COMMENTARY

AF Ablation: Esophageal Monitoring Harmful or Helpful?

John Mandrola

Disclosures

April 28, 2015

Doctors who perform AF ablation fall into two categories: those who have had a patient with atria-esophageal fistula and those who have not.

This tragic, often deadly, complication instills fear in all of us who burn the left atrium. I chose the word tragic because that is the problem with AF ablation: patients who die from the procedure would not have died from the disease AF.

When calls come from patients 2 to 4 weeks out from ablation, I (literally) feel a tinge of tightness—in an uh-oh sort of way.

In the matter of esophageal injury during AF ablation, there are two big challenges.

One is anatomy. The front wall of the esophagus resides just behind the back wall of the left atrium. Students of histology know that the posterior wall of the left atrium varies in thickness, and sometimes it can be precariously thin. Heat applied to the left atrium can cause thermal injury to the wall of the esophagus—probably by occlusion of arterioles in the esophageal wall. Thermal damage can lead to tissue breakdown and connection (fistula) from atrium to esophagus, which then leads to air embolus, stroke, infection, and usually death.

The second challenge in understanding esophageal injury is its rarity. This makes it hard to study. You can't say one avoidance technique is better than another, because statistically speaking you need millions of patients to show a certain strategy prevents lesions.

And you know the problem with rare, unpredictable, and emotionally charged events. In the absence of evidence, we usually get eminence, eg, expert opinion. One widely accepted expert recommendation for the prevention of esophageal injury is to monitor luminal temperatures with a probe.[1] It makes sense intuitively—if temps rise during ablation, stop the burn. Thermal lesions will be avoided.

I talk to a lot of ablation docs. Almost every operator monitors esophageal temperatures—in the name of safety. If you suggest otherwise people look askance, as if to say you are reckless. It's easy to imagine an expert on a witness stand skewering a colleague for not using a temperature probe during an ablation.

But wait a minute.

A provocative study[2] from investigators in Germany not only challenges this status quo but suggests the act of monitoring esophageal temps actually increases the risk of thermal lesions after ablation. That's not a mistake. A strategy to prevent harm might just increase the risk of doing harm.

The study, published recently in Heart Rhythm, was elegant in its simplicity. Forty patients with AF had left atrial ablation with esophageal temperature monitoring and forty did not. Since atria-esophageal fistula is rare, they needed a surrogate. Here they used the presence of thermal lesions on endoscopy, which was performed in all patients within two days of the ablation.

Patients were well-matched in clinical characteristics. And there were no procedural differences among the groups. In both groups, power was limited to 25 W when ablating on the posterior wall, which is common practice.

Overall, 16% of patients had esophageal lesions after ablation. Thermal lesions in the esophagus were seen in 30% (12/40) of patients in the temperature-monitoring group vs 2.5% (1/40) in nonmonitored group.

In the discussion section, the authors note that other groups have reported thermal lesions in the postablation period, but their study was the first to suggest that monitoring by itself may have contributed to esophageal injury.

Citing the 2012 HRS/EHRA/ECAS expert consensus statement on AF ablation, the authors noted that there are no clear recommendations on avoiding esophageal injury. Two-thirds of the guideline writers used esophageal temperature monitoring.

Among the proposed reasons for their findings, the German researchers posited a false sense of security on the part of the operator: luminal temps may not reflect temps in the wall of the esophagus (they cited two animal studies[3,4] in support of this idea).

Another possibility is that the stainless-steel parts of the probe act as an antenna for inductive heating. In support of this mechanism, the authors cited a case report[5] of a pulmonary vein isolation using duty-cycled phased RF ablation.

Comments

This is a striking study because of its paradoxical findings. Fear and intuition drive scores of electrophysiologists to use temperature monitoring. Now we have a signal that our well-intentioned efforts to be safe could actually be harmful.

More may not be better. Imagine that.

The most obvious thing to say about this is how fear clouds our statistical minds. We aim to protect the outer wall of the esophagus but we measure the luminal temperature. In this case, measuring the wrong surrogate lulls the operator into a false sense of safety.

The other intriguing possibility is that fear obscured our view of physics. Might it not have been predictable that a large stainless-steel electrode could act as a heat antenna? Induction of heat through tissue is not a new principle.

I can think of other add-on procedural measures in AF ablation that have not been well studied but are done in the name of patient safety. These include preprocedural CT scans (added radiation), preprocedure transesophageal echocardiograms in low-risk patients (added risk of another procedure), and even intracardiac ultrasound (added vascular access and nidus of thrombus). Be clear, I am not saying these examples cause harm, only that they have not been conclusively proven safe or effective.

I contacted Dr Patrick Müller (Heart Center Bad Neustadt, Germany), the lead author of this study. He told me his group is currently doing similar studies with different esophageal probes. I look forward to those data. It is possible that other temperature probes may not associate with esophageal lesions.

In the meantime, the most effective way to prevent esophageal injury is to avoid burning the left atrium. Recent data from the LEGACY[6] and other trials[7] show that we now have effective and safe means to treat many patients with AF without exposing them to thermal energy.

But when we do choose to ablate in the left atrium, treading lightly on the posterior wall seems wise. I have changed my technique such that I now ablate the anterior ridges first so as to minimize the RF burden posteriorly. I use low-watt, short-duration burns and accept the fact that gaps may occur in the future. I avoid cumulative burns in proximity to the esophagus. I often "give an area rest" and come back to it later. I employ the Golden Rule of Ablation: you can always burn more, but you can't undo burns.

JMM

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