2.

Double-loop reentrant circuit and method to measure electrical discontinuity from Patient 5. Panels A–B: Sinus rhythm activation map and anatomical landmarks. Panels C–D: extrastimulation activation map. Panels E–F: sustained reentrant VT activation map. Estimated and actual isthmus perimeter and functional block line location are derived in panels B and F (gray and black lines, respectively). Insets to the right of maps (top to bottom): sinus rhythm electrograms that are circled in the map in panel B, ECG during sinus rhythm, key, and ventricular tachycardia electrograms at same location as shown in B.