Milestone 3: Accuracy of Registration of Integrated ICE based ARFI and Biosense CARTO Tracking system
While it is important to be able to characterize ablation lesions with ARFI, it adds significant value to this system to be able to use this information to steer the catheter to gaps in a lesion line in order to rapidly and effectively implement a repair. CARTO electroanatomical is used commonly by the general EP community, and at Duke University Medical Center by Dr. Bahnson to outline chamber anatomy, track lesion locations, and map the spread of activation on the tissue. An integrated CARTO-ICE catheter will enable tracking of the imaging catheter in the same pseudo image. Because the CARTO system can measure both position and orientation of the catheter tip, the direction and angular extent of the ultrasound imaging plane can be included in the cartoon image to facilitate positioning the ICE catheter to best image an ablation site. In essence, this will allow registration of the CARTO pseudo-image to the ICE image. The goal of this Milestone is to confirm the technique and to measure its accuracy both in vitro and in vivo.
The utility of the combined CARTO/AcuNav will depend markedly on how well a catheter can be positioned, using CARTO guidance, into a gap in a lesion line imaged using ICE based ARFI. The location in space of an imaged spot is predicted by the combined system by the following process: 1) determine the 3D position and orientation of the combined CARTO/ ICE catheter in space using the CARTO system 2) create a line representing the transducer array in space 3) measure the distance and azimuthal angle to the imaged spot in the ultrasound image 4) predict the spot location in three space using the location and orientation of the transducer from 2) and the angle and distance from 3). The point in space would then be inserted into the CARTO cartoon and an ablation catheter steered to that location using the cartoon image.
We will test this process in vitro using the chamber described in section D.3. Three catheter size holes will be drilled in a line at 1 cm intervals into the lid of the chamber over the tissue. The chamber will be placed in the magnetic field of the CARTO system and with the lid removed an outline of the chamber and tissue surface made in the standard way by moving the ablation catheter to specific locations in the chamber. The lid will then be replaced and an ablation catheter lowered through the outside 2 holes and small lesions created and marked in the CARTO image. The combined ICE/CARTO imaging catheter will be inserted as shown in Figure 11 and adjusted to image the two lesions by rotating the catheter. A spot will be marked in the image locating the gap between the lesions. The location of the spot will be predicted and placed in the CARTO cartoon. The ablation catheter will be inserted into the middle hole and lowered to the tissue. The position will be measured using the CARTO system and a third lesion created. The distance between the location predicted by the combined system and the CARTO measured location of the lesion will be measured on the CARTO display. The tissue will be removed and the locations of the lesions verified (should be linear 1 cm separation). The procedure will be repeated at least 20 times and the mean distance (always >0) between the predicted and actual location calculated. Also, a mean vector (from predicted to actual) will be calculated to determine if there is a bias error in the system.
To verify this process in vivo a very similar study will be done in the sheep atria.
Animal Preparation: 12 - 60 k g sheep of either sex will be anesthetized with, intubated, ventilated, and maintained metabolically stable with fluids, electrolytes. Blood gas and electrolyte measurements will be made hourly and corrections made as needed. An 12 fr sheath will be inserted into each femoral vein and each external jugular for catheter access. Under fluoroscopic guidance, a 10 fr ICE imaging catheter (AcuNav, Johns on & Johnson) will be inserted and advanced to the level of the right atrium (RA). The three-lesion sequence described above will be repeated in three lines in the RA on the lateral wall of the IVC/SVC junction and 3 times on the posterior RA. The animal will be euthanized and the heart extracted, and the lesions exposed and photographed. The location of the third lesion relative to the first two will be compared to the measured locations in the CARTO image. These anatomical locations for the lesions were chosen as the geometry was thought to change least when the tissue is excised, examined, and the lesion locations measured. A mean distance error will be calculated by comparing the lesion locations on the CARTO system to those on the tissue. The CARTO system measurements will then be compared to those calculated from the combined ICE/ CARTO measurement. A mean distance error and a mean error vector will be calculated as above.