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Activation Time Determination by High‐Resolution Electrograms. Introduction: To identify the optimal criteria for activation time (AT) determination of bipolar electrograms from normal hearts, a high‐resolution cross electrode array comprising 128 unipolar electrodes of 500‐μm spacing was used to record extracellular potentials from the left ventricular epicardium of 12 dog hearts.

Methods and Results: Recordings were made during broad wavefront propagation (B wave) local elliptical wavefront propagation (E wave). Characteristics of 863 bipolar electrograms (1‐mm spacing) were constructed from unipolar data standardized for differences in polarity, then classified morphologically. Features for bipolar AT determination were compared to the time of the negative peak of the firrst temporal derivative of a unipolar electrogram situated mid‐way between the bipoles. During B wave, three distinct morphologies were …