P.1. Supraventricular Arrhythmias

Objectives We set out to separate atypical from typical atrial flutter (AFL) by analyzing subtle variability in atrial wavefronts and AV nodal conduction from ECG and intracardiac analysis. Methods and Results In 42 patients undergoing AFL ablation (21 typical, 21 atypical), we filtered ECG atrial waveforms via sliding-correlation of F-wave templates to their ecgs over time. Waveforms were spatially variable if ECG loops in XY (V5/avf), YZ (avf/V1) and XZ (V5/V1) planes failed to exceed our validated threshold (>1.3). Compared to typical AFL, atypical AFL showed greater wavefront variability (21/21 vs 1/21 cases; p<0.001), greater CL standard deviation (6.98±7.02 ms vs 3.10±1.62 ms; p=0.023), AV conduction that was less likely to be an integer multiple of AFL cycle length (10/21 vs 19/21; p=0.003), and greater AH variability (155±79 vs 61±75 ms; p = 0.015) for a given atrial cycle length. Conclusions typical AFL shows wider variations in AV conduction and AH interval than typical AFL, that likely reflects subtly greater wavefront variability. This may have implications for ablation and may help explain transitions to fibrillation.