Three-Dimensional Mapping in Interventional Electrophysiology: Techniques and Technology

Douglas L. Packer, M.D.

Disclosures

J Cardiovasc Electrophysiol. 2005;16(10):1110-1116. 

In This Article

Available Mapping Technology

While no single system can completely provide this list of features, several currently available sophisticated platforms come close to these goals.[1,3,4] The Carto XP system provides a combined electroanatomic means of mapping cardiac arrhythmias. With this approach, the patient is positioned over a tripod emitting three electromagnetic waves at unique frequencies. Each beam is registered by one of three specifically tuned coils embedded in the mapping catheter tip to specify location in 3D space, when the catheter tip is considered against a reference catheter. An electrogram recorded at that site is thereby archived within that positional context. The direction of the catheter tip, along with its pitch, yaw, and roll attitude creates an orientation vector, which is also displayed. Using this approach, local tissue activation at each successive recording site produces activation maps within the framework of the acquired surrogate geometry. In addition, this system stores both unipolar and bipolar signals, to give a snapshot view of global and local voltage at each one of the recording sites. The "QWIKMAP" variation on this electroanatomic theme allows simultaneous, direct multipoint mapping from two locations along the catheter, which along with calculated "trace" points are used to create chamber geometry and activation maps.

Noncontact mapping was also developed during the 1990s to allow simultaneous recording of electrical activation from multiple sites within a single cardiac chamber. For this approach, a 64-electrode mesh, mounted on the outside surface of a 18 × 40 mm balloon is positioned in the cardiac chamber of interest. Using 5.6 kHz currents driven from the rings on the mesh catheter and ablation tips, the ablation catheter tip is located in 3D space by sensing the resulting potentials on the mesh electrodes. Using locations at multiple roving sites, the endocardial surface, or "boundary" of the chamber is sequentially established. This is displayed as a 3D object, also providing a surrogate geometry framework for activation display. Nearly 3,300 calculated virtual electrograms, reflecting voltage transients from the endocardial surface or boundary, are created using an inverse solution to the LaPlace equations. Activation occurring over the course of a cardiac cycle is reflected by unipolar or bipolar activation signals spreading across the cardiac chamber.[3] Both voltage and activation timing maps can be displayed on the system monitor.

An additional mapping approach, based on currents across the thorax, has also been developed as originally applied in the LocaLisa system. This technology has undergone substantial additional development in the NavX iteration. For NavX maps, low level separable currents are injected from three orthogonal electrode pairs positioned of the body surface. The specific position of a catheter tip within the chamber can be established, based on the three resulting potentials measured in the recording tip with respect to a reference electrode seen over the distance from each patch set to that recording tip. Sequential positioning of a catheter at multiple sites along the endocardial surface of a specific chamber then establishes that chamber's geometry, as seen in Figure 2. In addition to mapping at specific points, there is additional interpolation, providing a smooth surface, onto which activation voltages and times can be registered. As with other systems, around 50 points are required to establish the surface geometry and activation of a chamber at appropriate resolution. The NavX system also permits the simultaneous display of multiple catheter electrode sites, and also reflects real-time motion of both ablation catheters and those positioned elsewhere in the heart.

NavX map of the left atrium and accompanying pulmonary veins as established during ablative intervention for atrial fibrillation. Shown are the right and left superior pulmonary veins (RS and LS) manifested as teal-colored mapping spheres. The right middle pulmonary veins (RM) is shown in green, and the inferior veins (RI and LI) in blue. The position of the esophagous posterior to the left atrium (E) is shown by the white spheres; ablation lines are catalogued as brown disks. CS = coronary sinus catheter; MV = mitral valve annulus.

A fourth system under current release is based on ultrasound-distance ranging. For this RPM (Real-time Position Management) system, three catheters, fitted with microtransducers, are positioned into the right ventricle and coronary sinus, with a third catheter used as a roving ablation or mapping catheter. The performance of this system utilizes the transmission of ultrasound signals between transducers on any one of these catheters. The distance between catheters is based on calculations from the velocity of sound transmission in the heart and the time required from transmission to reception.[1] Triangulation between transducers on all three catheters establishes the location of the mapping catheter tip. As with the noncontact mapping systems, the geometry generated with this approach is built from the inside out, with point-to-point sequential catheter positioning. Figure 3 shows a map of the left atrium created during an ablative intervention for atrial fibrillation. Because of multiorder interpolation for establishing the surface geometry, critical fixed or "snap" points must be specified and incorporated into the chamber geometry to prevent interpolation obliteration from obscuring intersections of uniquely shaped structures such as pulmonary veins.

Left atrial volume rendering using the RPM system. Shown are the left atrial contours, related pulmonary veins, and ablation site annotations. The mapping catheter position in the coronary sinus is shown by the white arrows. The pink dots indicate the site of wide-area circumferential ablation around each pulmonary vein. RS = right superior pulmonary veins; LS = left superior pulmonary veins; LI = left inferior pulmonary vein; RI = right inferior pulmonary vein.

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