Annotation of a wavefront

An apparatus, comprising:

• a probe having a distal end portion and being adapted for insertion into a heart of a living subject;
• a pair of electrodes located along the distal end portion configured to be placed in proximity to a myocardium of a human subject;
• and
• a processor configured to perform:
• receiving a bipolar ECG signal from a location in the heart from the pair of electrodes;
• receiving a unipolar ECG signal from the location in the heart from a selected one electrode of the pair of electrodes;
• computing a local unipolar minimum derivative of the unipolar signal at a plurality of times of occurrences of the local unipolar minimum derivative;
• computing a bipolar derivative of the bipolar signal;
• evaluating a ratio of the bipolar derivative to the local unipolar minimum derivative at the plurality of times of occurrences of the local unipolar minimum derivative;
• annotating each time of occurrence as a time of activation of the myocardium at the location in the heart when the ratio is greater than a preset threshold value;
• merging two annotations that arise from a single occurrence as a single annotation;
• evaluating features of the annotations and assigning a confidence level to each feature;
• eliminating annotations that have a confidence level below a threshold;
• and
• generating a local activation time map using the remaining annotations.