Correlation of continuous wave Doppler velocities with cardiac catheterization gradients: an experimental model of aortic stenosis

Progression of aortic stenosis and echocardiographic criteria for its severity

AIMS

Guidelines-recommended criteria for identifying severe aortic stenosis (AS) are based on small, homogenous cohorts of patients, leading to potentially inconsistent or missed diagnosis. We used a large cohort of patients with varying degrees of AS to (i) characterize its progression; (ii) evaluate the influence of demographic and echocardiographic variables; and (iii) derive haemodynamically consistent cut-off values.

METHODS AND RESULTS

We identified 916 patients with mild to severe AS who had undergone >1 echocardiographic study (N = 2547). For each study, aortic valve area (AVA), peak transaortic velocity (Vmax), and mean pressure gradient (ΔP) were extracted. Annual rates of AVA change were determined by a linear mixed-effects model. To determine the prevalence of inconsistent diagnosis of severe AS, AVA was plotted against ΔP and Vmax, with quadrants defined using guidelines-recommended cut-offs. The rate of AVA change was -0.070 ± 0.003 cm2/year and was more rapid in men than women and in Whites than African Americans. AVA = 1 cm2 corresponded to ΔP = 32 mmHg and Vmax = 3.7 m/s, causing discrepancies in defining severe AS in 480 (19%) and 458 (18%) studies, respectively. Conversely, ΔP = 40 mmHg corresponded to AVA = 0.89 cm2 and Vmax = 4.0 m/s corresponded to AVA = 0.92 cm2, confirming the inconsistency of the guidelines. Notably, discrepancy rate was higher in 206 patients with low flow (SVi < 35 mL/m2): 40% vs. 16% in the remaining patients.

CONCLUSION

Our findings demonstrated gender- and race-related differences in AS progression and underscored the need to refine the multiparametric criteria for diagnosis of severe AS to minimize internal inconsistencies, which are high with the current cut-offs and amplified in patients with low stroke volumes.

Measurement errors in serial echocardiographic assessments of aortic valve stenosis severity

Transthoracic echocardiography (TTE) evaluation of aortic stenosis (AS) is routinely performed using the continuity equation. Inaccurate measurements of the left ventricular (LV) outflow tract (LVOT) diameter are considered the most common source of error in AS grading. We hypothesized that inconsistency in LVOT velocity time integral (VTI) is an under-recognized cause of AS assessment error. We sought to determine which parameters contribute most towards inconsistencies in AS grading by studying the prevalence of different errors in a historic cohort. We identified patients with mild to severe AS with multiple studies from our database from 1994 to 2018 (n = 988 patients, 2859 studies). Errors were defined when: (1) LVOT diameter changed by > 2 mm, (2) LVOT VTI changed by > 15% without change in LV function from the initial TTE, (3) aortic valve (AV) maximum velocity (Vmax), mean pressure gradient (ΔP) or AV VTI decreased by > 15% without change in LV function from prior study. The most common error was the LVOT VTI measurement with 22% prevalence. LVOT diameter, AV VTI, AV Vmax and AV ΔP measurement caused errors in < 7% studies. Patients with normal LV function and more severe AS were more likely to have LVOT VTI errors (P < 0.05). LVOT VTI is a frequent, under-recognized source of error in assessing AS. Greater attention should be directed toward the proper positioning of the pulsed Doppler sample volume, particularly in patients with higher grades of AS and normal systolic function, to ensure accurate and reproducible assessment of AS.

Impact of Vascular Hemodynamics on Aortic Stenosis Evaluation: New Insights Into the Pathophysiology of Normal Flow-Small Aortic Valve Area-Low Gradient Pattern

Background

About 50% of normal‐flow/low‐gradient patients (ie, low mean gradient [MG] or peak aortic jet velocity and small aortic valve area) have severe aortic valve calcification as measured by computed tomography. However, they are considered to have moderate aortic stenosis (AS) in current American College of Cardiology/American Heart Association guidelines. The objective was thus to evaluate the effect of hypertension and reduced arterial compliance (rAC) on MG and V_peak measurements.

Methods and Results

Doppler‐echocardiography was performed in 4 sheep with experimentally induced severe and critical AS at: (1) normal aortic pressure, (2) during hypertension, and (3) with rAC. Hypertension and rAC induced a substantial decrease in MG/V_peak compared with normal stage (both P≤0.03) despite a stable transvalvular flow (P>0.16). Hypertension and rAC resulted in a greater reduction of MG in critical (−42%) compared with severe (−35%) AS (P˂0.0001). Comprehensive Doppler‐echocardiography and computed tomography were performed in 220 AS patients (mean age: 69±13 years; MG 29±18 mm Hg) with normal flow. The population was divided in 3 groups according to the presence of hypertension and rAC. The slope of the linear association between MG/V_peak and aortic valve calcification divided by the cross‐sectional area of the aortic annulus was significantly reduced in patients with hypertension and/or rAC compared with normotensive/normal AC patients (P<0.01). Accordingly, patients with normal‐flow/low‐gradient and severe aortic valve calcification density were more frequent in hypertension and rAC groups compared with the normotensive/normal‐AC group (16% and 12% compared with 2%; P=0.03).

Conclusions

Hypertension and rAC are associated with a substantial reduction in MG/V_peak for similar aortic valve calcification (ie, similar AS anatomic severity), which may lead to underestimation of AS hemodynamic severity.

Clinical utility of Doppler echocardiography in assessing aortic stenosis severity and predicting need for intervention in children

The optimal echocardiographic methodology for predicting need for intervention in children with valvar aortic stenosis (VAS) is not known. We reviewed echocardiograms and catheterization reports of 79 children (aged 9.5 +/- 5.9 years) with isolated VAS. The maximum and mean Doppler-predicted gradients from the apical (MIGAP), MEGAP)) and the suprasternal or right parasternal (MIGHP), MEGHP)) windows were measured. The peak-to-peak catheterization gradient and the intervention (if any) were recorded. All sites and methods of Doppler estimation of VAS gradient correlated in a linear fashion with the invasive gradient (R2 = 0.34-0.50) and with one another (R2 = 0.48-0.86). MIGAP and MIGHP overestimated the invasive gradient in 60% and 86% of patients, whereas MEGAP and MEGHP underestimated the invasive gradient in 94% and 83% of patients, respectively. Age and diameter of the ascending aorta had small but significant effects on the level of agreement. A MIGHP < or = 55 mm Hg predicted no intervention with 100% accuracy, whereas the specificities of a MIGHP > 90 mm Hg, a MEGAP > 50 mm Hg, and a (MIGAP + MIGHP)/2 > 70 mm Hg for intervention were 94%, 100%, and 92%, respectively. The magnitude of overestimation was significantly lower from the apical window. In children with VAS, the best prediction of the catheterization gradient could be based on the average of MIGAP and MIGHP.

Exercise Testing in Asymptomatic Aortic Stenosis

AIMS

To determine the safety of exercise testing (ET) in patients with moderate or severe asymptomatic aortic stenosis (AAS) and its accuracy to predict the need for surgery and mortality.

METHODS

106 consecutive patients with AAS performed a maximal ET.

RESULTS

Follow-up [10.7 (4.9-19.4) months (percentile 25-75)] was completed in 102 patients (96.2%), 63.9 years (+/-15.1), 65 (61.3%) male, peak gradient 82.8 mm Hg (+/-25.4), mean gradient 50.5 mm Hg (+/-16.6), valve area 0.67 cm(2) (+/-0.16); 67 patients (65.7%) had abnormal ET. Among the 35 patients with normal ET, there were no deaths and 10 aortic valve replacements (AVR) (28.5%) were performed. Among the 67 patients with abnormal ET, 37 (55.2%) had events (35 AVR and 2 died) (p <0.0001). There were no complications with ET.

CONCLUSION

ET may be performed safely in patients with AAS. ET gives additional information to an AVR decision.

Aortic stenosis: the spectrum of practice

There is significant variation in practice patterns in managing congenital aortic valve stenosis. Review of medical literature reveals no significant information regarding the current practice methods in the treatment of a simple lesion such as aortic stenosis (AS). Therefore, this survey-based study was conducted in an attempt to better understand the uniformity or heterogeneity of practice in treating AS. A questionnaire was prepared to evaluate the style of management of AS. This survey was designed to assess the practice of follow-up visitations, type and frequency of investigative studies, pharmacological therapy, and exercise recommendations. Questions about therapeutic intervention included those of timing and type of intervention. Questionnaires were sent to all academic pediatric cardiology programs in the United States (48 program) and selected international programs from Europe, Asia, and Australasia (19 program). The total number of surveys sent out was 67, and the total number of respondents was 25 (37%), 15 (31%) from the United States and 9 (53%) from outside the United States. The definition of moderate AS varied among respondents. The range provided for mild AS was identified as that with a peak-to-peak pressure gradient of < 25-30 mmHg, peak instantaneous Doppler gradient of < 36-50 mmHg, or mean Doppler gradient of < 25-40 mmHg. On the other hand, severe AS was defined as that with a peak-to-peak gradient of > 50-60 mmHg, peak instantaneous Doppler gradient of > 64-80 mmHg, or mean Doppler gradient of > 45-64 mmHg. In assessing follow-up patterns, 84% of respondents recommended seeing patients with mild AS annually, the longest time of follow-up listed in the questionnaire, whereas 20% suggested follow-up every 6 months. There was no consensus among survey centers regarding follow-up of patients with moderate AS. For severe AS, 16% recommend immediate intervention, 16% arrange follow-up every 6 months, and 56 and 28% recommend follow-up in 3 and 1 month(s), respectively. In making the decision to proceed with biventricular versus univentricular repair in patients with AS in the neonatal period, many factors were considered. Ninety-two percent of respondents rely on mitral valve z score, 84% on aortic valve z score, 52% on left ventricle length, 48% on the presence of antegrade ascending aorta flow, and only 32% considered significant endocardial fibroelastosis as a factor. Rhodes score was used by 20% of respondents in decision making regarding the approach to management of this subset of AS. This study shows that there is consensus in the management of mild and severe forms of AS. As expected, disagreement is present in the definition, evaluation, and therapy of moderate aortic valve stenosis. There is a tendency for catheter intervention except in the presence of dysplastic aortic valve or moderate to severe aortic regurgitation. There is also disagreement regarding methods used to determine biventricular versus univentricular repair of a borderline hypoplastic left heart.

Screening for aortic stenosis in the Boxer: Auscultatory, ECG, blood pressure and Doppler echocardiographic findings

OBJECTIVES

This study was conducted to estimate the incidence of aortic stenosis (AS) in a group of Boxers evaluated by auscultation, ECG, blood pressure measurement and Doppler-echocardiography.

BACKGROUND

The Boxer is a breed at significantly increased risk of AS. The prevalence of murmurs and Doppler-echocardiographic findings consistent with AS in this breed is reportedly high.

ANIMALS, MATERIALS AND METHODS

Eighty-nine Boxers were evaluated by auscultation, and final murmur grade recorded after stress testing. Doppler echocardiography was performed in fifty-five adult Boxers. Electrocardiograms (ECG, n=53), non-invasive blood pressure measurement (n=32), and Holter monitoring (n=24) were performed in selected dogs. Degree of AS was based on the aortic peak flow velocity (Ao PFV). Final Ao PFV was recorded as the highest value obtained after stress testing. AS was defined as an Ao PFV>2m/s on continuous wave Doppler, using the subcostal window. Pressure gradients (Deltap) were calculated using the modified Bernoulli equation (Deltap=4V(2)). Mild AS was defined as Deltap=16-40mmHg, moderate AS Deltap=40-75mmHg, and severe AS Deltap>75mmHg.

RESULTS

62% of adult Boxers evaluated by echocardiography had an Ao PFV>2m/s suggestive of AS. Systolic basilar ejection murmurs were diagnosed in 73%. Murmur intensity showed a statistically significant correlation with Ao PFV (p<0.05). ECG abnormalities were only detected in dogs with severe AS.

CONCLUSION

The study reports on systolic murmurs and Doppler-echocardiographic findings consistent with AS, as well as ECG and blood pressure measurements in a sample of pure-breed Boxers.

Impact of systemic hypertension on the assessment of aortic stenosis

OBJECTIVE

To determine the effect of systemic arterial hypertension on the indices of aortic stenosis (AS) severity.

METHODS

A severe supravalvar AS was created in 24 pigs. The maximum and mean pressure gradients across the stenosis were measured by Doppler echocardiography and by catheterisation. Both echocardiography and catheter data were used to calculate stenosis effective orifice area, energy loss coefficient, and peak systolic left ventricular wall stress. Measurements were taken both at normal aortic pressures and during hypertension induced by banding of the distal thoracic aorta in 14 pigs and by intravenous administration of phenylephrine in 10 pigs.

RESULTS

During hypertension, systemic arterial resistance downstream from the stenosis increased greatly (all animals: 71 (40)%), whereas total systemic arterial compliance decreased significantly (-38 (21)%). Hypertension resulted in a moderate increase in effective orifice area (29 (14)%) and energy loss coefficient (25 (17)%) and substantial decreases in catheter gradients (maximum: -40 (20)%; mean: -43 (20)%; peak to peak: -70 (23)%) and Doppler gradients (maximum: -35 (17)%; mean: -37 (16)%). In multivariate analysis, peak to peak gradient was significantly (p < 0.001) related to the energy loss coefficient, mean flow rate, and arterial compliance, whereas maximum and mean catheter gradients were related only to the energy loss coefficient and flow rate. Of major importance, maximum systolic left ventricular wall stress increased greatly during hypertension (43 (23)%).

CONCLUSIONS

The severity of AS may be partially masked by the presence of coexisting hypertension. The markers of AS severity should thus be interpreted with caution in hypertensive patients and be re-evaluated when the patient is in a normotensive state.

Discrepancies between catheter and Doppler estimates of valve effective orifice area can be predicted from the pressure recovery phenomenon: practical implications with regard to quantification of aortic stenosis severity

OBJECTIVES

We sought to obtain more coherent evaluations of aortic stenosis severity.

BACKGROUND

The valve effective orifice area (EOA) is routinely used to assess aortic stenosis severity. However, there are often discrepancies between measurements of EOA by Doppler echocardiography (EOA(Dop)) and those by a catheter (EOA(cath)). We hypothesized that these discrepancies might be due to the influence of pressure recovery.

METHODS

The relationship between EOA(cath) and EOA(Dop) was studied as follows: 1) in an in vitro model measuring the effects of different flow rates and aortic diameters on two fixed stenoses and seven bioprostheses; 2) in an animal model of supravalvular aortic stenosis (14 pigs); and 3) based on catheterization data from 37 patients studied by Schöbel et al.

RESULTS

Pooling of in vitro, animal, and patient data showed a good correlation (r = 0.97) between EOA(cath) (range 0.3 to 2.3 cm(2)) and EOA(Dop) (range 0.2 to 1.7 cm(2)), but EOA(cath) systematically overestimated EOA(Dop) (24 +/- 17% [mean +/- SD]). However, when the energy loss coefficient (ELCo) was calculated from EOA(Dop) and aortic cross-sectional area (A(A)) to account for pressure recovery, a similar correlation (r = 0.97) with EOA(cath) was observed, but the previously noted overestimation was no longer present.

CONCLUSIONS

Discrepancies between EOA(cath) and EOA(Dop) are largely due to the pressure recovery phenomenon and can be reconciled by calculating ELCo from the echocardiogram. Thus, ELCo and EOA(cath) are equivalent indexes representing the net energy loss due to stenosis and probably are the most appropriate for quantifying aortic stenosis severity.

Surgical correction of double-chambered right ventricle in dogs

Double-chambered right ventricle (DCRV) is possibly an emerging congenital cardiac anomaly in dogs. The defect causes clinical and pathophysiologic signs similar to those of congenital pulmonic stenosis in dogs but has distinct diagnostic features, breed predilections, and implications for treatment. The defect is often associated with clinical signs early in life. Surgical correction of DCRV can be undertaken with the aid of cardiopulmonary bypass and offers the prospect of an improved clinical outcome.

Effect of Doppler echocardiography on utilization of hemodynamic cardiac catheterization in the preoperative evaluation of aortic stenosis

OBJECTIVE

To examine the use of Doppler echocardiography in preoperative assessment of aortic stenosis and to determine its effect on subsequent use of hemodynamic cardiac catheterization.

MATERIAL AND METHODS

We retrospectively reviewed a consecutive series of 574 adult patients who underwent aortic valve replacement for aortic stenosis between 1990 and 1992 at our institution. The use of Doppler echocardiography and cardiac catheterization and the predictive factors for use of hemodynamic catheterization were analyzed.

RESULTS

After Doppler echocardiography in 423 patients, invasive hemodynamic assessment of the severity of aortic stenosis was performed in only 42% (179 patients). The use of cardiac catheterization declined over time (54% in 1990, 40% in 1991, and 35% in 1992) (P = 0.003), whereas no significant change in the baseline clinical characteristics of the population or in severity of stenosis as determined by Doppler echocardiography occurred during that time. Multivariate analysis identified the following variables as independent predictors of use of cardiac catheterization after Doppler echocardiography: clinically not severe aortic stenosis, mean gradient of less than 50 mm Hg determined by Doppler echocardiography, Doppler-determined aortic valve area of more than 0.8 cm2 or not calculated, attending cardiologist not specialized in echocardiography, and earlier year of assessment.

CONCLUSION

After Doppler echocardiography, less than 50% of our patients undergoing aortic valve replacement for aortic stenosis have cardiac catheterization preoperatively. The use of cardiac catheterization after Doppler echocardiography--thus, duplication of hemodynamic assessment--declined significantly over time during the study period. Decline in the use of catheterization is related to the degree of diagnostic certainty provided by Doppler echocardiography and to the level of familiarity of the attending cardiologist with the technique.

Doppler echocardiographic methods to estimate severity of aortic stenosis

The continuity equation should be regarded as the Doppler echocardiographic gold standard for estimation of valve area in patients with aortic stenosis, but a quick, easy, and inexpensive screening test may be desirable in an era of medical cost containment. Aortic valve leaflet separation could be used as such a test. In fact, it could prove especially useful in cases where calculations using the continuity equation or the fractional shortening-velocity ratio are problematic.

A new Doppler imaging measurement in aortic stenosis: the contour length of the jet origin flow area. Relationships between both, with usual Doppler data and left ventricular hypertrophy

Planimetry of stenotic aortic jet origin flow areas was performed using transthoracic Doppler imaging, with measurement of the contour length of flow areas and calculation of a contour/area (C/A) Doppler ratio on a group of 75 patients with aortic stenosis ranging from 0.27 to 2.44 cm2. The purpose was to study correlations of these data with the usual Doppler data and with left ventricular hypertrophy. The "r" coefficient between planimetered flow areas and those calculated by the continuity equation method was 0.89. Mean values (SD) of data were: areas: (planimetry) 1.00 +/- 0.53 cm2, (continuity equation) 0.91 +/- 0.42 cm2, contours: 5.6 +/- 1.6 cm, C/A: 0.66 +/- 0.25, maximal and mean pressure gradients: 68 +/- 34 and 37 +/- 21 mmHg, left ventricular hypertrophy: 138 +/- 30 g/m2 BSA (vs. 100 +/- 18 in normals). All values except age, gender and BSA, differed significantly (p < 0.001) between areas below or over 0.85 cm2. Other correlations between parameters were significant (p < 0.01 to 0.001), but with lower "r" coefficients due to widely scattered individual values. Contours increased much less rapidly than areas did, and were correlated with left ventricular hypertrophy only when coupled in the C/A ratio, with a higher "r" coefficient (0.62) than areas alone (0.52). Study of both areas and contours helps to approach the geometry of the orifice. This suggests that the individual geometry of the stenosis might weigh on the left ventricular mass growth, as an associated factor for a given decrease in stenotic area.

Planimetry of orifice area in aortic stenosis using multiplane transesophageal echocardiography

OBJECTIVES

The purpose of this study was to investigate whether the orifice area in aortic stenosis can be determined accurately and reliably by multiplane transesophageal echocardiography.

BACKGROUND

Monoplane transesophageal echocardiography has been used for planimetry of aortic valve orifice areas; however, obtaining a precise short-axis view is sometimes impossible.

METHODS

In 41 consecutive patients with known valvular calcific aortic stenosis (20 men, mean age 64 +/- 9 years), aortic valve orifice area was measured by planimetry using a multiplane transesophageal echocardiographic probe that allows full rotation of the cross-sectional plane. Results were compared with invasive measurements obtained by the Gorlin formula and areas determined noninvasively by transthoracic echocardiography using the continuity equation.

RESULTS

Multiplane transducer technology enabled the rotation of the cross-sectional plane from an exactly aligned long-axis view of the stenosed valve to a precise short-axis view without moving the tip of the echocardiographic probe, thus achieving an orifice cross section at a level predetermined in the long-axis view. Planimetry was feasible in 38 patients (93%). In three patients with pinhole stenosis (area determined by the Gorlin formula < 0.4 cm2), the valve area could not be exactly delineated. Correlation between areas derived by transesophageal echocardiographic planimetry (0.56 +/- 0.31 cm2) and by the Gorlin formula (0.58 +/- 0.31 cm2) was excellent (r = 0.95; standard deviation of regression [SDR] = 0.054; Y = 0.92X + 0.085, where Y = Gorlin area and X = planimetry area). Correlation between Gorlin- and continuity equation-derived areas (0.65 +/- 0.46 cm2) was r = 0.79; for continuity equation- and transesophageal planimetry-derived areas it was r = 0.83. Severe aortic stenosis (valve area < or = 0.75 cm2) was predicted with high sensitivity (96%) and specificity (88%).

CONCLUSIONS

Multiplane transesophageal echocardiography is a practical and accurate clinical tool for the assessment of the severity of aortic stenosis.

Hemodynamic assessment of aortic stenosis

The decision to operate in patients with aortic stenosis is based on the presence of symptoms and hemodynamically significant valvular obstruction. The strengths and limitations of cardiac catheterization and Doppler echocardiography are compared, and the concept of "critical" aortic stenosis is discussed. The recommendation of aortic valve replacement must take into account the symptom status, the hemodynamic significance of the lesion, and the size and type of valve to be implanted.

Doppler echocardiographic findings in adults with severe symptomatic valvular aortic stenosis. Balloon Valvuloplasty Registry Echocardiographers

Baseline echocardiographic data in 680 adults (mean age 78 years) undergoing balloon aortic valvuloplasty at 24 medical centers were analyzed to describe the degree of outflow obstruction in patients with symptomatic aortic stenosis. Maximal aortic jet velocity ranged from 2.3 to 6.6 m/s (mean 4.4 +/- 0.8) and continuity equation valve area ranged from 0.1 to 1.4 cm2 (mean 0.6 +/- 0.2). Of note, 36% had a jet velocity less than or equal to 4.0 m/s but only 3% had a valve area greater than 1.0 cm2 due to a high prevalence of impaired systolic function (54%). Outflow tract diameter was poorly correlated with body surface area (p = 0.26), although the group mean diameter was smaller in women than in men (1.9 +/- 0.2 vs 2.1 +/- 0.3 cm, p = 0.0001). Mean pressure gradient was related closely to maximal gradient (r = 0.92) and to maximal jet velocity (mean delta P = 2.4 V2 + 0.75 mm Hg). Simpler measures of aortic stenosis severity were correlated with Doppler and invasive valve area as follows: maximal jet velocity (r = -0.36 and -0.32), mean gradient (r = -0.33 and -0.29), outflow tract to jet velocity ratio (r = 0.67 and 0.40), and the fractional shortening velocity ratio (r = 0.29 and 0.22). This study demonstrates marked variability in stenosis severity in symptomatic adults referred for balloon aortic valvuloplasty. The absence of a predictable relation between outflow tract diameter and body size emphasizes the importance of this measurement in each patient if definition of valve area is needed.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of cardiac catheterization and Doppler echocardiography in the decision to operate in aortic and mitral valve disease

Clinical decisions utilizing either Doppler echocardiographic or cardiac catheterization data were compared in adult patients with isolated or combined aortic and mitral valve disease. A clinical decision to operate, not operate or remain uncertain was made by experienced cardiologists given either Doppler echocardiographic or cardiac catheterization data. A prospective evaluation was performed on 189 consecutive patients (mean age 67 years) with valvular heart disease who were being considered for surgical treatment on the basis of clinical information. All patients underwent cardiac catheterization and detailed Doppler echocardiographic examination. Three sets of two cardiologist decision makers who did not know patient identity were given clinical information in combination with either Doppler echocardiographic or cardiac catheterization data. The combination of Doppler echocardiographic and clinical data was considered inadequate for clinical decision making in 21% of patients with aortic and 5% of patients with mitral valve disease. The combination of cardiac catheterization and clinical data was considered inadequate in 2% of patients with aortic and 2% of patients with mitral valve disease. Among the remaining patients, the cardiologists using echocardiographic or angiographic data were in agreement on the decision to operate or not operate in 113 (76% overall). When the data were analyzed by specific valve lesion, decisions based on Doppler echocardiography or catheterization were in agreement in 92%, 90%, 83% and 69%, respectively, of patients with aortic regurgitation, mitral stenosis, aortic stenosis and mitral regurgitation. Differences in cardiac output determination, estimation of valvular regurgitation and information concerning coronary anatomy were the main reasons for different clinical management decisions. These results suggest that for most adult patients with aortic or mitral valve disease, alone or in combination, Doppler echocardiographic data enable the clinician to make the same decision reached with catheterization data.

Validation and applications of indexed aortic prosthetic valve areas calculated by Doppler echocardiography

Doppler echocardiographic evaluation of aortic valve prostheses is based on the use of variables heretofore validated mostly for native valves. Accordingly, this study examined the validity and relative usefulness of the Doppler valve gradient and area measurements in 31 patients (mean age 69 +/- 10 years) 20 +/- 4 months after implantation of a given type of aortic bioprosthesis ranging in size from 19 to 29 mm. Valve area data obtained with both the standard and simplified continuity equations were compared with known in vitro prosthetic valve area measurements and an excellent correlation was obtained between the standard and simplified continuity equations (r = 0.98, SEE +/- 0.07 cm2, p less than 0.0005) and between in vivo and known in vitro prosthetic valve areas (r = 0.86, SEE +/- 0.16 cm2, p less than 0.0005). Peak gradient ranged from 10.8 to 75.0 mm Hg (mean 35 +/- 16) and mean gradient from 7.6 to 43.7 mm Hg (mean 20.5 +/- 9.5). The correlations between prosthetic valve gradient and in vivo area were r = -0.53, SEE +/- 14 mm Hg and r = -0.49, SEE +/- 8.63 mm Hg for peak and mean gradient, respectively. These relations were improved by indexing valve area by body surface area. The best correlations were obtained between indexed valve area and a quadratic function of the gradient (r = -0.72, SEE +/- 11.72 mm Hg and r = -0.70, SEE +/- 7.28 mm Hg for peak and mean gradient, respectively), reflecting a curvilinear relation.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic quantitation of cross-sectional area under various hemodynamic conditions: an experimental validation in a canine model of supravalvular aortic stenosis

The hemodynamic effects on cross-sectional area calculated with the continuity equation were assessed in canine experiments. In 13 open chest dogs, 46 supravalvular aortic stenoses were created by aortic root banding. The cross-sectional area of the stenosis was calculated by Doppler echocardiography with application of the continuity equation before and after the following hemodynamic interventions: protocol 1, atrial pacing at 90, 120, 150 and 180 beats/min after sinus node crush; protocol 2, preload reduction by mild and severe clamping of the inferior vena cava; and protocol 3, afterload augmentation by mild and severe clamping of the descending aorta. In each observation, a dimension of the stenosis was directly measured by two-dimensional echocardiography, and the cross-sectional area was determined as a reference standard. As a result of the hemodynamic interventions, significant changes were observed in stroke volume and pressure gradient (protocol 1), in cardiac output, stroke volume and pressure gradient (protocol 2) and in heart rate, cardiac output and pressure gradient (protocol 3). Despite these changes in hemodynamic variables, the Doppler-derived cross-sectional area showed no significant change for a given stenosis. In addition, areas calculated with the continuity equation (x) agreed well with those determined by two-dimensional echocardiography (y) (r = 0.96, p less than 0.001, y = 0.97x + 0.02, SEE = +/- 0.06 cm2). Thus, it is concluded that Doppler echocardiography with application of the continuity equation accurately predicts the stenotic cross-sectional area over a wide range of hemodynamic conditions in supravalvular aortic stenosis.

Usefulness of the Doppler mean gradient in evaluation of children with aortic valve stenosis and comparison to gradient at catheterization

To assess the usefulness of the Doppler mean gradient as a noninvasive indicator of the need for intervention, 33 children (ages 3 months to 20 years) with valvular aortic stenosis (AS) underwent a 2-dimensional and Doppler echocardiographic examination a median of 1 day before cardiac catheterization. The clinical decision for intervention was based on finding a catheterization peak-to-peak pressure gradient of greater than 75 mm Hg or from 50 to 75 mm Hg in the presence of symptoms or an abnormal exercise treadmill test result. Of the 33 patients, 23 required intervention. The decision for intervention was compared to the Doppler mean gradient, and the Doppler peak and mean gradients were compared to the catheterization peak-to-peak gradient. All 12 patients with a Doppler mean gradient greater than 27 mm Hg had intervention and had a catheterization peak-to-peak gradient of greater than or equal to 75 mm Hg. All 3 patients with a Doppler mean gradient less than 17 mm Hg had no intervention and had a peak-to-peak gradient less than 50 mm Hg. The remaining 18 patients with Doppler mean gradients between 17 and 27 mm Hg comprised an intermediate group in whom the Doppler mean gradient alone did not predict the need for intervention. From a chi-square table, a Doppler mean gradient greater than 27 mm Hg predicted the need for intervention with 100% specificity (no false positives) and 52% sensitivity (11 false negatives).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of aortic valve gradients by transseptal technique: implications for noninvasive evaluation

The peak instantaneous aortic valve gradient derived from Doppler echocardiography is commonly used to predict the severity of aortic stenosis. Peak instantaneous gradient should not be equated with the mean gradient or "peak to peak" gradient measured at cardiac catheterization. The primary purpose of this study is to assess the relationship between the aortic valve gradients, using a two-catheter transseptal technique in 102 patients with aortic stenosis, mixed aortic stenosis and regurgitation, and following aortic valve replacement. These cases were drawn from a series of 111 consecutive transseptal procedures for patients with isolated aortic valve disease. No major complications occurred, and the most common reason for technical failure was inability to engage the atrial septum in postoperative patients. Although the peak instantaneous gradient correlates well with the mean gradient in aortic stenosis (r = .94, P less than .001), mixed stenosis and regurgitation (r = .95, P less than .001), and after aortic valve replacement (r = .86, P less than .001), it systematically overestimates both the mean gradient and the peak to peak gradient. Neither the peak instantaneous nor the mean gradient correlates highly with aortic valve area in aortic stenosis (r = -.48, P less than .01 peak; r = -.58, P less than .001 mean gradient), mixed aortic stenosis and regurgitation (r = -.39, P NS peak; r = -.42, P NS mean gradient) or following aortic valve replacement (r = -.26, P NS peak; r = -.53, P less than .01 mean gradient). Systolic time intervals also were analyzed from the simultaneous left ventricular and ascending aortic pressure tracings.(ABSTRACT TRUNCATED AT 250 WORDS)

Internal consistency of echocardiographic estimates of the severity of left ventricular outflow obstruction

To determine their internal consistency, M-mode and Doppler echocardiography were used to estimate the gradient across the left ventricular outflow tract during 74 evaluations of 50 infants, children, and young adults with congenital valvular (n = 43), subvalvular (n = 6), and supravalvular (n = 1) aortic stenosis. By M-mode the gradient was estimated from the wall-stress formula (left ventricular pressure = 225 x wall thickness/end-systolic diameter) minus systolic blood pressure determined by sphygmomanometry. Doppler (pulsed or continuous wave) methods utilized the Bernoulli formula (gradient = 4 x V2). There was good agreement between the M-mode and Doppler estimates of outflow gradient in most patients (r = 0.69, standard error of the estimate = 26.9). In 46 of 74 comparisons (62%) the two estimates differed by less than 20 mm Hg, and the estimates placed the patient in the same clinical class (mild, moderate, or severe). In 22 patients undergoing cardiac catheterization, there was only a fair correlation between the M-mode (r = 0.50) and Doppler (r = 0.58) gradients and those obtained at catheterization. Each noninvasive technique yielded major overestimates or underestimates of the gradient in several instances. The M-mode and Doppler techniques for estimating the severity of congenital aortic stenosis are complementary. Their combined use minimizes but does not totally eliminate errors of overestimation or underestimation of outflow gradient.

Pressure recovery distal to a stenosis: potential cause of gradient "overestimation" by Doppler echocardiography

Doppler ultrasound is currently being widely applied to measure intracardiac pressure gradients noninvasively. In comparative invasive studies, it is generally assumed that pressure is effectively uniform distal to the stenosis. As the poststenotic jet expands, however, its velocity decreases, and pressure is recovered to the extent permitted by turbulence, so that the measured gradient will be lower if the distal catheter is positioned downstream from the vena contracta. This can lead to apparent Doppler "overestimation" of the pressure gradient because of this phenomenon of pressure recovery. This study demonstrates that pressure recovery can be important in a variety of clinical settings studied by in vitro models. Although most prominent in streamlined tunnels modeled after the obstruction in patients with hypertrophic cardiomyopathy, these effects are important even for central stenoses at physiologic flow rates. Because precise catheter position is not always known or controlled, these findings suggest an important advantage for Doppler gradient estimation, because it provides the maximal gradient at the vena contracta, which determines the load on the proximal chamber.

Hemodynamic progression of aortic stenosis in adults assessed by Doppler echocardiography

Doppler echocardiography was used to follow the hemodynamic severity of aortic stenosis. First, the reproducibility of repeat recordings (mean interval 28 +/- 36 days) of aortic jet velocity, made by two independent observers, was tested in 38 adults with aortic stenosis and unchanged clinical status. The two recordings of maximal velocity correlated well (r = 0.96, y = 0.88x + 0.46m/s, SEE = 0.21 m/s) with a mean coefficient of variation of 3.2%. Repeat recording of left ventricular outflow tract velocity by two independent observers in 10 other patients with aortic stenosis also correlated well (r = 0.94, y = 1.06x + 0.0 m/s, SEE = 0.06 m/s) with a mean coefficient of variation of 4.6%. Next, Doppler echocardiography was used to study 42 patients with aortic stenosis (mean age 66 years) over a follow-up interval of 6 to 43 months (mean 20). Maximal aortic jet velocity increased by 0.36 m/s per year (range -0.3 to +1.0 m/s per year). Mean transaortic pressure gradient changed by -7 to +23 (mean 8) mm Hg/year. Aortic valve area by the continuity equation (n = 25) decreased by 0 to 0.5 cm2/year (mean decrease 0.1 cm2/year). Some patients had a worsening of stenosis (decrease in valve area) even though they had no change or a decrease in pressure gradient, because of concurrent decreases in transaortic volume flow. Twenty-one patients (50%) developed new or progressive symptoms of aortic stenosis necessitating valve replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler estimation of pressure gradient in pulmonary stenosis: maximal instantaneous vs peak-to-peak, vs mean catheter gradient

We undertook a study to identify the hemodynamic significance of a Doppler-derived gradient across a stenotic pulmonary valve. Furthermore, we attempted to define the optimal plane for velocity data acquisition. A total of 17 children with valvar pulmonary stenosis were evaluated using Doppler echocardiography. Flow-velocity profiles were obtained from both the parasternal and subxiphoid windows. Ten of 17 patients were studied before and after balloon valvotomy. Therefore, 27 different transvalvar gradients were assessed by Doppler and these data were compared with the catheter-derived maximal instantaneous, peak-to-peak, and mean pressure gradients. The maximal Doppler gradient correlated well with the catheter-derived peak-to-peak pressure gradient (r = 0.95) and catheter maximal instantaneous pressure gradient (r = 0.95). Although these correlation coefficients were similar, the Doppler maximal gradient consistently overestimated the peak-to-peak catheter gradient by as much as 25%-40%. Such an overestimation was not observed when we compared the maximal Doppler gradient with the catheter-derived maximal instantaneous gradient. Moreover, the regression line of the latter comparison closely approximated the line of identity. The correlation coefficient between Doppler mean and catheter mean gradients was only 0.91. Doppler velocities were best derived when multiple transducer positions were employed to interrogate pulmonary artery velocity.

Experimental validation of Doppler echocardiographic measurement of volume flow through the stenotic aortic valve

In aortic stenosis, evaluation of aortic valve area by the continuity equation assumes that the volume of flow through the stenotic valve can be measured accurately in the left ventricular outflow tract. To test the accuracy of Doppler volume-flow measurement proximal to a stenotic valve, we developed an open-chest canine model in which the native leaflets were sutured together to create variable degrees of acute aortic stenosis. Left ventricular and aortic pressures were measured with micromanometer-tipped catheters. Volume flow was controlled and varied by directing systemic venous return through a calibrated roller pump and back to the right atrium. Because transaortic volume flow will not equal roller pump output when there is coexisting aortic insufficiency (present in 67% of studies), transaortic flow was measured by electromagnetic flowmeter with the flow probe placed around the proximal descending thoracic aorta, just beyond the ligated arch vessels. In 12 adult, mongrel dogs (mean weight, 25 kg), the mean transaortic pressure gradient ranged from 2 to 74 mm Hg, and transaortic volume flow ranged from 0.9 to 3.2 l/min. In four dogs, electromagnetic flow that was measured distal to the valve was accurate compared with volume flow determined by timed collection of total aortic flow into a graduated cylinder (n = 24, r = 0.97, electromagnetic flow = 0.87 Direct +0.13 l/min). In eight subsequent dogs, electromagnetic flow was compared with transaortic cardiac output measured by Doppler echocardiography in the left ventricular outflow tract as circular cross-sectional area [pi(D/2)2] x left ventricular outflow tract velocity-time integral x heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiographic observations during percutaneous aortic balloon valvuloplasty

To evaluate the hemodynamic changes occurring with percutaneous aortic balloon valvuloplasty for aortic stenosis, Doppler echocardiography was performed during the procedure in 16 patients. During balloon inflation, peak velocity and ejection time of the aortic valve systolic signals increased (26 and 30%, respectively; p less than 0.001). Aortic regurgitation deceleration time decreased from 1,337 to 625 ms (p less than 0.001). In three patients, aortic regurgitation stopped before end-diastole; in four patients, end-diastole forward flow across the aortic valve was documented. The deceleration time of the mitral valve inflow signal decreased from 303 to 194 ms (p less than 0.001) during balloon inflation, concurrently with an increase in left ventricular diastolic pressure. Mitral regurgitation signals became more prominent during inflation in 10 patients. Changes that occur during balloon inflation in the aortic valve include progressive left ventricular outflow obstruction, equalization of diastolic aortic and left ventricular pressures and changes in diastolic compliance.

Prediction of the severity of aortic stenosis by Doppler aortic valve area determination: prospective Doppler-catheterization correlation in 100 patients

Two-dimensional and Doppler echocardiography was performed prospectively in 100 patients with aortic stenosis who were undergoing clinically indicated cardiac catheterization. The purpose of this study procedure was to determine various Doppler variables predictive of the severity of aortic stenosis and to compare Doppler- and catheterization-derived aortic valve areas. Doppler-derived mean gradient correlated well with corresponding gradient by catheterization (r = 0.86). Peak Doppler aortic flow velocity greater than or equal to 4.5 m/s and Doppler-derived mean aortic gradient greater than or equal to 50 mm Hg were specific (93 and 94%, respectively) for severe aortic stenosis (defined as catheterization-derived aortic valve area less than or equal to 0.75 cm2) but were not sensitive (44 and 48%, respectively). Doppler-derived aortic valve area calculated by the continuity equation correlated well with catheterization-derived aortic valve area calculated by the Gorlin equation when either the time-velocity integral ratio (r = 0.83) or the peak flow velocity ratio (r = 0.80) between the left ventricular outflow tract and the aortic valve was used in the continuity equation. A velocity ratio of less than or equal to 0.25 alone was sensitive (92%) in detecting severe aortic stenosis. Therefore, use of various Doppler-derived values allows reliable noninvasive estimation of the severity of aortic stenosis.

A practical application of Doppler echocardiography for the assessment of severity of aortic stenosis

This study evaluated a strategy that makes optimal use of Doppler echocardiography for estimating the severity of valvular aortic stenosis (AS). Fifty-eight patients with no more than moderate aortic insufficiency who underwent cardiac catheterization were evaluated with two-dimensional echocardiography and Doppler velocimetry to determine the peak velocity across the stenotic valve and aortic valve area (AVA) by means of the continuity equation. All 33 peak Doppler velocities of greater than or equal to 4 m/sec had critical AS (AVA less than or equal to 0.8 cm2 at catheterization). Conversely, six of seven patients with Doppler velocities of less than or equal to 3 m/sec had noncritical AS. The patient with a falsely low peak velocity had severely depressed left ventricular function. Doppler velocity alone was inadequate in determining severity of AS for patients with velocities between 3 and 4 m/sec. The continuity equation proved accurate in estimating AVA in the 46 patients for whom catheterization and ultrasound data were sufficient to compare calculated AVA (r = 0.81), and was also accurate for those patients with peak Doppler velocities between 3 and 4 m/sec (r = 0.90). These results suggest that Doppler velocimetry alone is adequate in determining critical vs noncritical AS in many patients, while the continuity equation should be applied for patients with peak velocities between 3 and 4 m/sec as well as in patients with severely depressed cardiac function.

Doppler evaluation of bioprosthetic and mechanical aortic valves: data from four models in 107 stable, ambulatory patients

To test the applicability of Doppler ultrasound in the evaluation of prosthetic valve function, 107 patients with normal ejection fractions in whom Starr-Edwards, Björk-Shiley, Carpentier-Edwards, and Hancock models had been implanted in the aortic position were examined. Maximal transvalvular velocity was recorded by non-imaging continuous wave Doppler ultrasound. Means of maximal velocities by model and size ranged from less than 2 to 4 m/sec. The Starr-Edwards valve showed the highest velocities, the Björk-Shiley the lowest, and the bioprosthetic models showed velocities in between. A significant inverse relation between velocity and size, and standard deviations averaging +/- 14% enabled the technique to measure differences between sizes of the same model. Aortic regurgitation was detected in 24% of the patients. This study, conducted in well and stable patients, established values for maximal velocity across normally functioning aortic mechanical and tissue prostheses of different models and sizes. The intersubject variability was relatively small which, together with a previously shown minimal intrasubject variability, was testimony to a methodology that should prove useful in longitudinal postoperative evaluations.

Pivotal role of aortic valve area calculation by the continuity equation for Doppler assessment of aortic stenosis in patients with combined aortic stenosis and regurgitation

Aortic regurgitation (AR) may result in overestimation of the aortic pressure gradient by continuous wave Doppler in patients with mixed aortic valve disease. However, few data are available regarding the effect of AR on noninvasive estimates of aortic valve area by the continuity equation. Therefore, 25 patients with angiographically documented severe AR and peak systolic aortic velocities of greater than 2.5 m/s were studied by continuous wave Doppler to determine the accuracy of pressure gradient and aortic valve area calculations in assessing the severity of aortic stenosis (AS) in this patient population. Peak instantaneous pressure gradient showed a general correlation to but was overestimated by Doppler (r = 0.78, Doppler = 0.70 catheter + 19.9) and did not predict aortic valve area. Mean pressure gradient by Doppler correlated more closely with catheter mean gradient (r = 0.86, Doppler = 0.79 catheter + 6.1) but was a poor predictor of the severity of AS. In contrast, the continuity equation accurately predicted the aortic valve area by catheterization (r = 0.92, Doppler = 0.89 catheter -0.08). Thus, the continuity equation provides a reliable estimate of aortic valve area in patients with severe AR and should be used to evaluate the extent of AS in such patients when high systolic aortic velocities are present.

Quantitative applications of Doppler cardiography in congenital heart disease

Doppler ultrasound has rapidly become a valuable tool in the noninvasive investigation of cardiac hemodynamics. Although based on secure principles, accurate application of this methodology to quantitative measurements necessitates a thorough understanding of both Doppler physics and instrumentation. Over the past several years a large body of clinical and animal data verifying the accuracy of Doppler determination of pressure and flow data at various sites in the cardiovascular system, as well as the potential sources of error in acquisition and interpretation of blood velocity recordings, has been published. Quantitative use of Doppler in congenital heart disease, with emphasis on limitations of existing studies and issues particular to this patient population, is reviewed.

Evaluation of normal prosthetic valve function by Doppler echocardiography

Previous investigations have suggested that Doppler echocardiography is useful in detecting dysfunction in aortic (AVR) and mitral prostheses (MVR). However, to diagnose abnormalities, the spectrum of normal velocities through these valves must be established. Therefore, we used Doppler echocardiography to study 100 patients with 105 prosthetic valves that had no clinical evidence of valve dysfunction 9 +/- 8 days postoperatively. There were 66 Carpentier-Edwards (C-E), 23 St. Jude (S-J), and 16 Ionescu-Shiley (I-S) valves. In 70 AVR, the peak instantaneous gradient was 26.4 +/- 8.2 Hg, mean systolic gradient was 15.6 +/- 5 mm Hg, and gradients varied inversely with valve size, although differences were significant only when comparing the smallest vs the largest valve sizes (p less than or equal to 0.03). Peak instantaneous gradients greater than 36 mm Hg occurred only in AVR size 23 or smaller. There were no significant differences in gradients among C-E, S-J, and I-S AVR. In 35 MVR, mean gradient was 6.9 +/- 2.3 mm Hg and valve area was 2.7 +/- 0.8 cm2; neither varied significantly with valve size. However, S-J MVR group had smaller mean gradients and larger effective valve area than C-E bioprosthetic MVR (p = 0.01 and p = 0.05, respectively). Regurgitation was more common in AVR (26%) than in MVR (9%), p = 0.04, although all instances were mild and clinically silent. We conclude that normal AVR and MVR of a given size and type have a predictable range of Doppler echocardiographic parameters. Doppler evidence of mild regurgitation is a frequent finding in normal AVR and MVR.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of outflow tract pressure gradients by continuous wave Doppler in children

Continuous wave Doppler echocardiography was used to estimate pressure gradients in 27 children with right or left ventricular outflow tract obstruction. The pressure gradients predicted by Doppler were compared to peak-to-peak and instantaneous gradients measured at cardiac catheterization. When the Doppler study was performed the pressure gradient obtained at catheterization was not known to the examiner. A correlation coefficient of 0.76 was found for the comparison between the Doppler predicted gradient and the peak-to-peak gradient and 0.78 for the comparison with the instantaneous pressure gradient. Clinically significant obstructions could be reliably separated from insignificant obstructions by the Doppler technique.

Determination of right ventricular pressure in the presence of a ventricular septal defect using continuous wave Doppler ultrasound

Continuous wave Doppler ultrasound was employed in 38 patients with ventricular septal defects, many with associated lesions, to measure the velocity (V) of the shunted blood. Using the modified Bernoulli equation (delta P = 4V2) the pressure difference (delta P) between the ventricles was determined. In 22 patients both right ventricular and either left ventricular or ascending aortic pressure were measured at the time shunt velocity was determined. In another 16 patients these measurements were not obtained simultaneously but in most they were done within 24 hours of each other. In the entire group, measured pressure differences between the ventricles (or aorta and right ventricle) ranged from 0 to 97 mm Hg (mean 52 +/- 24). On the basis of velocity measurements the pressure difference ranged from 7 to 112 mm Hg (mean 51 +/- 24). A close correlation was found between the two methods (r = 0.95, SEE = 7.8 mm Hg). This accuracy was not altered by associated lesions. These findings indicate that by the use of continuous wave Doppler interrogation right ventricular pressure can be accurately measured in the presence of a ventricular septal defect.

Systematic correlation of continuous-wave Doppler and hemodynamic measurements in patients with aortic stenosis

The purpose of this study was to compare estimates of pressure gradients obtained from continuous-wave (CW) Doppler recordings with direct pressure measurements derived from cardiac catheterization in patients with aortic stenosis. Forty patients who underwent cardiac catheterization for evaluation of aortic stenosis were prospectively studied with CW Doppler spectral recordings of the aortic valve prior to catheterization. Thirty-three patients underwent a second Doppler examination simultaneously with pressure recordings in the catheterization laboratory. Nineteen of the patients had catheterization pressures measured using high-fidelity, micromanometer-tip catheters. Doppler and pressure tracings were digitized using a microprocessor-based computer with a software program which allowed for calculation of maximal instantaneous, mean, and peak-to-peak gradients, plus ejection and acceleration times. Maximal instantaneous gradient by CW Doppler showed an excellent correlation with maximal instantaneous catheterization gradient (r = 0.93, SEE = 9 mm Hg). The correlation of maximal instantaneous Doppler gradient with peak-to-peak catheterization gradient was also linear (r = 0.85, SEE = 12 mm Hg), but there was a consistent overestimation of peak-to-peak gradient in 38 of 40 cases (mean = 17 mm Hg). Mean gradient as calculated by the two techniques correlated best of all measurements performed (r = 0.95, SEE = 6 mm Hg). When patients were grouped into subsets of mild (0 to 25 mm Hg), moderate (25 to 50 mm Hg), and severe (greater than 50 mm Hg) levels of stenosis, the correlation of maximal instantaneous Doppler and peak-to-peak catheterization gradients were r = 0.22, 0.44, and 0.77, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)