OBJECTIVES: This study sought to describe a new adverse effect of percutaneous radiofrequency(RF) ablation for atrial fibrillation(AF). BACKGROUND: Extension of the RF lesion beyond atrial myocardium may affect mediastinal structures other than the esophagus. METHODS: Circular mapping-guided isolation of the pulmonary veins was performed in two different electrophysiology laboratories, either individually and supplemented by ostial and posterior left atrial(LA) ablation or two by two with a series of ostial and posterior LA lesions. The RF energy was delivered point by point through a 5-mm open-tip irrigated catheter(40W maximum) or an 8-mm-tip catheter(45W maximum). RESULTS: In four(two in each electrophysiology laboratory) of 367 patients undergoing catheter ablation for AF, abdominal pain and distension developed within 48 h after the procedure. Investigation showed acute pyloric spasm and gastric hypomotility, probably the result of LA endocardially delivered RF affecting the periesophageal vagi. Complete spontaneous recovery occurred in two patients, but laparoscopic esophagojejunal anastomosis and endoscopic intra-pyloric Botulinum toxin injection, respectively, were performed to remedy delayed gastric emptying in two patients. CONCLUSIONS: Thermal injury during endocardial LA RF energy delivery may extend into the mediastinum and rarely may involve the periesophageal nerves, resulting in a syndrome of acute delayed gastric emptying. Marked anatomic variability of periesophageal vagi renders it difficult to reliably avoid the area overlying this plexus, therefore, we advocate a reduction in maximum RF power and application duration on all of the posterior LA to try to avoid this complication. OBJECTIVES: This study sought to describe a new adverse effect of percutaneous radiofrequency (RF) ablation for atrial fibrillation (AF). BACKGROUND: Extension of the RF lesion beyond atrial myocardium may affect mediastinal structures other than the esophagus. METHODS: Circular mapping-guided isolation of the pulmonary veins was performed in two different electrophysiology laboratories, either individually and supplemented by ostial and posterior left atrial (LA) ablation or two by two with a series of ostial and posterior LA lesions. The RF energy was delivered point by point through RESULTS: In four (two in each electrophysiology laboratory) of 367 patients undergoing catheter ablation for AF, abdominal pain and distension developed within 48 h after the procedure. Investigation showed acute pyloric spasm and gastric hypomotility, probably the result of LA endocardially delivered RF affecting the perie Complete spontaneous recovery occurred in two patients, but laparoscopic esophagojejunal anastomosis and endoscopic intra-pyloric Botulinum toxin injection, respectively, were performed to remedy delayed gastric emptying in two patients. CONCLUSIONS: Thermal injury during endocardial LA RF energy delivery may extend into the mediastinum and rarely may involve the periesophageal nerves, resulting in a syndrome of acute delayed gastric emptying. Marked anatomic variability of periesophageal vagi renders it difficult to sure avoid the area overlying this plexus, therefore, we advocate a reduction in maximum RF power and application duration on all of the posterior LA to try to avoid this complication.