Introduction: A P wave duration of more than 110 msec is a sign of interatrial conduction impairment. Bayes syndrome is defined as the presence of interatrial block associated with recurrent atrial arrhythmias.

Objective: T he purpose of this study is to determine the relationship between left atrial volume and the pre-sence of Bayes syndrome in patients who have under-gone atrial fibrillation ablation.

Methods: We selected 105 consecutive patients who underwent catheter ablation for atrial fibrillation over a 2-year period (June 2017 – May 2019). Ablation was performed using Ensite Velocity (Saint Jude) or Carto 3 (Biosense Webster) three-dimensional system. Befo-re the procedure patients performed cardiac CT which was later integrated into the 3D mapping system and measurement of left atrial volume was made. The du-ration of the P wave was measured in the inferior le-ads: D2, D3, avF and an average of the three values was made.

Results: Of the 105 patients, 74 (70.4%) were male with a mean age of 58 years. There were no significant differences in age or sex between patients with Bayes syndrome and patients with a P wave duration under 110 msec. Significant differences in left atrial volume in patients with Bayes syndrome were found compared to patients with a P wave duration <110 msec (p<0.05). Using the ROC curves we found that a left atrium vo-lume of >50 ml/m² can differentiate between patients with interatrial block and patients without interatrial block.

Conclusions: The presence of Bayes syndrome in pa-tients who have had catheter ablation of atrial fibrilla-tion is associated with increased left atrial volume. The occurrence of interatrial conduction disturbance on the surface ECG is an indirect sign of a dilatated atrium with a volume of >50 ml/m².