Modeling Analysis of Thermal Lesion Characteristics of Unipolar/Bipolar Ablation Using Circumferential Multipolar Catheter

Round 1

Reviewer 1 Report

The authors performed a three-dimensional computational model of a circumferential catheter (CMC) used for pulmonary vein isolation. The computational model is validated against in vitro experiments performed by them. Unipolar (MEU) and bipolar (MEB) modes are compared to assess their efficiency in creating contiguous lesions (without gaps). Although the paper has interest and the computational model is relatively realistic, the manuscript should be improved in order to be published.

The most important concern is that they are using a model to evaluate the lesion continuity without considering fluid dynamics, which is necessary in order to assess the accurate surface lesion widths. As it is assessed in previous computational studies [ref 36], the lesion surface width is overestimated using thermal convection coefficients to model the circulating blood flow. Therefore, this is a high limitation of this study and with the current model is not possible to address any conclusion about which ablation mode is more efficient to ensure lesion continuity. The blood dynamics should be addressed in order to be consider this paper for publication.

Another important aspect is that the simulations are performed with constant voltage which is not used in clinics with this type of electrode. The results could be different using constant power and could not be useful to give any indications for clinical practice. In addition, they are using different voltage level for MEU mode (60 V) and MEB (30V), the efficacy of the ablation modes should be compared with the same power level.

Despite all these limitations, the conclusions are scarce and imprecise, since they did not clarify in which applications is better to use one mode or the other one.

Other minor suggestions:

• Why a 0.1 mm insertion depth was selected in the computational model? It was measured in some way in the experimental set-up? How it was measured in the experiments? Clarify this aspect.
• Replace “endocardium” by “myocardium” in all the text
• This sentence does not have any sense: “each electrode was applied with a root mean squared value of RF voltage of 60V”. Remove and replace by “each electrode was applied with a constant voltage of 60 V”.
• Provide more details about the control algorithm
• Figure 4: Include in the plots the 50˚C isotherm to mark the lesion contour

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The article is written carefully and clearly. The assumptions and background of the article are presented well. Also the language of the work is good.

The goal of the paper is to analyze the lesion characteristics being the result of the ablation process using circumferential multipolar catherer. Two modes of CMC have been investigated: unipolar (MEU) and bipolar (MEB). Two 3D computational models have been constructed on Comsol Multiphisics which have been experimentally validated. All the details of the computational models as well as the experiment have been also clearly explained.

I only have a few questions that I'd like to know the answer to:

1. In the section 4.2 the Authors have pointed three main limitation of their model. Is this possible to point the one of them which is the most crucial from the point of the modeling of such kind of problems?
2. Heat transfer in the domain of biological tissue is described by the Pennes formula, but in the recent years the dual-phase-lag equation is often use for this kind of problems. Are the Authors going to use this approach in their future works?
3. The lesion in the paper is characterized by two dimensions (d and D) and isothermal surface of 50 degC (Fig. 5). Have the authors considered or they going to use the use of the Arrhenius scheme in their work as a parameter for describing the area of thermally-damaged tissue?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors improved the previous version of the manuscript. They have redone the simulations with constant power, which is the common ablation mode used in clinics with this type of device. However, the main limitation of this paper is still present, since they didn’t model the blood flow circulation with fluid dynamics. In order to be able to assess in a quantitative and realistic way which ablation mode is more efficient to achieve continuous lesions (without gaps), it is necessary to quantify accurately lesion surface widths and this is only possible modelling fluid dynamics. The authors should clarify this important aspect with more detail in the limitations of the paper and the fact that their conclusions are only qualitative but not quantitative and they can not extrapolate until a realistic approach would be done.

In addition, in the conclusion section (and in the abstract), the authors should clarify which ablation mode is more appropriate to achieve a specific clinical outcome (i.e. they should indicate the clinical application).

Author Response

Point 1: The authors improved the previous version of the manuscript. They have redone the simulations with constant power, which is the common ablation mode used in clinics with this type of device. However, the main limitation of this paper is still present, since they didn’t model the blood flow circulation with fluid dynamics. In order to be able to assess in a quantitative and realistic way which ablation mode is more efficient to achieve continuous lesions (without gaps), it is necessary to quantify accurately lesion surface widths and this is only possible modelling fluid dynamics. The authors should clarify this important aspect with more detail in the limitations of the paper and the fact that their conclusions are only qualitative but not quantitative and they can not extrapolate until a realistic approach would be done.

Reply：Thank you very much for your comments. We have shifted the points of fluid dynamics to the first place in the limitation section. Additional description about the limitation and the importance of fluid dynamic has been complemented (from line 367).

 

Point 2: In addition, in the conclusion section (and in the abstract), the authors should clarify which ablation mode is more appropriate to achieve a specific clinical outcome (i.e. they should indicate the clinical application).

Reply：We have added some conclusion about the possible clinical applications related to the MEU and the MEB modes in the conclusion section (from line 405), also made a brief description of it in the abstract.

Round 3

Reviewer 1 Report

Although the paper has important limitations, which they should be adressed in future work, the authors have indicated these limitations in the current version of the manuscript. Therefore, I agree that the manuscript can be accepted in the current version.