Methodology Considerations in Phase Mapping of Human Cardiac Arrhythmias

Abstract

Background Phase analysis of cardiac arrhythmias, particularly atrial fibrillation (AF), has gained interest due to the ability to detect organized stable drivers (rotors) and target them for therapy. However, the lack of methodology details in publications on the topic has resulted in ongoing debate over the phase mapping technique. By comparing phase maps and activation maps we examined advantages and limitations of phase mapping. Methods and Results 7 subjects were enrolled. We generated phase maps and activation maps from ECGI-reconstructed epicardial unipolar electrograms (EGMs). For ventricular signals, phase was computed with: i) pseudo-empirical mode decomposition (pEMD) detrending, and ii) a novel Moving Average (MVG) detrending approach. For AF signals, MVG was modified to incorporate cycle length (CL) changes (MVG-DCL). Phase maps were visually analyzed to study phase singularity points and rotors. Results show that phase is sensitive to CL choice, a limitation that was addressed by the MVG-DCL algorithm. MVG-DCL was optimal for AF analysis. Phase maps helped to highlight high-curvature wavefronts and rotors. However, for some activation patterns phase generated non-rotational singularity points and false rotors. Conclusions Phase mapping computes singularity points and visually highlights rotors. As such, it can help to provide a clearer picture of the spatiotemporal activation characteristics during AF. However, it is advisable to incorporate EGM characteristics and the time-domain AT sequence in the analysis, to prevent misinterpretation and false rotor detection. Therefore, for mapping complex arrhythmias, a combined time-domain activation and phase mapping with variable CL appears to be the most reliable method.

Relationship Between Fibrosis Detected on Late Gadolinium-Enhanced Cardiac Magnetic Resonance and Re-Entrant Activity Assessed With Electrocardiographic Imaging in Human Persistent Atrial Fibrillation

“…In addition, and for practical reasons, AF was not re-induced in the present study after ablation of a first set of re-entrant drivers. Similarly, we acknowledge that processing ECGI signals with phase mapping can lead to over-detection of re-entrant activities (40). The mode of AF induction was heterogeneous in the studied population (pacing induced in patients presenting in sinus rhythm, spontaneous in others).…”

Fibrosis and Atrial Fibrillation: Computerized and Optical Mapping

“…(12) In our recent review,(7) we described how the same intramural microanatomic reentrant AF driver could be visualized differently at the atrial epi- vs. endocardial surfaces as either 1) complete reentry 2) partial reentry 3) stable breakthrough/ focal activity or 4) unstable breakthroughs due to the heart-specific complexity of the 3D atrial wall (Figure 3A). Furthermore, at low millimeter resolution or after phase signal processing,(13) 3D transmural microanatomic reentry may be indistinguishable from rotor type activity. (36)…”

“…(7,13) Accurately identifying drivers may be aided by defining heart-specific structural fingerprints to reliably locate AF drivers. (7) This review will focus on the role of 3D fibrosis architecture of human atria as an AF driver fingerprint that facilitates mechanisms of AF maintenance.…”

The continuous challenge of AF ablation: From foci to rotational activity

“…44 The method used by our group, Focal Impulse and Rotor Modulation (FIRM), uses such a combined activation and phase approach. 45,46 However, it is unresolved to what extent conflicting studies reflect mapping methods, patient selection, species specificities or other differences.…”