EDITORIAL Muscular architecture of the mitral isthmus: anatomical determinants for catheter ablation

This editorial refers to ‘The anatomical characteristics of three different endocardial lines in the left atrium: evalu-ation by computed tomography prior to mitral isthmus block attempt ’ by Y. Cho et al., on page 1104 Early electrophysiological studies demonstrated the presence of an isthmus of conductive tissue in the low lateral left atrium (LA) during ablation of left free-wall accessory pathways.1 These studies introduced the LA ‘isthmus ’ concept—a site of intra-atrial conduction block that shows the latest atrial activation during sinus rhythm. Although this posteroinferior area of the lateral LA wall between the orifice of the left inferior pulmonary vein (PV) and the mitral annulus cannot be considered an anatomic entity, it is now termed by electrophysiologists as the LA isthmus, or mitral isthmus. Linear ablation connecting the inferior margin of the ostium o