Separating atrial flutter from atrial fibrillation with apparent electrocardiographic organization using dominant and narrow F-wave spectra

OBJECTIVES The purpose of this study was to separate atrial flutter (AFL) with atypical F waves from fibrillation (AF) with "apparent organization." BACKGROUND We hypothesized that F-wave spectra should reveal a dominant and narrow peak in AFL, reflecting its single macro-re-entrant wave front, but broad spectra in AF, reflecting multiple wave fronts. METHODS We identified 39 patients with electrocardiograms (ECGs) of "AFL/AF" or "coarse AF" from 134 consecutive patients referred for ablation: 21 had AFL (18 atypical, 3 typical), 18 had AF, and all were successfully ablated. Filtered atrial ECGs were created by cross-correlating F waves to successive ECG time points. Dominant peaks between 3 and 10 Hz were identified from power spectra of X (lead V-5), Y (aVF), and Z (V-1) axes, and for each, we calculated height (relative to two adjacent spectral points) and area ratio to envelopes of bandwidth 0.625, 1.25, 2.5, 3.75, and 5 Hz (range 0 to 1, where higher ratios reflect narrower peaks). RESULTS Dominant peaks had greater relative height for AFL than AF (three-axis mean: 14.2 +/- 6.4 dB vs. 6.6 +/- 2.1 dB; p < 0.001). Peak area ratios were also higher for AFL than AF for all envelopes (p < 0.001). For the 2.5-Hz envelope, the separation (0.61 +/- 0.14 vs. 0.35 +/- 0.05, respectively; p < 0.001) enabled a ratio >= 0.44 to identify all cases of AFL from AF (p < 0.001). A panel of seven cardiologists blinded to clinical data provided lower diagnostic accuracy (82.1%; p < 0.01). CONCLUSIONS In ambiguous ECGs with atypical F waves, spectral evidence for a solitary activation cycle separates AFL from AF with "apparent organization." This approach might improve bedside ECG diagnosis and shed fight on intra-atrial organization of both rhythms.