Application of registration for ablation: a marriage of technologies

While the number of catheter ablation (CA) procedures for many arrhythmias is decreasing, that for treatment of atrial fibrillation (AF) continues to increase. The discovery that ectopic impulses originating in the pulmonary veins (PV) plays a major role in the genesis of AF episodes [1] has led to the concept of PV isolation to prevent clinical AF episodes. A variety of techniques have been used to accomplish this, including segmental ostial ablation guided by electrophysiologic mapping [2] as well as long ablation lines that more widely circumscribe PVs (independent of mapping) [3]. It follows that, whichever strategy is employed, the operator needs to have some knowledge of the location of the patient’s PVs since there can be substantial interand intra-patient variability in the number, size and arrangement of PV ostia [4,5]. Several techniques have been employed to obtain information about PV anatomy, including PV angiography, intracardiac echocardiography and simply probing the left atrial wall for vein orifices during the ablation procedure, and multislice 3dimensional computed tomography (CT) and magnetic resonance imaging (MRI) or angiography (MRA) performed prior to the procedure. While the latter imaging modalities produce superbly detailed views of PV anatomy, it has heretofore only been possible to use these images in parallel with an ablation procedure due largely to technical difficulties with registration—the process of “synchronizing” previously obtained images with spatial data being acquired live in the electrophysiology (EP) laboratory, typically with fluoroscopy. Extended exposure to ionizing radiation from fluoroscopy poses an increasing hazard to the operator, staff and patient [6,7]. Several manufacturers of EP recording equipment have put considerable effort into trying get these detailed images to “talk to” their in-laboratory recording systems. As it is, the operator has to resort to translating these static images into what is seen on fluoroscopic screens. The technologies are like a boy and girl at a middle school dance: they are in the same room, but not directly interacting. With the paper by Dickfeld et al. in this issue of the Journal [8], MR images have finally been introduced to an EP laboratory catheter position recording system—and they seem to have gotten along pretty well. To do this, the authors used skin markers on their experimental animals during the MRI study and transmitted the imaging data to the EP laboratory (where animals were taken immediately after the MRI). There, the same markers were touched with the mapping catheter tip and proprietary software was used to “register” the marker locations in 3-D space with their locations on the previously-acquired MR images. Once the images were thus synchronized with live catheter position changes, the authors could manipulate the catheters very precisely and reproducibly. Specific sites were selected for catheter tip destinations (inferior vena cava, fossa ovalis, left atrial appendage) and radiofrequency ablation performed at these locations. The ablation lesions were inspected after sacrificing the animals. The authors found that they could maneuver the catheter using their navigation system with an accuracy of 3.9 ± 2.1 mm (the ablation lesion diameters averaged 4.6 ± 0.4 mm). This precision of catheter placement is comparable to that of existing computerized systems for recording catheter tip locations [9–12]. Of great interest, Dickfeld’s results were obtained without any use of fluoroscopy. Dickfeld et al’s results have major implications for how complex ablation procedures may be performed in the future. Improved accuracy of catheter positioning could improve procedural efficacy and safety, decreasing or eliminating the risk of perforation and PV stenosis. Atrial septal puncture could become as routine as obtaining a His bundle recording. Dramatic reductions or elimination of fluoroscopic exposure could enhance the safety of prolonged ablation procedures for EP personnel and patients. Continuous lines of ablation lesions could be made in the cavotricuspid isthmus for treatment of atrial flutter; connecting