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

Assets and Limitations of 3D Mapping Systems

Each system has considerable strengths and some limitations. The Carto system provides a highly accurate geometric rendering of a cardiac chamber with a straightforward geometric display. The position of the mapping tip at any point in time is readily apparent from a tip icon, providing that the tip is at or beyond the rendered chamber geometry. This system allows a straightforward annotation of cardiac valves and veins on the surface of a cardiac chamber. It is possible to create an individual map of each pulmonary vein, SVC or IVC as a more robust reflection of structure geometry. Activation maps are straightforward, to the extent that the underlying circuit is appropriately sampled by a sufficient number of acquisition sites to resolve the underlying process. Respiratory artifact is limited.

This approach has several limitations, however. Since the acquisition of anatomic and physiologic points is based on sequential site sampling, an arrhythmia must be inducible and hemodynamically stable. Single ventricular premature contractions (VPCs) or atrial premature contractions (APCs) or nonsustained events can be mapped, although at the expense of an appreciable amount of time. Since only sequential events are used to establish the maps, data acquisition during rapid VT, for example, is not possible. Nevertheless, mapping based on underlying voltage is very useful for mapping scar borders as described elsewhere.[2] Annotation of ablative sites is straightforward, although the "red" tip displayed during ablation is counterproductive, in that it is lost in the red background of the earliest site of activation of an arrhythmia or among previously annotated ablative sites. Another limitation of the Carto XP system is the requirement of a separate Biosense Webster catheter for each case. No other catheter types can be used with this system, and bidirectional steerable catheters are not available. The magnetic signal also creates interference with other EP lab recording systems. The QWIKMAP mapping approach has been forwarded as a means of mapping multiple sites simultaneously. The surface geometries so created can be somewhat distorted if the chamber under examination distends with the mapping catheter. When including both tip points and shaft points, the chamber geometries tend to be artificially large. Annotation of the location of specific ablative sites on the surface geometry with this new software can be a laborious process.

The noncontact mapping approach does permit a straightforward means of assessing activation, as seen in the real-time voltage excursions.[3] Given the underlying technology, it is possible to map out an entire cardiac cycle of an entire chamber, without requiring sequential point-to-point acquisitions. This is particularly well suited for localizing the origin of nonsustained arrhythmias, APCs or VPCs, or very rapid VT with hemodynamic compromise. The system can also map multiple cardiac cycles in real time, which disclose changes in activation sequence from one beat to the next. Obviously, the chamber geometry must first be established through current injection from the ablation or mapping catheter at a variety of different sites. An additional advantage of this system is that any catheter from any manufacturer can be used in conjunction with this mapping platform.

Although much progress in the development of this system has been made, some limitations remain. Activation maps, expressed in terms of isochronal activation times are not as easily produced. In addition, the acquired geometry with the current version of software is somewhat distorted, requiring multiple set points to clearly establish the origin and shape of complicated structures such as the left atrial appendage or pulmonary veins. Otherwise, these structures can be lost in the interpolation between several neighboring points. Some loss of accuracy of localization can occur with mapping at endocardial sites more than 4 cm away from the balloon surface.[3] Positioning the noncontact balloon array into the left atrium also makes it more difficult to manipulate an ablation catheter around the outside of the balloon. Low voltage generating acquisition sites may also be missed. Synchronized mapping of multiple chambers requires multiple systems, and maps are highly sensitive to changes in filtering frequencies.

The NavX approach likewise establishes a straightforward geometry. With this approach, the locations of veins or even the esophagus are established and readily displayed by the juxtaposition of multiple mapping marker, or "Sphere Stacking," spheres along the length of that vein, as seen in Figure 2. The size of each marker is based on size "selection" rather than actual vessel dimensions. A recent software upgrade allowing point-to-point activation mapping for the NavX system has also been released. This is a substantial improvement, permitting the same kind of activation mapping and display as possible with other systems, with the similar advantage of specified voltage mapping as well. This point-to-point mapping, however, is only suited for sustained arrhythmias or frequently recurrent APCs, VPCs, or nonsustained arrhythmia. This can be augmented by the addition of noncontact mapping to the procedure. With the NavX system, any brand of catheter can be utilized. Respiratory motion has been radically reduced in recent software versions.

Some limitations exist. With individual interpolation schemes, significant anatomic distortions in complex structures can occur unless a family of fixed points is incorporated into the geometry to preserve critical junctions between those structures. Appropriate filtering has decreased this problem. The "flashlight" approach to identifying and displaying the specific location of a catheter at the geometry surface with the NavX system can be arduous, again requiring a meticulous rendering of anatomy in the first place, and oversizing of the anticipated lesion size to register the catheter tip position on the map surface. In this regard, the use of the ESI locator line is substantially easier for tracking catheter tip position.

The RPM system remains in evolution. A reasonable geometry is established with point-to-point mapping, although the operator must be cautious in obtaining multiple roving and "snap" points to clearly establish the limits of chamber geometry. This is as seen at the accompanying intersection with other complex structures such as pulmonary veins in Figure 3. Ablative lesions on the surface of this geometry are readily catalogued, although deformation of the surface geometry or "learning" in the process of point-to-point ablation is possible, but not automatic and ablation locations can be lost to the internal side of the geometry. There is a transparency function that allows one to see through the walls and identify these sites, but the application of this utility proceeds along a steep learning curve. A downside of the RPM system is the requirement of specified 7 F catheters fitted with the ultrasound transducers. Substantial ongoing work is being done with each system, to overcome some of these specific limitations.

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