Modeling esophageal protection from radiofrequency ablation via a cooling device: an analysis of the effects of ablation power and heart wall dimensions

Mechanisms of action behind the protective effects of proactive esophageal cooling during radiofrequency catheter ablation in the left atrium

Proactive esophageal cooling for the purpose of reducing the likelihood of ablation-related esophageal injury resulting from radiofrequency (RF) cardiac ablation procedures is increasingly being used and has been Food and Drug Administration cleared as a protective strategy during left atrial RF ablation for the treatment of atrial fibrillation. In this review, we examine the evidence supporting the use of proactive esophageal cooling and the potential mechanisms of action that reduce the likelihood of atrioesophageal fistula (AEF) formation. Although the pathophysiology behind AEF formation after thermal injury from RF ablation is not well studied, a robust literature on fistula formation in other conditions (eg, Crohn disease, cancer, and trauma) exists and the relationship to AEF formation is investigated in this review. Likewise, we examine the abundant data in the surgical literature on burn and thermal injury progression as well as the acute and chronic mitigating effects of cooling. We discuss the relationship of these data and maladaptive healing mechanisms to the well-recognized postablation pathophysiological effects after RF ablation. Finally, we review additional important considerations such as patient selection, clinical workflow, and implementation strategies for proactive esophageal cooling.

Proactive esophageal cooling during laser cardiac ablation: A computer modeling study

BACKGROUND AND OBJECTIVES

Laser ablation is increasingly used to treat atrial fibrillation (AF). However, atrioesophageal injury remains a potentially serious complication. While proactive esophageal cooling (PEC) reduces esophageal injury during radiofrequency ablation, the effects of PEC during laser ablation have not previously been determined. We aimed to evaluate the protective effects of PEC during laser ablation of AF by means of a theoretical study based on computer modeling.

METHODS

Three-dimensional mathematical models were built for 20 different cases including a fragment of atrial wall (myocardium), epicardial fat (adipose tissue), connective tissue, and esophageal wall. The esophagus was considered with and without PEC. Laser-tissue interaction was modeled using Beer-Lambert's law, Pennes' Bioheat equation was used to compute the resultant heating, and the Arrhenius equation was used to estimate the fraction of tissue damage (FOD), assuming a threshold of 63% to assess induced necrosis. We modeled laser irradiation power of 8.5 W over 20 s. Thermal simulations extended up to 250 s to account for thermal latency.

RESULTS

PEC significantly altered the temperature distribution around the cooling device, resulting in lower temperatures (around 22°C less in the esophagus and 9°C in the atrial wall) compared to the case without PEC. This thermal reduction translated into the absence of transmural lesions in the esophagus. The esophagus was thermally damaged only in the cases without PEC and with a distance equal to or shorter than 3.5 mm between the esophagus and endocardium (inner boundary of the atrial wall). Furthermore, PEC demonstrated minimal impact on the lesion created across the atrial wall, either in terms of maximum temperature or FOD.

CONCLUSIONS

PEC reduces the potential for esophageal injury without degrading the intended cardiac lesions for a variety of different tissue thicknesses. Thermal latency may influence lesion formation during laser ablation and may play a part in any collateral damage.

Atrioesophageal Fistula Rates Before and After Adoption of Active Esophageal Cooling During Atrial Fibrillation Ablation

BACKGROUND

Active esophageal cooling reduces the incidence of endoscopically identified severe esophageal lesions during radiofrequency (RF) catheter ablation of the left atrium for the treatment of atrial fibrillation. A formal analysis of the atrioesophageal fistula (AEF) rate with active esophageal cooling has not previously been performed.

OBJECTIVES

The authors aimed to compare AEF rates before and after the adoption of active esophageal cooling.

METHODS

This institutional review board (IRB)-approved study was a prospective analysis of retrospective data, designed before collecting and analyzing the real-world data. The number of AEFs occurring in equivalent time frames before and after adoption of cooling using a dedicated esophageal cooling device (ensoETM, Attune Medical) were quantified across 25 prespecified hospital systems. AEF rates were then compared using generalized estimating equations robust to cluster correlation.

RESULTS

A total of 14,224 patients received active esophageal cooling during RF ablation across the 25 hospital systems, which included a total of 30 separate hospitals. In the time frames before adoption of active cooling, a total of 10,962 patients received primarily luminal esophageal temperature (LET) monitoring during their RF ablations. In the preadoption cohort, a total of 16 AEFs occurred, for an AEF rate of 0.146%, in line with other published estimates for procedures using LET monitoring. In the postadoption cohort, no AEFs were found in the prespecified sites, yielding an AEF rate of 0% (P < 0.0001).

CONCLUSIONS

Adoption of active esophageal cooling during RF ablation of the left atrium for the treatment of atrial fibrillation was associated with a significant reduction in AEF rate.

Improved 1-year outcomes after active cooling during left atrial radiofrequency ablation

BACKGROUND

Active esophageal cooling during pulmonary vein isolation (PVI) with radiofrequency (RF) ablation for the treatment of atrial fibrillation (AF) is increasingly being utilized to reduce esophageal injury and atrioesophageal fistula formation. Randomized controlled data also show trends towards increased freedom from AF when using active cooling. This study aimed to compare 1-year arrhythmia recurrence rates between patients treated with luminal esophageal temperature (LET) monitoring versus active esophageal cooling during left atrial ablation.

METHOD

Data from two healthcare systems (including 3 hospitals and 4 electrophysiologists) were reviewed for patient rhythm status at 1-year follow-up after receiving PVI for the treatment of AF. Results were compared between patients receiving active esophageal cooling (ensoETM, Attune Medical, Chicago, IL) and those treated with traditional LET monitoring using Kaplan-Meier estimates.

RESULTS

A total of 513 patients were reviewed; 253 received LET monitoring using either single or multi-sensor temperature probes; and 260 received active cooling. The mean age was 66.8 (SD ± 10) years, and 36.8% were female. Arrhythmias were 60.1% paroxysmal AF, 34.3% persistent AF, and 5.6% long-standing persistent AF, with no significant difference between groups. At 1-year follow-up, KM estimates for freedom from AF were 58.2% for LET-monitored patients and 72.2% for actively cooled patients, for an absolute increase in freedom from AF of 14% with active esophageal cooling (p = .03). Adjustment for the confounders of patient age, gender, type of AF, and operator with an inverse probability of treatment weighted Cox proportional hazards model yielded a hazard ratio of 0.6 for the effect of cooling on AF recurrence (p = 0.045).

CONCLUSIONS

In this first study to date of the association between esophageal protection strategy and long-term efficacy of left atrial RF ablation, a clinically and statistically significant improvement in freedom from atrial arrhythmia at 1 year was found in patients treated with active esophageal cooling when compared to patients who received LET monitoring. More rigorous prospective studies or randomized studies are required to validate the findings of the current study.

Procedural time reduction associated with active esophageal cooling during pulmonary vein isolation

BACKGROUND

Active esophageal cooling is increasingly utilized as an alternative to luminal esophageal temperature (LET) monitoring for protection against thermal injury during pulmonary vein isolation (PVI) when treating atrial fibrillation (AF). Published data demonstrate the efficacy of active cooling in reducing thermal injury, but impacts on procedural efficiency are not as well characterized. LET monitoring compels pauses in ablation due to heat stacking and temperature overheating alarms that in turn delay progress of the PVI procedure, whereas active esophageal cooling allows avoidance of this phenomenon. Our objective was to measure the change in PVI procedure duration after implementation of active esophageal cooling as a protective measure against esophageal injury.

METHODS

We performed a retrospective review under IRB approval of patients with AF undergoing PVI between January 2018 and February 2020. For each patient, we recorded age, gender, and total procedure time. We then compared procedure times before and after the implementation of active esophageal cooling as a replacement for LET monitoring.

RESULTS

A total of 373 patients received PVI over the study period. LET monitoring using a multi-sensor probe was performed in 198 patients, and active esophageal cooling using a dedicated device was performed in 175 patients. Patient characteristics did not significantly differ between groups (mean age of 67 years, and gender 37.4% female). Mean procedure time was 146 ± 51 min in the LET-monitored patients, and 110 ± 39 min in the actively cooled patients, representing a reduction of 36 min, or 24.7% of total procedure time (p < .001). Median procedure time was 141 [IQR 104 to 174] min in the LET-monitored patients and 100 [IQR 84 to 122] min in the actively cooled patients, for a reduction of 41 min, or 29.1% of total procedure time (p < .001).

CONCLUSIONS

Implementation of active esophageal cooling for protection against esophageal injury during PVI was associated with a significantly large reduction in procedure duration.

Effect of esophageal cooling on ablation lesion formation in the left atrium: Insights from Ablation Index data in the IMPACT trial and clinical outcomes

INTRODUCTION

The IMPACT study established the role of controlled esophageal cooling in preventing esophageal thermal injury during radiofrequency (RF) ablation for atrial fibrillation (AF). The effect of esophageal cooling on ablation lesion delivery and procedural and patient outcomes had not been previously studied. The objective was to determine the effect of esophageal cooling on the formation of RF lesions, the ability to achieve procedural endpoints, and clinical outcomes.

METHODS

Participants in the IMPACT trial underwent AF ablation guided by Ablation Index (30 W at 350-400 AI posteriorly, 40 W at ≥450 AI anteriorly). A blinded 1:1 randomization assigned patients to the use of the ensoETM® device to keep esophageal temperature at 4°C during ablation or standard practice using a single-sensor temperature probe. Ablation parameters and clinical outcomes were analyzed.

RESULTS

Procedural data from 188 patients were analyzed. Procedure and fluoroscopy times were similar, and all pulmonary veins were isolated. First-pass pulmonary vein isolation and reconnection at the end of the waiting period were similar in both randomized groups (51/64 vs. 51/68; p = 0.54 and 5/64 vs. 7/68; p = 0.76, respectively). Posterior wall isolation was also similar: 24/33 versus 27/38; p = 0.88. Ablation effect on tissue, measured in impedance drop, was no different between the two randomized groups: 8.6Ω (IQR: 6-11.8) versus 8.76Ω (IQR: 6-12.2; p = 0.25). Arrhythmia recurrence was similar after 12 months (21.1% vs. 24.1%; 95% CI: 0.38-1.84; HR: 0.83; p = 0.66).

CONCLUSIONS

Esophageal cooling has been shown to be effective in reducing ablation-related thermal injury during RF ablation. This protection does not compromise standard procedural endpoints or clinical success at 12 months.

Active esophageal cooling during radiofrequency ablation of the left atrium: data review and update

INTRODUCTION

Radiofrequency (RF) ablation of the left atrium of the heart is increasingly used to treat atrial fibrillation (AF). Unfortunately, inadvertent thermal injury to the esophagus can occur during this procedure, potentially creating an atrioesophageal fistula (AEF) which is 80% fatal. The ensoETM (Attune Medical, Chicago, IL), is an esophageal cooling device that has been shown to reduce thermal injury to the esophagus during RF ablation.

AREAS COVERED

This review summarizes growing evidence related to active esophageal cooling during RF ablation for the treatment of AF. The review presents data demonstrating improved outcomes related to patient safety and procedural efficiency and suggests directions for future research.

EXPERT OPINION

The use of active esophageal cooling during RF ablation reduces esophageal injury, reduces or eliminates fluoroscopy requirements, reduces procedure duration and post-operative pain, and increases long-term freedom from arrhythmia. These effects in turn increase patient same-day discharge rates, decrease operator cognitive load, and reduce cost. These findings are likely to further accelerate the adoption of active esophageal cooling.

Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research

This review begins with a rationale of the importance of theoretical, mathematical and computational models for radiofrequency (RF) catheter ablation (RFCA). We then describe the historical context in which each model was developed, its contribution to the knowledge of the physics of RFCA and its implications for clinical practice. Next, we review the computer modeling studies intended to improve our knowledge of the biophysics of RFCA and those intended to explore new technologies. We describe the most important technical details of the implementation of mathematical models, including governing equations, tissue properties, boundary conditions, etc. We discuss the utility of lumped element models, which despite their simplicity are widely used by clinical researchers to provide a physical explanation of how RF power is absorbed in different tissues. Computer model verification and validation are also discussed in the context of RFCA. The article ends with a section on the current limitations, i.e. aspects not yet included in state-of-the-art RFCA computer modeling and on future work aimed at covering the current gaps.

Preventing esophageal complications from atrial fibrillation ablation: A review

Atrioesophageal fistula is a life-threatening complication of ablation treatment for atrial fibrillation. Methods to reduce the risk of esophageal injury have evolved over the last decade, and diagnosis of this complication remains difficult and therefore challenging to treat in a timely manner. Delayed diagnosis leads to treatment occurring in the context of a critically ill patient, contributing to the poor prognosis associated with this complication. The associated mortality risk can be as high as 70%. Recent important advances in preventative techniques are explored in this review.

Preventative techniques used in current clinical practice are discussed, which include high-power short-duration ablation, esophageal temperature probe monitoring, cryotherapy and laser balloon technologies, and use of proton pump inhibitors. A lack of randomized clinical evidence for the effectiveness of these practical methods are found. Alternative methods of esophageal protection has emerged in recent years, including mechanical deviation of the esophagus and esophageal temperature control (esophageal cooling). Although these are fairly recent methods, we discuss the available evidence to date. Mechanical deviation of the esophagus is due to undergo its first randomized study. Recent randomized study on esophageal cooling has shown promise of its effectiveness in preventing thermal injuries. Lastly, novel ablation technology that may be the future of esophageal protection, pulsed field ablation, is discussed.

The findings of this review suggest that more robust clinical evidence for esophageal protection methods is warranted to improve the safety of atrial fibrillation ablation.

Proactive esophageal cooling protects against thermal insults during high-power short-duration radiofrequency cardiac ablation

BACKGROUND

Proactive cooling with a novel cooling device has been shown to reduce endoscopically identified thermal injury during radiofrequency (RF) ablation for the treatment of atrial fibrillation using medium power settings. We aimed to evaluate the effects of proactive cooling during high-power short-duration (HPSD) ablation.

METHODS

A computer model accounting for the left atrium (1.5 mm thickness) and esophagus including the active cooling device was created. We used the Arrhenius equation to estimate the esophageal thermal damage during 50 W/ 10 s and 90 W/ 4 s RF ablations.

RESULTS

With proactive esophageal cooling in place, temperatures in the esophageal tissue were significantly reduced from control conditions without cooling, and the resulting percentage of damage to the esophageal wall was reduced around 50%, restricting damage to the epi-esophageal region and consequently sparing the remainder of the esophageal tissue, including the mucosal surface. Lesions in the atrial wall remained transmural despite cooling, and maximum width barely changed (<0.8 mm).

CONCLUSIONS

Proactive esophageal cooling significantly reduces temperatures and the resulting fraction of damage in the esophagus during HPSD ablation. These findings offer a mechanistic rationale explaining the high degree of safety encountered to date using proactive esophageal cooling, and further underscore the fact that temperature monitoring is inadequate to avoid thermal damage to the esophagus.

Impact of Active Esophageal Cooling on Fluoroscopy Usage During Left Atrial Ablation

Risks to collateral structures exist with radiofrequency (RF) ablation of the left atrium to obtain pulmonary vein isolation (PVI) for the treatment of atrial fibrillation. Passive luminal esophageal temperature (LET) monitoring is commonly utilized, but increasing data suggest limited benefits with LET monitoring. In contrast, active cooling of the esophagus has been shown to significantly reduce esophageal injury. Active cooling of the esophagus also avoids the need for stopping and repositioning an LET probe during use, which may reduce the need for fluoroscopy use. This study aimed to measure the impact on fluoroscopy use during RF ablation with esophageal cooling using a dedicated cooling device in a low-fluoroscopy practice. All patients who underwent PVI over a one-year timeframe by a single provider were analyzed. Patients undergoing PVI prior to the incorporation of an esophageal cooling protocol into standard ablation practice were treated with traditional LET monitoring. Patients treated after this point received active esophageal cooling, in which no LET monitoring is utilized. A total of 280 patients were treated; 91 patients were treated using LET monitoring, and 189 patients were treated with esophageal cooling. The mean total fluoroscopy time before the implementation of the esophageal cooling protocol in 91 patients was 194 seconds [standard deviation (SD): 182 seconds] per case, with a median of 144 seconds. The mean total fluoroscopy time after implementation in 189 patients was 126 seconds (SD: 120 seconds) per case with a median of 96 seconds, representing a reduction of 35% per case (p < 0.0001, Mann-Whitney U test). In this largest study to date of active esophageal cooling during PVI, a 35% reduction in fluoroscopy time compared with patients who received LET monitoring was found. This reduction was seen despite an already low fluoroscopy usage rate in place.