Introduction: The unipolar electrogram (UEG) allows simultaneous multi-site assessment of cardiac excitation and recovery and is widely used in electrophysiological research and in the cathlab. A simple models was previously proposed to explain its morphology in terms of local and remote activity.
Aim: (1) To test the model against in-vivo human data. (2) To use the model to investigate: (A) Accuracy of standard repolarization measurements; (B) Factors affecting unipolar substrate mapping and (C) Interactions between APD and UEG T-wave alternans.
Methods: UEGs were recorded in 10 patients using a multi-electrode sock (240 UEGs) during ventricular pacing (CL=500 ms). Local action potentials showing same activation and repolarization sequence as measured in-vivo were generated by analytical functions. Local UEG were simulated as the difference between the local action potential and a position-independent component representing remote activity defined as the average of all action potentials. Morphological similarity between simulated and recorded UEGs was assessed using Person’s cc. Simulations were conducted to investigate points (A)-(C).
Results: 1,756 UEGs were included based on signal quality. Correlation between recorded and simulated UEGs was cc=0.92 (0.79-0.97) (median Q1-Q3 pooling together recordings from all patient). Simulation studies showed: (A) Standard method for RT assessment is accurate but caution should be used when analysing 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 surrogate for local APD alternans as it can be observed in sites without APD alternans due to variations in the remote component.
Conclusions: Good agreement was found between the simple model’s output and in-vivo human data. The simple model provides a framework to improve the understanding and clinical utility of the UEG.