Systems and methods for cardiac fast firing (e.g., atrial fast firing) detection perform frequency analysis on channels of collected cardiac waveform data and test the data for outlier frequency complex content that is of higher frequency than baseline frequency complex content associated with cardiac fibrillation (e.g., atrial fibrillation) or other arrhythmogenic activity. Anatomical regions from whence the cardiac fast firing originates can be displayed in real time on an epicardial surface map via a graphical display, aiding administration of therapy. Prior to such detection, QRST complex removal can be performed to ensure that ventricular activity does not infect the atrial fast firing analysis. A frequency-based method for QRST complex removal is also disclosed.
