Vector field heterogeneity as a novel omnipolar mapping metric for functional substrate characterization in scar-related ventricular tachycardias

BACKGROUND: Vector field heterogeneity (VFH) is a novel omnipolar metric to quantify local propagation heterogeneities that may identify functionally critical sites for ablation in scar-related ventricular tachycardia (VT). OBJECTIVE: This study aims to assess the diagnostic value of VFH to identify abnormal propagation patterns during ventricular substrate mapping and compare VFH in VT isthmus sites (IS), low-voltage bystander area (LVA) , and normal voltage areas (NVAa). METHODS: Substrate maps acquired with a 16-pole grid catheter in patients with scar-related VT were segmented into sites corresponding to IS, LVA, and NVA (defined as omnipolar voltages > and <1.5 mV) based on corresponding VT activation maps. For each 4 × 4 electrode-array acquisition, omnipolar-derived vector maps of the directions of electrical propagation were computed offline, and a VFH value per clique ranging from 0 (perfect planar wave) to 1 (maximal disorganization) derived. RESULTS: Sixteen patients were studied (56.3% ischemic), evaluating 9 endocardial and 7 epicardial substrate maps. VFH metric at IS was 0.57 ± 0.26, LVA 0.52 ± 0.34, and NVA 0.16 ± 0.24. VFH at IS was higher (more disorganized) than at LVA (P < .001). VFH in NVA was significantly lower (ie, more homogeneous) compared with IS and LVA (P < .001, respectively). Within the isthmus, highest heterogeneity was recorded at entry (0.61 ± 0.24), lowest at exit sites (0.44 ± 0.27). CONCLUSION: VFH mapping identified a significant increase in electrical heterogeneity at IS compared with bystanders with highest heterogeneity at the entrance. Yet, absolute differences were small, and substantial overlap among sites was recorded, precluding its use as a stand-alone mapping approach. VFH may be integrated in existing mapping strategies as complementary information to support identification of ablation targets.