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Figure 6 An example of fast Fourier transformation (FFT) analysis of lead V1 before (A) and after (B) electrogram-guided ablation. A 10-s fragment of the 60-s sample was magnified to better illustrate the electrograms in both panels. Electrograms before QRST subtraction are shown in green. After the QRST subtraction, the electrograms are shown in red.