Fig 4 Electroanatomical map of left atrium in patient with persistent atrial fibrillation undergoing pulmonary vein isolation. Computed tomogram before ablation procedure is merged with three dimensional electroanatomical map of left atrium created during ablation. Left atrium is viewed from a posterior (panel A) and superior (panel B) orientation, with left atrium appendage on left. Dots represent sites of delivery of radiofrequency energy. Radiofrequency lesions encircle both left and right pulmonary veins, avoiding posterior wall of left atrium, and a line of radiofrequency ablation is seen along the mitral isthmus (region extending from left inferior pulmonary vein to mitral annulus)