The intention of this mini-review is to help identify the location, characteristics and methods for monitoring the esophagus during ablative therapies of the left atrium. Anatomic Location and Features of the Esophagus Under normal circumstances, the esophagus descends along the mid-lateral wall of the left atrium, usually near the antrums of the left pulmonary veins. Figures 1A through 1D are different views of three-dimensional reconstructions of the left atrium and the esophagus. This was performed using standard contrast media for the left atrium, with the patient having swallowed barium contrast material prior to the CT scan being performed. Because the contrast was swallowed several minutes prior to the CT being performed, the entire boundary of the esophagus cannot be appreciated. We attempted this procedure on multiple patients, with this limitation occurring in most of them. It should be noted that the recurrent laryngeal nerve, which is the "motor nerve" of the larynx, runs down the anterior esophagus and terminates contact with the esophagus along the roof of the left atrium. It then extends in a posterior direction along the inferior border of the aortic arch. Ablation along the roof of the left atrium has recently been sited to cause transient injury to the left recurrent laryngeal nerve, and can cause hoarseness and vocal cord paralysis.2 This complication usually presents itself within 24 to 48 hours post ablation. Monitoring the Location of the Esophagus During Ablation Procedures One method that has been used for some time to monitor the esophagus is to place a catheter (either a multiple electrode catheter or temperature monitoring catheter) into the esophagus, and observe its location via fluoroscopy during the ablation procedure. Using a temperature probe can be a useful tool for structural visualization, as well as for providing analysis of RF energy levels/tissue temperatures during procedures. Recent studies have suggested that a minor time delay can occur between elevated temperatures in the left atrium and its detection by the temperature probe. Using a multipolar electrode catheter allows for both visualization of the esophagus and electrical analysis of the left atrium (Figure 2A), which has been proven to be beneficial for identifying triggers for atrial fibrillation within the left pulmonary veins. It can also differentiate the origination of atrial fibrillation from the left or right atria without performance of transseptal puncture.3 The limitation of using this method to determine the origin of pulmonary vein triggers is that variation of the esophageal course can occur. Figures 2B and 2C are both LAO fluoroscopic projections taken from two different patients. Each patient s esophagus takes an opposite course from the other. Some laboratories have also had the patient swallow Barium contrast prior to the ablation procedure, which will highlight the boundaries of the esophagus on fluoroscopy for several hours. Another tool for observation of the esophagus is the use of intracardiac echo. The esophagus can be imaged and monitored at the same time as the left pulmonary veins during ablation (Figure 3A). Unfortunately, though, it can be difficult to distinguish the esophagus from the coronary sinus (Figure 3B). The use of either a temperature probe or a multipolar electrode catheter can aid in differentiating between these two structures. The last method we ll discuss is the use of three-dimensional mapping systems, such as EnSite NavX system (Endocardial Solutions), to define the location of the esophagus in relation to the left atrium (Figure 3C). Although three-dimensional mapping systems can be very helpful for giving a generalized location of the esophagus, the limitation of using this alone for monitoring purposes is that the map of the esophagus remains in a fixed state. In reality, the esophagus continues to move when the patient swallows, when sedation levels and breathing changes occur, or when the posterior left atrium is stretched by catheter manipulation. As can be seen in Figure 3D, when the map of the left atrium was created, the posterior wall was pushed into the space we had originally created for the esophagus. Variations of Esophageal Location Though the esophagus commonly lies along the posterior-lateral wall of the left atrium, it can also vary in its location and proximity to the heart.4 Minor variances are quite common, with the most common being either location in the middle of the left atrium (Figure 4A) or descending from the left superior pulmonary vein to the right inferior pulmonary vein (Figure 4B). Occasionally, dramatic variations can be seen, especially in patients who are morbidly obese (Figure 4C), have kyphosis (Figure 4D) or scoliosis. Conclusion Though very uncommon, and one of the most rare complications for atrial fibrillation ablative procedures is damage to the esophagus and its surrounding structures. While no method has proven to be concrete for avoiding these complications, certain measures can be taken to help with locating and monitoring the esophagus during left atrial ablations.