A medical device system performs a method for determining presence of scar tissue through an implanted lead having an electrode for cardiac pacing and sensing. A sensing module senses heart activity with the electrode to produce a unipolar electrogram (EGM) waveform. A processor receives the unipolar EGM waveform and extracts two or more features representative of heart activity at the electrode. Scar tissue is identified at the site of the first electrode based upon at least two of the extracted features indicating scar tissue.