Fig. 1

Perimitral flutter - electrograms and 3D imaging. a: Fractionated electrograms (marked by underline) were recorded by the ablation catheter (Abl) positioned at the MI. They belong to slow-conducting zone of clockwise perimitral flutter. b-d Electroanatomic shell of the LA after roof and MI line ablation. Left anterior oblique (LAO, 45°) (b) and postero-anterior (PA) view (c) with the left inferior pulmonary vein hidden to visualize the MI. Left superior oblique view (d) shows the free space area (black arrow) between LA endocardium and CS. CARTO tags definition: yellow = successful bipolar ablation point at the endocardium, dark red = unipolar ablation point at the endocardium, pink = unipolar ablation point within the CS, blue = mitral annulus, gray = scar. LAA = left atrial appendage