Background: Brugada syndrome (BrS) is an inherited ion-channel disorder in which characteristic ECG changes of J-point elevation and T‑wave inversion may occur in the precordial leads on the 12-lead ECG (V1-V3), though its pathophysiological mechanisms remain unclear. The repolarisation hypothesis poses alterations in the transient outward potassium current (Ito) of the epicardial right ventricular outflow tract (RVOT) leading to ECG changes. Whilst supported by experimental wedge studies and 2D/3D slab models, this theory is yet to be systematically studied in human-based biventricular models. Aims: To investigate the effect of increasing Ito transmural gradient in the RVOT on APs and corresponding ECG manifestations. Methods: Biventricular geometry was reconstructed from automated CT-segmentation and mesh generation from a confirmed BrS patient. Fibres and universal ventricular coordinates (UVCs) were generated using CARPentry Studio. Simulations were run with CARPentry (NumeriCor GmbH, Graz, Austria). To establish a baseline, a fascicular-based conduction model with a fast-conducting subendocardial layer was employed. Early activation sites were inferred via Sobol sampling of fascicle UVC locations to maximise correlation between simulated (~1400 reaction-Eikonal simulations) and average ECG from ~51,000 UKBioBank participants. Apicobasal and transmural AP heterogeneities were incorporated. Isolating the role of Ito in ECG patterns, monodomain simulations were performed with ionic modifications in the RVOT. We applied increasing, linear transmural gradients of conductance, Gto, multipliers (epi-mid), with endocardium unchanged. Electrodes were positioned on a CT-segmented torso surface, and extracellular potentials were computed using the phie-recovery method to compute ECGs. Results: The increased transmural gradient due to epicardial Gto increase, causing a more pronounced Phase1 notch, yielded increasingly elevated J‑points in V1-3. Delayed epicardial repolarisation reversed the normal T‑wave due to larger repolarisation dispersion transmurally. Conclusion: We show that increased Gto along with transmural AP heterogeneity is sufficient to produce ECG features characteristic of BrS, namely J-point elevation and T-wave inversion.