The EnSite Array™ system (St. Jude Medical) provides a noncontact mapping technique to create a 3-D electroanatomic map without point-by-point contact electrograms. It involves a 9 Fr multielectrode EnSite Array™ Catheter mounted on a 7.5 ml balloon with 64 insulated filaments acting as noncontact electrodes. The EnSite Array™ is deployed in the cardiac chamber of interest and used as a reference to create 3-D anatomical geometry by sweeping any conventional catheter throughout the cardiac chamber to define the endocardial borders. After the creation of the anatomical geometry, the far-field potentials are recorded and processed to create 3,360 virtual unipolar electrograms.2,3 The computed voltage data from these electrograms can be displayed on the anatomical model of the cardiac chamber to generate an electroanatomic map.

The main advantage of this system is having the ability to map a non-sustained, hemodynamically unstable or difficult-to-induce arrhythmia, in which a single cycle of tachycardia is utilized to create an activation map. In addition, any catheter from any manufacturer can be used with this mapping system. Limitations include possible difficulty in deploying the balloon catheter in some chambers due to its size or shape; the volume occupied by the balloon may limit the movement of the ablation catheter in a small chamber. In contrast, in large chambers like a dilated left ventricle, virtual electrograms may be inaccurate if the endocardial surface is at a distance from the balloon surface. Unipolar mapping may record far-field signals, making it difficult to identify the local activation. On the other hand, low endocardial voltages may be too weak to be detected by the balloon catheter. Although this system is not particularly useful for AF ablation, on the device therapy front, it is a quicker strategy to delineate the spread of the depolarization wavefront in the heart failure patient.

EnSite NavX™ System Overview

This mapping system is based on localization of multiple electrodes using an electrical field generated by three pairs of surface electrodes placed on the patient’s body along three orthogonal axes. The patches emit a low-amplitude 5.7 kHz signal, and conventional catheters are localized by measuring the electrical potential or field strength received by them. The fundamental principle underlying EnSite NavX™ (St. Jude Medical) navigation is that of an impedance-based measure, which is dependent on the voltage gradient that exists across tissue when a current is applied through the surface electrodes. This mapping system can be used to localize up to 12 catheters and 64 electrodes. A geometric model of a cardiac chamber can be created by maneuvering any catheter with multiple electrodes to localize the endocardial borders. An electroanatomic map is generated by acquiring and displaying the activation and voltage data on this model. A reference intracavitary electrode is required, the position of which needs to be stable in order to maintain the accurate position of the electroanatomic map. The value of a secure reference cannot be overemphasized, as a significant shift can frequently lead to restarting the entire case.