Figure 4.

Relationship of Sense Protocol Functional Late Potentials to a Mapped VT Circuit

(A) Activation mapping of ventricular tachycardia (VT) in a patient with previous anterior myocardial infarction as shown in Video 1. The high-density grid is placed on the critical isthmus, with mid-diastolic signals recorded on the right; it can be seen that the activation sequence goes from spline A to spline D, demarking the entrance and exit of the VT diastolic channel (white arrow). (B) Late potentials (LP) color timing map during sinus rhythm (left) and sense protocol pacing (right) showing a greater region of LP during the sense protocol corresponding to the mapped diastolic pathway of VT. (C) Example of local LP delay and splitting of LP during sense protocol (second beat) along the mapped diastolic pathway of VT. (D) Entrainment from site close to pole D1 on the high-density grid (gray dot) shows concealed entrainment with a post-pacing interval of 18 ms, and a stimulus to QRS duration <30% VT cycle length, indicating entrainment at a VT exit site.