In the setting of persistent atrial fibrillation (AF), the current ablation strategy combines pulmonary vein (PV) isolation and substrate modulation. Substrate modulation can be performed either by linear lesion deployment or by complex fractionated atrial electrogram (CFE) elimination. These two substrate modulation methods can be either exclusive or complementary. However, although the methodology and end-point of linear lesion deployment have been clearly established, CFE identification and elimination is a somewhat subjective and poorly reproducible technique.1-10 Furthermore, even though identification methods of CFEs using dedicated software have recently been developed,11 their utilisation is empirical and arbitrary since the exact role played by CFEs within the AF process, their underlying mechanism and therefore their identification in humans remain elusive.
The OneMap™ tool (St Jude Medical; St Paul, MN), a new software feature of the EnSite Velocity™ System (St Jude Medical), was created for simultaneous collection of anatomical and electrical data points to facilitate ablation procedures. The OneMap tool, combined with the new Inquiry™ AFocus™ II duodecapolar diagnostic catheter (DDC) (St Jude Medical), provides faster data collection with the necessary detail to efficiently diagnose complex arrhythmias. A preliminary study was performed using the OneMap tool to compare acquisition criteria, the time needed to create maps, the number of collected points and the relevance of CFE mapping with DDC versus a 4mm irrigated ablation catheter (ABL), the Therapy™ Cool Path™ Duo (St Jude Medical).
Ten patients undergoing persistent AF were enrolled. After left atrial scanning, the DDC was used first for 3D anatomy reconstruction. A CFE map was simultaneously and automatically acquired for each patient using the OneMap tool. A second CFE map was created with the ABL as a reference.
OneMap is a powerful tool that enables the collection of points from one or multiple (up to 128) electrodes on single or multiple catheters. It also enables the creation of multiple anatomical maps and electrical activity of the cardiac cavity. The electrograms are recorded with a 2kHz sampling rate, which improves the signal quality (higher resolution). Moreover, the precise spatial and anatomical visualisation provides repeatable catheter location information. The Inquiry AFocus II is a diagnostic catheter that provides more detailed geometry and high-density mapping with a double spiral. The Therapy Cool Path Duo is a 4mm ABL. The tip of this catheter has 12 holes to provide homogeneous irrigation and low temperatures during radiofrequency abllation (RFA), with lower flow rates of 10ml/minute.
Mapping with the OneMap Tool
A multiple-pole diagnostic catheter is introduced into the left femoral vein and placed on the coronary sinus ostia. One electrode on this catheter is considered as a reference during left atrium mapping. An SL0™ sheath (St Jude Medical) is introduced into the right femoral vein to perform a transseptal puncture with a Brockenbrough needle in order to reach the left atrium. The DDC is then brought inside the SL0 sheath and positioned in the left atrium to map geometry and electrical activity (see Figure 1). The CFE mapping parameters are adjusted as follows: four seconds to collect CFE data in a specific zone; sensitivity threshold to detect CFE activity and interior/exterior projection. We wanted to ensure we captured at least four seconds, as studies have demonstrated that at least four-second signal durations are necessary for accurate CFE identification. For the mapping, the left atrium is split into 11 segments: ostium and antrum of pulmonary veins, posterior, anterior and lateral walls, the floor, the roof, the septum and the appendage. The anatomy of each region is continuously recorded, while the CFE, the amplitude of which is at the sensitivity threshold, is acquired when the catheter is immobilised for four seconds. As soon as all zones are completed, the anatomical and electrical map is saved on the EnSite Velocity System (see Figure 2).
For both catheters, the time needed to create a map, the number of collected points and the number of CFE regions were registered. The correlation between CFE maps was also analysed.
The results of this study are presented in Tables 1 and 2. The two reconstructed anatomies can be superimposed with computed tomography (CT). With the DDC, more points were collected (485±173 versus 183±37) and the time needed to create the CFE maps was shorter (12±4 versus 24±2 minutes). Thirty-nine zones were detected with the DDC and 35 with the ABL. The correlation rate was 80%; however, four additional regions were detected with the DDC (an increase of 11%).
Advantage Of Complex Fractionated Atrial Electrogram Maps
The ablation of persistent AF remains a challenge for the practitioner. The procedures are long and are based on extensive ablation of triggers (pulmonary veins) and substrate (CFE). The role of CFE in maintaining AF is well demonstrated and it therefore represents a good target.12,13 Making an automatic CFE map enables quantification of the affected area, localisation of the substrate to be ablated and establishment of the chronology of each patient's ablation.14-16 Thus, the presence of fractionated potentials at the vein antrum level will prompt the decision to perform their anatomic ablation by widely circling them. The fractionated potential area also appears to be a sign of the degeneration of the atrial wall and a prognostic factor for arrhythmia evolution.
Mapping Techniques and a New Diagnostic Tool
The currently available software for the acquisition of fractionated potentials of 3D navigation systems is reliable.17 It is based on a signal analysis algorithm that incorporates duration, amplitude and fractioning of the signal. The distal tip of the catheter was applied to the atrial wall at each location for four seconds to ensure its stability and the signals collected. The result of the analysis appears in coloured areas on a 3D geometry of the left atrium obtained previously or simultaneously. Making these maps is often a fastidious process, requiring extensive mapping of the atrium, which increases the duration of the procedure. On the other hand, the acquisition occurs through a 4mm-long ablation catheter and a vast area of the atrium remains unexplored. Several multi-electrode catheters, notably circular decapolar or pentabranch catheters, have already been trialled for exploration of the left atrium signal, with good correlation; 18 however, their geometry and incompatibility with navigation systems have prevented their use becoming widespread.
The new circular catheter under discussion includes a double coil enabling the simultaneous collection of 20 points in a 3cm2 circular area. The navigation software, by measuring spatial interpolation between electrodes, rejects those points estimated to be too far from the area. The risk of wrongly estimating the CFE areas by faulty contact of some dipoles is minimal. In our experience, we have easily and rapidly recorded the CFE areas at the veins, floor, roof and septum levels without fear of losing our transseptal access, thanks to the catheter's circular shape. Recording at the vein ostia and antrum levels has also been facilitated. The localisation of the CFEs matched the template, but their number and area were larger, enabling mapping and therefore a more precise ablation. Conversely, two regions are difficult to access with a lesser contact on the mitral ring (lateral side) and the anterior wall. At these sites, the ablation catheter performed better, explaining our results. A bi-directional deflection would improve the handling of this catheter and enhance the mapping of these tricky regions. The acquisition times were faster with the high-density mapping catheter in all cases. The completion of a map was achieved in 12 minutes on average compared with 24 minutes for a standard catheter.
The principal limitation is that, due to the small population size, we have not been able to measure the impact of more extensive mapping of the procedure's instant and long-term success. This could be addressed by additional prospective multicentre studies.
The two reconstructed anatomies can be superimposed in this preliminary study: the DDC demonstrated that automatic CFE mapping using the OneMap tool is feasible, with 80% correlation to ABL mapping. Also, acquisition criteria are improved. The OneMap tool reduces the overall time required to create a map by 50% and cuts the procedure time in half from 24 to 12 minutes. The high quality of the signal makes it possible to more precisely locate the CFE zones.