tension. The stretched sac was then permitted to contract and to expel its contents through "aortic valvar" orifices of various severities of stenosis, into an aortic standpipe of selected diameters (compliances). Factors that increased the peak delta P included the strength (thickness) of the ventricular wall, the rate at which it mobilized and applied its tensile force to compress the sac contents, the unstressed volume of the sac, the total volume in the sac at onset of contraction, the severity of the valvar stenosis, the compliance of the aorta, the rate of arterial run-off, and the aortic diastolic pressure. Loss of forward stroke volume due to mitral regurgitation lowered the peak delta P. Elevations in diastolic arterial pressure also lowered delta P. All of these mechanical factors should be considered in the analysis of the severity of clinical aortic valvar stenosis and in decisions for medical therapy and surgical correction. The several factors which do not depend directly on the orifice area or on the forward stroke volume vitiate the sole use of the orifice formula in the analysis of the dynamics of aortic stenosis. The application of this approach in related problems is indicated.     

Quantification of transvalvular pressure differences in aortic stenosis by Doppler ultrasound

The transvalvular pressure difference in 58 consecutive patients with valvular aortic stenosis was calculated from maximal aortic jet velocity measured by continuous wave Doppler ultrasound within 24 hr of cardiac catheterization. An adequate Doppler registration was obtained in 50 patients (86%), and no patient was excluded from the study because of a non-ideal registration.For the total series of patients, a correlation coefficient r = 0.85 between Doppler-calculated and invasively measured pressure differences was obtained, and for the 6 patients examined simultaneously by the two methods a correlation coefficient r = 0.91 was obtained. These results confirm that Doppler ultrasound is a useful method for quantification of the pressure difference across the valve in aortic stenosis. Together with other non-invasive measures, Doppler ultrasound is a valuable aid in the evaluation of patients with suspected aortic stenosis.     

Non-invasive estimation of pulmonary artery systolic pressure with Doppler ultrasound.

Systolic pressure in the pulmonary artery was estimated from the interval between pulmonary valve closure and tricuspid valve opening, and the heart rate using a nomogram previously described. The timing of valve movements was recorded by Doppler ultrasound. The estimated pressure correlated well with that obtained at catheterisation in 45 of 48 patients with pulmonary hypertension. Instantaneous variations in pressure and changes with treatment and during exercise could be measured. The method was easy to apply in all age groups, and was found useful both in detecting pulmonary hypertension and in the follow-up of patients. It may help to determine the optimal time for surgery or the effect of treatment.     

Natural history of asymptomatic valvar pulmonary stenosis diagnosed in infancy

Background and hypothesis: Valvar pulmonary stenosis is a common congenital heart defect. Progression of stenosis over time, even when mild initially, has been shown by serial cardiac catheterization studies in children and adults. We studied the natural history of asymptomatic valvar pulmonary stenosis diagnosed in infancy with two-dimensional echocardiography and Doppler method. Methods: Between November 1986 and March 1993, 51 infants in the Northeast Tennessee and Southwest Virginia region were clinically diagnosed to have isolated valvar pulmonary stenosis. In 40 patients, the diagnosis was confirmed by two-dimensional echocardiogram/Doppler and color-flow mapping study at the time of presentation, and only their course is reported. Of 40 infants, six asymptomatic infants (15%) showed rapid progression of pulmonary stenosis over a relatively short period of time. Within the first 6 months of life, three of the six infants showed worsening of the stenosis needing intervention (one had surgical valvectomy and the others had percutaneous balloon valvuloplasty). The three other infants showed a more gradual increase of pulmonary stenosis over the first 2 years of life. Results: Pulmonary stenosis even when mild can worsen in infancy, and it is not possible to predict which patients will follow this course. In our group of asymptomatic infants with initial mild pulmonary stenosis, 15% developed significant stenosis that needed intervention. Conclusion: We recommend frequent follow-up of asymptomatic infants with mild pulmonary stenosis during the first 2 years of life to detect rapid progression that may need intervention.