Next Evolution in Esophageal Temperature Monitoring: The New MATRIX₁₂ M™

Interview With Chirag Barbhaiya, MD

© 2024 HMP Global. All Rights Reserved.

Any views and opinions expressed are those of the author(s) and/or participants and do not necessarily reflect the views, policy, or position of EP Lab Digest or HMP Global, their employees, and affiliates.

EP LAB DIGEST. 2024;24(5):18,20.

In this feature interview, EP Lab Digest talks with Chirag Barbhaiya, MD, about his initial experience and first-in-human cases using the new MATRIX₁₂ M probe (CIRCA Scientific, Inc) (Figure 1). 

How many atrial fibrillation (AF) ablation procedures do you perform annually? Are AF ablations a critical component of your practice?
I perform about 250 AF ablations per year, and researching ways to perform the procedure more safely and effectively is a passion of mine. Given the increasing prevalence of AF, ablation of AF is a large and growing part of both my practice and EP practices all around the country. 

Atrio-esophageal fistula is a devastating, though rare, complication possible in AF ablations. How important is it to take steps to reduce the risk of this complication during your AF ablation procedures?
The benefits of the AF ablation procedure are, acutely, about ameliorating symptoms and improving how patients feel. Longer term, if the procedure is done well with low complications, there are more benefits related to overall health. Since we are not acutely saving lives during AF ablation, avoiding the rare but devastating complication of atrio-esophageal fistula is incredibly important. One of the main challenges in avoiding atrio-esophageal fistula has been that there are no proven techniques to reduce incidence—it is statistically difficult to show that any intervention can effectively reduce the frequency of something that occurs so rarely. 

Heart Rhythm Society (HRS) guidelines recommend monitoring esophageal temperature during AF ablations. When did you start doing this and why?
Esophageal temperature monitoring is more about how you monitor than it is about monitoring itself. Temperature monitoring with a single-point esophageal temperature probe is very common and has been around for about as long as it has been recognized that esophageal injury can occur with AF ablation. I think the reason that esophageal temperature monitoring has not thus far been well correlated with a reduction in esophageal injury is because the tools available have not really been sensitive enough to pick up esophageal heating over a broad enough surface area and in a quick enough time frame that one could use the absence of an observed temperature rise to translate into an absence of esophageal heating. So, one of the interesting and exciting things about the MATRIX temperature probe is that the amount of spatial coverage that it has is far greater than any temperature monitoring tool that was previously available.

What is your current strategy for avoiding heating or cooling of the esophagus during AF ablations? Can you briefly describe how esophageal temperature is monitored during an AF case in your practice?
We were fortunate to do some research with the S-CATH (CIRCA Scientific, Inc), the prior version of the temperature probe, when we started doing high-power short-duration ablation for AF. Using insights that we gained from that research, we learned about the severity and radius of esophageal heating with a given high-power short-duration lesion. Based on what we learned from that experience, my primary means of avoiding esophageal injury has been to avoid heat stacking on the esophagus (Figure 2). Therefore, in areas on the posterior left atrium that are at any risk for esophageal injury, I make sure to avoid delivering consecutive adjacent lesions over the esophagus that could result in effectively doubling or tripling the amount of esophageal heating from a single lesion. A single high-power short-duration radiofrequency (RF) ablation lesion can cause a 7°C esophageal temperature increase, so the math gets unfavorable pretty quickly if heat stacking is allowed. 

If you could optimize your current solution, how would you do so?
When the S-CATH came out, it was far more sensitive than any tool that preceded it, but there were still substantial areas of the esophagus that did not have effective temperature monitoring. Therefore, one had to assume a high risk of esophageal heating everywhere there could be esophagus, and accordingly adjust timing of adjacent lesions over a very large area of the posterior left atrium. What we have noticed with our initial experience with the MATRIX is that in all the areas overlying the esophagus, we are reliably detecting esophageal heating. So, the absence of apparent esophageal heating may be a more reliable indicator that the ablated area is not causing significant esophageal heating. Studies still need to be done to back this up, but my impression is that when we do not see esophageal heating with the MATRIX temperature probe, we will be able to ablate much more confidently, and therefore, consecutively and efficiently, in those areas, since we are more certain there is not a risk of esophageal injury in those locations. 

Is the industry working on anything to meet this need to avoid heating or cooling of the esophagus during AF ablations?
There are a lot of approaches that people are taking. Given the severity of the problem and the uncertainty on how best to avoid it, there are several approaches for trying to avoid esophageal injury with AF ablation. This includes deviating the esophagus or cooling the esophagus. Different techniques for each have been developed, and there are respected labs that are using all these approaches. My personal approach has been to be a little skeptical of esophageal deviation because of the potential for mechanical trauma with movement of the esophagus, and the uncertainty around whether one is actually deviating enough while also being sure not to create more of an injury risk by stretching the esophagus over the back wall of the atrium during ablation. The concerns that I have around esophageal cooling are that RF is ultimately a thermal ablation modality, and if you are really cooling the esophagus to the extent that some of these approaches are, I find it hard to believe that the cooling does not extend to the left atrium, and thereby, limit the effectiveness of the procedure. Overall, each approach aims to balance safety and effectiveness, and finding that right balance thus far has been a challenge. 

How does the MATRIX compare with other new technologies in helping with fast temperature response times?
There are 2 main improvements over previously available temperature monitoring technologies. First, the temperature probe is visible on electroanatomic mapping. So, for operators who are interested in zero-fluoroscopy approaches, you can have effective temperature monitoring without needing to utilize fluoroscopy for localization of the temperature probe. That is kind of a secondary benefit, but as someone who is interested in fluoroscopy reduction and fluorofree ablation, I appreciate that addition to the device. The more important piece is the increase in surface area of the esophageal temperature sensors. On the previous version of the CIRCA temperature probe, there were focal sensors that were a few millimeters in size. There were 12 of them, so there was a substantial amount of coverage, but there were still substantial areas of the esophagus that were unmonitored. In the areas that were immediately over the sensors, you would see significant temperature rises, but much smaller temperature rises at locations between sensors. Because of the larger plates that are used to house the sensors, in the regions that overlay the esophagus, we are now seeing contiguous areas of severe heating where you would expect to see it, and it tapers off and goes to zero as you move away from the esophagus. So, we are much more reliably seeing heating where we would expect to see it, which makes us feel like in regions where we are not seeing esophageal heating, we can much more confidently say that those areas are at lower risk of esophageal heating and injury. 

How does the MATRIX provide integration of the esophagus/probe on 3-dimensional cardiac mapping systems?
A novel feature of the MATRIX temperature probe, in addition to the temperature sensors, is the inclusion of 4 electrodes that are used to visualize the core of the temperature sensor such that it can be positioned over the area of greatest esophageal coverage or heating during the ablation (Figure 3). The primary benefit of this is the positioning of the temperature sensor, which was previously done fluoroscopically, can now be done using electroanatomic mapping. An additional point to highlight is that there has been a concern that having uninsulated metal within the esophagus would be a risk for having greater heating, because it could act as a heat sink for RF, and both the actual temperature sensors and the electrodes that are utilized for localization on electroanatomic mapping are insulated such that the risk of any of those serving as a heat sink for RF energy is minimized.

What else has changed for you during your initial experience with MATRIX?
The primary difference with MATRIX compared to prior temperature sensors is the confidence that I have when we do not see heating on the temperature probe. It means we are actually not heating the esophagus. The spatial coverage of all the probes that have preceded MATRIX has been significantly less. I do not think we have been able to use the negative predictive value of prior temperature sensors in the way that we will be able to with MATRIX. 

Is there anything else different with the new system that you have noticed? 
A novel software feature that has become available concurrently with MATRIX is the ability to quantify the amount of esophageal heating that we are seeing in a given patient [with an included area under the curve calculation]. What that means and how to interpret that data is an open question and it is an area of investigation for us. But previously, when people have investigated the severity of esophageal heating, it has been a simple gauge of how high the temperature got during the procedure. However, with the ability now to quantify the area under the curve of the temperature sensor over a programmable baseline, we can quantify in a much more meaningful way how much esophageal heating occurred during the case as well as understand the time course and severity. This data may have implications for identifying patients who may be at higher risk and need a greater vigilance of post-ablation monitoring and/or consideration of things such as esophageal scoping, if the data pans out for that being a useful intraoperative surrogate marker for esophageal injury risk. 

In summary, what are your key takeaways? 
The 2 most interesting and useful aspects of the MATRIX are the visualization on electroanatomic mapping and the vastly greater surface area that is being monitored simultaneously without needing to move the probe or make any other adjustments during the procedure. So, I think those are both very positive developments. 

Given the benefits of MATRIX, how will your AF ablations be changed with its use and would you recommend its use to your colleagues?
My initial experience has been very positive, and I am optimistic that with this greater degree of spatial coverage and the rapid temporal response of the temperature probe that we will be able to use esophageal temperature monitoring in a way that allows us to ablate more confidently when we are not seeing esophageal heating. The scientist in me ultimately wants to see the data to back that up, but at this point, I am optimistic that that is what we are going to see. 

Disclosure: Dr Barbhaiya has completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. He reports consulting fees from Biosense Webster and Abbott. 

This content was published with support from CIRCA Scientific, Inc.