Study of the omnipolar EGM reconstruction for robustness against wavefront propagation in epicardial signals
Authors: Ruiperez-Campillo S , Castells F , Crespo M , Pancorbo L , Guill A , Chorro F J , Merino J L , Casado-Arroyo R , Millet J 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: Public Institution(s). Main funding source(s): National Research Program, Ministerio de Ciencia e Innovación, Spanish Government, Instituto de Salud Carlos III.

Background
Characterisation of electrophysiological substrate is commonly performed by examining cardiac tissue locally by using high-density (HD) arrays of equispaced electrodes – e.g. Advisor™ HD Grid Mapping Catheter, Sensor Enabled™ (SE). These allow creating activation maps of local tissue and substrate exploration. Recently, a novel operation mode arouse: the omnipole, which overcomes many limitations of bipolar and unipolar electrograms, as they are claimed to be orientation independent. Nevertheless, the current technique to reconstruct omnipolar EGMs has pitfalls as the estimation of some incidence angles of the propagation wavefront. We propose a novel reconstruction method to estimate omnipolar EGMs which overcomes the angle dependence weakness of the current one, providing a more robust EGM representation. We hypothesise that this technique will improve reconstruction of electrophysiological signals.

Methods
Prior electrophysiological experiments on isolated rabbit hearts were used [1], including recordings with a 128-electrode array 1mm apart over ventricular epicardium at 37ºC, with bipolar electrode stimulation. Four-electrodes cliques were designed from these experiments, with different inter-electrode distances as depicted in fig. 1A, reconstructing the current, and novel omnipolar configuration. Metrics to assess the quality of the EGM signals were designed, including the bipolar loop area, and the ratio of the bipolar components of the omnipole (ox and oy) – see fig. 1B. The bipoles were calculated from unipolar EGMs, the signal was corrected with the 45º offset in the cross, the propagation angle was then detected, and the local activation time (LAT) was estimated.

Results
In the bipole plots, it was observed that the morphology of the bipolar loop gets distorted with an increase in the interelectrode distance – thinner for distances &lt;2mm. There is a direct relation between the areas in the bipolar loop and the inter-electrode distance (see fig. 2A). Furthermore, the values of the area in the cross are always comparable to the best performing triangular clique. For the ratio of bipoles, the relation is inversely to distance (see fig. 2B), similarly, the performance of the cross is comparable to the best performing triangular omnipole.

Conclusion
For reconstructing omnipolar EGMs, inter-electrode distances smaller than 2mm should be employed. Furthermore, if that condition is satisfied, the novel omnipolar reconstruction method proposed based on the cross configuration is more accurate and robust to wavefront propagation, given that the omnipolar EGM performs similarly or better than the best triangular configuration – and which triangle is fixed for the whole procedure, being the current reconstruction method less robust. Thus, a new standpoint to omnipolar reconstruction in high density electrode catheters is open, towards the design of new devices, and the practice in the clinic.