Overcoming Uncertainties in Electrogram-Based Atrial Fibrillation Mapping: A Review.

In clinical rhythmology, intracardiac bipolar electrograms (EGMs) play a critical role in investigating the triggers and substrates inducing and perpetuating atrial fibrillation (AF). However, the interpretation of bipolar EGMs is ambiguous due to several aspects of electrodes, mapping algorithms and wave propagation dynamics, so it requires several variables to describe the effects of these uncertainties on EGM analysis. In this narrative review, we critically evaluate the potential impact of such uncertainties on the design of cardiac mapping tools on AF-related substrate characterization. Literature suggest uncertainties are due to several variables, including the wave propagation vector, the wave's incidence angle, inter-electrode spacing, electrode size and shape, and tissue contact. The preprocessing of the EGM signals and mapping density will impact the electro-anatomical representation and the features extracted from the local electrical activities. The superposition of multiple waves further complicates EGM interpretation. The inclusion of these uncertainties is a nontrivial problem but their consideration will yield a better interpretation of the intra-atrial dynamics in local activation patterns. From a translational perspective, this review provides a concise but complete overview of the critical variables for developing more precise cardiac mapping tools.

Beamforming-inspired Spatial Filtering Technique for Intracardiac Electrograms.

Bipolar electrograms (EGM) are widely used to assess intracardiac electrical activity and to find the atrial fibrillation-related sources. However, the interpretation of bipolar EGM is not straightforward. Variables including bipolar lead (vector) orientation relative to the wave propagation dynamics significantly impact the EGM and EGM-derived measures, which are clinically used to select target sources for catheter ablation. In this study, left atrial unipolar EGM were recorded using a 4 × 4 grid of 16 unipolar electrodes. A set (node) of 4 unipolar EGM were used to construct possible 6 bipolar EGM to evaluate the measurement uncertainty within a particular node. A novel beamforming-inspired spatial filtering (BiSF) method is proposed to reduce the potential measurement uncertainty inevitable in bipolar EGM. A set of three bipolar lead orientations that were constructed using a common unipolar electrode towards three different directions at 45°s, were added to form beamforming EGM. Finally, two beamforming EGM were intertwined to acquire BiSF EGM for a node. Results show greater signal power gain (at least around 10dB) for all BiSF EGM with better or similar signal-to-noise ratio as compared to their respective bipolar counterparts. In conclusion, reduced uncertainty in BiSF EGM improve the interpretation of EGM and EGM-derived measures used in clinical practice after further validation on a larger dataset.