How to use pace mapping for ventricular tachycardia ablation in postinfarct patients

Figure 1. (A) Pacing correlation map of a left ventricular tachycardia on an inferior myocardial infarction scar. The color scale depicts the percentage of correlation (from 0 = purple to 100% = red) between the paced QRS and the 12‐lead reference QRS of the ventricular tachycardia. The VT isthmus borders are suggested by two parallel white lines (see further in the text for explanations on how to define isthmus borders on a pacing correlation map). White dots indicate pacing sites. (B) Bipolar left ventricular voltage map of the same clinical case.

Figure 2. Pacing correlation map of a left ventricle during sinus rhythm. The color scale depicts the percentage of correlation (from 0 = purple to 100% = red) between the paced QRS and the reference QRS (here in sinus rhythm). The green point is taken as the pace mapping reference. In healthy tissue, pacing on sites in close proximity to each other (green and blue dots) will result in a very similar percentage correlation. The further away the pacing sites are, the more the morphology of the QRS obtained will differ (gray and yellow dots).

Figure 3. Focal pattern with points of good correlation. (A) Simulated case: the pacing correlation map shows a centrifugal pattern that suggests a focal activation pattern. Indeed, the percentage of correlation of the paced QRS is inversely proportional to the distance between the pacing site and the VT exit site. (B) Clinical case that shows a pacing correlation map in a patient with a focal ventricular tachycardia originating from the right ventricular outflow tract (RVOT). The color scale depicts the percentage of correlation between the paced QRS and the focal VT reference QRS. (C) Propagation map of a focal VT originating from the RVOT.

Figure 4. Focal pattern with missing points of good correlation. (A) Simulated case in which, despite the dense and homogenous distribution of pacing sites all over the endocardial surface of the ventricle, it is not possible to identify a perfect matching area. Instead, the PM map identifies an area of moderate correlation in the range of 70%−79%. (B) Clinical case of an endocardial left ventricular (LV) pacing correlation map. The best PM correlation point (orange star) and area (white circle) show centrifugal activation, and a poor PM correlation point (green star) is also highlighted. (C) Epicardial LV PM: a perfect match is identified on the epicardial side of the inferoapical wall (red star and red circle), with a centrifugal pacing correlation map pattern in the LV epicardium. (D) Analysis: there is a perfect match on the epicardial side of the LV (red star) and a poor match on the endocardial side (green star). Separated by a short distance, these pacing sites therefore produce ECGs showing a totally different morphology. This abrupt change in QRS morphology suggests a slow conduction zone between these pacing sites. The area highlighted by the orange star in the LV endocardium can…

Figure 5. (A) Simulated case presenting the third typical feature during pace mapping: abrupt transition between points with bad and excellent correlation. In the case of points with a mismatch in the immediate vicinity of the exit zone, an area with abrupt transition is highlighted and it corresponds to the location of the VT isthmus. The virtual line, bounding the points with a perfect match from the points with a poor match, represents the mid‐isthmus line and divides the entry and exit area of the isthmus. When pacing around this area is performed, areas of intermediate matching are found laterally to the isthmus mid‐line: lateral borders of the isthmus. Finally, this pacing correlation map, as an analog of an activation map, reveals the VT circuit. (B) Clinical case presenting two pacing sites 10 mm apart. One shows a perfect match of 95% with the VT morphology and the other one shows a mismatch with a −8% concordance with the VT. This abrupt transition in QRS morphology identifies the VT isthmus and the color‐coding reveals the VT circuit. (C) In this same patient, the pacing correlation map and the VT activation map are depicted side by side and look absolutely identical.

Figure 6. Examples of two VT circuits and the corresponding S‐QRS measurements within the “good correlation” area. Panel A shows a consistent decrease in the S‐QRS from the mid‐isthmus to the exit of the circuit, whereas Panel B shows discrepancies within a large area of good correlation (within the scar) of the S‐QRS measurements, suggesting bystander areas. Panel C illustrates Panel A map: S‐QRS duration within the area of good correlation decreases progressively along the path from the mid‐isthmus line to the exit. Panel D illustrates Panel B map: S‐QRS measurements in the area of good correlation help to discriminate between the VT isthmus and bystander areas.

Figure 7. Simulated case of pacing in the VT isthmus bounded by functional barriers. Theoretically, when pacing immediately after (A) and before (B) the mid‐isthmus line, the resulting 12‐lead ECG would be very similar given the centrifugal propagation of the wavefront from the pacing site not bounded by lateral anatomical barriers. Although this has not been observed in our clinical practice, it could be a limitation of pacing correlation maps.