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Optimizing Catheter Navigation for AF Ablation: Do Not Just Follow the Map!

Three-dimensional (3D) images created from segmentation of CT or CMR images can display the left atrial (LA) anatomy in remarkable detail. In particular, the pulmonary vein and left atrial appendage size, morphology, and location can be displayed very clearly and, given the enormous anatomic variability of these structures, these 3D images may greatly assist catheter ablation of atrial fibrillation (AF). An appealing concept has been to import these 3D images into an electro-anatomical mapping system, orientate or register them to the true LA position to then allow catheter navigation within the 3D image.1,2 The real-time update of the catheter tip location and the marking of ablation lesions on the detailed 3D image may potentially improve quality of lesion sets, reduce complications and reduce procedure and fluoroscopy times. Ideally, the registration process should be quick and easy but currently the process is somewhat cumbersome and prone to error. In this edition of the Journal, Fahmy et al. report on their clinical evaluation of 3D CT image integration for AF ablation using CartoMergeTM (Biosense Webster Inc., Diamond Bar, CA, USA) and their strategy to minimize error using intracardiac echocardiography (ICE).3 One hundred and twenty-four patients undergoing AF ablation had CT scan segmentation performed on the CARTO XPTM Image Integration Module to create a 3D image. Registration of this image with the catheter geometry of the heart was performed in two stages: (1) Landmark registration was performed by acquiring points on the electroanatomical mapping system using ICE (and a circular mapping catheter in the pulmonary veins) to confirm the catheter tip location at the time of acquisition. The corresponding point was marked on the 3D CT. The process was repeated 4 or 5 times in different areas including the posterior aspect of the pulmonary veins, the left atrial appendage, the anterolateral mitral annulus, the ostium of the coronary sinus and the superior vena cava. Registration was performed by overlaying the catheter geometry with the more detailed 3D CT image using an algorithm of ‘best fit’ to shift its orientation to produce the minimum average error between all landmark points and their corresponding point on the 3D image. If the individual landmark error (distance between original landmark points and their corresponding