A bipolar electrogram and a unipolar electrogram are recordedfrom electrodes of a probe, and differentiated with respectto time. Peaks are identified in the differentiated bipolarelectrogram. An activity window is defined that includesbipolar activity about the peaks. An extreme negativevalue in the differentiated unipolar electrogram within theactivity window is reported as a unipolar activation onset.In one aspect, an annotation is selected from candidate minimain the differentiated unipolar electrogram within the activitywindow by excluding candidates that fail to correlatewith activity in the bipolar electrogram.
