Donate Help Contact The AHA Sign In Home
American Heart Association
Circulation
Search: search_blue_button Advanced Search
« Previous Article | Table of Contents | Next Article »
Circulation. 1998;98:1205-1211

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Leung, D. Y.
Right arrow Articles by Thomas, J. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Leung, D. Y.
Right arrow Articles by Thomas, J. D.

(Circulation. 1998;98:1205-1211.)
© 1998 American Heart Association, Inc.

Clinical Investigation and Reports

Application of Color Doppler Flow Mapping to Calculate Orifice Area of St Jude Mitral Valve

Dominic Y. Leung, MBBS, MRCP(UK); James Wong, MD, PhD; Leonardo Rodriguez, MD; Min Pu, MD; Pieter M. Vandervoort, MD; ; James D. Thomas, MD

From the Cardiovascular Imaging Center, Department of Cardiology, Cleveland Clinic Foundation, Cleveland, Ohio. Dr Leung is now at the Department of Cardiology, Prince Henry Hospital, Sydney, NSW, Australia. Dr Vandervoort is now at Hartcentrum Limburg, Genk, Belgium.

Correspondence to James D. Thomas, MD, Department of Cardiology, Desk F15, Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195. E-mail thomasj{at}cesmtp.ccf.org


*    Abstract
up arrowTop
 *Abstract
down arrowIntroduction
 down arrowMethods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Background—The effective orifice area (EOA) of a prosthetic valve is superior to transvalvular gradients as a measure of valve function, but measurement of mitral prosthesis EOA has not been reliable.

Methods and Results—In vitro flow across St Jude valves was calculated by hemispheric proximal isovelocity surface area (PISA) and segment-of-spheroid (SOS) methods. For steady and pulsatile conditions, PISA and SOS flows correlated with true flow, but SOS and not PISA underestimated flow. These principles were then used intraoperatively to calculate cardiac output and EOA of newly implanted St Jude mitral valves in 36 patients. Cardiac output by PISA agreed closely with thermodilution (r=0.91, {Delta}=-0.05±0.55 L/min), but SOS underestimated it (r=0.82, {Delta}=-1.33±0.73 L/min). Doppler EOAs correlated with Gorlin equation estimates (r=0.75 for PISA and r=0.68 for SOS, P<0.001) but were smaller than corresponding in vitro EOA estimates.

Conclusions—Proximal flow convergence methods can calculate forward flow and estimate EOA of St Jude mitral valves, which may improve noninvasive assessment of prosthetic mitral valve obstruction.


Key Words: mitral valve • prosthesis • echocardiography


*    Introduction
up arrowTop
 up arrowAbstract
 *Introduction
down arrowMethods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Assessment of prosthetic heart valve function with current techniques is imprecise. Transvalvular gradients obtained by catheterization or Doppler echocardiography are indicative of prosthetic valve obstruction1 but are highly flow-dependent. Furthermore, pressure recovery occurs in some prosthetic designs, resulting in discrepancies between catheter and Doppler pressure gradients.2 3 4 5 6

Analogous to native valve area, prosthetic orifice area is a more flow-independent measure of obstruction. Unfortunately, the Gorlin formula may be unreliable in this setting,7 and the pressure half-time method,8 widely used in native mitral stenosis, has not been validated for prosthetic valves. Pulsed-wave Doppler has been used to calculate prosthetic aortic valve area9 but is more problematic for prosthetic mitral valves.

Analysis of the proximal flow convergence region on color flow mapping can quantify mitral regurgitant severity10 11 12 13 14 15 16 17 18 19 as well as low-velocity flow across relatively large orifices such as stenosed native mitral valves20 and atrial septal defects.21 However, the utility of the proximal flow convergence to measure prosthetic forward flow and effective orifice area (EOA) is unclear.

The aim of this study was to investigate, in flow models and in the operating room, the feasibility and accuracy of measuring flow across St Jude valves and calculating their EOAs by analyzing the flow convergence region proximal to the prosthesis by use of color Doppler mapping.


*    Methods
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 *Methods
down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Theoretical Background
The theory of the proximal flow convergence method is well described.10 12 13 17 18 Briefly, flow converges on a small orifice as concentric hemispheric shells of decreasing surface area and increasing velocity. For a specific contour of velocity va and radius r from the orifice (highlighted as the blue-red aliasing boundary on color Doppler), the instantaneous flow rate Q is given by Q=2{pi}r2va. However, relatively low-velocity flow across large orifices such as prosthetic valves causes flattening of the isotachs and underestimation of flow,22 but this can be countered by multiplying Q by v/(v-va), where v is the peak transorifice velocity.

(1)
The isovelocity surface area can also be calculated by the segment-of-spheroid (SOS) method23 24 using the chord (p) from the zenith of the contour to its outer edge (Figure 1Down):

(2)
EOA then is given by Q/v, where v is the transorifice velocity. Although localized high velocities and pressure recovery have been shown in the central orifice of the St Jude valve, we recently demonstrated that pressure recovery across the lateral orifices of mitral prostheses is limited.25 Because most flow passes through the side orifices, these were subsequently used in the EOA and stroke volume calculations.



View larger version (71K):
[in this window]
[in a new window]
  		Figure 1. Flow convergence zone proximal to St Jude mitral valve on color Doppler (left). Right, Same frame with color suppressed. Radius (r) is measured to level of annulus of prosthesis, and chord (p) is a segment of a spheroid.

In Vitro Models
Steady-Flow Model
This in vitro flow model was described in detail previously10 : a Plexiglas model with 2 chambers (proximal, 28x20x8.5 cm [HxWxL]; distal, 90 cm long) divided by a septum with a mount for prosthetic heart valves. St Jude heart valves (3 each of 23, 25, 27, 29, and 31 mm) were mounted with the leaflets oriented vertically to eliminate gravity effect. Flow, a 1% to 2% aqueous suspension of cornstarch, entered the proximal chamber from an upper reservoir whose height could be adjusted to vary transorifice pressure and flow rate and then passed through the mounted prosthetic valve under constant hydrostatic pressure causing steady flow. Flow rate was measured by the average of 3 to 5 timed collections. At least 3 different flow rates were examined for each valve size. Measurement variability was expressed as mean percent error for all flow rates studied, given by the SD of a set of timed collection measurements divided by their mean. Flow rates were chosen to simulate normal mitral transprosthetic velocities.

Pulsatile-Flow Model
To examine the effects of flow pulsatility on our method, St Jude heart valves (23, 25, 27, 29, and 31 mm) were studied in triplicate in the mitral position of a left heart pneumatic pump model. Cardiac output was measured by timed collections, with variability expressed as mean percent error. Four cardiac outputs were examined for each prosthesis, with heart rate constant at 70 bpm.

Echocardiographic Study
A Hewlett-Packard Sonos 1500 system was used with 2.5- or 3.5-MHz phased-array transducers held by an adjustable-clamp system to yield an imaging plane perpendicular to the leaflets to show 3 distinct orifices. Flow velocities across the center and side orifices were interrogated separately with continuous-wave (CW) Doppler. Color flow images of the proximal convergence zone were obtained with 3 different aliasing velocities between 17 and 41 cm/s and stored digitally on 650-MB optical disks and recorded onto 2-in VHS videotape.

Clinical Study
Patients
Patients in regular rhythm without significant tricuspid regurgitation who were undergoing St Jude mitral valve replacement were considered for the study. Cardiac output was measured in triplicate by thermodilution. The size of the implanted prosthetic heart valve was recorded.

Echocardiographic Examination
Intraoperative transesophageal echocardiography was performed with HP Sonos 1500 or Acuson 128XP with 5-MHz probes when patients were stable after weaning from cardiopulmonary bypass. Images of the prosthesis showing 3 distinct orifices were obtained at a depth of 6 to 10 cm. Velocities across the center and side orifices were obtained by CW Doppler during suspended respiration, and the pressure half-time (t1/2) of the E wave was measured.8 Images of the proximal convergence zone were obtained with a color aliasing velocity between 17 and 26 cm/s,11 reducing sector size to maximize frame rate (generally 18 to 22 frames per second), and stored on optical disks and/or VHS videotape. Thermodilution cardiac output was obtained simultaneously.

Data Analysis and Calculations
Steady-Flow Model
We selected 5 frames with a clear blue-red aliasing boundary to measure r and p, assuming the valve orifice to be at the prosthetic annular level. Prosthetic EOA was given by Qc/v for the hemispheric proximal isovelocity surface area (PISA) method and by Qp/v for the SOS method.

Pulsatile-Flow Model
Stroke volume was calculated by multiplying Qc or Qp by the time-velocity integral normalized by the peak transorifice velocity, v. Cardiac output was given by the stroke volumex70 bpm. Prosthetic EOA was given by (1) Qc/v for the PISA method, (2) Qp/v for the SOS method, and (3) the modified Gorlin equation:

where {Delta}p is the mean gradient across the St Jude side orifice by CW Doppler.

Clinical Study
Forward stroke volume across the prosthetic orifice was calculated by multiplying Qp or Qc by the time-velocity integral normalized by v. The product of stroke volume and heart rate yielded cardiac output. Prosthetic EOA was calculated by (1) Qc/v (PISA), (2) Qp/v (SOS), (3) 220/t1/2 (pressure half-time),8 and (4) the modified Gorlin equation above. In both the clinical and in vitro studies, the localized high velocities in the small central orifice were disregarded and the side orifice velocities used in the calculations.25

Statistical Analysis
In Vitro Models
Flow rates and cardiac outputs calculated by (1) PISA and (2) SOS were each compared with timed collections by linear regression, with the difference between calculated and measured flow ({Delta}Q) expressed as mean±SD. These 3 measurements of flow were also compared by repeated-measures ANOVA. Calculated in vitro EOAs were reported as mean±SD for each size, and the triplicate prostheses were compared by ANOVA. Center and side orifice velocities were compared by paired Student's t test. To evaluate the impact of aliasing velocities on flow estimation in the pulsatile model, {Delta}Q for 3 ranges of va (<=20, 21 to 29, and >=30 cm/s) were compared by ANOVA, with {Delta}Q for PISA and SOS in each range compared by paired Student's t test. {Delta}Q by PISA and SOS were also correlated with va by linear regression.

Clinical Study
Cardiac outputs calculated by (1) PISA and (2) SOS were each compared with thermodilution by linear regression, with the difference between Doppler and thermodilution cardiac output expressed as mean±SD. These 3 cardiac output measurements were also compared by repeated-measures ANOVA. In vivo EOA (reported for each valve size as mean±SD) calculated by (1) PISA, (2) SOS, and (3) pressure half-time method were each compared with Gorlin calculations and the geometric orifice area. Center and side orifice velocities were compared by paired Student's t test, with the difference expressed as mean±SD. Statistical significance was defined as a 2-tailed P<0.05.

Interobserver and Intraobserver Variability
Ten randomly selected color Doppler images and continuous Doppler recordings from the in vitro and clinical studies were used to assess interobserver and intraobserver variability in measurement of the radius r and chord p of the proximal convergence. Variability was expressed as the ratio of the difference between the 2 measurements to their mean.26


*    Results
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 *Results
down arrowDiscussion
 down arrowReferences
 
In Vitro Models
Steady-Flow Model
Flow rates ranged from 218 to 406 cm3/s, with mean error in the timed collections of 1.7±1%. The peak velocities through the center orifices (153.9±39.6 cm/s; range, 82.9 to 245 cm/s) were significantly higher than that through the side orifices (133.1±32.4 cm/s; range, 73.5 to 190 cm/s, {Delta}v=20.9±10.9 cm/s, P<0.001). The ratio of the side to center velocities was 0.87±0.04. PISA and SOS flow rates correlated well with the timed collections (Figures 2Down and 3Down), but compared with PISA, SOS underestimated true flow rate ({Delta}Q=-29.8±42.3 versus 0.7±28.2 cm3/s, P<0.001), also significant by repeated-measures ANOVA (P<0.0001). PISA and SOS EOAs (y) correlated with but underestimated the geometric orifice area (x) significantly (PISA: y=0.52x+0.43, r=0.87, P<0.001, {Delta}=-1.47±0.50 cm2; SOS: y=0.61x-0.09, r=0.87, P<0.001, {Delta}=-1.6±0.45 cm2, Table 1Down). There was no significant variation in EOAs for the 3 sets of prostheses by ANOVA.



View larger version (23K):
[in this window]
[in a new window]
  		Figure 2. Correlation between flow rate measured by timed collections (x axis) and flow rate calculated by conventional hemispheric PISA method (y axis) in in vitro steady-flow study (top). Dotted line represents line of identity. Bottom, Differences between the 2 measurements against their means.



View larger version (23K):
[in this window]
[in a new window]
  		Figure 3. Correlation between flow rate measured by timed collections (x axis) and flow rate calculated by SOS (y axis) in in vitro study (top). Bottom, Differences between the 2 measurements against their means.


View this table:
[in this window]
[in a new window]
  		Table 1. EOA (Mean±SD) of St Jude Valves in the Steady Flow Model

Pulsatile-Flow Model
Cardiac output ranged from 1.6 to 8.6 L/min, with a mean of 5.9 L/min and variation in the timed collections of 2.2±1.3%. The ratio of side to center orifice velocity was 0.83±0.11. The cardiac output calculated by PISA agreed closely with timed cardiac output (y=0.997x-0.09, r=0.95, P<0.001, {Delta}Q=-0.11±0.59 L/min, P=NS), but SOS showed poorer correlation (y=0.81x+0.52, r=0.88, P<0.001) and significant underestimation of flow ({Delta}Q=-0.55±0.82 L/min, P<0.001), significantly worse (P<0.0001) than the PISA calculations. PISA and SOS EOAs correlated with but underestimated geometric orifice areas (r=0.79 and 0.78, respectively, Table 2Down), without significant variation among the 3 sets of prostheses by ANOVA.


View this table:
[in this window]
[in a new window]
  		Table 2. EOA (Mean±SD) of St Jude Valves in the Pulsatile Flow Model

By SOS, {Delta}Q was -0.88±0.7 L/min for aliasing velocities <=20 cm/s, -0.49±0.9 L/min for 21 to 29 cm/s, and -0.28±0.8 L/min for >=30 cm/s (P=0.07 by ANOVA). SOS {Delta}Q was significantly worse than PISA {Delta}Q for <=20 cm/s (-0.05±0.4 L/min, P<0.001) and 21 to 29 cm/s (0.12±0.3 L/min, P=0.007) but not for >=30 cm/s (-0.38±0.8 L/min, P=NS). There were opposite but nonsignificant linear trends between aliasing velocity and {Delta}Q for PISA (r=-0.24, P=NS) and SOS (r=0.24, P=NS).

Clinical Study
The study population comprised 36 patients (26 women, 58±11 years old). At the time of study, 24 were AV paced, with the remainder in sinus rhythm. Heart rate was 92±10 bpm.

The peak and mean velocities through the center orifice (161±29 and 97±16 cm/s, respectively) were significantly higher than through the side orifices (137±23 and 86±14 cm/s, respectively, {Delta}peak=23.6±11 cm/s, P<0.001 and {Delta}mean=11±6.5 cm/s, P<0.001), with a side-to-central velocity ratio of 0.86±0.05 (Figure 4Down).



View larger version (154K):
[in this window]
[in a new window]
  		Figure 4. CW Doppler examination of flow across central and side orifices of St Jude mitral valve in a patient. Note higher flow velocities across central compared with side orifice.

Cardiac output by thermodilution (x) was 5.2±1.2 L/min (3.3 to 8.1 L/min), with close agreement by PISA (y=1.018x-0.21, r=0.91, {Delta}CO=-0.05±0.55 L/min, Figure 5Down) but underestimation by SOS (y=0.79x-0.21, r=0.82, {Delta}CO=-1.33±0.73 L/min, Figure 6Down), P<0.001 for the significance of this difference by repeated-measures ANOVA (P<0.001).



View larger version (20K):
[in this window]
[in a new window]
  		Figure 5. Correlation between thermodilution cardiac output (CO, x axis) and CO calculated by conventional PISA method (y axis) in clinical study (top). Bottom, Differences between the 2 measurements against their means.



View larger version (20K):
[in this window]
[in a new window]
  		Figure 6. Correlation between thermodilution cardiac output (CO, x axis) and CO calculated by SOS method (y axis) in clinical study (top). Bottom, Differences between the 2 measurements against their means.

Table 3Down and Figure 7Down summarize EOA calculated by the different methods. EOA by the modified Gorlin equation was significantly smaller than the geometric orifice area provided by the manufacturer (y=0.37x+0.24, r=0.64, P<0.001, {Delta}= -2.5±0.5 cm2, P<0.001). PISA EOA agreed closely with Gorlin valve area (y=0.78x+0.7, r=0.75, P<0.001, {Delta}=0.3±0.28 cm2, P<0.001) and also underestimated the geometric area (y=0.48x+0.05, r=0.8, P<0.001, {Delta}= -2.15±0.43 cm2, P=0.001). Similarly, SOS EOA agreed with Gorlin area (y=0.64+0.41, r=0.68, P<0.001, {Delta}= -0.23±0.3 cm2, P<0.001) and underestimated the geometric area (y=0.42x-0.23, r=0.76, P<0.001, {Delta}=-2.7±0.46 cm2). Orifice area calculated by pressure half-time showed very poor (inverse) agreement with both Gorlin (y=4.9-1.01x, r=-0.44) and geometric valve area (y= -0.44x, r=-0.33).


View this table:
[in this window]
[in a new window]
  		Table 3. In Vivo EOA (Mean±SD) of St Jude Mitral Valves



View larger version (11K):
[in this window]
[in a new window]
  		Figure 7. EOAs of St Jude valves calculated by 4 different methods and their corresponding geometric orifice area. T1/2 indicates pressure half-time method; Gorlin, modified Gorlin equation.

Interobserver and Intraobserver Variabilities
In vitro interobserver variabilities in the measurement of proximal convergence radius and chord were 3.3±3.8% and 3.9±2.9%, respectively, with intraobserver variabilities of 3.5±1.4% and 2.1±1.1%, respectively. In the clinical study, interobserver variabilities for r and p were 3.6±3.2% and 3.2±2.4%, respectively, with intraobserver variabilities of 4.1±3.4% and 5.3±2.9%, respectively.


*    Discussion
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 *Discussion
down arrowReferences
 
The proximal convergence method, a recently developed color Doppler technique for quantification of mitral regurgitation,10 11 12 13 14 15 16 17 18 19 has been validated in experimental and clinical studies for calculation of regurgitant stroke volume and effective regurgitant orifice area.10 11 12 13 14 15 16 17 18 The same principle has been used to calculate mitral stenotic orifice area, where there is relatively low-velocity flow across a finite orifice.20 Extending this concept to mitral valve prostheses is reasonable, because the planar nature of the ring obviates much of the need to correct for proximal flow constraint, which is often necessary for mitral stenosis20 and regurgitation.27 Moreover, the difficulties commonly encountered in locating the convergent focus28 are eliminated, because the level of the orifice is defined by the prosthetic annulus. However, the finite size and relatively low transorifice velocity of a mitral prosthesis are associated with isotach flattening near the orifice.22 Fortunately, the resultant flow underestimation can largely be corrected by a correction factor, v/(v-va), where v is the transorifice velocity and va the aliasing velocity.22

The SOS method has been advocated as an alternative to the conventional hemispheric modeling of the proximal convergence flow field. This method has the advantage that only 1 measurement, p, is required, compared with the more accurate hemielliptical model.23 24 However, total forward flow by SOS, although well correlated to actual flow in our models and clinical study, showed systematic underestimation, which will merit further study.

Effective Prosthetic Orifice Area
All prosthetic valves are inherently mildly stenotic. Analogous to stenotic native valve area, prosthetic orifice area, incorporating flow and pressure gradient, gives a more flow-independent measure of prosthetic resistance. Although the continuity equation and pressure half-time methods8 29 are accepted Doppler techniques for native mitral and aortic stenosis, effective prosthetic orifice area has been more elusive.30 Although Doppler has been used in flow models to calculate effective prosthetic valve areas31 and the continuity equation has been used clinically for prosthetic aortic valves,9 32 a reliable noninvasive method to estimate prosthetic mitral orifice area clinically is still lacking.

The present study demonstrated that the pressure half-time method has little value in measuring effective prosthetic orifice areas, actually showing an inverse relation to valve size. We have previously shown that the pressure half-time method is unreliable immediately after balloon valvuloplasty33 because of abrupt changes in transvalvular gradient and chamber compliance. In the present study, the pressure half-time was measured immediately after mitral valve replacement, when sudden changes in net chamber compliance and transvalvular gradient might have contributed to the inaccuracy of the pressure half-time method for effective prosthetic valve area.

The effective prosthetic valve areas in our clinical study are consistent with some published studies31 but smaller than others.34 35 36 Baumgartner et al31 calculated EOA in a pulsatile-flow model with the Gorlin formula and Doppler gradients and obtained values similar to our in vivo EOA. However, in the same study, EOAs were significantly larger when catheter gradients were used with the Gorlin formula. Similarly, Yoganathan and his group obtained significantly larger EOAs with the catheter-based Gorlin formula both in vitro35 and in vivo,36 related to the overestimation of catheter gradients by Doppler34 due to the phenomenon of pressure recovery.25 Interestingly, Baumgartner et al observed larger EOAs in their steady in vitro model than in the pulsatile one. This is supported by a preliminary study by Trujillo et al,37 who showed that for rigid circular orifices, Doppler continuity EOAs during steady flow are consistently larger than in pulsatile-flow conditions. Further preliminary data show flow dependency of EOA in pulsatile conditions.37 38 In our clinical study, the relatively fast heart rate and therefore lower stroke volume observed just after cardiopulmonary bypass may contribute to smaller calculated EOAs. In addition, the geometry surrounding the prosthesis in vivo and the presence or absence of the mitral subvalvular apparatus may also have important effects on the calculated EOA.

Limitations
The major limitation in all studies examining effective prosthetic orifice area is the lack of a proper, universally accepted "gold standard." Various references have been used, including geometric, Gorlin, continuity, and half-time EOAs. However, true in vivo EOA may vary for a given prosthesis depending on physiological conditions, shown by the range in reported EOA in our and prior studies. In vitro results suggest that flow pulsatility affects EOA. Our data showed consistent results across 3 valves of each size, suggesting relatively little actual interprosthesis variance.

Clinical Application
Although we would not recommend this technique for routine assessment of mitral prostheses (because of the need for transesophageal echocardiography), we have found it quite useful in relatively subtle or questionable situations of prosthetic obstruction. When a leaflet is completely stuck by thrombus or pannus, this is usually evident by direct 2-dimensional imaging and a high transprosthetic gradient in the presence of a low-output state. In contrast, the PISA EOA is helpful for assessing nonobvious obstruction or, conversely, ruling it out when a high gradient occurs in a high-output state.

Conclusions
This is the first study to demonstrate that mitral prosthetic EOA can be measured noninvasively by proximal flow convergence methods. We examined the St Jude prosthesis because it is the mostly commonly implanted prosthetic valve; because its hydrodynamic profile is among the most complex, this technique is likely to be applicable to other types of prostheses. This may improve the management of patients with mitral prostheses by allowing accurate detection and assessment of prosthetic valve obstruction independent of transvalvular flow.


*    Acknowledgments
 
This study was supported in part by grant NCC9-60 from the National Aeronautics and Space Administration, Houston, Tex, with valve prostheses provided by St Jude Medical, Inc, Minneapolis, Minn.


*    Footnotes
 
Presented in part at the 44th Annual Scientific Session of the American College of Cardiology, March 19–22, 1995, New Orleans, La, and at the 6th Scientific Sessions of the American Society of Echocardiography, June 14–16, 1995, Toronto, Canada.

Received December 19, 1997; revision received May 14, 1998; accepted May 20, 1998.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
 up arrowResults
 up arrowDiscussion
 *References
 

  1. Nanda NC, Cooper JW, Mahan EF, Fan P. Echocardiographic assessment of prosthetic valves. Circulation. 1991;84(suppl I):I-228–I-239.
  2. Baumgartner H, Khan S, DeRobertis M, Czer L, Maurer G. Discrepancies between Doppler and catheter gradients in aortic prosthetic valves in vitro: a manifestation of localized gradients and pressure recovery. Circulation. 1990;82:1467–1475.[Abstract/Free Full Text]
  3. Baumgartner H, Schima H, Tulzer G, Kuhn P. Effect of stenosis geometry on the Doppler-catheter gradient relation in vitro: a manifestation of pressure recovery. J Am Coll Cardiol. 1993;21:1018–1025.[Abstract]
  4. Baumgartner H, Khan S, DeRobertis M, Czer L, Maurer G. Effect of prosthetic aortic valve design on the Doppler-catheter gradient correlation: an in vitro study of normal St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves. J Am Coll Cardiol. 1992;19:324–332.[Abstract]
  5. Levine RA, Jimoh A, Cape EG, McMillan S, Yoganathan AP, Weyman AE. Pressure recovery distal to a stenosis: potential cause of gradient "overestimation" by Doppler echocardiography. J Am Coll Cardiol. 1989;13:706–715.[Abstract]
  6. Baumgartner H, Schima H, Kuhn P. Discrepancies between Doppler and catheter gradients across bileaflet aortic valve prostheses. Am J Cardiol. 1993;71:1241–1243.[Medline] [Order article via Infotrieve]
  7. Cannon SR, Richards KL, Crawford MH, Folland ED, Pierpont G, Sethi GK, Hammermeister KE. Inadequacy of the Gorlin formula for predicting prosthetic valve area. Am J Cardiol. 1988;62:113–116.[Medline] [Order article via Infotrieve]
  8. Hatle L, Angelsen B, Tromsdal A. Non-invasive assessment of atrioventricular pressure half-time by Doppler ultrasound. Circulation. 1979;60:1096–1104.[Abstract/Free Full Text]
  9. Chafizadeh ER, Zoghbi WA. Doppler echocardiographic assessment of the St. Jude Medical prosthetic valve in the aortic position using the continuity equation. Circulation. 1991;83:213–223.[Abstract/Free Full Text]
  10. Vandervoort PM, Rivera JM, Mele D, Palacios IF, Dinsmore RE, Weyman AE, Levine RA, Thomas JD. Application of color Doppler flow mapping to calculate effective regurgitant orifice area: an in vitro study and initial clinical observations. Circulation. 1993;88:1150–1156.[Abstract/Free Full Text]
  11. Utsunomiya T, Doshi R, Patel D, Mehta K, Nguyen D, Henry WL, Gardin JM. Calculation of volume flow rate by the proximal isovelocity surface area method: simplified approach using color Doppler zero baseline shift. J Am Coll Cardiol. 1993;22:277–282.[Abstract]
  12. Utsunomiya T, Ogawa T, Tang HA, Doshi R, Patel D, Quan M, Henry WL. Doppler color flow mapping of the proximal isovelocity surface area: a new method for measuring volume flow rate across a narrowed orifice. J Am Soc Echocardiogr. 1991;4:338–348.[Medline] [Order article via Infotrieve]
  13. Rivera JM, Vandervoort PM, Thoreau DH, Levine RA, Weyman AE, Thomas JD. Quantification of mitral regurgitation with the proximal flow convergence method: a clinical study. Am Heart J. 1992;124:1289–1296.[Medline] [Order article via Infotrieve]
  14. Chen C, Koschyk D, Brockhoff C, Heik S, Hamm C, Bleifeld W, Kupper W. Noninvasive estimation of regurgitant flow rate and volume in patients with mitral regurgitation by Doppler color mapping of accelerating flow field. J Am Coll Cardiol. 1993;21:374–383.[Abstract]
  15. Enriquez-Sarano M, Seward JB, Bailey KR, Tajik AJ. Effective regurgitant orifice area: a noninvasive Doppler development of an old hemodynamic concept. J Am Coll Cardiol. 1994;23:443–451.[Abstract]
  16. Enriquez-Sarano M, Bailey KR, Seward JB, Tajik AJ, Krohn MJ, Mays JM. Quantitative Doppler assessment of valvular regurgitation. Circulation. 1993;87:841–848.[Abstract/Free Full Text]
  17. Recusani F, Bargiggia GS, Yoganathan AP, Raisaro A, Valdes-Cruz LM, Bertucci C, Gallati M, Moises VA, Simpson IA, Tronconi L, Sahn DJ. A new method for quantification of regurgitant flow rate using color Doppler flow imaging of the flow convergence region proximal to a discrete orifice: an in vitro study. Circulation. 1991;83:594–604.[Abstract/Free Full Text]
  18. Bargiggia GS, Tronconi L, Sahn DJ, Recusani F, Raisaro A, De Servi S, Valdes-Cruz LM, Montemartini C. A new method for quantitation of mitral regurgitation based on color flow Doppler imaging of flow convergence proximal to regurgitant orifice. Circulation. 1991;84:1481–1489.[Abstract/Free Full Text]
  19. Simpson IA, Sahn DJ. Quantification of valvular regurgitation by Doppler echocardiography. Circulation. 1991;84(suppl I):I-188–I-192.
  20. Rodriguez L, Thomas JD, Monterroso V, Weyman AE, Harrigan P, Mueller LN, Levine RA. Validation of the proximal flow convergence method: calculation of orifice area in patients with mitral stenosis. Circulation. 1993;88:1157–1165.[Abstract/Free Full Text]
  21. Rittoo D, Sutherland GR, Shaw TR. Quantification of left-to-right atrial shunting and defect size after balloon mitral commissurotomy using biplane transesophageal echocardiography, color flow Doppler mapping, and the principle of proximal flow convergence. Circulation. 1993;87:1591–1603.[Abstract/Free Full Text]
  22. Rodriguez L, Anconina J, Flachskampf FA, Weyman AE, Levine RA, Thomas JD. Impact of finite orifice size on proximal flow convergence: implications for Doppler quantification of valvular regurgitation. Circ Res. 1992;70:923–930.[Abstract/Free Full Text]
  23. Ge S, Jones M, Shiota T, Yamada I, DeGroff CG, Teien DE, Baptista AM, Sahn DJ. Quantification of mitral flow by Doppler color flow mapping. J Am Soc Echocardiogr. 1996;9:700–709.[Medline] [Order article via Infotrieve]
  24. Ge S, Jones M, Shiota T, Yamada I, Valdes-Cruz L, Sahn DJ. Quantification of flow and effective orifice size for mitral bileaflet mechanical valves: validation of a new color Doppler "segment of spheroid" flow convergence method in an animal model. Circulation. 1993;88(suppl I):I-642. Abstract.
  25. Vandervoort PM, Greenberg NL, Pu M, Powell KA, Cosgrove DM, Thomas JD. Pressure recovery in bileaflet heart valve prostheses: localized high velocities and gradients in central and side orifices with implications for Doppler-catheter gradient relation in aortic and mitral position. Circulation. 1995;92:3464–3472.[Abstract/Free Full Text]
  26. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307–310.[Medline] [Order article via Infotrieve]
  27. Pu M, Vandervoort PM, Griffin BP, Leung DY, Stewart WJ, Cosgrove DM, Thomas JD. Quantification of mitral regurgitation by the proximal convergence method using transesophageal echocardiography: clinical validation of a geometric correction for proximal flow constraint. Circulation. 1995;92:2169–2177.[Abstract/Free Full Text]
  28. Vandervoort PM, Thoreau DH, Rivera JM, Levine RA, Weyman AE, Thomas JD. Automated flow rate calculations based on digital analysis of flow convergence proximal to regurgitant orifices. J Am Coll Cardiol. 1993;22:535–541.[Abstract]
  29. Nakatani S, Masuyama T, Kodama K, Kitabatake A, Fujii K, Kamada T. Value and limitations of Doppler echocardiography in the quantification of stenotic mitral valve area: comparison of the pressure half-time and the continuity equation methods. Circulation. 1988;77:78–85.[Abstract/Free Full Text]
  30. Wilkins GT, Gillam LD, Kritzer GL, Levine RA, Palacios IF, Weyman AE. Validation of continuous-wave Doppler echocardiographic measurements of mitral and tricuspid prosthetic valve gradients: a simultaneous Doppler-catheter study. Circulation. 1986;74:786–795.[Abstract/Free Full Text]
  31. Baumgartner H, Khan SS, DeRobertis M, Czer LS, Maurer G. Doppler assessment of prosthetic valve orifice area: an in vitro study. Circulation. 1992;85:2275–2283.[Abstract/Free Full Text]
  32. Rothbart RM, Castriz JL, Harding LV, Russo CD, Teague SM. Determination of aortic valve area by two-dimensional and Doppler echocardiography in patients with normal and stenotic bioprosthetic valves. J Am Coll Cardiol. 1990;15:817–824.[Abstract]
  33. Thomas JD, Wilkins GT, Choong CY, Abascal VM, Palacios IF, Block PC, Weyman AE. Inaccuracy of mitral pressure half-time immediately after percutaneous mitral valvotomy: dependence on transmitral gradient and left atrial and ventricular compliance. Circulation. 1988;78:980–993.[Abstract/Free Full Text]
  34. Rashtian MY, Stevenson DM, Allen DT, Yoganathan AP, Harrison EC, Faughan P, Rahimtoola SH. Flow characteristics of four commonly used mechanical heart valves. Am J Cardiol. 1986;58:743–752.[Medline] [Order article via Infotrieve]
  35. Yoganathan AP, Chaux A, Gray RJ, Woo YR, DeRobertis M, Williams FP. Bileaflet, tilting disc and porcine aortic valve substitutes: in vitro hydrodynamic characteristics. J Am Coll Cardiol. 1984;3:313–320.[Abstract]
  36. Gray RJ, Chaux A, Matloff JM, DeRobertis M, Raymond M, Stewart M. Bileaflet, tilting disc and porcine aortic valve substitutes: in vivo hydrodynamic characteristics. J Am Coll Cardiol. 1984;3:321–327.[Abstract]
  37. Trujillo NP, Kwon J, Kringlen M, Gill E, Shandas R, Valdez-Cruz L. Comparison of effective orifice area calculations using the continuity equation in steady and pulsatile flow. J Am Coll Cardiol. 1996;Feb:233A. Abstract.
  38. Shandas R, Jones M, Solowiejcyk D, Manduley R, Yamada I, Valdes-Cruz L. Flow dependency of the Doppler continuity equation for bileaflet mechanical valves: studies in an animal model. J Am Coll Cardiol. 1996;Feb:234A. Abstract.



This article has been cited by other articles:


Home page
 Eur J EchocardiogrHome page
N. Namboodiri, O. Shajeem, J. A. Tharakan, R. Sankarkumar, T. Titus, A. Valaparambil, S. Sivasankaran, K. M. Krishnamoorthy, S. P. Harikrishnan, and S. K. Dora
Doppler echocardiographic assessment of TTK Chitra prosthetic heart valve in the mitral position
Eur J Echocardiogr, March 18, 2008; (2008) jen030v1.
[Abstract] [Full Text] [PDF]

Home page
 Eur J EchocardiogrHome page
N. Namboodiri, O. Shajeem, J. A. Tharakan, R. Sankarkumar, T. Titus, A. Valaparambil, S. Sivasankaran, K. M. Krishnamoorthy, S. P. Harikrishnan, and S. K. Dora
Doppler echocardiographic assessment of TTK Chitra prosthetic heart valve in the mitral position
Eur J Echocardiogr, February 27, 2008; (2008) jen001v2.
[Abstract] [Full Text] [PDF]

Home page
 CirculationHome page
R. Shandas, J. Kwon, and L. Valdes-Cruz
A Method for Determining the Reference Effective Flow Areas for Mechanical Heart Valve Prostheses : In Vitro Validation Studies
Circulation, April 25, 2000; 101(16): 1953 - 1959.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Leung, D. Y.
Right arrow Articles by Thomas, J. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Leung, D. Y.
Right arrow Articles by Thomas, J. D.

Circulation Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search
Copyright © 1998 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited.