Inter-patient variability of local cycle length and duty cycle distribution of the atrial fibrillation substrate beyond pulmonary vein isolation
Authors: Unger L A , Schmidt K , Haas A , Vacanti G , Widder J , Luik A 
Published: May 2024

Abstract
Appropriate targets for catheter ablation of atrial fibrillation (AFib) beyond pulmonary vein isolation (PVI) are still controversially discussed. Various approaches such as ablation of complex fractionated atrial electrograms (EGMs), areas with spatio-temporal dispersion, and areas with increased rotor density have not been reproducible or failed to improve clinical success rates. The local cycle length (CL) and duty cycle (DC) distribution during AFib offer novel measures to characterize the atrial substrate.
This study aims at providing first insights into the inter-individual variability of observed CL and DC distributions, their interdependence, and their correlation to the duration of AFib episodes to improve the individual characterization of the AFib substrate and tailor ablation strategies in future.
In patients with recurrence of AFib despite PVI, a high-resolution 3D map was recorded at baseline during AFib. Intracardiac EGMs were preprocessed to improve local signal quality and far field suppression. EGMs were recorded with the multipolar, basket-shaped high-density mapping catheter. Local CL and DC distribution were visualized using a scatter plot and histograms. CL quantifies the time between subsequent local activations, DC quantifies the fraction of CL with local EGM activity, and the confidence (conf) feature quantifies the spatiotemporal consistency of EGM morphology. Only EGMs with conf &gt; 0.6 are analysed. Feature calculation does not only take into account single EGMs but a weighted conglomerate of all acquisitions within a series of beats. Adjustable CL and DC thresholds allow highlighting regions within the 3D map for individual spatial analysis.
14 patients (7x paroxysmal AFib, 7x persistent AFib) were enrolled. All subjects underwent repeat ablation after PVI due to recurrence of AFib. CL and DC histograms were of highly individual shape. The most prevalent feature value varied from 158ms to 263ms for CL and from 38% to 96% for DC; histogram widths (inter-quartile-range) from 10ms to 34ms and from 26% to 36%, respectively. Normal distributions, multimodal distributions, and skewed distributions exhibiting a dominant peak were observed for CL. Both the most prevalent CL and the width of the distribution were highly individual. DC was observed to be normally to equally distributed with mostly broad bandwidths. Linear regression revealed a positive dependency between the most prevalent CL and the width of CL distributions. The most prevalent value and the width of both CL and DC did not differ significantly for the paroxysmal and persistent subgroup. Compare figure for detailed results.
CL and DC distributions can help to characterize the highly individual type of AFib. The presented results suggest that there will not be a one-size-fits-all ablation approach for the AFib substrate. Further research is needed to identify clusters of similar pattern and individually adjust the ablation strategy.