Testing a Simple Model of the Unipolar Electrogram in the Intact Human Heart and Examples of Applications

The unipolar electrogram (UEG) is widely used in electrophysiological research and in the cathlab. We aimed to test a previously proposed simple model of the UEG against in-vivo human data and to use the model to investigate: (A) Accuracy of repolarization measurements; (B) Factors affecting UEG substrate mapping and (C) Interactions between APD and UEG T-wave alternans. UEGs were recorded in 10 patients using a multi-electrode sock. Local action potentials showing same activation and repolarization sequence as measured in-vivo were generated using analytical functions. Local UEGs were simulated as the difference between the local action potential and a position-independent component representing remote activity. Morphological correlation between recorded and simulated UEG was cc = 0.92 (0.79 – 0.97) (median Q1-Q3, N = 1, 756). Simulation studies showed: (A) Caution should be used when analyzing biphasic T-waves and T-waves associated with either very early or late repolarization. (B) Substrate mapping using UEG amplitude depends on the activation sequence and its total duration. (C) UEG TWA is not a specific surrogate for local APD alternans as it can be observed in sites without APD alternans due to variations in the remote component. In conclusion, the simple model provides a framework to improve the understanding and clinical utility of the UEG.