Evaluation of Esophageal Damage During Conventional Pulmonary Vein Ablation Procedures and Potential Strategies to Protect the Esophagus. Pilot Study.

1. THEORETICAL FRAMEWORK. APPROACH TO THE PROBLEM

Background and justification

Atrial fibrillation is the most common type of heart arrhythmia. Electrical isolation of the pulmonary veins in the left atrium with ablation is standard therapy in the invasive treatment of atrial fibrillation. One of the risks of this intervention is thermal lesion of the esophagus, since it is in contact with the posterior wall of the left atrium. The energy applied for electrical isolation via either radiofrequency or cryotherapy can cause thermal lesions due to proximity with the esophagus and the vagus nerve/parasympathetic nervous system of the upper digestive tract. The incidence is not well established and data in the existing scarce publications show a very wide range, from 3 to 60%, according to the definition and means of the study used. The most recent systematic studies show values around 40-50%. The lesions observed vary in degree, from erythema or minor erosion to ulcers of the esophageal mucosa, including local hematomas, spasms, and esophageal/gastric motility disorders and even atrial-esophageal fistula, the extreme consequence of thermal esophageal lesion; the incidence of the latter is low (0.25%), but it has an elevated mortality. The best examination to diagnose and evaluate these lesions in all phases is upper digestive endoscopy or fibro esophagogastroscopy. Although it is routine in digestive services throughout the world, enabling the direct visualization and characterization of lesions, this technique is not performed systematically after ablation procedures, which explains the contradictory data in the literature.

Likewise, the possible long-term consequences of minor lesions are unknown, which, in a large number of patients are totally asymptomatic. For this reason, it cannot be ignored that acute tissue damage, however minimal, could lead to future changes in the form of late onset chronic esophageal pathology. The incidence and magnitude of esophageal involvement has been directly related to the ablation technique and protocol. Most available studies have been carried out in centers with ablation protocols that are significantly more aggressive than those used in our care facility. For this reason, the investigators do not have reliable data regarding the size of the problem in our center, which could present some differential characteristics.

To date, the prevention of these esophageal lesions has entailed: limits in the energy applied on the posterior wall of the left atrium (less power or shorter application time); monitoring of the luminal esophageal temperature during radio frequency or cryotherapy applications; stopping application early if certain temperatures considered risky were reached. However, the success of luminal esophageal temperature monitoring in preventing lesions varies widely, given that the temperature probes are very thin with respect to the total diameter of the esophagus, their position varies with respect to the cardiac tissue treated, and contact with the esophageal mucosa is inconstant. In fact, it has been reported that the temperature probes used for monitoring can contribute to increasing thermal lesions, given that their metal elements can boost direct heating/cooling of the tissue and make the lesion larger and last longer. In fact, the incidence of esophageal lesions is very similar, independent of the use of the temperature probe, or if it is a single or multi-sensor. Another controversial aspect of these temperature probes is that their use can lead to - at least potentially and in pursuit of safety - shorter, limited applications, which could cause incomplete non-transmural lesions and hamper the correct treatment of patients, thereby becoming a factor that increases the recurrence of atrial fibrillation. In addition, these probes should be deployed during the procedure so they are as close as possible to the application site (right or left veins depending on the time), which increases the procedure and fluoroscopy time, with consequent risks for both the patient and the medical team. All these limitations, together with significant economic cost overruns have meant that the use of this approach in our care facilities has been minimal and only for research purposes.