Exploring Ventricular Repolarization Gradients in Control Subjects Using the Equivalent Dipole Layer.

The electrical activity underlying the T-wave is less well understood compared to the QRS complex. In this study we aim to investigate the relationship between T-wave morphology and the underlying ventricular repolarization gradients using the equivalent dipole layer (EDL). Body-surface-potential-maps (67-leads) were obtained in nine control subjects. Subject specific CT/MRI-based anatomical heart/torso models with electrode positions were created. The boundary element method was used to compute the transfer matrix to account for the volume conductor effects. The source strength at each ventricular node of the EDL was defined by the shape of the transmembrane potential (TMP). A new template for the TMP was created and different slopes were tested for the plateau phase of the TMP. Three ventricular gradients were applied: a) transmural, b) interventricular c) apicobasal and d) combined. Realistic T-waves could be simulated for all three ventricular repolarization gradients with the apico-basal gradient resulting in the best fit. Combination of all three gradients further improved the match between measured and simulated T-waves, indicating that all three gradients are required in the genesis of the T-wave. The knowledge obtained in this study will be used to optimize the initial estimate in our EDL based inverse procedure.