Dear Dr. Saengsin,

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Atnafu Mekonnen Tekleab, M.D, MPH

Academic Editor

PLOS One

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Additional Editor Comments:

I would like to thank the authors for their very interesting and clinically relevant research work. In addition to addressing the comments raised by the reviewers, I would like to request the authors to address the following issues. Particularly, I would like to invite the authors special attention related to the methods and conclusion section of the study since there are major issues raised by the reviewers.

• Line 145-146: “The cardiac function was evaluated by a single experienced imaging pediatric cardiologist (KS).” I assume that KS is the first author of this manuscript. If that is the case, isn’t there an observer bias? How about the impact of using single assessor on the impact of the accuracy of the data set?
• Lines 168- 172: what was the basis to determine sample size by taking the mean bias of 5 and SD of 8? Do you think these values help to produce a stable model? Needs elaboration!
• Line 168: sample size calculated using pilot study. Why sample was not calculated based on previous study findings?
• Lines 171- 172: States that “calculations were performed using a two sampled-paired t-test”.  However, comparison of RVEF by 3DE vs CMR is agreement comparison, not a difference in means comparison. Please explain this.
• Lines 162- 163: What is the importance of using LOA alongside P10? Do the two parameters convey different info?
• Lines 186-192:
  Mean bias is reported, but 95% limits of agreement are missing.
• RVESVi correlation is stated as interval (r = 0.90–0.88) and its bias is described as “minimal”. What odes “minimal bias” means?
• Lines 196- 204: Please, explain the clinical relevance of such a small difference between the 2D and 3D GLS of RV strain values though the two have a statistically significant difference.
• Lines 232- 235: it appears an overstated claim.
• Lines 237- 252: The discussion mentions the “strong correlation” between 3DE and MRI as an indicator of agreement between the two diagnostic modalities. However, correlation indicates association not agreement between two diagnostic modalities. Please check and revise accordingly as it may mislead readers.
• Lines 256- 259: The authors stated that “Our study demonstrated that 3DE RV GLS has a moderate correlation with 2DE GLS. Three-DE RV GLS had significantly more negative values than 2DE-derived RV-GLS. This suggests that 3D RV GLS imaging may provide a more sensitive detection of RV myocardial deformation compared to 2D assessment..”.  It may be misleading to infer that the 3DE RV GLS has more negative values than 2DE RV-GLS and that implies better performance of 3DE RV GLS. Please, check it and revise accordingly.
• Lines 277- 283: The authors attributed the lack of statistical significance to the “small sample size”. However, you also claimed that the study was adequately powered (power 90%). Hence, the two ideas seem to contradict.
• Lines 305- 316: The limitations of the study mentioned under this paragraph appear to be general rather than specific to their study. Here are the reasons: small sample size is mentioned as limitation while you already told us in the methods section that the study was adequately powered; image quality is mentioned as limitation for 3DE while you told us that you have excluded cases that had poor image quality; result differences based on vendor specific strain analysis is mentioned as limitation though that was not related to the current study. Please clarify or revise accordingly.
• Does good AUC imply good agreement between 3DE and CMR and vise-versa? Also, the CMR is both used as gold standard and comparator. Give us short explanation in the discussion.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Thank you for the opportunity to review the paper.

1. My general comments about the research work

The research tries to address a clinically relevant and challenging long-term issue in patients who had undergone surgical repair for Tetralogy of Fallot (both staged and primary repair).The study design is appropriate with detailed imaging protocols and a gold standard (CMR). The attempt to minimize physiologic variability impacts by doing the imaging studies on the same day is another strength of the study. However, in view of the modest correlation observed between 3D ECHO and CMR in quantification of right ventricular systolic function, the clinical implication of the research findings is slightly overstated.

2. Specific comments for improvement

• Methods section: whether the 2D/3D echocardiographer is blinded from the CMR findings and vise versa is unclear to avoid bias.

• Discussion: The study fails to sufficiently explain/discuss the discrepancy between the 3D ECHO and CMR with respect to RV systolic function assessment. Due to the modest correlation between 3D ECHO and CMR in RV systolic function assessment in the study, the first statement on clinical implications appear to be slightly overstated.

Reviewer #2: This study addresses a significant clinical issue in adult congenital heart disease (ACHD), specifically the onset of right ventricular (RV) systolic dysfunction following the repair of Tetralogy of Fallot. It introduces an alternative method for assessing RV volume and function in these patients, aside from the gold standard of cardiac magnetic resonance imaging (CMR). The research also compares the commonly used two-dimensional echocardiography (2DE) for evaluating RV volumes and myocardial deformation in patients with repaired Tetralogy of Fallot. The study met its power calculation requirements (29 required, 46 enrolled, 43 analyzed), which enhances the credibility of its findings. By defining RV dysfunction as an RV ejection fraction (RVEF) of less than 48%, the study establishes a clear threshold for diagnostic utility analysis. The use of Bland-Altman plots to evaluate bias and receiver operating characteristic (ROC) curves (area under the curve, AUC) to assess diagnostic accuracy is an appropriate statistical approach for a validation study. The writing maintains a professional tone and adheres to standard medical reporting. The results logically progress from baseline characteristics to direct comparisons of volumes, strain parameters, and ultimately to diagnostic performance.

The authors indicate that the study data cannot be publicly shared due to institutional regulations. However, data can be accessed through the Institutional Ethics Committee at the Faculty of Medicine, Chiang Mai University, for researchers who meet confidentiality criteria. This approach limits the availability of the study data.

The research was conducted between November 2023 and December 2024, but ethical approval was obtained from the Institutional Review Board at the Faculty of Medicine of Chiang Mai University in June 2025. Typically, ethical approval should precede data collection.

Patients with suboptimal 3D echocardiographic images (such as those with large RVs) as well as those with significant residual shunts and arrhythmias were excluded from the study. This exclusion is noteworthy, as these patients are crucial for integrating imaging modalities into clinical care and assessing the need for follow-up procedures like pulmonary valve replacements.

While the study's title indicates that it includes patients with repaired Tetralogy of Fallot, it is important to note that 32.6% of participants were only palliated. This subgroup may exhibit different pressure and volume dynamics affecting their right ventricles compared to fully repaired patients, given that surgical repair influences RV volume, function, and strain patterns. Furthermore, a correlation could have been better established between the timing of the study and the duration since repair.

Although CMR is generally more expensive and technically complex, three-dimensional echocardiography (3DE) may be more accessible and cost-effective. However, the study should address considerations regarding cost, required technical expertise, and the availability of 3DE software for broader implementation. Additionally, it would be beneficial to discuss the validity and applicability of TomTec Imaging Systems, which is used for this study, for assessing RV volume, function, and myocardial strains in non-cardiac patients.

Finally, the authors acknowledge that 3DE tends to underestimate volumes compared to CMR. It would be useful to include a brief commentary on whether this underestimation is systematic (consistently lower) or random, as systemic bias could be corrected in clinical practice using an adjustment factor.

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Reviewer #1: No

Reviewer #2: No

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Utility of Three-Dimensional Echocardiography for Evaluating Right Ventricular Size and Function and Ventricular Myocardial Deformation in Repaired Tetralogy of Fallot

PONE-D-25-55797R1

Dear Dr. Saegsin,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Atnafu Mekonnen Tekleab, M.D, MPH

Academic Editor

PLOS One

Additional Editor Comments (optional):

Reviewers' comments: