Comparing intraoperative transesophageal and postoperative transthoracic echocardiography findings in mitral valve surgery: what changes?

OBJECTIVES Intraoperative transesophageal echocardiography (iTEE) has an important role in diagnosing the results of mitral valve (MV) replacement and repair. However, intraoperative Doppler features may be dissimilar from those measured at the postoperative follow-up period due to hemodynamic variations. There are no studies regarding MV surgery and comparisons between iTTE and postoperative transthoracic echocardiography (post-TTE). We aimed to evaluate the Doppler flow profiles observed in iTEE after MV replacement and repair and compare them with those observed in post-TTE. METHODS We conducted an observational study of 76 patients who underwent MV surgery (replacement or repair) over a 10-month period. iTEE was performed with Doppler evaluation (mean pressure gradient [MPG] and functional area). Patients were re-evaluated with TTE 72 hours after surgery (post-TTE). iTEE and post-TTE Doppler values were then compared and correlated. RESULTS The patients’ mean age was 59 ± 18 years and 55% were women. The prevalence of severe mitral regurgitation and severe mitral stenosis was 77.6% and 22.4%, respectively. MV repair was performed in 71% of cases. iTEE Doppler parameters correlated with post-TTE parameters, with minimal differences, specially in the MV repair group. The postoperative MPG was +0.4 ± 1 mmHg higher in the MV repair group and +1.0 ± 1.8 mmHg in the MV replacement group. There was global improvement in terms of systolic pulmonary artery pressure, although left ventricular ejection fractions were slightly reduced during the postoperative evaluation. CONCLUSIONS Our study demonstrates the usefulness of iTEE and its importance in establishing possible reference values for postoperative follow-ups.


Introduction
Mitral valve (MV) disease, particularly mitral regurgitation (MR), is a growing global health problem that affects millions worldwide 1,2 . Fortunately, mitral repair is potentially curative and often provides excellent long-term event-free survival 3 . MV repair is indicated for patients with symptomatic severe regurgitation and asymptomatic patients with evidence of left ventricular dysfunction. Repair may also be indicated for asymptomatic patients with severe regurgitation and normal ventricular function 3 .
Although MV repair is superior to replacement, repair is currently accomplished in about 60% of cases (no higher than 85% cases in the most optimally selected subgroups) 3,4 .
Transesophageal echocardiography (TEE) is indispensable for the optimal management of mitral disease. MV repair is currently facilitated by the accurate assessment of MV anatomy and MR mechanisms through comprehensive TEE 5,6 . Additionally, intraoperative TEE (iTEE) has become a routine monitoring technique for heart-valve surgery evaluation, and has been reported to improve outcomes after the termination of cardiopulmonary bypass (CPB) 7,8,9 . Notably, the intraoperative Doppler features of prosthetic valves, especially those pertaining to flow-dependent parameters, such as peak velocity and mean pressure gradient (MPG), may be dissimilar to those measured at the postoperative follow-up period. This may be due to changes in hemodynamic status, the management of intraoperative cardiac output via inotropes, changes in preload, CPB-induced myocardial edema, and depressed myocardial contractility 7,8 .
To the best of our knowledge, there are no studies regarding MV surgery and comparisons between intraoperative echocardiographic observations and 72-hour post-surgery echocardiographic observations. Consequently, the aim of our study was to determine the iTEE characteristics and Doppler flow profiles of MVs after repair and replacement and correlate them with postoperative transthoracic echocardiography (post-TTE) data obtained at 72 hours after surgery.

Study population
We conducted an observational study of 76 patients that underwent MV surgery from

Intraoperative evaluation
In the operating room, an adult-size TEE probe was inserted into patients after anesthesia induction, and their heart was inspected using an ultrasound system (Vivid TM E95, GE Healthcare). CPB was established and MV repair or MV replacement was performed. Next, inotropic infusions were performed for all patients before CPB weaning. These perfusions were done in accordance with institutional protocols. Then, the TEE examination of repaired MVs or prosthesis was done by an echocardiographer when stable hemodynamic parameters were attained.

Assessing MV repair
The iTEE evaluation assessed MV residual regurgitation, which was done through color

Statistical analysis
The normality of continuous variables was assessed via histogram observation and the Kolmogorov-Smirnov test. Continuous variables were expressed as mean ± standard deviation, and categorical variables as percentage. Student's t-test or ANOVA was used for group comparisons. Individual variables were assessed for homogeneity of variance using Levene's test. For categorical variables, the chi-square test or Fisher's exact test was used, as appropriate. A paired t-test was performed to compare pre-TTE, post-TTE, and iTEE parameters.
A P value (two-sided) of < 0.05 indicated statistical significance. Stata software (Stata IC for Windows, version 14, Lakeway Drive, TX, USA) was used for all statistical analyses.

Study population
The study population's characteristics are described in Table 1. The patients' mean age was 59 ± 18 years and 55% were female. The prevalence of MR and MS was 77.6% and 22.4%, respectively. The etiology of MR was rheumatic in 25% of cases, degenerative in 61%, endocarditis in 5%, and secondary in 8.5%. The etiology of MS was rheumatic in all cases. MV repair was performed in 71% of cases (64% underwent total annuloplasty and 36% partial posterior annuloplasty). In MV repair surgery, 83% cases were performed for MR and 17% for MS. MV replacement occurred in 29% patients (64% performed for MR cases and 46% performed for MS cases). MV replacement occurred in 29% cases; replacement with mechanical prothesis occurred in 6.6% (n = 5) patients. Patients  Table 2. Overall, there was a slight reduction in biventricular function from pre-surgery to post-surgery, as determined by LVEF and TAPSE. Ventricular dimensions did not significantly vary between MS patients. Regarding the type of surgery, there was no significant difference in RVD values after MV repair (p = 0.221), and LVDDs did not significantly vary after MV replacement (p = 0.182).

MPG and estimated functional areas
MPG values and estimated functional mitral areas assessed by iTEE and post-TTE are described in Table 3 and Figure 1.
In patients who underwent MV repair, there were no significant differences between iTEE and post-TTE in terms of derived MPG values (p = 0.084) and estimated functional mitral areas (p = 0.665) (postoperative MPG was +0.4 ± 1 mmHg higher than intraoperative MPG). In regard to the type of MV repair, there was no significant differences in iTEE MPG values between patients who underwent total mitral annuloplasty (2.9 ± 1.4 mmHg) and those that underwent partial annuloplasty (2.6 ± 1.4 mmHg) (p = 0.448). No significant differences were observed in the post-TTE MPG values between such patients as well (total mitral annuloplasty, 3.1 ± 1.3 mmHg; partial annuloplasty, 3.4 ± 1.6 mmHg; p = 0.494).
In patients that underwent MV replacement, the post-TTE MPG values were significantly higher than the iTEE MPG values (postoperative MPG was +1.0 ± 1.8 mmHg higher than intraoperative MPG, p = 0.016), but there were no significant differences between the iTEE and post-TTE estimated functional prosthesis areas (p = 0.653).
In regard to post-surgery MR grades, the majority of cases were classified as mild during iTEE, and there were no significant differences in MR grade after the post-TTE evaluation ( Table 3)..

Discussion
Our study results revealed a correlation between iTEE Doppler parameters and postoperative TTE parameters with minimal differences, particularly in patients submitted to MV repair. There was also global improvement in terms of sPAP, although LVEF and TAPSE were slightly reduced during the postoperative evaluation.
iTEE has become an essential assessment tool in heart-valve surgeries [10][11][12] , and it is particularly important in evaluating the anatomy of the MV 5,6,13 , namely in MV repair 5,6 .
MV repair is preferred over MV replacement for treating degenerative MV disease 14 . In our study, about 70% of patients underwent MV repair, which is a relevant proportion when compared with other reports 3,4 . In patients who underwent MV repair, the mean iTEE MPG value was 2.8 ± 1.5 mmHg and the mean post-TTE MPG value was 3.1 ± 1.4 mmHg. These results are highly similar to those reported in a previous study, in which the mean iTEE MPG value was 3.1 ± 1.4 mmHg and the mean post-TTE MPG value was 3.5 ± 1.6 mmHg 15 .
Additionally, in regard to the type of MV repair, there were no significant differences in the iTEE MPG and post-TTE MPG values between patients who underwent either total or partial annuloplasty. Previous studies have reported that, compared to partial rings, complete rings may be associated with higher MV gradients 16 . Another report also supports the concept that restrictive annuloplasty results in small valve gradients 15 .
However, in our cohort, only the iTEE MPG values were higher in the total annuloplasty group, and only the post-TTE MPG values were higher in the partial annuloplasty group.
Hence, with these inconclusive data, we cannot confirm whether the hemodynamic effects of MV repair in our study are consistent with what has been previously reported. TEE evaluation in the post-CPB period has important effects in the outcomes of valve replacement surgeries 9,17 . Even so, there are few reports describing iTEE Doppler characteristics of repaired MVs and prosthetic MVs. This has led us to evaluate iTEE Doppler features and correlate them with post-TTE data. Post-CBP Doppler derided velocities and gradients depend on several hemodynamic effects, like inotropes, surgical bleeding and blood transfusion 9,18 . Post-CBP changes in loading conditions lead to changes in stroke volumes, which modify Doppler velocities and pressure gradients 9,17,18 .
Therefore, the ability of these flow-dependent parameters to accurately and reliably represent repaired valve/prosthetic valve function is questionable.
The most important limitation in our study is that the evaluated pressure gradient across the MV is highly dependent on hemodynamics, and it cannot solely be relied on for the assessment of valve stenosis. Moreover, the gold standard for detecting MS is 3D derived valve area, which is highly feasible and has added value in all other aspects of postoperatively assessing MV repair/replacement 19,20 . Nonetheless, even not using 3Dechocardiography, we have shown that calculating the valve area by the simplest method (using the pressure half-time) intraoperatively correlates with post-TTE measurements.
In our study, MPGs and functional areas attained during the intraoperative period and third postoperative day globally were not significantly different, particularly in the MV repair group. This suggests that when Doppler assessment is performed after optimizing loading conditions and hemodynamics during the intraoperative period, the function of prostheses may be accurately reproduced in the postoperative period, which was when prostheses were evaluated in stable loading conditions. Therefore, intraoperative Doppler values could be regarded as reference values for postoperative ultrasonic follow-up studies, especially after MV repair.
A minor limitation in this study is the fact that subjects were selected from a single tertiary referral center. A multicenter study involving a diverse ethnic population with different heights, weights, and body surface areas would be superior in generalizing echocardiographic characteristics. Moreover, although we obtained satisfactory conclusions from 76 patients, the inclusion of a larger number of subjects would offer more accurate and reliable results.

Conclusion
In our study, iTEE Doppler parameters correlated with postoperative TTE parameters with minimal differences, especially in patients who underwent MV repair. There was global improvement in terms of sPAP, although LVEF was slightly reduced during the postoperative evaluation. Our study demonstrates the usefulness of iTEE and its importance in establishing possible reference values for postoperative follow-ups to increase the chance of favorable outcomes.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.