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Image integration for catheter ablation: Searching for the perfect match
EDITORIAL COMMENTARY
Image integration for catheter ablation: Searching for the perfect match Li-Fern Hsu, MBBS From the Department of Cardiology, National Heart Centre, Singapore. Accurate definition of cardiac anatomy and precise tracking of catheter positions during catheter ablation procedures are integral to a safe and successful outcome. As ablation techniques have evolved in scope and complexity, imaging and navigational technology have evolved concurrently to facilitate these complex procedures. Catheter ablation of atrial fibrillation (AF) has progressed significantly since the initial discovery of focal triggers originating from the pulmonary veins (PVs).1 Although PV isolation remains the cornerstone of most current ablation strategies, the isolating lesion set has moved away from the PV ostia into the atrium, and additional ablation in the form of linear lesions joining anatomic structures, focal ablation at sites of fractionation, or isolation of adjoining structures, such as the coronary sinus or left atrial appendage, may be necessary for some patients with paroxysmal AF and most patients with persistent and permanent AF.2 At the same time, advances in imaging technology have facilitated these complex ablation procedures. Intracardiac echocardiography can guide catheter positioning and power titration for ablation and provide information on cardiac anatomy.3 Nonfluoroscopic three-dimensional mapping and navigation systems, with their ability to track catheters online and record ablation points, can be particularly helpful when used during ablation to create long linear lesions or for focal ablation of fractionated atrial electrograms. They also have demonstrated evidence for reduced fluoroscopic dependence and procedural duration.4 However, the limitations of these systems have been recognized. In addition to being heavily operator dependent, the geometry or electroanatomic maps created by these systems are only an approximation to the true anatomy of the cardiac chambers, and important but subtle anatomic variations, such as the precise location of the PV–left atrial junction, size and location of the left atrial appendage, and presence and location of ridges and pouches, are not well defined. A highly detailed anatomic representation of the left atrium can be obtained by computed tomography (CT) or Address reprint requests and correspondence: Dr. Li-Fern Hsu, Department of Cardiology, National Heart Centre, Mistri Wing, 17 Third Hospital Avenue, Singapore 168752, Singapore. E-mail address: hsu_li_fern@nhc. com.sg.
magnetic resonance imaging (MRI). Current technology has made it possible to import the CT or MRI scan into a threedimensional navigation system and register it with the onlineacquired map to guide ablation. The software (CartoMerge, Biosense Webster, Diamond Bar, CA, USA) superimposes and aligns the CT or MRI image with the electroanatomic map, allowing real-time mapping and tracking of the ablation catheter tip within the patient’s own anatomy. This has been validated in several clinical studies, which demonstrate a clinically relevant degree of accuracy5–7 and suggest improved outcomes.8 In this issue of Heart Rhythm, Brooks et al9 present their experience of CT image integration using the novel software NavX Fusion (St. Jude Medical, St. Paul, MN, USA) for AF ablation. This system represents an advance in available technology, as the software enables the cardiac geometry to be dynamically molded or fused to the CT image. In addition, all catheters can be displayed and geometry creation expedited using the circular PV mapping catheter. Although the process of integration appeared cumbersome, beginning with geometry creation, field scaling (correction for impedance variations), and finally primary and secondary fusion, the time required to perform this was reasonably quick (22.1 ⫾ 11.3 minutes for map creation, and 12.7 ⫾ 2.6 minutes for fusion in the initial 15 patients). The registration error between the created chamber geometry and CT image was very small, with a mean surface-to-surface distance of 4.1 ⫾ 0.7 mm after field scaling and primary fusion, and 1.9 ⫾ 0.4 mm after secondary fusion. Real-time navigational error, measured from the ablation catheter tip to the geometry or CT surface over 10 anatomic locations, was 3.4 ⫾ 1.6 mm. Although both CartoMerge and NavX Fusion use fundamentally different methodologies and algorithms for mapping and image integration, they share similar factors affecting their accuracy. Starting with CT or MRI image acquisition, every step of the mapping and integration process may be a potential source of error. Accurate registration or fusion of the radiologic image with the acquired map requires operator-defined landmarks. Although early experience with the CartoMerge has provided useful lessons in the selection of landmarks,10 this remains, at best, subjective and operator dependent. Even with careful registration
1547-5271/$ -see front matter © 2008 Heart Rhythm Society. All rights reserved.
doi:10.1016/j.hrthm.2008.01.021
Hsu
Editorial Commentary
technique guided by intracardiac echocardiography, significant errors were observed.11,12 Brooks et al9 demonstrated impressive accuracy using the NavX Fusion; however, they rightly pointed out that comparison with CartoMerge should be viewed with caution. Navigational accuracy also was well within the range for effective clinical use, although this would have been strengthened if it was evaluated against intracardiac echocardiography or another real-time imaging modality.9 An important observation was that differences in rhythm at the time of CT image acquisition and ablation procedure did not affect accuracy. As this is the first published experience with NavX Fusion, future studies are expected. With the greater definition of cardiac anatomy provided by image integration, more accurate navigation and lesion placement resulting in increased efficiency and efficacy of ablation procedures logically would be expected. However, information on clinical outcomes is limited. Kistler et al8 demonstrated a better arrhythmia-free outcome in patients who underwent AF ablation guided by image integration compared to electroanatomic or noncontact mapping. However, there was a high rate of multi-PV recovery among the patients with AF recurrence who underwent repeat procedures. Clearly, the accuracy of lesion placement is just one of many factors determining the effectiveness of ablation. There was no significant reduction in procedural duration, and although a reduction in fluoroscopic time was demonstrated, the savings in radiation exposure would have been offset by the need for a preprocedural CT scan. In conclusion, it is important to acknowledge that although three-dimensional mapping systems with image integration have been widely adopted for ablation procedures, they still are prone to subjective inaccuracies. Clinical data are limited, and many theoretical benefits remain unproven. In
537 its present iteration, it should remain as just one of the tools facilitating complex catheter ablation procedures and should not distract us from established electrophysiologic principles and robust endpoints, such as electrogram morphology, changes in AF cycle length, vagal responses, and demonstration of PV isolation and linear conduction block.
References 1. Haissaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 1998;339:659 – 666. 2. Haissaguerre M, Sanders P, Hocini M, et al. Catheter ablation of long lasting persistent atrial fibrillation: critical structures for termination. J Cardiovasc Electrophysiol 2005;16:1125–1137. 3. Verma A, Marrouche NF, Natale A. Pulmonary vein antrum isolation: intracardiac echocardiography-guided technique. J Cardiovasc Electrophysiol 2005;15: 1335–1340. 4. Rotter M, Takahashi Y, Sanders P, et al. Reduction of fluoroscopy exposure and procedure duration during ablation of atrial fibrillation using a novel anatomical navigation system. Eur Heart J 2005;26:1415–1421. 5. Kistler PM, Earley MJ, Harris S, et al. Validation of three-dimensional cardiac image integration: use of integrated CT image into electroanatomic mapping system to perform catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:341–348. 6. Dong J, Dickfeld T, Dalal D, et al. Initial experience in the use of integrated electroanatomic mapping with three-dimensional MR/CT images to guide catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:459 – 466. 7. Malchano ZJ, Neuzil P, Cury RC, et al. Integration of cardiac CT/MR imaging with three-dimensional electroanatomical mapping to guide catheter manipulation in the left atrium: implications for catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:1221–1229. 8. Kistler PM, Rajappan K, Jahangir M, et al. The impact of CT image integration into an electroanatomic mapping system on clinical outcomes of catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:1093–1101. 9. Brooks AG, Wilson L, Kuklik P, et al. Image integration using NavX fusion: Initial experience and validation. Heart Rhythm 2008;5:526 –535. 10. Kistler PM, Schilling RJ, Rajappan K, et al. Image integration for atrial fibrillation ablation: pearls and pitfalls. Heart Rhythm 2007;4:1216 –1221. 11. Zhong H, Lacomis JM, Schwartzman D. On the accuracy of CartoMerge for guiding posterior left atrial ablation in man. Heart Rhythm 2007;4:595– 602. 12. Fahmy TS, Mlcochova H, Wazni OM, et al. Intracardiac echo-guided image integration: optimizing strategies for registration. J Cardiovasc Electrophysiol 2007;18:276 –282.
Image integration for catheter ablation: Searching for the perfect match Li-Fern Hsu, MBBS From the Department of Cardiology, National Heart Centre, Singapore. Accurate definition of cardiac anatomy and precise tracking of catheter positions during catheter ablation procedures are integral to a safe and successful outcome. As ablation techniques have evolved in scope and complexity, imaging and navigational technology have evolved concurrently to facilitate these complex procedures. Catheter ablation of atrial fibrillation (AF) has progressed significantly since the initial discovery of focal triggers originating from the pulmonary veins (PVs).1 Although PV isolation remains the cornerstone of most current ablation strategies, the isolating lesion set has moved away from the PV ostia into the atrium, and additional ablation in the form of linear lesions joining anatomic structures, focal ablation at sites of fractionation, or isolation of adjoining structures, such as the coronary sinus or left atrial appendage, may be necessary for some patients with paroxysmal AF and most patients with persistent and permanent AF.2 At the same time, advances in imaging technology have facilitated these complex ablation procedures. Intracardiac echocardiography can guide catheter positioning and power titration for ablation and provide information on cardiac anatomy.3 Nonfluoroscopic three-dimensional mapping and navigation systems, with their ability to track catheters online and record ablation points, can be particularly helpful when used during ablation to create long linear lesions or for focal ablation of fractionated atrial electrograms. They also have demonstrated evidence for reduced fluoroscopic dependence and procedural duration.4 However, the limitations of these systems have been recognized. In addition to being heavily operator dependent, the geometry or electroanatomic maps created by these systems are only an approximation to the true anatomy of the cardiac chambers, and important but subtle anatomic variations, such as the precise location of the PV–left atrial junction, size and location of the left atrial appendage, and presence and location of ridges and pouches, are not well defined. A highly detailed anatomic representation of the left atrium can be obtained by computed tomography (CT) or Address reprint requests and correspondence: Dr. Li-Fern Hsu, Department of Cardiology, National Heart Centre, Mistri Wing, 17 Third Hospital Avenue, Singapore 168752, Singapore. E-mail address: hsu_li_fern@nhc. com.sg.
magnetic resonance imaging (MRI). Current technology has made it possible to import the CT or MRI scan into a threedimensional navigation system and register it with the onlineacquired map to guide ablation. The software (CartoMerge, Biosense Webster, Diamond Bar, CA, USA) superimposes and aligns the CT or MRI image with the electroanatomic map, allowing real-time mapping and tracking of the ablation catheter tip within the patient’s own anatomy. This has been validated in several clinical studies, which demonstrate a clinically relevant degree of accuracy5–7 and suggest improved outcomes.8 In this issue of Heart Rhythm, Brooks et al9 present their experience of CT image integration using the novel software NavX Fusion (St. Jude Medical, St. Paul, MN, USA) for AF ablation. This system represents an advance in available technology, as the software enables the cardiac geometry to be dynamically molded or fused to the CT image. In addition, all catheters can be displayed and geometry creation expedited using the circular PV mapping catheter. Although the process of integration appeared cumbersome, beginning with geometry creation, field scaling (correction for impedance variations), and finally primary and secondary fusion, the time required to perform this was reasonably quick (22.1 ⫾ 11.3 minutes for map creation, and 12.7 ⫾ 2.6 minutes for fusion in the initial 15 patients). The registration error between the created chamber geometry and CT image was very small, with a mean surface-to-surface distance of 4.1 ⫾ 0.7 mm after field scaling and primary fusion, and 1.9 ⫾ 0.4 mm after secondary fusion. Real-time navigational error, measured from the ablation catheter tip to the geometry or CT surface over 10 anatomic locations, was 3.4 ⫾ 1.6 mm. Although both CartoMerge and NavX Fusion use fundamentally different methodologies and algorithms for mapping and image integration, they share similar factors affecting their accuracy. Starting with CT or MRI image acquisition, every step of the mapping and integration process may be a potential source of error. Accurate registration or fusion of the radiologic image with the acquired map requires operator-defined landmarks. Although early experience with the CartoMerge has provided useful lessons in the selection of landmarks,10 this remains, at best, subjective and operator dependent. Even with careful registration
1547-5271/$ -see front matter © 2008 Heart Rhythm Society. All rights reserved.
doi:10.1016/j.hrthm.2008.01.021
Hsu
Editorial Commentary
technique guided by intracardiac echocardiography, significant errors were observed.11,12 Brooks et al9 demonstrated impressive accuracy using the NavX Fusion; however, they rightly pointed out that comparison with CartoMerge should be viewed with caution. Navigational accuracy also was well within the range for effective clinical use, although this would have been strengthened if it was evaluated against intracardiac echocardiography or another real-time imaging modality.9 An important observation was that differences in rhythm at the time of CT image acquisition and ablation procedure did not affect accuracy. As this is the first published experience with NavX Fusion, future studies are expected. With the greater definition of cardiac anatomy provided by image integration, more accurate navigation and lesion placement resulting in increased efficiency and efficacy of ablation procedures logically would be expected. However, information on clinical outcomes is limited. Kistler et al8 demonstrated a better arrhythmia-free outcome in patients who underwent AF ablation guided by image integration compared to electroanatomic or noncontact mapping. However, there was a high rate of multi-PV recovery among the patients with AF recurrence who underwent repeat procedures. Clearly, the accuracy of lesion placement is just one of many factors determining the effectiveness of ablation. There was no significant reduction in procedural duration, and although a reduction in fluoroscopic time was demonstrated, the savings in radiation exposure would have been offset by the need for a preprocedural CT scan. In conclusion, it is important to acknowledge that although three-dimensional mapping systems with image integration have been widely adopted for ablation procedures, they still are prone to subjective inaccuracies. Clinical data are limited, and many theoretical benefits remain unproven. In
537 its present iteration, it should remain as just one of the tools facilitating complex catheter ablation procedures and should not distract us from established electrophysiologic principles and robust endpoints, such as electrogram morphology, changes in AF cycle length, vagal responses, and demonstration of PV isolation and linear conduction block.
References 1. Haissaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 1998;339:659 – 666. 2. Haissaguerre M, Sanders P, Hocini M, et al. Catheter ablation of long lasting persistent atrial fibrillation: critical structures for termination. J Cardiovasc Electrophysiol 2005;16:1125–1137. 3. Verma A, Marrouche NF, Natale A. Pulmonary vein antrum isolation: intracardiac echocardiography-guided technique. J Cardiovasc Electrophysiol 2005;15: 1335–1340. 4. Rotter M, Takahashi Y, Sanders P, et al. Reduction of fluoroscopy exposure and procedure duration during ablation of atrial fibrillation using a novel anatomical navigation system. Eur Heart J 2005;26:1415–1421. 5. Kistler PM, Earley MJ, Harris S, et al. Validation of three-dimensional cardiac image integration: use of integrated CT image into electroanatomic mapping system to perform catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:341–348. 6. Dong J, Dickfeld T, Dalal D, et al. Initial experience in the use of integrated electroanatomic mapping with three-dimensional MR/CT images to guide catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:459 – 466. 7. Malchano ZJ, Neuzil P, Cury RC, et al. Integration of cardiac CT/MR imaging with three-dimensional electroanatomical mapping to guide catheter manipulation in the left atrium: implications for catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:1221–1229. 8. Kistler PM, Rajappan K, Jahangir M, et al. The impact of CT image integration into an electroanatomic mapping system on clinical outcomes of catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:1093–1101. 9. Brooks AG, Wilson L, Kuklik P, et al. Image integration using NavX fusion: Initial experience and validation. Heart Rhythm 2008;5:526 –535. 10. Kistler PM, Schilling RJ, Rajappan K, et al. Image integration for atrial fibrillation ablation: pearls and pitfalls. Heart Rhythm 2007;4:1216 –1221. 11. Zhong H, Lacomis JM, Schwartzman D. On the accuracy of CartoMerge for guiding posterior left atrial ablation in man. Heart Rhythm 2007;4:595– 602. 12. Fahmy TS, Mlcochova H, Wazni OM, et al. Intracardiac echo-guided image integration: optimizing strategies for registration. J Cardiovasc Electrophysiol 2007;18:276 –282.