Background
Perioperative evaluation of right ventricular (RV) systolic function is important to follow intraoperative changes, but it is often not possible to assess with transthoracic echocardiographic (TTE) imaging, because of surgical field constraints. Echocardiographic RV quantification is most commonly performed using tricuspid annular plane systolic excursion (TAPSE), but it is not clear whether this method works with transesophageal echocardiographic (TEE) imaging. This study was performed to evaluate the relationship between TTE and TEE TAPSE distances measured with M-mode imaging and in comparison with speckle-tracking TTE and TEE measurements.
Methods
Prospective observational TTE and TEE imaging was performed during elective cardiac surgical procedures in 100 subjects. Speckle-tracking echocardiographic TAPSE distances were determined and compared with the TTE M-mode TAPSE standard. Both an experienced and an inexperienced user of the speckle-tracking echocardiographic software evaluated the images, to enable interobserver assessment in 84 subjects.
Results
The comparison between TTE M-mode TAPSE and TEE M-mode TAPSE demonstrated significant variability, with a Spearman correlation of 0.5 and a mean variance in measurement of 6.5 mm. There was equivalence within data pairs and correlations between TTE M-mode TAPSE and both speckle-tracking TTE and speckle-tracking TEE TAPSE, with Spearman correlations of 0.65 and 0.65, respectively. The average variance in measurement was 0.6 mm for speckle-tracking TTE TAPSE and 1.5 mm for speckle-tracking TEE TAPSE.
Conclusions
Using TTE M-mode TAPSE as a control, TEE M-mode TAPSE results are not accurate and should not be used clinically to evaluate RV systolic function. The relationship between speckle-tracking echocardiographic TAPSE and TTE M-mode TAPSE suggests that in the perioperative setting, speckle-tracking TEE TAPSE might be used to quantitatively evaluate RV systolic function in the absence of TTE imaging.
Highlights
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TTE M-mode TAPSE and TEE M-mode TAPSE do not agree, and TEE M-mode TAPSE should not be used to quantify RV systolic function.
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Speckle-tracking echocardiography allows accurate TAPSE measurements for TTE and TEE imaging compared with TTE M-mode TAPSE.
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Speckle-tracking TEE TAPSE could be used to quantify RV systolic function in the perioperative setting when standard TTE methods are not possible.
Assessment of right ventricular (RV) systolic function can be challenging because of the nonstandard geometric shape of the right ventricle, and in the perioperative setting, the use of transthoracic echocardiographic (TTE) imaging is limited. Transesophageal echocardiographic (TEE) imaging is used as a monitoring tool to evaluate cardiac structure and function during cardiac surgical procedures. Although many left ventricular quantitative assessment techniques translate well between TTE and TEE imaging, methods of quantifying RV systolic function with TEE are not as well described. The American Society of Echocardiography offers guidelines for quantitative measurement of RV systolic function that include tricuspid annular plane systolic excursion (TAPSE), tissue Doppler motion of the tricuspid annulus (S′), and fractional area change; RV ejection fraction remains difficult to assess using conventional echocardiographic methods. Certain measurements are favored, such as TAPSE, which is a reliable and reproducible measurement of RV function, even in the setting of limited apical imaging. Guidelines indicate that the measurement is performed from the apical four-chamber window during TTE imaging, with a distance of ≥17 mm considered normal.
Perioperative measurements of RV systolic function are performed with TEE imaging because TTE imaging is often not possible because of constraints of the sterile surgical field. M-mode TAPSE obtained during perioperative TEE imaging has been used clinically but can result in nonparallel alignment of the M-mode cursor with motion of the tricuspid annulus toward the apex. This study was performed because TTE methods of assessing RV function are not available during most surgical procedures, and determining a method of quantifying RV systolic function, using either TEE M-mode TAPSE or speckle-tracking echocardiographic (STE) imaging, would add to the quantification of the right ventricle in the perioperative setting. STE imaging allows the tracking of a specific location in the myocardium or strain rates of the myocardium. It is hypothesized that STE imaging could be used to determine the longitudinal displacement of the tricuspid annulus during systole, when the motion of the annulus is not parallel to the ultrasound beam, as seen during TEE imaging.
A prior study in which the investigators compared TTE M-mode TAPSE distance with speckle-tracking TTE distance values demonstrated the validity and reliability of STE imaging to measure TAPSE distance, but no relationship between TTE and TEE measurements of RV function has been published. There were two aims of this study. The first was to determine if TTE M-mode TAPSE measurements are the same as the TEE M-mode TAPSE measurements. The second aim was to determine if STE TAPSE values for both transthoracic and transesophageal echocardiography are the same as the TTE M-mode TAPSE distances.
Methods
Study Population
After approval was obtained from our institutional review board, and using departmental funding, consent for intraoperative study image collection was sought from subjects undergoing elective cardiac surgical procedures. Associated cardiac surgical procedures are summarized in Table 1 . To be included in this prospective, observational study, subjects had to be scheduled for elective cardiac surgical procedures in which general endotracheal anesthesia was the planned anesthetic technique and TEE imaging would be performed as per our institutional standard for surgical management. Subjects would be excluded if TTE or TEE images could not be obtained. Sample size calculations suggested that 100 subjects would result in 81% power to detect a difference of 25%. A total of 249 elective cardiac surgical procedures were performed during the data collection period. Of these, 112 subjects provided consent, and images were collected from 102. Ten subjects granted consent but did not undergo imaging, because of an inability to acquire study images without interrupting the operating room schedule.
| Procedure | Number of subjects |
|---|---|
| CABG | 45 |
| CABG + AVR | 10 |
| CABG + CEA | 3 |
| CABG + MVR | 2 |
| CABG + ascending aortic replacement | 1 |
| AVR | 9 |
| AVR + ascending aortic replacement | 5 |
| AVR + MVR | 1 |
| MVR | 2 |
| MVR + TVR | 2 |
| TVR | 1 |
| Ascending aortic replacement | 5 |
| LVAD | 10 |
| LVAD + MVR | 1 |
| RV-to-PA conduit | 2 |
| Pericardiectomy | 1 |
Image Acquisition
Following the induction of general endotracheal anesthesia with the subject in the supine position, the TEE probe was placed before TTE imaging. All subjects were imaged while in a supine position without lateral tilt, and study TTE and TEE images were collected using an iE33 echocardiographic machine with an X5 TTE probe and an X7 TEE probe (Philips Medical Systems, Andover, MA). Imaging was performed after the induction of general endotracheal anesthesia to eliminate the possibility that variation observed between TTE and TEE imaging was the result of changes in cardiac function after the administration of anesthetic medications and/or the use of positive pressure ventilation. Two TTE images and two TEE images constituted the study examination; for TTE imaging, an apical four-chamber two-dimensional (2D) two-beat clip and a TTE M-mode TAPSE measurement from this position were obtained, and for TEE imaging, a midesophageal four-chamber (ME4C) 2D two-beat clip with the apex in a nonforeshortened position and rotated to keep the lateral tricuspid annulus within the scanning sector throughout the entire cardiac cycle and a TEE M-mode TAPSE measurement with the probe in the same position were obtained.
STE Image Analysis
All four study-related images were exported to a portable hard drive, and the two 2D clips were in a native data set Digital Imaging and Communications in Medicine format for postprocessing in a stand-alone QLAB (Philips Medical Systems) package with STE software. Using the tissue motion annular displacement (TMAD) option within the Cardiac Motion Quantification (CMQ) package of QLAB version 9.2, the TTE apical four-chamber and TEE ME4C loops were evaluated for the distance the tricuspid annulus moved toward the apex during the cardiac cycle. To determine STE TAPSE, the first point selected was a hyperechoic point within the lateral tricuspid annulus, which the cursor usually crosses with M-mode TAPSE. The second point was the medial tricuspid annulus, to avoid tracking the lateral annulus twice. The final point selected was at the apex, to serve as the reference to measure longitudinal displacement of the lateral tricuspid annulus. This sequence was performed for both TTE apical four-chamber and TEE ME4C images.
The reported result of STE TAPSE using the TMAD option does not reflect the full distance traveled when measuring TAPSE. The STE software is R wave gated and only displays motion toward the reference point. There is a negative displacement component at the end of the gated cycle, which is not displayed in the result unless the maximum and minimum distance values are each evaluated. These data were exported, and the total distance for STE TAPSE was calculated and entered into the study database. Study data were collected and managed using REDCap electronic data capture tools hosted within our institutional servers. The TTE and TEE M-mode TAPSE distances were entered into the REDCap study database manually as the TAPSE distances were measured at the time of image acquisition.
Interuser Variability
Two individual echocardiographers performed the STE evaluation using the TMAD option within CMQ, an experienced user and an inexperienced user of the software. The experienced user had been previously trained in the use of the CMQ program within QLAB, including strain and speckle-tracking packages, and used these features routinely. The inexperienced user had not previously used the CMQ package within QLAB but had experience obtaining and interpreting both TTE and TEE images. The collection and initial evaluation of the study images were completed by the experienced user, and after initial evaluation, the 100 subjects who had usable data were evaluated by the inexperienced user. The inexperienced user was blinded to the previously recorded results, and their measurements were placed in a second study database in REDCap to maintain blinding.
Statistical Analysis
Statistical evaluations were performed to test both the relationship between the data pairs and the variability within the data pairs. Spearman rank correlation coefficients and Pearson correlation coefficients were calculated to evaluate nonparametric dependence and linear dependence, respectively. Variability within the data sets was determined using a paired t test, and then equivalence was tested using an acceptable variation of 2.5 mm. Scatterplots were constructed to visually demonstrate the relationship of the data, with best-fit regression lines calculated that crossed the origin. All analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC).
Results
Descriptive Statistics
One hundred two subjects underwent image acquisition; two subjects had poor-quality images, and evaluation for the primary and secondary aims could not be obtained. Of these, one subject had inadequate TTE windows to allow M-mode TAPSE measurement, and one subject did not have adequate TTE 2D images to allow STE evaluation. A summary of subjects evaluated is presented in Figure 1 . Of the 100 subjects with complete information for analysis, 69 were men and 31 were women. The average age of male subjects was 62.8 ± 14.7 years and of female subjects was 67.4 ± 13.8 years. The average total time of image collection was 4.7 min.
Aim 1 Results: TTE M-Mode TAPSE versus TEE M-Mode TAPSE
Paired t tests between TTE M-mode TAPSE and TEE M-mode TAPSE demonstrated an average difference of 6.5 mm between the two measurements, and equivalence testing showed a lack of equivalence ( P = 1.00). Nonparametric Spearman correlation analysis demonstrated an association of 0.5 ( P < .0001), and the linear Pearson correlation coefficient was 0.45 ( P < .0001). A scatterplot with best-fit regression line ( Figure 2 A) demonstrated an equation of y = 0.64 x , showing nonequality of the comparison between standard TTE M-mode TAPSE and TEE M-mode TAPSE.
Aim 2 Results: TTE M-Mode TAPSE versus Speckle-Tracking TEE TAPSE
The comparison between TTE M-mode TAPSE and speckle-tracking TEE TAPSE using a paired t test demonstrated that the speckle-tracking TEE TAPSE measurement was on average 1.5 mm larger than the TTE M-mode value, and the equivalence test showed that the pairs were equivalent ( P = .017). Analysis showed a Spearman correlation coefficient of 0.65 ( P < .0001), and a Pearson correlation analysis showed a linear correlation coefficient of 0.62 ( P < .0001). A scatterplot ( Figure 2 B) demonstrated a best-fit regression line of y = 1.07 x .
TTE M-Mode TAPSE versus Speckle-Tracking TTE TAPSE
The association between TTE M-mode and speckle-tracking TTE TAPSE was assessed, and a close average was demonstrated in the paired t test, with the TTE M-mode TAPSE value 0.6 mm larger than the speckle-tracking TTE TAPSE value. The equivalence test showed no statistical difference within the data pairs ( P < .0001). The Spearman and Pearson correlation analyses demonstrated r values of 0.65 ( P < .0001) and 0.62 ( P < .0001), respectively. The scatterplot ( Figure 2 C) demonstrated a best-fit regression line equation of y = 0.95 x . A summary of these results is presented in Table 2 .
| TTE M-mode TAPSE vs TEE M-mode TAPSE | TTE M-mode TAPSE vs speckle-tracking TEE TAPSE | TTE M-mode TAPSE vs TTE TAPSE | |
|---|---|---|---|
| Difference between measurements (mm) | 6.5 | −1.5 | 0.6 |
| Equivalence testing (at 2.5 mm) | No ( P = 1.00) | Yes ( P = .017) | Yes ( P < .0001) |
| Spearman correlation coefficient | ρ = 0.5 ( P < .0001) | ρ = 0.65 ( P < .0001) | ρ = 0.65 ( P < .0001) |
| Pearson correlation coefficient | r = 0.45 ( P < .0001) | r = 0.62 ( P < .0001) | r = 0.62 ( P < .0001) |
| Regression line equation | y = 0.64 x ∗ | y = 1.07 x | y = 0.95 x |
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