Vector Field Heterogeneity (VFH) as a novel quantitative marker of electrical disarray in Arrhythmogenic CardioMyopathy (ACM) with ventricular tachycardia
Authors: Tonko J B , Ruiperez-Campillo S , Cabero-Vidal G , Rooney C , Ehnesh M , Millet-Roig J , Castells P , Lambiase P 
Published: October 2024

Abstract

Background
ACM is a hereditary condition characterized by fibrofatty infiltration and replacement of cardiac myocytes predominantly presenting with ventricular arrhythmias (VA). Cardiac imaging allows for detailed structural phenotyping of scar patterns in ACM. Yet, there is a lack of tools to objectively quantify the electrical substrate alterations that may enable a more precise identification of critical sites that predispose to VA.

Purpose
To quantify locally disorganized cardiac electrical propagation wavefronts using the Vector Field Heterogeneity (VFH) metric from high-density multi-electrodes in patients with ACM with VT and compare to healthy controls.

Methods
High density epicardial substrate maps acquired with a 16-pole grid catheter during SR or RV pacing in patients with ACM with VA, who underwent clinically indicated catheter ablation, were retrospectively reviewed. Patients with structurally normal heart and idiopathic VA with epicardial ablation were analysed as a control group. Unipolar contact mapping data was exported & processed offline. From the 4×4 electrode array EGMs, vector maps of the directions of electrical propagation for recorded sites were computed. The VFH was then computed as a quantitative measure of local heterogeneity of propagation, with higher VFH expected to correlate with sites of (micro)structural tissue alterations. VFH was compared between ACM and control patients as well as at sites of normal, border zone & scar based on omnipolar voltage in ACM patients (&gt;1.5mV, 0.5mV–1.5mV, &lt;0.5mV, respectively).

Results
10 patients with ACM (70% male, aged 52 ±18 years, ARVC 70%, biventricular 30%, RVEF 40.7±4.7%, LVEF 66±12%) and 2 patients with structurally normal heart (female, 38 & 61 years) were included. Epicardial maps had an average of 9258 ±5412 EGM points. Median VFH was statistically significantly higher in the ACM cohort compared to control for global maps (0.33±0.33 vs 0.13±0.22, p&lt;0.001) and at sites with voltage &gt;1.5mV (i.e. greater disorganization in ACM, p&lt;0.001). In ACM, assessment of VFH according to omnipolar voltage sites (as a surrogate of scar) showed a quantifiable statistically significant increase in electrical disorganized propagation at sites of lower voltage (&lt;0.5mV, median VFH 0.53±0.36) compared to borderzone (0.5-1.5mV, VFH 0.29±0.41) and normal voltage (&gt;1.5mV, VFH 0.15±0.26), p &lt;0.001 respectively.

Conclusion
Heterogenous electrical propagation as quantified by VFH is significantly increased in patients with ACM at sites of scar, but importantly also in areas of normal voltages when compared to non-ACM controls, possibly indicating microstructural alterations that are missed in traditional assessments of the arrhythmogenic substrate. Identifying and quantifying disorganized conduction patterns by VFH is a promising new mapping approach that could allow improved substrate characterization. Its diagnostic value to guide ablation therapy is currently being validated.VFH Metric ACM and ControlVFH Map Examples