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

Integrated, Anatomy-Based Mapping

The last 5 years have also seen the rapid development of integrated, anatomy-based mapping and ablation. This has been driven by a realization of both the critical coupling and dependence of arrhythmias on their underlying anatomy and the limitations of surrogate geometries of contemporary mapping systems for reflecting that anatomy.

Over this same time frame intracardiac ultrasound and rapid CT and MR systems have emerged as the mainstays of imaging in the EP lab.[1] Sixteen to sixty-four row helical CT and MR studies provide a broad "gestalt" or "anatomy library" of an individual patient at one point in time. Intracardiac ultrasound is highly useful to provide focused real-time images of the endocardial surfaces critical for positioning of catheters, establishment of catheter/tip tissue contact, and for monitoring energy delivery in the beating heart. Both changing tissue echogenicity and microbubbles reflect tissue heating, with the latter providing a signal for energy termination. In each of these tasks, ultrasound focuses on specific "books" and "shelves" within the "global library" established by prior CT on MR imaging.

Each company is actively working on image incorporation into their systems. Segmented CT volumes can be downloaded on the Carto and NavX platforms, with similar integration work underway for the RPM system. With each of these approaches, the chamber of interest is segmented out of the entire CT axial image set, although this requires substantial user effort to sculpt or segment out the chamber of interest. Both systems display the CT image volume along with the surrogate geometries rendered from sequential mapping for side-by-side comparison. While this is useful in correlating electrophysiology and CT anatomies, manipulating image files slows down general map processing time to a noticeable level.

Additional work is also underway to fully "register" the surrogate map onto actual CT anatomy.[1] At this point, the Carto system does accommodate merging the CT and electroanatomic map into one image, through matching 3–6 specific anatomic locations seen on both anatomic renderings. Displaying the ablation catheter and integrating its position onto the CT geometry is also possible.

True registration of mapping details onto the exact surface of the CT or MR anatomy, however, is not yet commercially available. This has been done in research studies, however. An example of full registration of an activation sequence generated by an APC, onto the underlying left atrial anatomy, as established in a patient with a left superior pulmonary vein AF focus by multirow CT scanning is shown in Figure 4. This kind of approach will be required for the creation of highly robust image-based system for guiding ablation. Obviously, substantial validation studies will be required to ensure a complete and appropriate match between the CT or MR anatomy and thesurrogate geometries created by point-to-point anatomic mapping.

Segmented CT rendering of the left atrium and pulmonary veins in a patient with a LSPV (left superior pulmonary vein) source of atrial fibrillation. Each pulmonary vein is shown in red and the registration of the noncontact map obtained during the APC is fully registered to the underlying CT volume. Atrial activation spreads from the APC origin (light blue) out of the left superior pulmonary vein toward the rest of the left atrium. (Used with permission of Packer DL. Evolution of mapping and anatomic imaging of cardiac arrhythmias. PACE 2004;27(7):10261049.)

From the information listed in Table 1 , recommendations can be made for choosing a specific mapping system for a particular interventional case. This choice will be shaped by the importance of a specific characteristic in the mapping process. In those cases where an undistorted anatomic rendering, with high spacial accuracy, is required, we use the Carto system. This has lesser problems with interstructure delineation and requires fewer fixed or snap points to preserve the "anatomy."

The Carto XP, NavX, and RPM systems all work well for mapping sustained, stable arrhythmias.

Mapping nonsustained arrhythmias, APCs, or VPCs is admittedly tediously with each of these three approaches. With these arrhythmias, the noncontact mapping array works very well, although the maps can be filter frequency dependent. The noncontact approach does provide a quick snapshot of activation during unstable VTs, obviating the need for long periods of tachycardia. On the other hand, the precision of mapping can be limited in the setting of various cardiomyopathies with ventricular enlargement.

We use mapping of an alternative characteristic, such as scar or voltage, as a very useful alternative to noncontact mapping. Carto performs very well in this regard. NavX also works reasonably well, with its dynamic substrate mapping capabilities. While each of these systems run in the same range for cost, the NavX system wins out in disposable cost, since any catheter can be used for the creation of the anatomy and voltage or activation maps. The same is true of the Local Lisa system, although its capabilities are limited to cataloguing the sites of ablation or other specifically marked structures. An ongoing added expense is required for catheter purchase with the RPM, Noncontact, and Carto systems.

In some cases, the choice of mapping system depends on the skill and experience of the operators. The user interface of the Carto and NavX systems are acceptably straightforward. The Noncontact system requires more steps in the creation of a user-friendly working geometry. Obviously, each of these systems is in the development stage and the various capabilities could change substantially over the next couple of years.

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