Combined endo- and epicardial pace-mapping to localize ventricular tachycardia isthmus in ischaemic and non-ischaemic cardiomyopathy

AIMS: A high-density pace-mapping can depict an abrupt transition in paced QRS morphology from a poor to excellent match, unmasking the critical component of ventricular tachycardia (VT) isthmus from the entrance to exit. We sought to assess pace-mapping at multiple sites within the endo- and epicardial scars to identify the VT isthmus in patients with ischaemic (ICM) and non-ischaemic cardiomyopathy (NICM). METHODS AND RESULTS: Colour-coded maps correlating to the percentage matches between 12-lead electrocardiograms during VT and pace-mapping [referred to as correlation score maps (CSMs)] were analysed. We studied 115 CSMs (80 endo- and 35 epicardial CSMs) in 37 patients (17 ICM, 20 NICM). The CSM with an abrupt change (AC) in pacemap score (AC-type) on the endocardium was more frequently observed in ICM than in NICM [11/39 (28%) vs. 1/41 (2%); P = 0.001]. Among 35 CSMs that were analysed by the combined endo- and epicardial mapping, 10 (29%) CSMs exhibited non-AC-type on the endocardium; however, AC-type was present on the opposite epicardium. Although 24 (69%) CSMs did not show AC-type on both the endocardium and epicardium, 16 of them had either an excellent (>90%) or poor (<0%) correlation score on either side, associated with isthmus exit or entrance, respectively. However, the remaining eight CSMs had neither excellent nor poor scores. CONCLUSION: The CSM may provide electrophysiological information to localize the endo- and epicardial VT isthmus. The absence of AC-type CSM on the endocardium, which is frequently observed in NICM, appears to indicate the sub-epicardial or intramural course of the critical isthmus.