Does image integration improve atrial fibrillation ablation outcomes, or are other aspects of the ablation the key to success?

Over the years, various imaging modalities have been used to guide ablation procedures. Technology has rapidly progressed from Two-dimensional fluoroscopic imaging to several different forms of 3D mapping systems using magnetic and impedance sensors, as well as automated imaging components derived from computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and rotational angiography. These have provided greater anatomic detail for accurate ablation. However, ablation outcomes rely not only on image guided proper lesion location, but also adequate catheter contact, power, duration of energy delivery, and overall ablation strategy. CT and MRI provide detailed 3D geometries of the chambers of the heart. Carto (Biosense Webster, Diamond Bar, CA, USA) and EnSite NavX (St Jude Medical, St Paul, MN, USA) mapping systems have the capability for integration of 3D CT and MRI images with electroanatomic maps. Image registration is typically done by matching distinct landmarks or fiducial points on the electroanatomic map with the CT (or MRI) image. The registration process can be optimized by manual adjustment, or using a more global surface registration algorithm. 1 , 2 The integrated image has an average accuracy of 1–3 mm. 1–3 However, individual points can be inaccurate by more than 10–15 mm. 1 , 4 Excessive catheter contact force applied during mapping can distort the map. 5 Bertaglia et al.6 , in this issue of Europace , report outcomes of a large Italian registry of atrial fibrillation (AF) ablations. The three imaging and ablation strategies that were compared included: segmental ostial pulmonary vein isolation (SOCA group, n = 240), circumferential pulmonary vein isolation guided by electroanatomic mapping (CARTO group, n = 107), and circumferential pulmonary vein isolation guided by electroanatomic mapping integrated with CT or MRI images (MERGE group, n = 226). Total procedure time was shortest in the SOCA group (184.9 ± 58.4 min) compared with the MERGE (210.3 ± 63.4 min) and CARTO groups (231.7 ± 70.7 min), P < 0.0001. However, fluoroscopy time was not significantly different between groups. This is in contrast to previous studies where fluoroscopy time was significantly reduced with the use of a 3D mapping system. 7 , 8 The authors noted that the study period included the early experience with CartoMerge, which may account for longer procedure and fluoroscopy times. Patients in the MERGE group had fewer atrial tachyarrhythmia recurrences over 12 months (22.6%) compared with the SOCA (44.6%) and CARTO groups (41.7%), P < 0.0001. The difference in outcomes is certainly thought provoking; however, the challenge with this type of multicenter registry is accounting for differences in ablation technique between individual operators who used image integration compared with those who did not. Figures 1 and 2 in the article by Bertaglia et al. , illustrate different operator ablation techniques. Even though both operators performed 3D imaging guided circumferential pulmonary vein isolation, different strategies were used for ablation lesion placement. The operator who used Carto ( Figure 1 of Bertaglia et al. ) appeared to use the 3D geometry as a rough guide for lesion application, whereas the operator who used CartoMerge ( Figure 2 of Bertaglia et al. ) performed a wider circumferential ablation lesion set and meticulously filled in all the ablation lesions gaps on the map. It is therefore unclear whether the mapping system led to different outcomes in these patients or whether it was the ablation strategy. It has also been shown that higher volume AF ablation centres have better outcomes on average. 9 It is not stated in this study if all 12 centres used CartoMerge or if just the larger centres had the newer technology. These and other related issues challenge this and all other non-randomized studies. Other studies that compared CT or MRI image integration with 3D mapping alone found mixed results. Kistler et al.7 , reported an initial non-randomized study of 94 AF patients who underwent either ablation guided by CT integrated 3D mapping (CartoMerge) or 3D mapping alone. The 25-week follow-up success rates documented by 7-day event recorder freedom from AF off anti-arrhythmic drugs was 60% in the 3D mapping group and 83% in the CT integrated mapping group ( P < 0.05). However, a subsequent randomized trial reported by the same group published in 2008 found different results. 10 When patients were randomized to AF ablation guided by either CT integrated mapping or 3D electroanatomic mapping alone, there was no significant difference in 6 months success rates free from AF recurrence (50 and 56%, respectively, P = 0.9). In addition, there was no significant difference in fluoroscopy time or procedure duration. Tang et al. also performed a prospective randomized trial of 3D electroanatomical mapping alone (CartoXP) compared with CT integration (CartoMerge) in 81 patient undergoing circumferential pulmonary vein isolation for treatment of paroxysmal AF. 11 CT integration significantly reduced fluoroscopy time (19.6 ± 7.5 min vs. 28.5 ± 12.8 min, P < 0.001) and procedure time (156 ± 25 min vs. 179 ± 21 min, P < 0.001) compared with 3D electroanatomic mapping alone. However, there was no significant difference in freedom from AF 12 months post-ablation (78.6% CartoMerge group compared with 74.4% in the Carto group, P > 0.50). These two randomized trials came to the same conclusion that image integration with CT did not improve ablation outcomes. When all other factors were consistent between study groups, image integration with CT or MRI did not improve ablation outcomes. The difference in conclusions about reduction in fluoroscopy time with image integration may reflect the learning curve associated with the introduction of new technology. Three-dimensional imaging has improved our understanding of location of ablation lesions relative to important structures such as the pulmonary vein ostia and the esophagus. More anatomic detail may allow for more accurate ablation lesion application, however, the minimum amount of imaging detail needed to achieve excellent outcomes is still debated. Bertaglia et al.6 have provided some thought provoking data from real world experience. While non-randomized trials, such as this, have shown an association between image integration and AF ablation outcomes, randomized trials have shown no difference in AF outcomes. 10 , 11 The improved ablation outcomes appear to be due to differences in other aspects of the ablation, outside of image integration alone. Imaging serves as a guide, while the actual energy delivery to the myocardium is the treatment. Conflict of interest: B.D.P.: Biosense Webster research grant. D.L.P.: Biosense Webster advisory board and research grant; Siemens Medical research grant; St Jude Medical consulting, research grant, and royalties.