On the right side of Figure 2, the scatter plots of paired LV indexed volumes are displayed together with 3-zone error grid analyses.21 The line of the fitted indexed volumes (purple) is above the line of the perfect correlation between 3D and 2D (green). Within the yellow zone of the 3-zone error grid, the discrepancies between 2D and 3D measurements have fewer clinical consequences than in the other zones. In the large uppermost and lowermost regions of yellow zone, even large discrepancies between 3D and 2D may occur without affecting the LV classification as severely dilated or normal, respectively. On the contrary, in the isthmus yellow section, 3D and 2D measurements must most closely agree. Therefore, the isthmus is the critical area, where even small discrepancies between 2D and 3D measurements may lead to a misclassification of the severity of the LV enlargement with possible clinical consequences. Most of the dots in Figure 2 (150 of 152 dots for iEDV and 141 of 152 dots for iESV) are plotted within this yellow zone. Dots in the orange zone would represent severe discrepancies between 2D and 3D measurements leading to a relevant misclassification of the LV dilation (e.g., LV classified as normal by 3D and as severely dilated by 2D); no dots in Figure 2 are plotted within the orange zone. The green zone represents some discrepancy in LV volumes between 2D and 3D (not as severe as in the orange zone). A minority of the dots is plotted in this zone (2 of 152 dots for iEDV, 1.3%, and 11 of 152 dots for iESV, 7.2%).
As shown in Table 4, there was no significant difference in EF measured by 3D and 2D TEE (median pairwise difference, −0.4% [95% PIs, −8.6% to 8.8%]; P = 0.227). Conversely, the LV indexed volumes measured by 3D echocardiography were significantly higher than those measured by the 2D echocardiography in the entire population. The same results were also confirmed in the stratification done by subgroups: normal, mildly abnormal, moderately abnormal, or severely abnormal EF and normal or dilated ventricular dimensions.
Three-dimensional–derived SV in the global population was 54 ± 20 mL and was progressively larger across the EF subgroups according to increase in EF (44 ± 12 mL in the severely abnormal systolic function subgroup; 51 ± 16 mL in moderately abnormal systolic function; 52 ± 18 mL in mildly abnormal systolic function; 57 ± 21 mL in the normal systolic function subgroups; P = 0.024).
Image Quality and Time Requirement
As shown in Table 2, the quality of 3D TEE images was optimal in more than half of the study population and resulted in similar 2D image quality (P = 0.206). It was necessary to repeat the 2D acquisition in 23 patients (for a total of 32 2D images) and the 3D acquisition in 19 patients to improve the image quality.
The time required for 2D and 3D imaging is compared in Figure 4. There was no difference in the time required for acquisition of 3D and 2D images (P = 0.805; pairwise difference = 2 seconds [95% PIs, −20 to 35 seconds]), but analysis of 3D images required significantly more time than 2D images (P < 0.001; pairwise difference = 117 seconds [95% PIs, 66 to 197 seconds]). A manual correction of the 3D automated border detection was required in 59% of the 3D TEE images in 73% of patients with abnormal EF and in 52% of those with normal EF (P = 0.009), especially at the level of the lateral apex (in 57 patients, 37%) and inferior apex (in 45 patients, 29%).
Figure 5 presents the inter- and intrareproducibility analyses for iEDV and iESV. In each graph, the distribution of the 3D and 2D measurements and the corresponding lines based on locally weighted polynomial regression are within the same range of values. Differences in repeated 3D versus 2D indexed volumes were not statistically significant, both considering interobserver reproducibility (iEDV: P = 0.125; pairwise difference, 0.26 ± 1.76 mL [95% PIs, −3.58 to 3.73 mL] and iESV: P = 0.126; pairwise difference, −0.16 ± 1.67 mL [95% PIs, −3.96 to 3.69 mL]) and intraobserver reproducibility (iEDV: P = 0.975; pairwise difference, −0.02 ± 1.20 mL [95% PIs, −2.32 to 2.08 mL] and iESV: P = 0.228; pairwise difference, −0.19 ± 1.13 mL [95% PIs, −2.47 to 2.53 mL]).
Considering interobserver reproducibility, we found coefficients of variation of 3.2% for 3D iEDV versus 2.9% for 2D iEDV (P = 0.195) and 7.9% for 3D iESV versus 8.9% for 2D iESV (P = 0.165). Considering intraobserver reproducibility, the calculated coefficients of variation were 2.0% for 3D iEDV compared with 2.2% for 2D iEDV (P = 0.781) and 4.1% for 3D iESV compared with 4.7% for 2D iESV (P = 0.280).
In the present study, we compared intraoperative 3D with 2D TEE for the evaluation of LV volumes and EF. Previous TTE studies have focused on 3D LV assessment, suggesting that 3D is more precise and accurate for LV volume quantification than 2D and offers reproducible information.4,9 However, less information is available regarding 3D TEE in the perioperative setting. In this study, we noted larger 3D LV volumes than 2D LV volumes and that 3D TEE needed longer analysis time with respect to 2D. Our results showed no difference in terms of LV EF, image quality, and reproducibility between 3D and 2D TEE.
LV Volumes and Function
Our results showed a difference between LV indexed volumes measured by 3D and 2D TEE as 3D volumes were larger than 2D volumes. This difference appeared statistically significant when tested by the Wilcoxon matched-pairs signed-ranks test and expressed as CIs of median pairwise differences. However, the median pairwise difference between 3D versus 2D volumes is on the order of a few milliliters (i.e., 3.3 mL/m2 for iEDV and 1.4 mL/m2 for iESV) and the PIs included the 0 value, indicating that the clinical relevance of these differences is small. This consideration is also supported by 3-zone error grid analysis of the LV indexed volumes showing that the difference between 3D and 2D measurements does not affect the LV classification as normal, mildly to moderately dilated, or severely dilated.
With respect to LV function, there were no differences between 3D and 2D EF, suggesting that the evaluation of LV global function by 3D TEE is comparable with 2D TEE. As EF is calculated from a simple algebraic equation ([EDV − ESV]/EDV), a systematic upshift of 3D LV volumes versus 2D LV volumes leads to a cancelation in the differences between 3D and 2D EF.
The 3D echocardiography also allowed us to assess the LV function by means of 3D-derived SV. Quantification of LV cardiac output by 3D TTE echocardiography has been validated against thermodilution24 or MRI.11 A good correlation between 3D-derived SV and thermodilution was reported by Culp et al.25 However, there were significant bias and wide limits of agreement, limiting the overall accuracy of the 3D TEE measurements. In our study, we found that 3D-derived SV progressively decreased according to worsening in 2D-derived EF.
Image Quality and Time Requirements
The success rate for 3D image acquisition and analysis was equal to that of 2D echocardiography. The visualization of LV endocardium by 3D TEE was optimal to good in 85% of our study population, in line with encouraging data reported in the literature.26 In this study, 3D image quality was similar to 2D, the latter also being similar to previous data in the literature on endocardial visualization with 2D TEE.27
Although acquisition times were similar in 3D and 2D, 3D analysis to obtain LV volumes and EF required more time than 2D, and this could be a disadvantage of the use of 3D in the operating room. However, the 5-minute average needed to analyze LV with 3D was still compatible with the pace of our operating room activity. Moreover, 3D provides a complete characterization of LV including information on regional function,15,28 which would need additional time with 2D TEE. Although not the topic of the present study, evaluation of LV regional function is of potential importance during cardiac surgery to facilitate detection of myocardial ischemia.
Our data on intra- and interobserver reproducibility for 3D indexed volumes were satisfactory, and 3D reproducibility was similar to 2D reproducibility29 but failed to be clearly superior in contrast to TTE studies.4,8,10,11 These discordant results may be partly explained by the fact that our measurements were performed on TEE, unlike the previous TTE studies.
Some limitations of this study should be noted. First, 3D LV measurements in our patients were compared only with 2D values, both acquired with TEE and, as is well known, transesophageal imaging techniques involve difficulties in the visualization of the apex and lateral heart wall. A comparison with reference techniques such as MRI or 3D TTE would be necessary for final validation of 3D TEE measures. For this purpose, studies of 3D TEE in the echo laboratory appear to be more appropriate, being performed in hemodynamic conditions similar to the reference technique. Intraoperatively, we could not perform 3D TTE in the same hemodynamic conditions as TEE for technical reasons (surgical preparation was underway and a cardiologist trained in 3D TTE acquisition was not available). The validation of 3D TEE volumes measured intraoperatively against pre- or postoperative MRI would be logistically challenging. Second, no comparison between LV assessed by Philips Q-lab 3D-Advanced software and different 3D software was done, and 3D-derived SV was not compared with thermodilution. Third, this study was performed in patients undergoing elective cardiac surgery having hemodynamically stable conditions and sinus rhythm. Finally, a single operator acquired and analyzed both 2D and 3D images. Therefore, bias cannot be excluded in performing 2D and 3D measurements and analyses. However, all measurements were repeated by a second experienced operator and interobserver differences were small and not statistically significant.
In conclusion, intraoperative 3D TEE of LV demonstrated no differences compared with 2D TEE in terms of LV EF, image quality, and reproducibility. The 3D required more time compared with 2D TEE, and ventricular volumes measured by 3D TEE were larger than those obtained from 2D TEE. However, the difference between 3D and 2D volumes was on the order of a few milliliters and did not affect the classification of LV as normal, mildly to moderately dilated, or severely dilated using the 3-zone grid analysis, thus limiting the clinical relevance of these differences.
Name: Alessandra Meris, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Alessandra Meris has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
Name: Luisa Santambrogio, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Attestation: Luisa Santambrogio has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
Name: Gabriele Casso, MD.
Contribution: This author helped design the study and conduct the study.
Attestation: Gabriele Casso approved the final manuscript.
Name: Romano Mauri, MD.
Contribution: This author helped conduct the study.
Attestation: Romano Mauri approved the final manuscript.
Name: Albin Engeler, MD.
Contribution: This author helped conduct the study.
Attestation: Albin Engeler approved the final manuscript.
Name: Tiziano Cassina, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Attestation: Tiziano Cassina has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
We are very grateful for the statistical support provided by the Institut für Datenanalyse und Prozessdesign Zürcher Hochschule für angewandte Wissenschaften and to our nurses for their fruitful teamwork not only for this study, but also every day in the operating room.
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© 2014 International Anesthesia Research Society
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