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Figure 2 Temporal phase. (A) isthmus-dependent atrial flutter shows electrocardiogram (ECG) and correlations of labeled template to ECG, producing regular correlation time series. Peaks where r 1 identify recurrent F waves even if superimposed on QRS activity. Power (Fast Fourier Transform [FFT]) spectrum from correlation series shows atrial peak (10.53 dB) at 3.78 Hz. (B) Non-isthmus-dependent atrial flutter. Shows ECG with F waves that have some "typical" features but vary. Correlation time series show irregularity. Spectra show one atrial peak (16.72 dB) at 3.42 Hz. Non-isthmus-dependent atrial flutter was confirmed near a right atrial scar and ablated.