Noncontact Mapping
Satoshi Higa
Yenn-Jiang Lin
Ching-Tai Tai
Shih-Ann Chen
The curative ablation strategies of atrial fibrillation (AF) have rapidly evolved but have still not become standardized because the variable AF mechanisms make identification of the AF substrate using conventional approaches difficult (1, 2, 3, 4). Although the pulmonary vein (PV) isolation technique and/or circumferential ablation around the PV antrum can cure PV AF, this laboratory and several investigators have demonstrated that extra-PV ectopies and macroreentry can also initiate and maintain AF (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23). Furthermore, the mapping of the macroreentry that may occur after PV antrum isolation and identification of the critical isthmus of that tachycardia are also challenging issues when the tachycardia has an unstable form (24). Thus, conventional mapping techniques have some limitations in mapping extra-PV AF and unstable macroreentry because of their limited resolution and the need for sequential point-by-point acquisitions.
Currently, several mapping and catheter navigation systems are available to guide catheter ablation of AF. Each system possesses specific advantages and disadvantages and requires familiarity with its operation and interpretation of data. Noncontact mapping has been reported to have a specific advantage in mapping tachycardias with transient or changing activation sequences due to its capability of performing a single-beat analysis (25, 26, 27, 28, 29, 30, 31, 32, 33). Considering the relatively high incidence of extra-PV AF, this system is an important tool for guiding curative ablation of the various kinds of AF (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33). The aim of this chapter is to focus on the current state of knowledge of the noncontact mapping technique, including its indications, methodology, efficacy, safety, and the various pitfalls associated with catheter ablation in patients with paroxysmal and persistent AF.
Major Advantages of Noncontact Mapping for Catheter Ablation of Atrial FibrillationCurrently, several different 3-D mapping systems for guiding AF ablation are available. There are no prospective clinical trials comparing the efficacy and safety of each 3-D mapping system. Although the noncontact mapping system requires a special balloon catheter and the knowledge of how to interpret unipolar electrograms, this system has a clear advantage in AF ablation because of a unique feature that allows the simultaneous
acquisition of both electrical and anatomical data from the entire atrium, even during a single beat or during tachycardias with rapidly changing activation sequences (25, 26, 27, 28, 29, 30, 31, 32, 33). The other 3-D mapping systems, such as CARTO (Biosense, Webster, Inc.), EnSite NavX (Endocardial Solutions), LocaLisa (Medtronic), and RPM (Boston Scientific) systems, do not have this kind of function. Furthermore, the efficacy and safety of the noncontact mapping system for guidance of catheter ablation of various complex tachycardias have been well reported in numerous previous publications (20,23,25, 26, 27, 28, 29, 30, 31, 32, 33). Therefore, this system is considered an ideal mapping tool for guiding the ablation of AF, including ectopy-initiating AF and also macroreentrant circuits maintaining AF.
acquisition of both electrical and anatomical data from the entire atrium, even during a single beat or during tachycardias with rapidly changing activation sequences (25, 26, 27, 28, 29, 30, 31, 32, 33). The other 3-D mapping systems, such as CARTO (Biosense, Webster, Inc.), EnSite NavX (Endocardial Solutions), LocaLisa (Medtronic), and RPM (Boston Scientific) systems, do not have this kind of function. Furthermore, the efficacy and safety of the noncontact mapping system for guidance of catheter ablation of various complex tachycardias have been well reported in numerous previous publications (20,23,25, 26, 27, 28, 29, 30, 31, 32, 33). Therefore, this system is considered an ideal mapping tool for guiding the ablation of AF, including ectopy-initiating AF and also macroreentrant circuits maintaining AF.
The Fundamentals and General Features of the Noncontact Mapping SystemThe noncontact mapping system (EnSite Array, Endocardial Solutions Inc., St. Paul, MN) is an advanced 3-D mapping and catheter navigation system, consisting of a multielectrode array (MEA) and amplifier connected to a computer workstation (20, 21, 22, 23,25, 26, 27, 28, 29, 30, 31, 32, 33). The MEA catheter (9 Fr) consists of a 7.5-mL balloon, which is woven braid of 0.003-inch wires possessing 64 unipolar electrodes insulated by laser etching. This system can collect, record, and display more than 3,000 reconstructed electrograms without any point-by-point manipulation of mapping catheters, and construct a 3-D computer model of the virtual endocardium, providing a geometry matrix from the inverse solution.
Theoretically, endocardial geometry has been defined as an expanded MEA surface, and the inverse solution to Laplace’s equation is applied for processing amplified far-field signals (voltage sensitivity, 10 microvolt; sampling frequency, 1.2 kHz) from the MEA catheter using a ring electrode as a reference, mounted 16 cm proximal to the MEA. The reconstructed electrograms (virtual electrograms) generated from the signals sensed by the MEA can be displayed as waveforms themselves and also can be superimposed onto the virtual endocardium, producing real-time 3-D isopotential maps, with a color range representing the voltage amplitude as tools for the interpretation of wavefront propagation. The noncontact mapping system can allow nonfluoroscopic 3-D navigation with any standard EP catheter—this capability is called the EnGuide navigation system. This function visualizes the real-time position of the electrodes on standard EP catheters, relative to the position of the MEA. After the MEA catheter is connected to the EnSite system, the location of the roving catheter electrode appears in the map display as an EnGuide locator. The patient interface unit (PIU) sends a 5.6 kHz signal through the roving catheter electrode. The E1 and E2 ring electrodes on the MEA catheter alternately receive and return the 5.6 kHz signal to the PIU. Using the strength of the 5.6 kHz signal sensed by the 64 electrodes on the MEA catheter and the respective electrode location on the MEA, the 3-D position of the electrode on the EP catheter can be precisely displayed on the reconstructed endocardium.
Procedure for Using the Noncontact Mapping SystemHow to Insert and Position the MEA Catheter
The use of the noncontact mapping system in our laboratory has been previously described in detail (20, 21, 22, 23,26,28,29). A sheath (9-10.5 Fr) placed in the femoral vein
is used to introduce the MEA catheter. Considering the aggressive anticoagulation therapy used during noncontact mapping, especially in LA-sided procedures, a gentle venous puncture to introduce the vascular sheath can help avoid any vascular complications. Before the deployment of the MEA catheter in the atrium, physicians need to maintain an activated clotting time around 250 sec for right atrial (RA) and 350 sec for left atrial (LA) mapping in order to prevent thrombus formation. The MEA catheter is deployed over a 0.035-inch guidewire, which has been advanced to the superior vena cava (SVC) for RA mapping (via the left femoral vein) and to the left superior PV for LA mapping (via the right femoral vein) (Fig. 8.1).
is used to introduce the MEA catheter. Considering the aggressive anticoagulation therapy used during noncontact mapping, especially in LA-sided procedures, a gentle venous puncture to introduce the vascular sheath can help avoid any vascular complications. Before the deployment of the MEA catheter in the atrium, physicians need to maintain an activated clotting time around 250 sec for right atrial (RA) and 350 sec for left atrial (LA) mapping in order to prevent thrombus formation. The MEA catheter is deployed over a 0.035-inch guidewire, which has been advanced to the superior vena cava (SVC) for RA mapping (via the left femoral vein) and to the left superior PV for LA mapping (via the right femoral vein) (Fig. 8.1).
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