The optimal approach to identify sites to target with ablation during ventricular substrate mapping for ventricular tachycardia remains debated. Our study aims to evaluate the diagnostic utility of a novel propagation organization metric, the omnipolar-based local vector field heterogeneity (VFH), to differentiate functionally critical sites from bystander areas during ventricular substrate mapping to inform ablation strategy. We compared VT isthmus sites, low-voltage bystander areas (LVAs), and normal voltage areas (NVAs). The substrate maps from nine patients were segmented by domain-experts according to these sites, and the VFH metric was calculated for each region. We performed statistical analyses of VFH values across the three sites, identifying statistically significant differences between each pair of regions (p < 0.001). The VFH mapping revealed a statistically significant increase in electrical heterogeneity at critical isthmus sites compared to LVAs and NVAs. Clinical Relevance -- The VFH metric is a promising new substrate mapping strategy to identify targets for catheter ablation in scar-related ventricular tachycardias.