Continuous Multi-Electrode Mapping: Single-Center Experience

The field of cardiac electrophysiology has evolved significantly over the past two decades. We are now able to treat more complex arrhythmias with better safety, efficacy, and efficiency. Great advances have occurred in catheter technology, especially with contact force sensing catheters, which improve efficacy and efficiency of catheter ablation. One of the most important breakthroughs in our field, however, has been the creation and constant evolution of electroanatomic mapping (EAM) systems. The first EAM systems were developed in the 1990s and allowed for the creation of activation maps of clinical arrhythmias, lesion tagging, and non-fluoroscopic catheter navigation. EAM has revolutionized the field of electrophysiology, allowing us to treat ever more complex arrhythmias with greater precision and efficiency. 

Newer generations were more precise, and have allowed detailed mapping and 3D reconstruction of cardiac anatomy while integrating other imaging modalities such as cardiac CT, MRI, and real-time intracardiac echocardiography.  

In spite of advancements in anatomic reconstruction, point-by-point mapping of arrhythmias can be challenging and time consuming. The first technology created to address this issue was multi-electrode mapping (MEM), whereby multiple electroanatomic points could be obtained simultaneously with multi-pole catheters (i.e., circular mapping catheter, PentaRay NAV catheter, or decapolar catheter). This significantly reduced the time required to map certain arrhythmias, and also facilitated the creation of detailed voltage maps of the atria and ventricles.

However, as more patients present with more difficult substrates and arrhythmias, there was a greater need for more detailed and quicker mapping. Continuous multi-electrode mapping is a method designed to automate the mapping process by allowing one to obtain a large number of points automatically in a shorter period of time, without the need for manual adjudication of collected points. Using multi-electrode catheters, three-dimensional maps with hundreds (or even thousands) of points can be obtained in a few minutes. 

We have been using the Carto^® CONFIDENSE^™ Module (Biosense Webster, Inc.) for continuous multi-electrode mapping for over a year now. It has automated much of the multi-electrode mapping process. As a result, activation and voltage maps can be created in minutes. In most cases, a detailed voltage map can be created quickly while simultaneously building chamber geometry.

The CONFIDENSE^™ Module has been incorporated into our workflow for most ablation procedures and all of our atrial fibrillation (AF) ablations. The ease of creating a high-density voltage map of the left atrium led us to change our workflow to incorporate this technology for every AF ablation. This, in turn, has led to increases in efficiency and also a better understanding of the left atrial substrate.

Data Acquisition and Processing

The CONFIDENSE^™ Module automatically collects activation and voltage points. As the multi-electrode catheter is moved around the chamber being mapped, points are taken simultaneously from each electrode pair, provided some physician-defined conditions are met. The system continuously analyzes intracardiac electrograms (EGMs) from multiple electrode pairs, and either accepts or rejects each recorded heartbeat depending on the signal quality, cycle length, distance from the 3D shell created, etc. Although completely automated once mapping is initiated, careful planning and programming of features and filters is key in obtaining the best results. The CONFIDENSE^™ Mapping Module consists of the following four new technologies (Figure 1).

Continuous Mapping

Traditional multi-electrode mapping allows rapid acquisition of a large quantity of data used to generate detailed and high-density maps. The adjudication and validation of the information acquired through multi-electrode mapping often required a detailed manual process.  

Continuous Mapping enables filtered continuous acquisition of electroanatomical points, and thus acquires only points that meet a set of pre-defined filters. These filters, which are user-defined, include: Cycle Length, Local Activation Time (LAT) Stability, electrode position stability, Tissue Proximity, force filter, points’ density, and respiratory gating. The Continuous Mapping filter settings may vary depending on the arrhythmia being mapped, the type of mapping catheter used, and the user’s particular workflow.

Tissue Proximity Indicator (TPI)

The system uses an impedance-based algorithm to detect catheter proximity to the tissue. This feature is a key component to improve the accuracy of continuous mapping. The real-time change in impedance in each electrode of the multi-pole mapping catheter is used to decide if there is proximity to the tissue. Only when TPI recognizes proximity to the tissue, a point is taken. Once mapping is started, the electrodes will change color, indicating tissue proximity. If other parameters are met (such as cycle length, LAT stability, etc.), then an LAT or voltage point is taken. This is done simultaneously for each one of the electrode pairs on the multi-electrode mapping catheter.

Therefore, a slight change in our workflow is necessary to improve the accuracy of TPI. Moving the catheter around the chamber before mapping is started will give the system time to build the base “impedance map” in the background.
Alternatively, mapping can be conducted with the TPI feature disabled. In this case, only points taken at a close proximity to the chamber’s 3D reconstruction will be applied to the map. The allowable distance, or proximity to the shell, is programmable and typically left at a few mm (3-4 mm is what we most commonly use).

Wavefront Annotation

While points are acquired, local activation times are automatically annotated based on the unipolar and bipolar signals of each electrode pair. Wavefront annotation uses the maximum negative slope (-dV/dT) for local activation time. 

Each unipolar deflection is examined against its simultaneous bipolar activity in order to eliminate annotations on areas of far-field unipolar activation. 

Map Consistency

This feature evaluates the acquired map and identifies points whose LATs are deemed as being inconsistent in comparison with neighboring points. The Map Consistency feature can automatically flag inconsistent points, which can be deleted from the map.

Our Clinical Experience

Unlike with traditional mapping, continuous mapping eliminates the need to manually adjudicate each point. Therefore, the initial steps of setting up map parameters and filter thresholds will certify that the points obtained truly represent the clinical arrhythmia being mapped (rather than erroneously taking catheter ectopy or non-clinical arrhythmia) and that they are in proximity to the cardiac tissue.

We currently follow these steps when using the CONFIDENSE^™ Module for continuous mapping:

1.    Setting up the map:
a.    Reference: It is critical to use a reference electrode with stable signals and without interference of far-field signals.
b.    Cycle Length Range and Stability: This filter will allow for only points that truly represent the clinical arrhythmia to be acquired during mapping. We typically set up the tachycardia cycle length ± 30 ms as the CL range to be mapped.
c.    LAT stability: This filter will allow for only points that represent a continuous activation timing to be taken. 
d.    Internal points: In order to certify that internal points are not applied to the map, one can either use the Tissue Proximity Indicator (TPI) or select a filter that will only include points within a certain distance from the 3D anatomical reconstruction.
e.    Scar filter: Low amplitude signals, below a programmable threshold can be automatically designated as scar and they will not have an LAT assigned to them.
f.    Respiratory Gating: This feature is used to gate the point acquisition during the respiratory motion. Points are taken only during the end-expiratory phase. By changing the inspiratory/expiratory ratio to 1:4 for those patients that are mechanically ventilated, we have increased the window of time for mapping, rendering greater efficiency and precision.

2.    Mapping:
a.    We typically apply some transparency to the map and display where points have been taken. 
b.    The catheter is moved slowly as we watch where points are being taken before moving to a new mapping location.
3.    Post-Processing:
a.    Once the map is finished, there are features used to check the consistency of the points taken. Internal points or activation points that are inconsistent with neighboring points can be automatically detected and/or deleted.

Since the introduction of the Carto^® CONFIDENSE^™ Module at our institution in August 2014, we have used it to perform almost 500 AF ablations and continue to use it daily. Specifically, we now use it with the fast anatomical mapping (FAM) method during every AF ablation. As soon as we obtain transseptal access, we use a multi-electrode catheter to build the 3D geometry of the left atrium while the CONFIDENSE^™ Module is used to simultaneously obtain EAM points to construct a voltage map. Typically within 3-5 minutes, we have built a 3D map of the left atrium and have collected around 1000 voltage points.

These high-density voltage maps help us better understand the left atrial substrate and guide our AF ablations. This EAM system is also used during simple and complex macro-reentrant arrhythmia cases as well as during focal atrial tachycardia cases. Ventricular arrhythmias can also be mapped using the PentaRay catheter.

Voltage Maps

High-density voltage maps allow us to identify areas of low voltage that may be secondary to tissue fibrosis or prior ablation. It can also aid in the identification of gaps in prior ablation lines in patients undergoing repeat procedures. These areas can be targeted for ablation. (Figure 2)

Similar high-density maps may be created without continuous mapping (and using point-by-point or MEM instead), but it could incur longer mapping times.

Continuous Mapping Vs Conventional Mapping

There are some key differences between continuous and conventional mapping. Figure 3 highlights some of these differences. The most important change is that it eliminates the need for the operator to annotate each and every point. The annotation process is done automatically, and points are accepted or rejected based on several filters that are set up before mapping initiates. The system also provides information on tissue proximity and can filter data accordingly.

Maps generated with continuous mapping may have hundreds or even thousands of points. Therefore, unlike traditional mapping where a few inaccurate points can be visually identified on a map and corrected, it is time prohibitive to make a manual correction on a map created using continuous mapping. Automatic correction of the maps can remove internal and inconsistent points.

We have found that carefully setting up the map using the steps described here has allowed us to very efficiently create accurate maps when compared with traditional mapping.

Conclusion

EAM mapping systems continue to evolve. In our experience, continuous multi-electrode mapping systems can significantly increase the efficiency and density of activation and voltage maps, providing us with important information about the arrhythmia and arrhythmogenic substrate. Along with contact force sensing catheters, this new technology has allowed us to continue making improvements in the treatment of patients with complex arrhythmias.

Disclosures: Drs. Rajendra and Arciniegas have no conflicts of interest to report regarding the content herein. Dr. Osorio reports personal fees from Biosense Webster, Inc. during the conduct of the study.