5.

Transient double-loop reentry (Patient 8). A–B: sinus rhythm activation map (same as Figure 4A–B). C–D: the extrastimulation cycle leading to the reentrant VT episode which was mapped as shown at the bottom of the figure. E–F: transient reentrant VT circuit. Note relatively small isthmus size and entrance point compared with sustained tachycardia episodes. Overlaid on this map is the sinus rhythm estimate of the isthmus perimeter (gray lines). Portions of the circuit boundary coincide with an additional area with sharp transition in sinus rhythm activation time (dotted gray line in panels B and F).