- Email: [email protected]
Intraoperative Electroanatomic Mapping
Intraoperative Electroanatomic Mapping Takashi Nitta, MD, PhD, Jiro Kurita, MD, PhD, Hiroshige Murata, MD, PhD, Hiroya Ohmori, MD, Shun-ichiro Sakamoto, MD, PhD, Masami Ochi, MD, PhD, and Kazuo Shimizu, MD, PhD Division of Cardiovascular Surgery and Department of Cardiology, Nippon Medical School, Tokyo, Japan
Purpose. An electroanatomic mapping system using an electromagnetic navigation technology constructs a 3-dimensional structure of the heart with high geometric accuracy of the data that provides a precise localization of the substrates of arrhythmias. The system was tested for the feasibility and efficacy in intraoperative mapping.
Evaluation. The system was used in 19 patients with ventricular tachycardia or other arrhythmias. The focus or reentrant circuit of the tachycardia was precisely located and a map-guided procedure was successfully performed in all patients. Cardiopulmonary bypass allowed for the tachycardias to be mapped without any hemodynamic compromise. Conclusions. Intraoperative mapping using the electroanatomic mapping system enables a precise localization of the tachycardia substrate. (Ann Thorac Surg 2012;93:1285– 8) © 2012 by The Society of Thoracic Surgeons
M
ultisite simultaneous mapping has been the gold standard in intraoperative electrophysiologic studies [1–3]. The mapping method is capable of displaying and analyzing the activation sequence of the atria or ventricles by recording only a few or even a single cardiac beat. Because the spatial resolution of this method depends heavily on the number and density of the electrodes, it requires hundreds of electrodes with a high density for a precise analysis of the arrhythmias, and the geometric accuracy of the data depends on the spatial consistency of the electrode locations on the actual heart and on the graphic display of the atria or ventricles. An electroanatomic mapping system that has been widely used in catheter laboratories (CARTO System, Biosense Webster, Diamond Bar, CA) uses an electromagnetic navigation technology to construct a 3-dimensional (3-D) structure of the heart and draw an activation map on the figure simultaneously [4, 5]. Although the method requires a stable cardiac rhythm during data acquisition, it allows for a 3-D anatomic reconstruction of the atria and ventricles, with a high geometric accuracy of Accepted for publication Dec 19, 2011. Presented at the Surgical Motion Picture Session of the Forty-seventh Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 31–Feb 2, 2011. Address correspondence to Dr Nitta, Division of Cardio vascular Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan; e-mail: [email protected].
© 2012 by The Society of Thoracic Surgeons Published by Elsevier Inc
the data assured by the magnetic field technology, providing a more precise localization of the focus or reentrant circuit of arrhythmias [6]. We examined the feasibility and efficacy of the electroanatomic mapping system for intraoperative mapping of arrhythmias.
Technology The system uses magnetic field technology to accurately locate the tip of the catheter and simultaneously record the electrogram from the catheter. The system consists of an external ultralow magnetic field emitter mounted in a location pad, a miniature passive magnetic field sensor embedded within a catheter electrode (NAVISTAR catheter, Biosense Webster), and a data processing unit (CARTO, Biosense Webster). The location pad, which is usually placed beneath the operating table, carries 3 coils separately mounted. Each coil generates a magnetic field with a different frequency of 2, 2.2, and 3 KHz with a magnitude of 0.05 to 0.5 Gauss. The magnetic field decays as a function of the distance from the coil. The location sensor in the catheter measures the strength of the magnetic field of each frequency, and the distance from each coil is calculated. The spatial location of the sensor is determined as an intersection of three theoretic spheres with radii that are the distances measured by the sensor (Fig 1). The 3-D figures of the atria and ventricles are reconstructed by connecting neighboring locations determined 0003-4975/$36.00 doi:10.1016/j.athoracsur.2011.12.081
NEW TECHNOLOGY
Description. The strength of the magnetic field is measured by a location sensor with three different frequencies generated by a location pad placed beneath the operating table, and the spatial location of the sensor is determined. By roving the catheter on the heart while the local electrogram is recorded simultaneously, the 3-dimensional figure of the heart is reconstructed and an activation or voltage map is generated.
1286
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
Ann Thorac Surg 2012;93:1285– 8
Fig 1. The magnetic field (shaded area) is effective with a 1-mm spatial accuracy within a theoretic cylinder with a 10-cm radius and 20-cm height located 18 cm above the location pad. NEW TECHNOLOGY
by roving the catheter over the epicardium or endocardium of the heart (Fig 2). The catheter also has a locatable electrode composed of the tip and ring electrodes, and the local electrogram is recorded simultaneously. The electrophysiologic data are analyzed and the activation or voltage map is generated. The map is superimposed on the figure as color-coded contours on a real-time basis or displayed as a dynamic propagation map. Recent versions of the system, CARTO XP and CARTO 3, have a function called CARTOMERGE that enables preoperative computed tomography or magnetic resonance images to be used to reconstruct the endocardial and epicardial surfaces of the heart and then be merged with the activation or voltage maps (Fig 3).
Fig 3. This epicardial activation map constructed by electroanatomic mapping shows the heart in the left anterior oblique cranial projection. The intraoperatively recorded data were superimposed on preoperatively recorded computed tomography scan images. The earliest activation of the ventricular tachycardia is located at the high lateral left ventricle around the origin of the left circumflex coronary artery. IM ⫽ intermediate artery; LAA ⫽ left atrial appendage; LAD ⫽ left anterior descending artery; LCA ⫽ left coronary artery; LCX ⫽ left circumflex artery.
Technique Preoperative Settings Before the operation, the location pad is properly placed underneath the operating table. An external reference patch that provides location reference data to the CARTO system is also placed on the patient’s back, just underneath the heart. The heart should be positioned 18 to 38 cm above the location pad and within a 10-cm-radius circle from the center of the pad to assure a 1-mm spatial accuracy (Fig 1). The feasibility of the CARTO system must be checked before the patient’s chest is scrubbed. An unsterilized NAVISTAR catheter is roved over the anterior chest of the patient, and the position of the patient or the location pad is adjusted to obtain an effective magnetic field to sufficiently cover the atria or ventricles. Electrocardiograms from the limbs leads and a left-sided precordial lead, usually V5, are displayed on the system to monitor the QRS or P wave morphologies during the data acquisition.
Intraoperative Mapping
Fig 2. Simultaneous recording of electrograms and the location of the electrode are shown. The NAVISTAR catheter electrode is roved directly on the ventricular epicardium.
The atrial or ventricular epicardium is mapped by roving the NAVISTAR catheter electrode directly around on the epicardium to simultaneously record the local electrograms and location of the electrode (Fig 2). In patients with ventricular tachycardia (VT), the ventricular epicardium is mapped during sinus rhythm or pacing to construct voltage maps and record fractionated or other abnormal electrograms that suggest delayed activation.
Ann Thorac Surg 2012;93:1285– 8
Clinical Experience Intraoperative mapping using the CARTO system was approved by the Institutional Review Board. Written informed consent was received from all patients before the intraoperative electrophysiologic study and operation.
Patient Characteristics Between March 2006 and May 2011, the CARTO system was used for intraoperative mapping in 19 patients (15 men and 4 women) who were aged an average of 56 ⫾ 18 years (range, 23 to 79 years). Fifteen patients had medically refractory VT and underwent map-guided surgical intervention for VT. All patients had undergone one to eight failed sessions of catheter ablation, including epicardial ablation in 4 patients, before the operation. Two patients had ischemic VT and 13 had nonischemic VT. Nine patients had a defibrillator implanted at the time of the operation. Two patients with sick sinus syndrome and partial atrial standstill underwent voltage mapping of the atria to identify an epicardial location with remaining viable myocardium for a myocardial electrode implantation and were implanted with a pacemaker. One patient had a recurrent conduction over a posterior septal atrioventricular accessary pathway after multiple sessions of catheter ablation and underwent a surgical ablation of the accessary pathway. Another patient, with persistent atrial tachycardia from the age of 5 years old, underwent a thoracoscopic and map-guided procedure.
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Feasibility of Intraoperative Electroanatomic Mapping Patients were placed supine on the operating table and underwent a median sternotomy, except for 1 patient who underwent a thoracoscopic procedure from a right anterior oblique position. The thicknesses of the operating table and the above matted pad were approximately 10 cm and 5 cm, respectively. Because the position of the location pad was properly adjusted preoperatively to allow the electromagnetic field to effectively cover the entire epicardium of the atria or ventricles, the electromagnetic technology was stable throughout the period of the mapping, and the intraoperative mapping was effectively accomplished in all patients. The duration required for the intraoperative mapping ranged from 20 to 80 minutes. No deaths or complications occurred related to the intraoperative mapping.
Hemodynamic Support by Cardiopulmonary Bypass The number of QRS morphologies of the VT induced and mapped intraoperatively ranged from 1 to 4. When the morphology of the VT changed into a different morphology during mapping, the electrograms were saved as a different data set and another activation map for the VT was constructed. Hemodynamic support with CPB was extremely useful to allow for the sustenance and mapping of rapid and hemodynamically unstable VTs for more than 30 minutes. None of the VTs deteriorated into ventricular fibrillation during the mapping. Because the accessary pathway was located at the posterior septum in the patient with Wolff-ParkinsonWhite syndrome, intraoperative mapping was performed with the aid of CPB and a heart positioner. This technique enabled good exposure of the region while maintaining stable hemodynamics and ensuring the geometric accuracy of the data. In the other patients, the atrial mapping was performed without CPB.
Comment Intraoperative Mapping Electroanatomic mapping was feasible and useful for intraoperative mapping of VT and other arrhythmias. During the same period, we also used a 256-channel simultaneous mapping system in patients with atrial fibrillation to examine the pattern of the atrial activation and determine the ideal lesion set in the individual patients [3]. The characteristics of the two mapping modalities were compared (Table 1). The major advantage of the electroanatomic mapping was the excellent spatial accuracy that is extremely important in the operation for arrhythmias. Increasing the spatial accuracy may improve the efficacy of the surgical intervention and decrease the invasiveness of the procedure. The excellent spatial accuracy in the electroanatomic mapping is achieved by the simultaneous recording of the electrogram and electrode location, so the electrophysiologic data are memorized with their 3-D geometric data into the computer. The activation and voltage maps are displayed on the 3-D constructed figures that are
NEW TECHNOLOGY
Ventricular tachycardia is then induced by programmed electrical stimulation using the implanted defibrillator or external stimulator with or without a continuous infusion of isoproterenol. Before VT induction, patients are cannulated and undergo cardiopulmonary bypass (CPB) to support any hemodynamic instability during the VT. The induced VT is characterized by the axis and morphologies of the QRS complex and compared with the clinical VTs. Activation and voltage maps are constructed as colorcoded contours on a 3-D reconstructed epicardial figure of the heart. The local activation times are determined using the QRS complex as a reference to construct activation maps. The activation maps are analyzed and compared with the preoperative electrophysiologic data, and the earliest activation site or reentrant circuit of the VT is determined. In the activation mapping of the atrium, reference electrodes are placed on an atrial site to determine the local atrial activation times. In the patients with WolffParkinson-White syndrome, ventricular activation mapping during atrial pacing and atrial activation mapping during ventricular pacing or atrioventricular reentrant tachycardia are performed to localize the accessary pathway across the atrioventricular groove.
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
1288
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
Ann Thorac Surg 2012;93:1285– 8
Table 1. Multisite Simultaneous Mapping and Electroanatomic Mapping
Spatial accuracy
Temporal accuracy
Multisite Simultaneous Mapping
Electroanatomic Mapping
Depends on the number of electrodes and consistency of the electrode location on the maps and the actual location on the heart Excellent
Excellent (direct correlation between the electrograms and electrode location on the heart) Limited in unstable rhythms
NEW TECHNOLOGY
exactly correlated with the local electrograms. The spatial accuracy can be further increased at the region of interest by sampling the data from adjacent multiple sites. In the multisite simultaneous mapping, the spatial accuracy can be increased as the number and resolution of the electrodes is increased. However, the spatial accuracy depends on the consistency of the electrode location on the maps and the actual location on the heart in each patient. The size and figure of the atria or ventricles can vary among patients, and as a result, the location of each electrode may also vary even if electrode-templates are made for individual patients based on the actual size and figure of the patient’s heart. One limitation of electroanatomic mapping is that this technique requires a stable rhythm and is not suitable for unstable arrhythmias, such as atrial fibrillation. Multisite simultaneous mapping using hundreds of electrodes is mandatory to map atrial fibrillation. Another limitation is that the technique requires considerable time. Sustenance of VT for minutes may deteriorate the hemodynamics and make the data acquisition impossible or degenerate the patient into ventricular fibrillation. Hemodynamic support by cardiopulmonary bypass allows the VT to be sustained without any hemodynamic compromise and enables sufficient data acquisition.
Intraoperative Use of the Electroanatomic Mapping System Because the electroanatomic mapping was developed for electrophysiologic studies using catheter electrodes, some refinements are desired for its use in intraoperative mapping. First, the electrode should be mounted on a malleable probe to be held securely or on a wearable ring to access the posterior aspect of the heart. A mouse-type or wireless location controllable probe would be an interesting option to be used in thoracoscopic or pericardioscopic operations. Second, the magnetic field should be wider or adjustable, because the operating table is thicker than the table used in the catheter laboratory and the position of the heart is occasionally changed by tilting
or raising the heart to access the electrode to the posterior or lateral aspect of the heart.
Disclosures and Freedom of Investigation No financial support was received for this study. The authors had full control of the study design, methods used, outcome parameters, data analysis, and production of this report.
References 1. Ideker RE, Smith WM, Wallace AG, et al. A computerized method for the rapid display of ventricular activation during the intraoperative study of arrhythmias. Circulation 1979;59: 449 –58. 2. Cox JL, Canavan TE, Schuessler RB, et al. The surgical treatment of atrial fibrillation. II. Intraoperative electrophysiologic mapping and description of the electrophysiologic basis of atrial flutter and atrial fibrillation. J Thorac Cardiovasc Surg 1991;101:406 –26. 3. Nitta T, Ohmori H, Sakamoto S, Miyagi Y, Kanno S, Shimizu K. Map-guided surgery for atrial fibrillation. J Thorac Cardiovasc Surg 2005;129:291–9. 4. Gepstein L, Hayam G, Ben-Haim SA. A novel method for nonfluoroscopic catheter-based electroanatomical mapping of the heart. In vitro and in vivo accuracy results. Circulation 1997;95:1611–22. 5. Shpun S, Gepstein L, Hayam G, Ben-Haim SA. Guidance of radiofrequency endocardial ablation with real-time threedimensional magnetic navigation system. Circulation 1997;96: 2016 –21. 6. Bhavani SS, Tchou P, Chung M, Fahmy T, Gillinov AM. Intraoperative electro-anatomical mapping and beating heart ablation of ventricular tachycardia. Ann Thorac Surg 2006;82: 1091–3.
Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
Purpose. An electroanatomic mapping system using an electromagnetic navigation technology constructs a 3-dimensional structure of the heart with high geometric accuracy of the data that provides a precise localization of the substrates of arrhythmias. The system was tested for the feasibility and efficacy in intraoperative mapping.
Evaluation. The system was used in 19 patients with ventricular tachycardia or other arrhythmias. The focus or reentrant circuit of the tachycardia was precisely located and a map-guided procedure was successfully performed in all patients. Cardiopulmonary bypass allowed for the tachycardias to be mapped without any hemodynamic compromise. Conclusions. Intraoperative mapping using the electroanatomic mapping system enables a precise localization of the tachycardia substrate. (Ann Thorac Surg 2012;93:1285– 8) © 2012 by The Society of Thoracic Surgeons
M
ultisite simultaneous mapping has been the gold standard in intraoperative electrophysiologic studies [1–3]. The mapping method is capable of displaying and analyzing the activation sequence of the atria or ventricles by recording only a few or even a single cardiac beat. Because the spatial resolution of this method depends heavily on the number and density of the electrodes, it requires hundreds of electrodes with a high density for a precise analysis of the arrhythmias, and the geometric accuracy of the data depends on the spatial consistency of the electrode locations on the actual heart and on the graphic display of the atria or ventricles. An electroanatomic mapping system that has been widely used in catheter laboratories (CARTO System, Biosense Webster, Diamond Bar, CA) uses an electromagnetic navigation technology to construct a 3-dimensional (3-D) structure of the heart and draw an activation map on the figure simultaneously [4, 5]. Although the method requires a stable cardiac rhythm during data acquisition, it allows for a 3-D anatomic reconstruction of the atria and ventricles, with a high geometric accuracy of Accepted for publication Dec 19, 2011. Presented at the Surgical Motion Picture Session of the Forty-seventh Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 31–Feb 2, 2011. Address correspondence to Dr Nitta, Division of Cardio vascular Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan; e-mail: [email protected].
© 2012 by The Society of Thoracic Surgeons Published by Elsevier Inc
the data assured by the magnetic field technology, providing a more precise localization of the focus or reentrant circuit of arrhythmias [6]. We examined the feasibility and efficacy of the electroanatomic mapping system for intraoperative mapping of arrhythmias.
Technology The system uses magnetic field technology to accurately locate the tip of the catheter and simultaneously record the electrogram from the catheter. The system consists of an external ultralow magnetic field emitter mounted in a location pad, a miniature passive magnetic field sensor embedded within a catheter electrode (NAVISTAR catheter, Biosense Webster), and a data processing unit (CARTO, Biosense Webster). The location pad, which is usually placed beneath the operating table, carries 3 coils separately mounted. Each coil generates a magnetic field with a different frequency of 2, 2.2, and 3 KHz with a magnitude of 0.05 to 0.5 Gauss. The magnetic field decays as a function of the distance from the coil. The location sensor in the catheter measures the strength of the magnetic field of each frequency, and the distance from each coil is calculated. The spatial location of the sensor is determined as an intersection of three theoretic spheres with radii that are the distances measured by the sensor (Fig 1). The 3-D figures of the atria and ventricles are reconstructed by connecting neighboring locations determined 0003-4975/$36.00 doi:10.1016/j.athoracsur.2011.12.081
NEW TECHNOLOGY
Description. The strength of the magnetic field is measured by a location sensor with three different frequencies generated by a location pad placed beneath the operating table, and the spatial location of the sensor is determined. By roving the catheter on the heart while the local electrogram is recorded simultaneously, the 3-dimensional figure of the heart is reconstructed and an activation or voltage map is generated.
1286
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
Ann Thorac Surg 2012;93:1285– 8
Fig 1. The magnetic field (shaded area) is effective with a 1-mm spatial accuracy within a theoretic cylinder with a 10-cm radius and 20-cm height located 18 cm above the location pad. NEW TECHNOLOGY
by roving the catheter over the epicardium or endocardium of the heart (Fig 2). The catheter also has a locatable electrode composed of the tip and ring electrodes, and the local electrogram is recorded simultaneously. The electrophysiologic data are analyzed and the activation or voltage map is generated. The map is superimposed on the figure as color-coded contours on a real-time basis or displayed as a dynamic propagation map. Recent versions of the system, CARTO XP and CARTO 3, have a function called CARTOMERGE that enables preoperative computed tomography or magnetic resonance images to be used to reconstruct the endocardial and epicardial surfaces of the heart and then be merged with the activation or voltage maps (Fig 3).
Fig 3. This epicardial activation map constructed by electroanatomic mapping shows the heart in the left anterior oblique cranial projection. The intraoperatively recorded data were superimposed on preoperatively recorded computed tomography scan images. The earliest activation of the ventricular tachycardia is located at the high lateral left ventricle around the origin of the left circumflex coronary artery. IM ⫽ intermediate artery; LAA ⫽ left atrial appendage; LAD ⫽ left anterior descending artery; LCA ⫽ left coronary artery; LCX ⫽ left circumflex artery.
Technique Preoperative Settings Before the operation, the location pad is properly placed underneath the operating table. An external reference patch that provides location reference data to the CARTO system is also placed on the patient’s back, just underneath the heart. The heart should be positioned 18 to 38 cm above the location pad and within a 10-cm-radius circle from the center of the pad to assure a 1-mm spatial accuracy (Fig 1). The feasibility of the CARTO system must be checked before the patient’s chest is scrubbed. An unsterilized NAVISTAR catheter is roved over the anterior chest of the patient, and the position of the patient or the location pad is adjusted to obtain an effective magnetic field to sufficiently cover the atria or ventricles. Electrocardiograms from the limbs leads and a left-sided precordial lead, usually V5, are displayed on the system to monitor the QRS or P wave morphologies during the data acquisition.
Intraoperative Mapping
Fig 2. Simultaneous recording of electrograms and the location of the electrode are shown. The NAVISTAR catheter electrode is roved directly on the ventricular epicardium.
The atrial or ventricular epicardium is mapped by roving the NAVISTAR catheter electrode directly around on the epicardium to simultaneously record the local electrograms and location of the electrode (Fig 2). In patients with ventricular tachycardia (VT), the ventricular epicardium is mapped during sinus rhythm or pacing to construct voltage maps and record fractionated or other abnormal electrograms that suggest delayed activation.
Ann Thorac Surg 2012;93:1285– 8
Clinical Experience Intraoperative mapping using the CARTO system was approved by the Institutional Review Board. Written informed consent was received from all patients before the intraoperative electrophysiologic study and operation.
Patient Characteristics Between March 2006 and May 2011, the CARTO system was used for intraoperative mapping in 19 patients (15 men and 4 women) who were aged an average of 56 ⫾ 18 years (range, 23 to 79 years). Fifteen patients had medically refractory VT and underwent map-guided surgical intervention for VT. All patients had undergone one to eight failed sessions of catheter ablation, including epicardial ablation in 4 patients, before the operation. Two patients had ischemic VT and 13 had nonischemic VT. Nine patients had a defibrillator implanted at the time of the operation. Two patients with sick sinus syndrome and partial atrial standstill underwent voltage mapping of the atria to identify an epicardial location with remaining viable myocardium for a myocardial electrode implantation and were implanted with a pacemaker. One patient had a recurrent conduction over a posterior septal atrioventricular accessary pathway after multiple sessions of catheter ablation and underwent a surgical ablation of the accessary pathway. Another patient, with persistent atrial tachycardia from the age of 5 years old, underwent a thoracoscopic and map-guided procedure.
1287
Feasibility of Intraoperative Electroanatomic Mapping Patients were placed supine on the operating table and underwent a median sternotomy, except for 1 patient who underwent a thoracoscopic procedure from a right anterior oblique position. The thicknesses of the operating table and the above matted pad were approximately 10 cm and 5 cm, respectively. Because the position of the location pad was properly adjusted preoperatively to allow the electromagnetic field to effectively cover the entire epicardium of the atria or ventricles, the electromagnetic technology was stable throughout the period of the mapping, and the intraoperative mapping was effectively accomplished in all patients. The duration required for the intraoperative mapping ranged from 20 to 80 minutes. No deaths or complications occurred related to the intraoperative mapping.
Hemodynamic Support by Cardiopulmonary Bypass The number of QRS morphologies of the VT induced and mapped intraoperatively ranged from 1 to 4. When the morphology of the VT changed into a different morphology during mapping, the electrograms were saved as a different data set and another activation map for the VT was constructed. Hemodynamic support with CPB was extremely useful to allow for the sustenance and mapping of rapid and hemodynamically unstable VTs for more than 30 minutes. None of the VTs deteriorated into ventricular fibrillation during the mapping. Because the accessary pathway was located at the posterior septum in the patient with Wolff-ParkinsonWhite syndrome, intraoperative mapping was performed with the aid of CPB and a heart positioner. This technique enabled good exposure of the region while maintaining stable hemodynamics and ensuring the geometric accuracy of the data. In the other patients, the atrial mapping was performed without CPB.
Comment Intraoperative Mapping Electroanatomic mapping was feasible and useful for intraoperative mapping of VT and other arrhythmias. During the same period, we also used a 256-channel simultaneous mapping system in patients with atrial fibrillation to examine the pattern of the atrial activation and determine the ideal lesion set in the individual patients [3]. The characteristics of the two mapping modalities were compared (Table 1). The major advantage of the electroanatomic mapping was the excellent spatial accuracy that is extremely important in the operation for arrhythmias. Increasing the spatial accuracy may improve the efficacy of the surgical intervention and decrease the invasiveness of the procedure. The excellent spatial accuracy in the electroanatomic mapping is achieved by the simultaneous recording of the electrogram and electrode location, so the electrophysiologic data are memorized with their 3-D geometric data into the computer. The activation and voltage maps are displayed on the 3-D constructed figures that are
NEW TECHNOLOGY
Ventricular tachycardia is then induced by programmed electrical stimulation using the implanted defibrillator or external stimulator with or without a continuous infusion of isoproterenol. Before VT induction, patients are cannulated and undergo cardiopulmonary bypass (CPB) to support any hemodynamic instability during the VT. The induced VT is characterized by the axis and morphologies of the QRS complex and compared with the clinical VTs. Activation and voltage maps are constructed as colorcoded contours on a 3-D reconstructed epicardial figure of the heart. The local activation times are determined using the QRS complex as a reference to construct activation maps. The activation maps are analyzed and compared with the preoperative electrophysiologic data, and the earliest activation site or reentrant circuit of the VT is determined. In the activation mapping of the atrium, reference electrodes are placed on an atrial site to determine the local atrial activation times. In the patients with WolffParkinson-White syndrome, ventricular activation mapping during atrial pacing and atrial activation mapping during ventricular pacing or atrioventricular reentrant tachycardia are performed to localize the accessary pathway across the atrioventricular groove.
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
1288
NEW TECHNOLOGY NITTA ET AL ELECTROANATOMIC MAPPING
Ann Thorac Surg 2012;93:1285– 8
Table 1. Multisite Simultaneous Mapping and Electroanatomic Mapping
Spatial accuracy
Temporal accuracy
Multisite Simultaneous Mapping
Electroanatomic Mapping
Depends on the number of electrodes and consistency of the electrode location on the maps and the actual location on the heart Excellent
Excellent (direct correlation between the electrograms and electrode location on the heart) Limited in unstable rhythms
NEW TECHNOLOGY
exactly correlated with the local electrograms. The spatial accuracy can be further increased at the region of interest by sampling the data from adjacent multiple sites. In the multisite simultaneous mapping, the spatial accuracy can be increased as the number and resolution of the electrodes is increased. However, the spatial accuracy depends on the consistency of the electrode location on the maps and the actual location on the heart in each patient. The size and figure of the atria or ventricles can vary among patients, and as a result, the location of each electrode may also vary even if electrode-templates are made for individual patients based on the actual size and figure of the patient’s heart. One limitation of electroanatomic mapping is that this technique requires a stable rhythm and is not suitable for unstable arrhythmias, such as atrial fibrillation. Multisite simultaneous mapping using hundreds of electrodes is mandatory to map atrial fibrillation. Another limitation is that the technique requires considerable time. Sustenance of VT for minutes may deteriorate the hemodynamics and make the data acquisition impossible or degenerate the patient into ventricular fibrillation. Hemodynamic support by cardiopulmonary bypass allows the VT to be sustained without any hemodynamic compromise and enables sufficient data acquisition.
Intraoperative Use of the Electroanatomic Mapping System Because the electroanatomic mapping was developed for electrophysiologic studies using catheter electrodes, some refinements are desired for its use in intraoperative mapping. First, the electrode should be mounted on a malleable probe to be held securely or on a wearable ring to access the posterior aspect of the heart. A mouse-type or wireless location controllable probe would be an interesting option to be used in thoracoscopic or pericardioscopic operations. Second, the magnetic field should be wider or adjustable, because the operating table is thicker than the table used in the catheter laboratory and the position of the heart is occasionally changed by tilting
or raising the heart to access the electrode to the posterior or lateral aspect of the heart.
Disclosures and Freedom of Investigation No financial support was received for this study. The authors had full control of the study design, methods used, outcome parameters, data analysis, and production of this report.
References 1. Ideker RE, Smith WM, Wallace AG, et al. A computerized method for the rapid display of ventricular activation during the intraoperative study of arrhythmias. Circulation 1979;59: 449 –58. 2. Cox JL, Canavan TE, Schuessler RB, et al. The surgical treatment of atrial fibrillation. II. Intraoperative electrophysiologic mapping and description of the electrophysiologic basis of atrial flutter and atrial fibrillation. J Thorac Cardiovasc Surg 1991;101:406 –26. 3. Nitta T, Ohmori H, Sakamoto S, Miyagi Y, Kanno S, Shimizu K. Map-guided surgery for atrial fibrillation. J Thorac Cardiovasc Surg 2005;129:291–9. 4. Gepstein L, Hayam G, Ben-Haim SA. A novel method for nonfluoroscopic catheter-based electroanatomical mapping of the heart. In vitro and in vivo accuracy results. Circulation 1997;95:1611–22. 5. Shpun S, Gepstein L, Hayam G, Ben-Haim SA. Guidance of radiofrequency endocardial ablation with real-time threedimensional magnetic navigation system. Circulation 1997;96: 2016 –21. 6. Bhavani SS, Tchou P, Chung M, Fahmy T, Gillinov AM. Intraoperative electro-anatomical mapping and beating heart ablation of ventricular tachycardia. Ann Thorac Surg 2006;82: 1091–3.
Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.