It shows the sequence of steps used for the voltage mapping technique to predict the slow AV node location. The same equipment, type of catheters and steps were used as described in Figure 21.25 A-D. The total recording time was 20 minutes but the video was shortened to 7.5 minutes for optimal viewing. The first 3 min. 45 sec are shown at 4x speed at the end of which the reference was changed briefly from the 20-pole catheter to the His catheter to enable more voltage mapping beneath the His catheter area. Then 2x speed and normal speed are intermittently used at end of voltage data point collection. The propagation map at normal speed starts at 4 minutes and the wave front collision at site of predicted slow pathway during the propagation map is shown at 5 min 17 sec. The added hand written black circle predicts the cryo ablation target. At 5 min 50 seconds, the cryoablation applications are displayed followed by individual placement. Cryo-applications 1-6 (blue circles) were 1-1.5 min in duration and were unsuccessful (inducible AVNRT during application). These applications were placed anteriorly towards the tricuspid valve annulus and slightly outside the voltage mapping-predicted slow pathway bridge area because the atrial electrograms appeared more ideal (low voltage, high frequency). Therefore, the electrograms (using conventional anatomic / electrogram approach) were thought to be inconsistent with the voltage map. However, despite the less than optimal slightly greater amplitude electrograms, when cryo-application 7 was applied closer to the voltage mapping-predicted slow pathway, immediate block in the slow pathway was recorded (using the S1-S2 atrial stimulation technique) at less than one minute. This application and subsequent “bonus” ones 8-12 (orange) were placed during 4 minute applications. No inducible AVNRT was evident after cryo 7. (Courtesy of Christopher C. Erickson, MD Children's Hospital & Medical Center, Professor of Pediatrics, University of Nebraska Medical Center; and John Prusmack, St. Jude Medical S.C., Inc.who assisted in the data acquisition, refinement and display.)