A Novel Mapping System for Panoramic Mapping of the Left Atrium

Objectives This study sought to use a novel panoramic mapping system (CARTOFINDER) to detect and characterize drivers in persistent atrial fibrillation (AF). Background Mechanisms sustaining persistent AF remain uncertain. Methods Patients undergoing catheter ablation for persistent AF were included. A 64-pole basket catheter was used to acquire unipolar signals, which were processed by the mapping system to generate wavefront propagation maps. The system was used to identify and characterize potential drivers in AF pre- and post-pulmonary vein (PV) isolation. The effect of ablation on drivers identified post-PV isolation was assessed. Results Twenty patients were included in the study with 112 CARTOFINDER maps created. Potential drivers were mapped in 19 of 20 patients with AF (damage to the basket and noise on electrograms was present in 1 patient). Thirty potential drivers were identified all of which were transient but repetitive; 19 were rotational and 11 focal. Twenty-six drivers were ablated with a predefined response in 22 of 26 drivers: AF terminated with 12 and cycle length slowed (≥30 ms) with 10. Drivers with rotational activation were predominantly mapped to sites of low-voltage zones (81.8%). PV isolation had no remarkable impact on the cycle length at the driver sites (138.4 ± 14.3 ms pre-PV isolation vs. 137.2 ± 15.2 ms post-PV isolation) and drivers that had also been identified on pre-PV isolation maps were more commonly associated with AF termination. Conclusions Drivers were identified in almost all patients in the form of intermittent but repetitive focal or rotational activation patterns. The mechanistic importance of these phenomena was confirmed by the response to ablation.

suggesting that current methods to ablate AF beyond the pulmonary veins (PV) are ineffective (6) there remains great interest in understanding and interrupting the mechanisms sustaining AF.
CARTOFINDER is a novel mapping system that uses the CARTO platform (Biosense Webster, Inc., Baldwin Park, California) as its foundation. It has been developed to map wavefront propagation using multipolar catheters, such as whole-chamber basket catheters, in an open format where location points and electrograms can be scrutinized. Early data using this system have suggested the presence of rotational activity in AF potentially compatible with rotors (7).
This study used the CARTOFINDER system to determine whether there were activation patterns suggestive of localized drivers in AF, in the form of rotational activity or focal activations, which were either stable or recurrent. To distinguish drivers from passive phenomena we hypothesized that they would be unaffected by ablation at remote sites, such as PV isolation, and would bring about a significant response when ablated. Through catheter manipulation the basket catheter was positioned to achieve the best possible atrial coverage. Once in a stable position a recording was taken with CARTOFINDER. A minimum of 2 recordings was taken per patient pre-PV and post-PV isolation. Attempts were made to reposition the basket catheter between recordings to further optimize position, but also just to vary the position of electrodes and orientation of splines slightly. If the operator believed that further catheter positioning could allow for better or different coverage further recordings were taken in a different position. In cases where the coronary sinus activation pattern was predominantly proximal to distal and the shortest LA cycle length (CL) was believed to be at the septum, additional mapping of the right atrium (RA) was permitted following PV isolation.
The CARTOFINDER system provides an evaluation of the coverage achieved as a percentage of the chamber surface area. This allows coverage to be compared between positions and so quantitatively guide catheter repositioning. The CARTOFINDER system calculates coverage through identifying the basket electrodes that are within 10 mm of the geometry. These are then projected onto the geometry and labeled as covering an area with a 10-mm radius.
The coverage achieved including these electrodes is then taken as a percentage of the geometry surface area excluding vascular and valvular structures. A potential driver was defined as repetitive patterns of activation that was either focal with radial activation over $2 consecutive wavefronts or rotational activity with $1.5 rotations of 360 (because these definitions have been used by others previously, NCT02113761). We also assessed: 1) the stability of these phenomena in terms of how many cycles were completed with each occurrence; 2) whether they were repetitive during the recording in which they were observed; and 3) how consistently these phenomena were observed over serial re- Recordings were taken before and after PV isolation to allow comparison of activation patterns. Recordings taken following PV isolation were used to guide ablation at sites identified as potential drivers.
The CL at the driver site was determined manually over the 30-s recording and was the mean interval between atrial complexes on unipolar electrograms recorded on the basket catheter. Where potential drivers were observed both pre-and post-PV isolation, the CL at the driver sites was recorded pre-and post-PV isolation and these measurements were compared.
AF CL was documented pre-PV isolation and monitored following isolation of each PV pair. AF CL was measured over 30 cycles using the PentaRay NAV catheter positioned in the LA appendage (LAA) (9).
Following PV isolation a 20-min waiting period was observed before ablation of potential drivers was commenced in the LA body. This was to avoid any delayed effect potentially attributable to PV isolation, which might influence AF CL during ablation at the sites of potential drivers.
To monitor the effect of ablation at the possible driver sites as identified on the post-PV isolation maps, the AF CL was again monitored through the PentaRay NAV catheter positioned in the LAA.
Although small changes in CL (usually 5 to 6 ms) have been used previously to determine a response to ablation (10,11), it was thought that ablation of a clear driver ought to have a more substantial effect.
Confirmed drivers were therefore defined as sites where ablation resulted in CL slowing of $30 ms, organization of the rhythm to an atrial tachycardia (AT), or termination to sinus rhythm. Ablation at driver sites was delivered with a contact force of 5 to 40 g, with a power of 30 to 40 W.
Ablation at sites with either focal or rotational activation was delivered as discrete focal points, aiming for the center of the focal or rotational activation.

RESULTS
Twenty patients were included in this study. Baseline characteristics are shown in Table 1    There was at least 1 driver with a positive response to ablation meeting the study definition in all patients.

RESPONSE TO ABLATION OF CONFIRMED DRIVERS.
Ablation at 12 of the 22 confirmed driver sites resulted in AF termination (Figures 2A to 2D), which accounted for 12 of the 19 patients (63.2%; 5 terminated to sinus rhythm and 7 to AT). The 7 ATs (3 cavo-tricuspidisthmus dependent flutter, 2 mitral-isthmus dependent flutter, and 2 roof-dependent flutter) were all successfully ablated with termination to sinus  Table 2.    proportion of patients post-PV isolation. The 2 potential explanations for this are either that we failed to detect drivers pre-PV isolation, or that there were genuinely more drivers present post-PV isolation. Several studies have shown an organizing effect of PV isolation (10,14). It is possible that PV isolation may eliminate areas of wavebreak and organizes wavefronts to form re-entry (15  Number of times a confirmed AF driver with either rotational (light grey) or focal activity (dark grey) was seen consecutively in a 30-s recording. Abbreviation as in Figure 1.
identify and characterize drivers in AF. These were focal or rotational activity, which were intermittent but recurred at the same sites repeatedly. Rotational activity often occurred in areas of low voltage suggesting structural remodeling. Targeting these drivers terminated AF in two-thirds of patients and slowed CL substantially in the remainder.
TRANSLATIONAL OUTLOOK: This study demonstrated clinical utility of the CARTOFINDER mapping system in targeting AF drivers. The endpoints were therefore electrophysiological.
Randomized controlled studies with long-term follow-up are needed to determine whether targeting these impacts outcomes.
The ideal way to identify drivers also remains to be seen and further comparisons of the findings with the currently available technologies remains desirable.