(Circulation. 2000;102:558.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
Assessment of Severity of Aortic Regurgitation Using the Width of the Vena Contracta
A Clinical Color Doppler Imaging Study
From the Division of Cardiovascular Diseases and Internal Medicine (C.M.T., M.E.-S., J.B.S., A.J.T.) and the Section of Biostatistics (K.R.B.), Mayo Clinic and Mayo Foundation, Rochester, Minn.
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Abstract |
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Background—The width of the vena contracta (VC-W), the smallest area of regurgitant flow, reflects the degree of valvular regurgitation and is measurable by color Doppler imaging, but this method has not been validated in aortic regurgitation (AR).
Methods and Results—We prospectively examined 79 patients with
isolated AR and 80 patients without regurgitation. The
VC-W was measured from the long-axis parasternal view and compared with
2 simultaneous reference methods (quantitative Doppler
and 2D echocardiography). In patients without
regurgitation, the agreement between methods was
excellent. In patients with AR, good correlations (all
P<0.0001) were obtained between VC-W and effective
regurgitant orifice (ERO) area and regurgitant volume recorded by
quantitative Doppler (r=0.89 and 0.90, respectively)
and 2D echocardiographic (r=0.90 and
0.89, respectively) methods. These correlations were similar with
eccentric or central jets (all P>0.60). The other
methods used showed good correlations of VC-W with aortographic grading
of AR (n=8, r=0.82, P=0.01), with the
proximal flow convergence method (n=53, r=0.85,
P<0.0001), and with left ventricular
end-diastolic volume (r=0.81,
P<0.0001). Sensitivity and specificity of VC-W 
6
mm for diagnosing severe AR (ERO 30 mm2) were 95%
and 90%, respectively.
Conclusions—For assessment of the degree of AR, VC-W shows good correlations with simultaneous quantitative measures (regardless of jet direction), shows good correlations with other methods of assessment of AR, and provides a high diagnostic value for severe AR. VC-W is a simple, reliable method that can be used clinically as part of comprehensive Doppler echocardiographic assessment of AR.
Key Words: aorta • valves • echocardiography • regurgitation
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Patients with aortic regurgitation (AR) of large degree may develop left ventricular dysfunction and heart failure due to volume overload.1 Accurate assessment of AR degree is a prerequisite to surgical decision making. Among methods available for assessing AR,2 3 4 5 color flow Doppler allows real-time visualization of the jet and is widely used for semiquantification of AR.6 7 8 In AR, regurgitant jet width measured by color flow Doppler correlates grossly with semiquantitative angiographic grading.6 7 8 9 However, the size of regurgitant jets depends on hemodynamic conditions,10 11 instrument settings,12 and hydrodynamic factors such as jet interaction with the receiving chamber,13 all factors affecting the diagnostic value of jet size.
Recently, considerable interest has focused on effective regurgitant orifice (ERO) area as a marker of regurgitant lesion severity2 14 15 less dependent on hemodynamic variations than regurgitant volume (RVol) and regurgitant fraction (RF).16 17 The ERO area corresponds hydrodynamically to the area of the vena contracta (VC),18 that is, the smallest area of regurgitant flow through the valve,19 which is significantly smaller than jet size.20 In vitro studies support the concept that VC size measured by color Doppler is related directly to regurgitant orifice size.21 22 23 In humans, direct and exact planimetry of ERO area with color flow Doppler is not yet clinically possible,8 20 and the width of the VC (VC-W) has been proposed as a surrogate for ERO size and validated in mitral regurgitation.20 24 25 26 27 Although the measurement of VC-W using color Doppler in AR has recently been pioneered in animal studies,19 28 clinical data in large series of patients are not yet available but are warranted.28
Therefore, we hypothesized that in AR, VC-W directly correlates with ERO area and has high diagnostic value for severe AR. To verify this hypothesis, we analyzed, in patients prospectively examined for AR of any degree, the relation between VC-W and ERO, RVol, and RF obtained simultaneously by previously validated methods.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Patient Population
Inclusion criteria were (1) isolated and pure AR of at least mild degree, as determined by standard color Doppler imaging; (2) simultaneous Doppler echocardiographic measurements, allowing quantitative assessment of AR; and (3) measurement of the VC-W. Exclusion criteria were (1) more than trace associated mitral disease, (2) associated aortic stenosis with mean gradient
25 mm Hg, (3)
inability to acquire both quantitative reference methods, and (4)
multiple or diffuse AR jets. In addition to patients with AR, 80 patients (46 male; age 57±15 years) without regurgitation had Doppler echocardiographic measurements performed prospectively to assess the accuracy of stroke volume measurements.
Echocardiographic Doppler Analysis
All echocardiographic data were collected during
the same examination without observed hemodynamic
change.
Color Doppler Echocardiography
Color Doppler imaging was performed with standard color
encoding and maximum Nyquist limit. The presence of an eccentric jet
was determined by the jet direction immediately below the regurgitant
orifice. The narrowest sector angle of imaging was selected to optimize
the frame rate. The gain was adjusted to the maximal color gain without
signal outside of flow areas.24 Jet width and ratio to
left ventricular outflow tract (LVOT) width could be
measured just below the valve, as previously described,6
in 66 patients.
The color Doppler images of the VC were obtained from parasternal
long-axis views. Transducer position was optimized to visualize the
flow convergence region and regurgitant flow proximal to, through, and
distal to the aortic valve. With a zoom of the region of interest,
meticulous care was taken to visualize the VC, defined as the narrowest
neck of regurgitant flow immediately downstream from the flow
convergence region (Figure 1
).
Measurement of VC-W was made in early to mid diastole
before quantitative reference methods were obtained. The values of 4
measurements were averaged in each patient. In 14 patients,
measurements of VC-W were repeated independently by a second
observer.
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Reference Methods
The ERO area and RF with both quantitative Doppler (QDop)
methods were calculated with the following formula2 3 :
ERO=RVol/RTVI and RF=RVol/aortic stroke volume, where RTVI is the
regurgitant time velocity integral of the AR jet obtained by
continuous-wave Doppler.
For QDop, RVol was calculated as the difference between aortic and mitral stroke volumes measured with pulsed Doppler. The mitral annulus diameter was measured along multiple axes to account for possible noncircular shape. For quantitative 2D echocardiography (Q2DE), RVol was calculated as the difference between left ventricular and mitral stroke volumes.
Other Methods
Left ventricular volumes were measured at
end-diastole and end-systole by the biplane method of
disks.3 29 Cardiac index was measured by use of mitral
stroke volume. In addition, in 8 patients, the angiographic grade of AR
was obtained, and in 53, the ERO of AR was calculated by the proximal
flow convergence method.30
Statistical Analysis
Descriptive results were expressed as mean±SD for continuous
variables and percentages for categorical variables. Groups
were compared by Student’s t test or
2 test. The VC-W was related to the ERO area,
RVol, and RF with linear regression and to categorical variables by
use of nonparametric regressions. Analyses were
performed in the entire group and in subgroups with eccentric and
central jets. Comparison of regression between subgroups used ANCOVA.
Various thresholds of VC-W along the entire range of values were tested
by increments of 0.5 mm to classify patients as having severe AR,
defined as an ERO area 30
mm2,2 RVol 60
mL,31 and RF 45%, and the sensitivity, specificity,
positive and negative predictive values, and odds ratio for diagnosing
severe AR were calculated. Areas under receiver operator curves for
diagnosing severe AR were calculated and compared with those of jet
width and jet/LVOT ratio. Statistical significance was accepted for
P<0.05.
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Results |
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Baseline Characteristics
Measurement of the VC of AR was attempted in 90 patients and visualized adequately in 79 (88%). The VC-W could not be visualized in 5 of the first 15 patients (33%) and 6 of the last 75 (8%) (in the latter, because of shadowing by aortic calcifications). The 79 patients (age, 58±18 years) with VC-W visualized constitute our study group (45 men and 34 women). Of the 79 patients, 77 were in sinus rhythm and 2 in atrial fibrillation. The cause of AR was degenerative valve disease in 29 patients, bicuspid valve in 16, aortic root dilatation in 15, dystrophic in 11, rheumatic in 4, and unclear cause in 4.
The baseline characteristics in the entire study group and in patients
with eccentric (n=37) or central (n=42) jets are listed in Table 1. The VC-W was smaller than jet
width (P<0.0001). AR was more severe in the eccentric jet
group with larger ERO and larger VC-W, but differences in jet width did
not reach statistical significance.
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VC-W and Quantitative Regurgitant Measurements
Close correlations were found between VC-W and ERO calculated with
QDop (r=0.90, P<0.0001, SEE=8
mm2) and Q2DE methods (r=0.90,
P<0.0001, SEE=8 mm2) (Figure 2). When a quadratic relationship was
used, the correlation coefficients were marginally improved (both
r=0.92), with a mild decrease of the SEE (7
mm2 for both reference methods). Good
correlations (all P<0.0001) were also found between VC-W
and RVol and RF determined by QDop (r=0.89 and 0.90, SEE=18
mL and 7%, respectively) and Q2DE (r=0.90 and 0.89,
SEE=18 mL and 7%, respectively) (Figures 3 and 4).
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Subgroup analysis showed similar correlations between VC-W and
ERO in 42 patients with eccentric jets (r=0.88 for both
methods, P<0.0001) and in 37 patients with central jets
(r=0.91 and 0.92, respectively; P<0.0001).
Correlations between VC-W and RVol or RF were also similar for
eccentric jets and central jets (all r>0.85, all
P<0.0001). The slopes of the regressions of VC-W to the
ERO, RVol, and RF were not different in eccentric and central jet
groups (all P>0.60) (Figure 5).
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VC-W and Other Methods
No significant relations were found between VC-W and ejection
fraction (P=0.20) and cardiac index (P=0.56).
Conversely, VC-W was related significantly to left
ventricular end-systolic and
end-diastolic volume index (r=0.65 and
r=0.81, respectively; P<0.0001). Also, VC-W
showed significant correlations with aortographic grading of AR (n=8,
r=0.82, P=0.01), with jet width and jet/LVOT
ratio by color flow imaging (r=0.82 and r=0.75,
both P<0.0001), and with ERO measured by the proximal flow
convergence method (n=53, r=0.85, P<0.0001).
Diagnostic Value of VC
With QDop and Q2DE, ERO 30 mm2 was
noted in 19 and 21 patients, RVol 60 mL in 26 and 27, and RF 45%
in 29 and 27, respectively. VC-W 6 mm was present in 24
patients. The analysis of the diagnostic value for
severe AR is presented in Table 2
for the QDop variables. Similar results were obtained with Q2DE.
For ERO, RVol, and RF, the 6-mm threshold of VC-W offers
consistently high odds ratios of severe AR with high sum of
sensitivity and specificity (boldface in Table
). The 5-mm threshold
provides high sensitivity and negative predictive value, so that with
VC-W <5 mm, the probability of missing severe AR is extremely
low. The 7-mm threshold provides high specificity and positive
predictive value, so that with VC-W 7 mm, the probability of
falsely diagnosing severe AR is extremely low.
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The diagnostic value of a VC-W 6 mm is confirmed by
the fact that compared with VC-W <6 mm, it was associated with
lower diastolic blood pressure (65±15 versus 77±11
mm Hg, P=0.0003) and larger left ventricular
end-diastolic diameter (64±9 versus 53±6 mm,
P<0.0001) and volume (153±41 versus 95±23
mL/m2, P<0.0001). The odds ratio
(95% CI) of severe left ventricular enlargement (120
mL/m2) with VC-W 6 mm was 29.0 (8.0 to
109).
The areas under the receiver-operator curve for diagnosing severe AR
with the thresholds noted in Table 2 for ERO, RVol, and RF were
0.98, 0.94, and 0.96 with QDop and 0.99, 0.95, and 0.99 with Q2DE,
respectively. These were higher than those of jet measurements for ERO
(both P<0.045) and RVol (both P<0.02) and
tended also to be higher for RF (P=0.18 and 0.055). These
differences were related to better correlations of ERO with VC-W than
with jet width and jet/LVOT ratio in the 66 patients in whom all
measurements were made (r=0.9 versus r=0.77 and
versus r=0.68, both P<0.0001), even when
nonparametric correlations were used (both
P<0.01).
Reproducibility of Measurements
For the 14 patients in whom VC-W was measured by a second
observer, interobserver variability was low, with highly significant
correlation between observers (P<0.0001, SEE=0.6 mm)
and low absolute difference between the 2 measurements (0.26±0.15
mm).
In the 80 patients without regurgitation, the absolute value of the difference between aortic and mitral stroke volumes was 4.1±3.1 mL and between left ventricular and mitral stroke volumes, 3.8±3.6 mL. In our laboratory, the absolute interobserver variability for RF is 4.6±3.3%. In AR patients, correlations between quantitative reference methods (QDop, Q2DE) and between these and the proximal flow convergence method were excellent for RVol (all r>0.91, SEE<10 mL) and ERO (all r>0.92, SEE<5 mm2).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The present study shows that color Doppler measurement of VC-W (1) can be performed in large numbers of patients with variable degrees and causes of AR; (2) is closely related to the ERO, RF, and RVol in patients with eccentric or central jets; (3) is closely related to other methods of assessment of the degree of AR; and (4) has a high diagnostic value for severe AR and therefore is a simple and useful method of assessment of the severity of AR.
Color Flow Imaging and Degree of AR
Color flow imaging shows regurgitant flows in real time, and
significant correlations between jet width and angiography have been
observed.6 8 However, this approach has limitations, and
as shown in Figure 1, jet spreading occurs after its exit from
the regurgitant orifice and is under the influence of complex
factors.22 The variable jet spreading or
constraint19 may explain the relatively high variability
of jet measurements32 and the influence on jet size of
factors independent of lesion severity.19 21 Jet width,
even immediately below the valve, is much larger than
VC-W,20 33 as demonstrated in the present study. Even
expressed as a ratio to LVOT, jet size does not carry similar
physiological significance and shows a
significantly poorer correlation with ERO than VC-W. Therefore, it is
reasonable to examine the possibility of assessing the degree of AR by
use of the more physiologically sound
analysis of regurgitant flow core34 by measurement
of VC-W, defined as the smallest color flow diameter at the junction of
flow convergence region and regurgitant jet.28
VC-W as an Index of Severity of AR
The concepts of ERO and VC have developed slowly from in
vitro studies,21 23 animal experiments,19 and
clinical series.20 24 35 The areas of ERO and VC are
equivalent and smaller than anatomic orifice area because of blood flow
contraction through the regurgitant orifice.18 Therefore,
clinical measurement of VC size20 24 26 35 or ERO
area2 14 15 30 provides unique information about
regurgitant lesion severity and is less dependent on loading changes or
heart rate than RVol and RF.16 17 In experimental studies,
VC size is relatively unaffected by flow rate and driving
pressure21 23 and by jet type.27 28
Recently, with the clarification of the concept of VC,34 pioneering animal studies using epicardial echocardiography suggested that VC size measured by color Doppler imaging was of great value for quantification of AR.19 28 To the best of our knowledge, the present study is the first large clinical series to analyze the value of VC-W measurement in AR. The present clinical data confirm recent experimental data19 28 and show that VC-W displays close correlation with independent measurements of ERO, RF, and RVol. VC-W is also strongly associated with other methods of assessment of AR, with clinical alterations due to AR, and with left ventricular enlargement. All these data confirm that in AR, measurement of VC-W, despite its simplicity, strongly reflects the degree of AR and has high diagnostic value for severe AR.
VC-W is not meant to replace ERO calculation, however, because of the
notable standard error in estimating ERO from VC-W. This may be a
result of measurements of the small dimension of VC-W or of potential
variations in shape of the regurgitant orifice. In the future, this may
be overcome by 3D reconstruction.36 Also, the VC-W does
not carry the physiological significance of RVol
and ERO.2 14 15 However, the major advantage of VC-W
measurement in comparison with other quantitative
standards2 3 8 37 is the simplicity of measurement of a
highly meaningful variable,19 20 which can be obtained
by use of multiple echocardiographic
views.38 A VC-W 6 mm provided a good
diagnostic value for severe AR, even with an eccentric jet.
Values of VC-W <5 mm or >7 mm provide excellent specificity
for nonsevere and severe AR. Therefore, VC-W should be included in the
tools for comprehensive assessment of AR degree.
Limitations of the Study
We evaluated VC-W, although VC area may appear more attractive.
Defining the entire VC area perfectly is currently
impossible8 but may be possible in the future with 3D
reconstruction.36 Also, lateral resolution problems of
echocardiography limit area but not width
measurements performed in the axial direction.22 23
Currently, the use of VC-W is supported by good correlations to all
references and small interobserver variability. Curvilinear relations
between VC-W and ERO are logical but provide marginally superior
correlations.
Patients with multiple or diffuse regurgitant jets were excluded, and the value of VC-W with these jets cannot be determined.24 This problem is of particular concern in patients with bicuspid valves, but in those who fulfilled criteria for inclusion in the present study, the correlations of VC-W with quantitative variables were highly significant (all r>0.83; P<0.0001) and not different from those with tricuspid valves (all P>0.16). Future studies of patients with multiple or diffuse jets should address the value of VC measurements in this setting.
Quantitative echocardiographic methods may be questioned, but their accuracy has been confirmed in multiple centers3 15 20 37 and used to validate the concept of the VC.20 Moreover, high correlations between reference methods and the new flow-convergence method30 and excellent results obtained in patients without regurgitation support the accuracy of these methods and confirm that the reference methods used do not represent a limitation.
The thresholds used to define severe AR are still tentative and
should be confirmed in large outcome studies. However, use of different
thresholds did not reduce the high diagnostic value of
VC-W. For example, the positive and negative predictive values of a
VC-W <5 mm for nonsevere AR with a threshold of RVol <50 mL were
91% and 83%, respectively, and with a threshold of ERO <25
mm2, 100% and 74%. Also, the predictive values
of VC-W 6 mm for severe AR with a threshold of RF 50% were
63% and 98%, respectively. Therefore, the thresholds used have little
bearing on the results.
Conclusions
This prospective study of patients with AR demonstrated that
measurement of VC-W with color Doppler imaging can be obtained in
large numbers of patients and provides a reliable assessment of AR,
even with eccentric jets. Thus, VC-W can be used clinically as part of
a comprehensive Doppler assessment of AR.
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Acknowledgments |
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Dr Tribouilloy was supported by a grant from the Federation Française de Cardiologie.
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Footnotes |
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Reprint requests to Maurice Enriquez-Sarano, MD, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
Received September 17, 1999; revision received February 11, 2000; accepted March 1, 2000.
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