Utility of Luminal Esophageal Temperature Monitoring During a Procedure With the New Cryoballoon

Introduction

 Medtronic recently launched the second generation of the cryoballoon for the treatment of drug-resistant paroxysmal atrial fibrillation (AF) by cryoablation procedure. With the addition of four new nitrous oxide spray ports from the original four-jet design, the new cryoballoon has the ability to more evenly distribute cold across the front half of the balloon surface. This redesign translates into several advantages, including: (1) more uniform and continuous lesion formation,¹ (2) more procedural efficiencies,^2,3 and (3) easier cryoballoon to pulmonary vein (PV) positioning without axial alignment requirement.^1-4 A reasonable assumption from these observed benefits is that the cryoballoon also has more effective left atrial (LA) tissue contact cooling because there is more balloon-cooling surface area,  and therefore, one may postulate that more attention must be given to avoid collateral cold transfer to delicate tissue structures immediately behind the LA posterior wall (e.g., esophagus, bronchi, nerve bundles, and lungs). In fact, we know that the cryoballoon can create an atrioesophageal (AE) fistula⁵ and that there is likely no energy source that is without some risk of collateral tissue damage during an AF ablation.

Although rare, AE fistula remains the most detrimental complication in any AF ablation procedure, with an overall mortality rate of 60% to 75%.^6-10Currently, it is postulated that AE fistula formation is the result of aberrant healing between the esophagus and LA posterior wall,¹¹ and in animal modeling it has been demonstrated that an esophageal lesion can later form an AE fistula which has been called the “two-hit” phenomenon.¹² Consequently, the current best practice regardless of energy source during an AF ablation is to “at all cost” avoid esophageal lesion formation. One way to monitor esophageal damage is to observe luminal esophageal temperature (LET) during the ablation procedure. During the usage of the first-generation cryoballoon, there were two studies that examined LET (Table 1). The Fürnkranz study found no cryothermal esophageal lesions after 38 patients were examined following cryoballoon ablation for AF.¹³ By contrast, the Ahmed study found a 17% esophageal lesion rate in 35 patients; however, there was no predictive esophageal temperature value that could accurately predict esophageal ulceration.¹⁴

More recently, two studies were completed using the second-generation cryoballoon with regard to LET monitoring (Table 1). In this second Fürnkranz study, 32 patients were examined, and the study demonstrated a 19% esophageal lesion rate when utilizing an ablation protocol of 240 seconds with one additional bonus application. More importantly, it determined that a minimum LET <12^o C predicted esophageal lesions with 100% sensitivity, 92% specificity, 100% negative predictive value, and 71% positive predictive value.¹⁵ Additionally, the Metzner study found a 12% incidence of esophageal thermal damage,¹⁶ and like the Ahmed study reported above, Metzner et al did find that LET continued to decrease even after cryoballoon termination of the freeze application. In the Metzner study, a LET of >10^o C prevented esophageal thermal lesions with 100% sensitivity and 93% specificity. By compelling data presentation from these studies, our EP laboratory instituted a protocol of regularly monitoring LETs during the cryoballoon AF ablation procedures. 

Several initial procedures were undertaken in which the single probe temperature monitor was positioned at the level of the cryoballoon before ablation via fluoroscopy inspection. A typical outcome was to observe a 1 or 2^o C drop in LET from the start of the ablation to the termination of an ablation, which would last typically four minutes in duration. In this article, we describe a recent case in which we observed the usefulness of LET monitoring.

CASE REPORT

The patient is a 60-year-old male with a five-year history of paroxysmal AF at the time of presentation. Five years ago, the patient underwent a focal radiofrequency (RF) catheter ablation for typical right-sided flutter. While the patient did maintain normal left ventricular (LV) function and LV chamber dimensional size, he did fail antiarrhythmic drug treatment on amiodarone. The patient experienced continued and frequent palpitations, and elected to have AF ablation treatment through cryoballoon ablation.

During this case, the first three PVs were ablated with the second-generation cryoballoon, with a typical 1 or 2^o C decrease in LET from the beginning to the termination of a single ablation (Table 2). On the first right inferior PV (RIPV) ablation, use of intracardiac Doppler echocardiography demonstrated full PV occlusion by the cryoballoon, yet the return gas temperature of the cryoballoon was a -39^o C at the lowest nadir. During this first ablation of the RIPV, it was decided that the cryoballoon must be predominantly in contact with the LA posterior wall as deduced from the more than 4^o C drop in LET, fluoroscopy, and intracardiac echocardiography visualization. Before the second cryoballoon ablation, the catheter was repositioned for a more anterior cardiac alignment. The resulting ablation detected no occlusion leaking, and a cryoballoon return gas nadir temperature of -43^o C was achieved. Furthermore, LET monitoring demonstrated that the esophagus was warming up during the ablation procedure (Table 2, bottom row LETs). The anterior cryoballoon alignment kept the balloon surface contact to the posterior wall at a minimum and allowed for the body temperature reheating of the esophagus even during the ablation procedure. More importantly, there was no further cold propagation to the esophagus during the second RIPV ablation which was confirmed by LET monitoring, and this patient was successfully ablated with the new cryoballoon without complication or AF recurrence.

Several important observations were made during this case. The utilization of an esophageal temperature monitor allowed the physician to observe the falling esophageal temperatures during the first RIPV ablation, and intracardiac echocardiography demonstrated complete cryoballoon occlusion. During the usage of the first-generation cryoballoon, the treating physician may have been tempted to increase the duration of freeze to 360 seconds (or more), believing that this was a suboptimal cryoablation with a gap in the occlusion (-39^o C cryoballoon nadir temperature). Now, this strategy of increasing freeze duration beyond four minutes is possibly unfavorable as collateral tissues are potentially at risk for further dropping in temperature, and it may be recommended to reposition the catheter for a second ablation. In this case, the second freeze of the RIPV demonstrated the benefit of close LET monitoring to prompt repositioning the cryoballoon catheter to a potentially safer and effective pulmonary vein location. 

Also, this case demonstrated that return gas temperature should not be the sole decision matrix when ablating with the cryoballoon. In fact, the second Fürnkranz study did not find a significant correlation between the minimum cryoballoon temperature (return gas temp) and the minimum recorded LET for any of the anatomical PVs.¹⁵ Our case conversely demonstrated that the warmest cryoballoon nadir temperature (-39^o C) actually brought about the coldest LET measurement at 240 seconds (30.4^o C). Furthermore, propagation cooling kept lowering the LET even after the cryoballoon had stopped freezing at 240 seconds, and a LET of 29.7^o C was achieved after the cryoballoon deflation in the first RIPV application. This continuation of cold propagation is in agreement with the Ahmed and Metzner studies, which determined that LET can continue to decrease even after termination of cryoablation before recovering into a normal body temperature.^14,16 Consequently, while ultra-cold cryoballoon return gas temperatures should still be avoided (temperatures below -60^o C); it should not be the sole monitoring parameter within a cryoballoon procedure.

DISCUSSION

During the usage of the first-generation cryoballoon, a narrow band of nitrous oxide cold delivery in the cryoballoon made it necessary to find adjunctive tools to assess successful occlusion. Testing occlusion by contrast agent leak detection on fluoroscopy was the first broad audience recommendation. Later, pressure monitoring proved to be effective,^17,18 and echocardiography was useful as well.^19,20 In the second-generation cryoballoon, LET monitoring has proven to be useful, which falls in line with the positive predictive value that has already been established with focal RF catheter usage.²¹ 

When deciding which LET probe to use, the U.S. physician is left with several single-probe models, most of which are esophageal stethoscopes with a temperature sensor. Only very recently was the ESOTEST system (FIAB), a three-sensor soft body temperature probe, approved for market in the U.S. Both the Fürnkranz and Metzner studies used a similar three thermocouple temperature probe that was available in Europe (SensiTherm, St. Jude Medical).^13,15,16 Regardless of the choice of esophageal temperature monitoring device, the physician and staff must be sure to select a monitor that is capable of measuring accurate temperatures to near or below 0^o C. Of note, some RF monitoring systems cannot accurately and precisely record esophageal temperatures below 20^o C.

Also, twelve-sensor rigid body temperature probes were recently tested for LET monitoring during focal RF ablations.²² The results determined that these rigid body multi-sensor probes caused more frequent and severe esophageal injuries when compared to single-probe models. It is likely that these twelve-sensor rigid body temperature probes should not be used with the cryoballoon. The distention of the esophagus by the twelve-sensor rigid body probes may be attributing to esophageal damage during AF ablations. While we await other clinical studies on adjunctive equipment usage or technical usage recommendations, the LET monitoring protocol remains a useful monitoring tool during cryoballoon procedures. This case demonstrates that continued LET recordings through the ablation procedure are as important as the final nadir temperature for assessing collateral cold transfer to adjacent tissue structures.

Finally, during this case, note that the “stop LET” of the first RIPV ablation had reached 29.7^o C. When LET reaches a reading closer to 15^o C, it is perhaps better to allow for esophageal rewarming with the addition of a waiting period rather than an immediate re-application of a cryothermal ablation. The risk of additive cold to the esophagus is too large.

Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest^®’s editorial board. 

Disclosures: Drs. Jiao and McKinnie have no conflicts of interest to report. Hae Lim, PhD declares a competing financial interest; he is an employee of Medtronic, Inc., a publicly traded company. 

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