Genesis of the T-wave through various modes of ventricular recovery patterns using the equivalent dipole layer model

Background: The equivalent dipole layer (EDL) relates local endocardial and epicardial transmembrane potentials to body surface potentials and can therefore be used to gain insight into cardiac activation and recovery. To use the EDL-source model for the inverse problem of electrocardiography, initial estimates for local activation times (LAT) and recovery times (LRT) are required because of its non-linear relation with body surface potentials. Objective: To develop an AT-independent initial RT estimate in the EDL-source model. Methods: Body surface mapping (BSM) and cardiac imaging were performed in 15 subjects. LAT and LRT were estimated using the EDL-source model. Various ventricular recovery patterns were tested to investigate the relation between recovery patterns and normal T-waves, including LAT-dependent-recovery and RT differences along transmural, interventricular, anterior-posterior and apico-basal axes. A new algorithm was developed based on the backwards modeling of the T-wave (BackRep) to identify the latest area of recovery. Correlation coefficient (CC) and relative difference (RD) between the recorded and computed T-waves were reported. Results: BackRep (CC = 0.89 [IQR:0.83–0.90]; RD = 0.63 [IQR:0.49–0.69]), outperformed the anatomical axes based recovery patterns (CC = 0.29 [IQR:0.21–0.46] – 0.79 [IQR:0.78–0.83]; RD = 1.02 [IQR:0.98–1.18] – 0.61 [IQR:0.57–0.68]) and LAT-based recovery pattern (CC = 0.63 [IQR:0.60–0.73]; RD = 4.35 [IQR:2.74–9.05]). Of the RT differences along the anatomical axes, the apico-basal recovery pattern showed the best match between recorded and computed T-waves. A significant apex-to-base RT difference was also found in the BackRep recovery maps. Conclusion: BackRep provides a reliable AT-independent initial RT estimate and supports the presence of an apex-to-base RT difference in normal T-wave morphology.