Initial Experience with the Carto® 3 Navigation System (See Full Title Below)

Initial Experience with the Carto^® 3 Navigation System: System Provides Enhanced Efficacy and Precision of Electroanatomical Mapping

Electrophysiologists at Gagnon Cardiovascular Institute were the first in the nation to use a new 3-D mapping system, acquiring the system in November 2009. In this article, the authors describe their experience using this advanced imaging technology. For more than a decade, electroanatomical navigation and mapping have vastly expanded the electrophysiologist’s ability to diagnose, treat, and cure an ever-expanding variety of cardiac rhythm disturbances. As with other mapping technologies, the early Carto navigation system (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA) enabled registration of electrical activity during sinus rhythm, as well as during various tachydysrhythmias, to create simultaneous activation, propagation, and voltage maps. Acquisition of point-by-point electrograms also permitted recreation of three-dimensional anatomic chambers and boundaries. Placement of electromagnets beneath the fluoroscopy table on which the patient is positioned, with creation of an extremely low magnetic field, enables the detection of sensors (copper wire coiled over a Ferrite cylinder in a unique pattern) incorporated into the tips of the large domed, deflectable, mapping-ablation catheters, in space. Utilization of aeronautical, global positioning system (GPS) based triangulation principles permits localization and registration of the catheter tip along six degrees of freedom in space including position (x, y, z) and rotation (roll, pitch, and yaw) to enable reconstruction of desired anatomical structures along with the site specific electrical activity.^1,2 Expanding beyond this, Biosense Webster’s Carto 3 navigation system has enhanced features to enable faster and broader mapping modalities. Nine magnets are positioned below the patient table in a “Locator Pad” and six reference patches are placed on the patient’s body, enabling a greater volume to be explored as well as better compensation for patient movements. The system also has the ability to use a gated or non-gated electrical reference. The non-gated timing allows for catheter movement to be tracked during fluoroscopy. While displaying and recording high quality electrograms, Carto 3 has the ability to visualize, highlight and pace from any electrode of a catheter connected to the system. While interrogation and programming of implanted pacemakers and automatic cardioverter defibrillators should preferably be undertaken prior to initiation of mapping, undesirable interactions are not common during use of the Carto 3 system. However, should such interventions be required during use of Carto 3 and the implanted rhythm control device not be detected, the Locator Pad may be temporarily deactivated. The system also now enables faster, near-CT quality anatomical recreation and catheter tip and curve tracking, while providing easier patient interface connections with automatic recognition of the type of catheters being utilized. The system incorporates a more intuitive drop-down menu to enable faster case set-ups and data manipulation. We think one of the most impressive features is the ability to create “Fast Anatomical Mapping (FAM)” without the need to select, confirm, and save electrogram recordings. Slight fluctuations in impedance measurements with the chosen mapping catheter enable construction of anatomical chambers without the need to select, record, and manipulate electrogram recordings. Although the system requires use of Biosense Webster electrode catheters, anatomical reconstruction can be facilitated, especially in the left atrium with the use of 20-pole circular (Lasso^®) electrode catheters, nearly as fast as one can move the catheter. Furthermore, FAM can be performed simultaneously with recording of localized electrical activity to enable more accurate electroanatomical representations. Several technologies also complement capabilities of the Carto 3 system. Impedance measurements may be visualized directly on the Carto 3 monitor, which can help confirm whether or not the mapping catheter is inside a vessel during mapping. In addition, during current delivery, the ablation parameters can now be monitored in real time on the screen. The ability to combine anatomical images from pre-segmented CT scans of selected chambers with electrogram derived3 and with Carto 3 FAM images improves chamber visualization. In addition, three-dimensional anatomical shells from ultrasound imaging can be recorded with CartoSound^™ (Biosense Webster, Inc.) technology and merged with the CT and FAM images to optimize anatomical recreation. Localization of adjacent structures (e.g., the esophagus) with the CartoSound system,⁴ and the EsophaStar™ esophageal mapping electrode (Biosense Webster, Inc.) can potentially minimize injury to collateral structures. Figure 1 shows a Carto 3 FAM projected in the posteroanterior (PA) orientation with radiofrequency (RF) lesions sets delivered to the antrum of the right pulmonary veins (PVs) – left atrial (LA) junction and the left superior and left inferior pulmonary veins as well as the left carina in a man with atrial fibrillation. The CartoSound 3 delineation of the esophagus is shown running closer to the right-sided PV-LA junction. Applications of RF energy (bold, red dots) were placed so as to avoid overlapping the esophageal projection as much as possible. Tracking of multiple mapping catheters is now possible. A hybrid of magnetic location technology and “current-based” impedance data enables real time tip and curve identification and tracking (termed Advanced Catheter Location, or ACL). In more two dimensional based procedures, such as slow AV pathway ablation in atrioventricular nodal reentrant tachycardia, the distance between electrogram recordings of interest on specific catheters (e.g., His bundle during slow AV pathway modification procedures) and the ablation catheter can be better judged to improve safety and efficacy. Such catheter tracking permits better targeting of sites to deliver RF energy in more complex, three dimensional based procedures, such as pulmonary vein isolation. The system allows the continued integration of catheter position and electrogram data to determine specific sites at which radiofrequency energy should be applied to achieve desired outcomes. Either from the start, or after initial antral ablation, residual PV-LA connections, identified as the most fused electrograms on circular 20-pole Lasso catheters can be highlighted and easily visualized. The ablation catheter tip can be manipulated to approximate the “lit up” electrodes to hasten successful outcomes. Several figures highlight the utility of FAM incorporated with other features of the Carto 3 electroanatomical mapping system. Figure 2 highlights a PA projection of the left atrial and pulmonary venous anatomy in a man with paroxysmal atrial fibrillation (AF) prior to ablation. The upper grey image depicts a FAM post transseptal catheterization and after mapping of the designated structures. As indicated, a 20-pole Lasso catheter is situated in the left superior pulmonary vein. A bidirectional mapping-ablation ThermoCool catheter is positioned in the right superior pulmonary vein. A 10-pole catheter positioned in the coronary sinus is visible. Representations of the esophagus are also present. The one with green vertical lines was obtained from CartoSound intracardiac ultrasound recordings, which have been integrated with the FAM and stop at the inferior margin of the left atrium itself. Alongside this structure is the esophagus as mapped with the Esophastar catheter, passed via the oropharyngeal route to the gastroesophageal junction twice at the onset of the study. The FAM images have been enhanced with proprietary smoothing software at the time of the study. Below, in pale blue, is an image from the CT scan of the left atrium and pulmonary veins from the same patient. The FAM and CT images correlate quite closely. A PA cranial oriented projection FAM in another individual undergoing antral pulmonary vein isolation is highlighted in Figure 3. The ThermoCool catheter is present at the antrum of the left inferior pulmonary vein and the Lasso catheter is positioned slightly inside the vein. Sites where RF energy has been delivered are designated as bold red dots. The distal aspect of the ThermoCool catheter is slightly proximal to poles 11 and 12 of the Lasso catheter where residual LA-PV electrical communication was suspected to be present. The mapped esophagus is seen to run closer to the right-sided pulmonary veins. The coronary sinus catheter is in close proximity to the left inferior pulmonary vein. On the right side of the figure, real time electrogram recordings from the reference bipole in the coronary sinus and from 10 bipolar recordings from the Lasso catheter are arranged vertically. A shallow right anterior oblique (RAO) cranial projection of an integrated CT scan and FAM of the left atrium and pulmonary veins in a woman with paroxysmal AF is depicted in Figure 4. A 20-pole Lasso catheter is present in the right superior pulmonary vein. The distal pole of the ThermoCool ablation catheter is abutting poles 5-7 of the Lasso catheter, targeting specific left atrial-pulmonary vein potentials. Toward the bottom of the figure, the electrodes and the shaft of a decapolar catheter which had been positioned in the coronary sinus are seen. The area of blue on the right of the figure demonstrates left atrial appendage registration from a previously obtained CT scan using CartoMerge^™ technology.³ Electrocardiographic tracings of monomorphic ventricular tachycardia in a woman undergoing electroanatomical mapping and ablation of right ventricular outflow tract tachycardia are seen on the left side of Figure 5. The middle panel depicts a merged FAM and activation map of the right ventricle in the RAO view. The right panel is a merged FAM and activation map of the right ventricle in the left anterior oblique (LAO) projection. The bold, red dots highlight the zone of earliest (pre-QRS) activity at the septal region where radiofrequency energy was delivered. The tachycardia terminated with the first application. Additional RF energy was administered to enlarge the ablation zone to ensure long-lasting efficacy. An RAO caudal projection with a sagittal cut-away view of a merged FAM and CT scan looking at a common left pulmonary vein in a woman undergoing pulmonary vein is shown in Figure 6. A 20-pole Lasso catheter is located at the LA-PV junction. The ThermoCool catheter is positioned at pole 9 of the Lasso catheter where an electrogram of interest was recorded. The bold red dots indicate points in the antrum where RF energy has been delivered. A FAM in the LAO projection of the right atrium and coronary sinus merged with an activation sequence map during typical atrial flutter in a patient is illustrated in Figure 7. Counterclockwise activation (red-purple) is present. Catheter positioning can be tracked with ACL. A decapolar catheter can be seen positioned in the coronary sinus. Regions where His bundle potentials are recorded are represented as flesh-colored dots. A ThermoCool mapping-ablation catheter is positioned at this area. A non-ablation, tip deflectable quadripolar catheter can be seen positioned in the posteroseptal region of the cavotricuspid isthmus. Carto 3 technology also enables evaluation of continuous fragmented electrical (CFAE) activity during atrial fibrillation⁵ to be mapped through an automated process and displayed in a color-coded manner on the electroanatomical maps. The system will highlight areas of the greatest frequency of, as well as the shortest interval between, such signals, using a nominal cut-off voltage value of 0.05–0.15 mV during 2.5-second sampling windows. In determining the presence or absence of CFAE, deflections within the voltage range are considered as CFAE if the signal duration is less than 50 ms and not greater than 120 ms. Each interval between such complexes in the 2.5-second window is considered a CFAE recording. If desired, the operator can alter these nominal values. An anteroposterior (AP) electroanatomical projection with superimposed CFAE mapping of the left atrium and pulmonary veins in a man with persistent AF post pulmonary vein isolation is shown in Figure 8. The CFAE map is overlayed onto the previously registered FAM. The esophagus is seen close to the right-sided pulmonary veins as recorded with CartoSound and Esophastar imaging. The red-shaded areas indicate areas where the shortest intervals between two consecutive CFAE recordings, referred to as the shortest complex interval (SCI), were recorded in the left atrium. The interval confidence level (ICL) quantitates the number of CFAE intervals sampled over 2.5-second intervals. Small, lighter red dots represent areas where the ICL is greatest (more than 7 complexes) and the pale blue dots indicate where an intermediate number of complexes (4-7 complexes) are present per 2.5-second interval. The bold, red dots demarcate areas where CFAE directed RF energy was applied. In addition, voltage measurements during real-time mapping and ablation can be utilized to select targets of interest for ablation as well as the effects of ablation. Zones of low amplitude electrograms (1.5 mV) to deliver RF energy may be targeted to treat various ventricular tachydysrrhythmias with greater accuracy and safety.⁶ Substantial declines in local electrogram voltage monitored during RF energy application may serve as markers of adequate localized tissue injury to achieve desired effects. Figure 9 highlights a merged, caudal view of a FAM and sinus rhythm voltage map of the left ventricle in a patient with a prior myocardial infarction and recurrent sustained monomorphic ventricular tachycardia. Areas of dense scar are demarcated in red (voltage Acknowledgement. The authors would like to thank Sharad Rathod, BS, MBA, Amit Patel, BS, MBA, and Timothy Meyn, BS of Biosense Webster, Inc. for their invaluable technical assistance.

References

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Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board. Disclosure: The authors report no financial interest in the products being discussed or other relationships which need to be disclosed.