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Dr. Vittorio Dall'Aglio - Medico Chirurgo specialista in Cardiologia - Pordenone
 

Quantification of Mitral Regurgitation: comparison Between Transthoracic and Transesophageal Color Doppler Flow Mapping


RENATA MIMO, M.D., UNA SPARACINO, M.D., GIAN L. NICOLOSI, M.D., GIOVANNI D’ANGELO, M.D., VITTORIO DALL’AGLIO. M.D., CHIARA LESTUZZI, M.D., DANIELA PAVAN, M.D., EUGENIO CERVESATO, PH.D., and DOMENICO ZANUTTINI, M.D.

Cardiologia, ARC, Ospedale Civile, Pordenone, Italy


We reviewed transthoracic (TTE) and transesophageal (TEE) echocardiograms of 100 consecutive patients: 63 male, 37 female, mean age 50 years (range 16-83 years), 32 with neoplastic disease, 18 aortic disease, 28 mitral value disease, and 22 with other diseases. Absence or presence of mitral regurgitation (defined as mild, moderate, or severe) was assessed. TEE showed mild mitral regurgitation in 26 patients where TTE was negative. The overall estimate of regurgitant lesion severity was concordant at TEE and TTE in 64% of cases. The overall estimate of regurgitant lesion severity was also greater by one grade in 1% of cases at TTE, and in 35% of cases at TEE. Maximal digitized jet areas were 3.60 ± 6.35 cm2 at TTE and 3.04 ± 3.79 cm2 at TEE (P = NS). Correlation was r = 0.69 (TEE = 0.41 TTE + 1.55; P < 0.001). TEE yielded a higher prevalence of mitral regurgitation than TTE with a trend toward greater overall estimate of mitral regurgitation at the semi-quantitative analysis. TTE and TEE showed similar mean results at the quantitative assessment of maximal jet areas. However, a highly significant random variability was observed in quantifying mitral regurgitation at TEE. (ECHOCARDIOGRAPHY, Volume 8, November 1991)

Address for correspondence and reprints:
Dott. Renata Mimo, Servirio di Emodinamica, Reparto di Cardiologia, Ospedale Civile, Via Montereale 24, 33170 Pordenone, Italy.

Color Doppler flow mapping allows the temporal visualization of mitral regurgitant jets.[1,2] Several studies have shown that this technique can be helpful in the semi-quantitative grading of mitral regurgitation by the transthoracic approach.[3-15]

Little information is available, however, on transesophageal color flow imaging of mitral valve regurgitation.[16-20] Previous information mainly deals with prosthetic mitral valves.[17,18,21-23] The purpose of this study was to compare transthoracic and transesophageal color Doppler flow mapping in the quantification of mitral regurgitation of native valves.

Methods

We reviewed the transthoracic (TTE) and transesophageal (TEE) echocardiograms of 100 unselected consecutive patients (63 male and 37 female, mean age 50 years; range 16—83 years), who underwent both examinations on the same day from March 1989 to February 1990 for several reasons. Thirty-two patients had neoplastic disease, 18 aortic disease, 28 native mitral valve disease, and 22 had other diseases. Patients with prosthetic valves in the mitral position were excluded. Eighty-three patients were in sinus rhythm, 15 in atrial fibrillation, and 2 had a VVI pacemaker implanted.

Transthoracic and transesophageal color Doppler studies were performed by using a commercially available system (Aloka SSD-870, Aloka, Tokyo, Japan), with 2.5- or 3.5-MHz transthoracic transducer and 5-MHz transesophageal single plane (in 45 patients) or biplane probes (in 55 patients).

Patients were examined with TEE after 4 hours of fasting and local anesthesia was given to the oropharynx.[18] Mild sedation was used with intravenous diazepam when necessary.

To optimize image quality of TTE and TEE, color Doppler gain was first turned down completely and then increased gradually until the static background noise just appeared.[9,10,12,18]

During transthoracic examination and for each standard approach and view (parasternal, apical and subcostal approaches; long-axis, short-axis, and four-chamber views), the transducer was angled and moved with small increments to obtain the maximal regurgitant signal in any given plane.[9,12,18]

For the transesophageal approach, we obtained cross-sectional, longitudinal, and four-chamber standard views.[18] All the possible intermediate nonstandardized views were also looked for in each patient. In fact, the transducer was angled and moved in order to obtain the maximal regurgitant signal in any given plane.[18]

All color Doppler flow imaging studies were stored on %-inch Sony U-matic videotape recorder (Model VO-5800PS, Sony Corp., Park Ridge, NJ, USA) for further analysis.

Retrospective and blind evaluations of color Doppler studies were performed independently by two observers. All the echocardiographic sections were reviewed.

Color Doppler Flow Mapping Evaluation

Qualitative and Semi-Quantitative Analysis. Color Doppler evaluation of mitral regurgitation was qualitative for the presence or absence of regurgitation.[10] For the semi-quantitative evaluation, three grades of severity were considered: mild, moderate, and severe, according to previously reported criteria,[10] which took into account width and depth of regurgitant jets from different
views. Mitral regurgitation was evaluated as being mild if the jet width was visually judged to be less than or equal to one third of the regurgitant chamber width; moderate if the jet width was visually judged to be more than one third and less than half of the regurgitant chamber width; and severe if the jet width was more than half of the regurgitant chamber width.[10] The maximal width of the jet was visually compared with the maximal width of the left atrium even though this could be observed in different views.[10] The color Doppler evaluation of regurgitant jets was performed not only in the large angle views but also in the 28° angle format in order to increase the frame rate.[10] The relationship between the size of the jet and that of the receiving chamber was made by an overall visual integration of all information deriving from the complete examination through all different transducer positions, in order to ensure exploration of the entire regurgitant chamber and allow adequate evaluation of the three-dimensional characteristics of the jet.[10] The depth of the jet was only considered as a secondary criterion mainly when the jet was received into a large chamber.[9,10] In fact. a deeper extension of the jet into the receiving chamber was considered an additional criterion of severity of the regurgitation itself, when the receiving chamber was large.[10] The prolonged duration of a large regurgitant flow during the cardiac cycle was also considered a secondary criterion of severity.[11,24] These two additional criteria were only applied occasionally in this series.

Quantitative Analysis. For the quantitative evaluation of maximal jet areas, the transthoracic and the transesophageal frame containing the largest area of the jet were identified by reviewing all echocardiographic sections by two observers who selected by agreement the optimal frame. Maximal transthoracic and transesophageal jet areas were then digitized twice, blindly and independently by each of the two observers following the outer border of the largest clearly definable flow disturbance.[10,13]
The area of disturbed flow that was traced in cluded central variance and aliased signals, as well as the immediately contiguous nonturbulent velocities that were moving in the same direction as the jet.[10,13] The results are the mean of the four measurements (two digitized areas by two observers).
 

Statistical Analysis

For statistical analysis, Spearman’s rank correlation method was used. Maximal color jet areas were analyzed by three-way analysis of variance.[26] We used a complete 100 x 2 x 2 (number of cases x used methods x observers) factorial model with repeated measures by the observers.[28] The factorial components "number of cases" and "observers" are random, while the factor "methods" is fixed. In this model the variability was regarded as coming from "number of cases," "methods used," "observers," the interaction of these factors, and the repetition of measures. The variability was given as absolute value (standard deviation of the corresponding component of variance) and as percentage of the mean. Significance of each component of variance was assessed by Fisher F test for variance. Linear regression analysis was also used as required.

Results

TEE showed mild mitral regurgitation in 26 patients where TTE was negative (Table I).

Concordance between the two observers for tile semi-quantitative assessment of mitral regurgitation was present in 98% of cases; in two cases concordance was reached by agreement.
The overall estimate of regurgitant lesion severity was concordant at TEE and TTE in 64% of cases (Table I). The overall estimate of regurgitant lesion severity was also greater by one grade in 1% of cases using TTE and in 35% of cases using TEE (Table I). Spearman’s rank correlation coefficient was r = 0.80 (t = 13.2; degrees of freedom = 98; P < 0.001).

For the quantitative evaluation, mean jet areas were 3.60 ± 6.35 cm2 at TTE and 3.04 ± 3.79 cm2 at TEE (P = NS). Three-way analysis of variance is reported in Table II. Interobserver variability was 8% and intraobserver variability was 8.6% (Table II). Variability induced by the interaction between the technique and the population was 98%. This means that analysis of variance showed in each patient a highly significant random variability between TTE and TEE (P < 0.001; Table H). Correlation coefficient between digitized jet areas at TTE and TEE was r = 0.69 (TEE = 0.41 TTE + 1.65; P < 0.001) (Fig. 1).

Figure 1. Regression analysis of regurgitant jet areas between transesophageal  echocardiography (TEE) and transthoracic echocardiography (TTE). A: slope =
0.41, intercept = 166, r = 0.69, P < 0.001, SEE = 2JS. B: identity line. See text  for details.


Discussion

Several studies have shown that color Doppler flow mapping can be helpful in the semi-quantitative grading of mitral regurgitation by the transthoracic approach in clinical settings.[1-15] Little information is available, on the other hand, on the assessment of mitral regurgitation by the transesophageal approach.[16,20]

The reported articles mainly deal with prosthetic mitral valves.[17,18,21-23] The purpose of our study was to try to compare transthoracic and transesophageal color Doppler flow mapping in the quantification of mitral regurgitation of native valves in the clinical setting. To achieve this goal, a consecutive unselected series of 100 patients, who underwent both TTE and TEE, were studied. Even though the studies were not done simultaneously, they were usually performed one after the other. Temporal variability was not considered important in this series, since heart rate and blood pressure were similar during both studies.

For semi-quantitative evaluation, we used a standardized approach, which has been used consistently in the last several years in our laboratory.[10] This method was compared to angiography for TTE with good agreement between the two techniques, even though an 18.5% underestimation and 11.5% overestimation was evident for the assessment of mitral regurgitation.[10] However, this was probably due  largely to the intrinsic differences between the two techniques.[10] On the one hand, the semi-quantitative evaluation of mitral regurgitation by color Doppler using the transthoracic approach has gained a wide clinical acceptance and is currently used as a reference non-invasive technique for clinical decision making.[19]

Furthermore, in this population of consecutive patients, there were no present indications to angiography for clinical decision making. The transthoracic color Doppler method has become the standard reference method for the non-invasive assessment of valvular regurgitation.[19] The transthoracic color Doppler method is in fact reproducible and allows reduction of the interobserver and intraobserver variability.[10] Furthermore, concordance between the blind observers in the semi-quantitative evaluation of mitral regurgitation was achieved in 98% of cases in the present study.

We have also shown that TEE yielded a higher prevalence of mitral regurgitation than transthoracic techniques in the same patients, i.e., that TEE seems to be more sensitive than TTE, since mild mitral regurgitation was visualized in 26 cases only by TEE. This is in agreement with previous data.[16,18,19,21] The overall estimate of regurgitant lesion severity was concordant using TEE and TTE in our series, in 64% of cases, while lesion severity was greater by one grade in 35% of cases using TEE and in only 1% of cases using TTE. This again indicates, for TEE, a trend towards a greater overall estimate of mitral regurgitation, as compared to the transthoracic approach, as evaluated by using our integrated overall semi-quantitative analysis of all recorded views (see Methods). Stevenson[26] has shown that the transmit frequency of the transducer is inversely related to the color jet (variance) area.

Therefore, the higher frequency transesophageal transducer should tend to produce a smaller jet area than that recorded using the lower frequency transthoracic transducer.  However, this should happen when the target is located at the same depth. We feel in fact that the closer relation to posterior structures by using the transesophageal approach is probably important in the determination of the color Doppler appearance of regurgitant jet areas, when compared to the transthoracic approach. This close relationship with the target can probably counterbalance, in individual cases, the effect due to the higher transducer frequency (Figs. 2 and 3).

With regard to the quantitative evaluation of digitized jet areas, our results suggest no significant difference between the two techniques. This can be explained by the fact that digitized maximal jet area is coming from only one frame where the maximal jet area is observed. We were careful in the identification of this frame, by reviewing the entire recorded examination. The frame was carefully selected from a cardiac cycle, which was considered as representative of the cardiac rhythm of the patient. This means that if the patient was in atrial fibrillation, the shortest and longest cardiac cycles were discarded. On the other hand, the semi-quantitative evaluation is derived from the three-dimensional information on the regurgitant jet. This information was visually constructed from the overall analysis of all possible recorded views from all different approaches. For the quantitative approach, the duration of the regurgitant flow could not be taken into account, since only one frame was analyzed. We did not use the ratio of regurgitant jet area to left atrium area, as reported by Helmcke et al.,[9] for two main reasons: first, the atrial size should be considered the same for both the transthoracic and transesophageal approaches, and second, some portion of the atrial cavity is frequently outside the imaging field in the transesophageal approach.

The use of the biplane transesophageal transducer did not seem to alter the results on the maximum regurgitant jet area recorded in this series. In fact, the selected maximal jet area was found in a longitudinal plane in only one case in this series (out of the 55 patients who were studied with the biplane probe) (Fig. 3). However, for the semi-quantitative overall analysis of lesion severity, the biplane transesophageal approach is probably more useful for a complete evaluation of the three-dimensional characteristics of the jet, especially with eccentric jets. The correlation between TTE and TEE was sub-optimal with a large standard estimation error. It appeared also that TEE seemed to give smaller regurgitant jets for large regurgitation areas (over 20 cm2) when compared to TTE (Fig. 1). This is probably due to the fact that color coding is limited by the proximal narrow part of the triangular section view (Fig. 2).
Another possible explanation could be the fact that higher transducer frequency has been used for TEE.[26]

Multivariate analysis showed that variability induced by the interaction between the techniques and the population was high (i.e., 98%). This means that analysis of variance showed in each patient a highly significant random variability between TTE and TEE (P < 0.001; Table II). This could be explained by the fact that the transesophageal approach gives complementary but different views when compared to the transthoracic approach. The wide random variability may also be due to: (1) closer relationship to posterior structures; (2) higher and single frequency transducers; (3) different sampling depth, which allowed different frame rate; (4) potential competition by different incoming flows; and (5) competition between color pixels and pixels occupied by gray signal (spontaneous contrast effect) using TEE.
 

Figure 2. Echocardiographic examination of a 46-year-old patient with mitral insufficiency due to prolapsing wive. The transthoracic examination was sub-optimal due to a poor acoustic window. Only the subcostal approach (modified four-chamber view in (A) allowed better visualization of the mitral regurgitant jet (arrows) by using the 2.5-MHz transducer. The transesophageal approach (B) showed a larger regurgitant jet probably due to the closer target position. The large regurgitant jet appears to be cut off at the edges of the color sector (arrow in B). This can explain in part the tendency to give smaller regurgitant jet for larger regurgitation areas by using transesophageal echocardiography, when compared to the transthoracic approach, by the quantitative analysis, la = left atrium; Iv = left ventricle; ra = right atrium.

Figure 3. Echocardiographic examination of a 62-year-old patient with mitral regurgitation due to endocarditis. The modified four-chamber view by the transthoracic approach (A) shows a small regurgitant central jet (arrows) by using a 3.5-MHz transducer. At the transesophageal approach (B), the longitudinal view obtained by the biplane probe shows a central jet, which appears larger than that of the transthoracic approach. la = left atrium; Iv = left ventricle.

Finally, the limitation induced on the color-coded area by the proximal narrow part of the sector can be important in some patients. The limitation on the number of possible cross-sectional views due to the anatomical constraint by the esophagus is also important. Multivariate analysis also showed that interobserver and intraobserver variability of the quantitative evaluation of mitral regurgitation was acceptable for clinical purposes (8% and 8.6%, respectively). This is in agreement with previously reported data.[10,12,13]

In conclusion, we feel that TTE and TEE should be considered as complementary and not mutually exclusive techniques in the quantification of mitral regurgitation in native valves.
TEE yields a higher prevalence of mitral regurgitation than TTE. There was also a trend toward a greater overall estimate of mitral regurgitation at the semi-quantitative analysis when compared to the transthoracic approach. On the other hand, transthoracic and transesophageal echocardiography showed similar mean results at the quantitative assessment of maximal jet areas from a single digitized frame.

However, a highly significant random variability was observed in the single patient. Caution must then be used in quantifying mitral regurgitation by TEE independently from TTE.
As with the transthoracic approach, clinical management of different and complementary information that comes from the transesophageal new window should be learned.

Summary

Absence or presence of mitral regurgitation (denned as mild, moderate, or severe) was assessed in 100 consecutive patients by TTE and TEE. TEE showed mild mitral regurgitation in 26 patients where TTE was negative. TEE yielded a higher prevalence of mitral regurgitation than TTE with a trend toward a greater overall estimate of mitral regurgitation at the semi-quantitative analysis. TTE and TEE showed similar mean results at the quantitative assessment of maximal jet areas. However, a highly significant random variability was observed in the quantification of mitral regurgitation at TEE.

References

1. Perry GY, Nanda CN: Recent advances in color Doppler evaluation of valvular regurgitation. Echocardiography 1987,6:503.

2. Grayburn PA, Pryor SL, Levine BD, et al: Day to day variability of Color Doppler flow jets in mitral regurgitation. J Am. Coll Cardiol 1989,14:936.

3. De Maria AN, Spain MG, Garrahy P, et al: Considerations in the quantitation of color Doppler flow imaging. Echocardiography 1987;6:495.

4. Cooper JW, Nanda NC, Philpot EF, et al: Evaluation of valvular regurgitation by color Doppler. J Am Soc Echocardiogr 1989;1:56.

5. Perry GJ, Nanda CN: Diagnosis and quantitation of valvular regurgitation by color Doppler flow mapping. Echocardiography 1986;6:493.

6. Yoshida K, Yoshikawa J, Shakudo M. et al: Color Doppler evaluation of valvular regurgitation in normal subjects. Circulation 1988;4:840.

7. Dumesnil JG: Regurgitation mitrale, tricuspidienne et aortique. Diagnostic et quantification. Ann Cardiol Angéiol 1988;37:493.

8. Bolger AF, Eigler NL, Mauer G: Quantifying valvular regurgitation. Limitations and inherent assumptions of Doppler techniques. Circulation 1988;78:1316.

9. Helmcke F, Nanda NC, Hsiung M, et al: Color Doppler assessment of mitral regurgitation with orthogonal planes. Circulation. 1987; 75:175.

10. Dall’Aglio V, D’Angelo G, Moro E, et al: Interobserver and echo-angio variability of two-dimensional colour Doppler evaluation of aortic and mitral regurgitation. Eur Heart J 1989;10:334.

11. Mohr-Kahaly S, Erbel R, Zenker G, et al: Semi-quantitative grading of mitral regurgitation by color coded Doppler echocardiography. Int J Cardiol 1989:23:223.

12. Smith M, Grayburn PA, Spain M, et al: Observer variability in the quantitation of Doppler color flow jet areas for mitral and aortic regurgitation. J Am Coll Cardiol 1988;11:579.

13. Spain MG, Smith MD, Grayburn PA, et al;  Quantitative assessment of mitral regurgitation by Doppler color flow imaging: Angiographic and hemodynamic correlations. J Am Coll Cardiol 1989,13:585.

14. Miyatake K, Izumi S, Okamote M, et al: Semi-quantitative grading of severity of mitral regurgitation by real time two dimensional Doppler flow imaging technique. JAm Coil Cardiol 1986:7:82.

15. Galassi AR, Nihoyannopoulos P, Pupita G, et al: Assessment of colour flow imaging in the grading of valvular regurgitation. Eur Heart J 1990;11:1101.

16. Geibel A, Kasper T, Hofinan HJ: Diagnostic impact of transthoracic and transesophageal color flow imaging in the quantification of mitral regurgitation. (Abstract) Eur Heart J 1989; 10 (Suppl):404.

17. Kleinman JP, Czer SC, De Robertis M, et al: A quantitative comparison of transesophageal and epicardial color Doppler echocardiography in the intraoperative assessment of mitral regurgitation. Am J Cardial 1989:64:1168.

18. Van den Brink RBA, Visser CA, Basart DCG, et al: Comparison of transthoracic and transesophageal color Doppler flow imaging in patients with mechanical prostheses in the mitral valve position. Am J Cardiol 1989; 63:1471.

19. Smith MD, Harrison MR, Pinton R, et al: Regurgitant jet size by transesophageal compared with transthoracic Doppler color flow imaging. Circulation. 1991;83:79.

20. Yoshida K, Yoshikawa J, Yamaura Y, et al: Assessment of mitral regurgitation by biplane transesophageal color Doppler flow mapping. Circulation 1990;82:1121.

21. Taams MA, Gussenhoven EJ, Cahalan MK, et al: Transesophageal Doppler color flow imaging in the detection of native and Bjork-Shiley mitral valve regurgitation. J Am Coll Cardiol 1989:13:95.

22. Daniel LB, Grigg LE, Weisel RD, et al: Comparison of transthoracic and transesophageal assessment of prosthetic valve dysfunction. Echocardiography 1990;7:2.

23. Mohr-Kahaly S, Kupferwasser I, Erbel R, et al: Regurgitant flow in apparently normal valve prostheses: Improved detection and semiquantitative analysis by two dimensional color coded Doppler echocardiography. J Am Soc Echocardiagr 1990,3:187.

24. Ohman EM, Shaughnessy ED, Adams DB, et al: In vitro analysis of jets by Doppler colour flow imaging: The importance of time to maximum jet area. Eur Heart J 1990;11:361.

25. Snedecor GW, Cochran WG: Statistical Methods. Sixth Edition. Ames, Iowa, The Iowa State University Press, 1967, p. 339.

26. Stevenson G: Two dimensional color Doppler estimation of the severity of atrioventricular valve regurgitation: Important effects of instrument gain setting, pulse repetition frequency and carrier frequency. J Am Soc Echocardiogr 1989;2:1.

KEY WORDS: mitral regurgitation, color Doppler echocardiography, transesophageal echocardiography

 

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