Multi-modal physiological parameter for mapping ablation lesions
Authors: Masse S , Anderson R D , Gonna H , Azam M A , Lai P F H , Deno D C , Nanthakumar K 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
In addition to variety of force time indices, electrophysiologist use peak to peak voltage (Vpp) and or S wave on unipolar electrogram to assess RF lesions they deliver. This strategy ignores cardiac conduction speed, direction, and wave curvature, all of which are affected by delivered lesion. Electrode array catheters such as the Advisor HD Grid allow individual cardiac wavefronts from sites to be characterized simultaneously in two dimensions from which vectorcardiograms can be derived. This underappreciated attribute of electrograms when integrated into activation mapping may provide new insights into the electrophysiologic state of tissue including wavefront amplitude, direction and velocity.

Objective
We tested the hypothesis that intracardiac vectorcardiogram loops contain aspects of properties that may better detect lesions compared to Vpp reduction and that a novel multi-modal approach will provide additional insights on wavefront interaction with substrate.

Methods
In 5 ex-vivo Langendorff perfused swine hearts, 56-pole (7 x 8 configuration) electrode arrays were sutured to the anterior epicardial left ventricle. Unipolar electrograms were acquired with UHN mapping system during programmed stimulation from all cardinal directions before and after creating RF ablation lesions. Vector loop maps were derived from orthogonal bipole pairs to study wavefront organization and voltage. Isochrone maps were generated from unipolar local activation times. Vector loop eccentricity was defined for each 4-electrode group as a function of loop’s major and minor axis lengths. Low values denote less eccentricity (more circular).

Results
An illustrative example of vector, loop and isochrone maps before and after ablation is shown in figures 1 and 2. Pre-ablation conditions show activation from a point stimulation on the left side with slender vector loops indicative of a relatively homogeneous linear conduction. In contrast, post-ablation vector loops are much less eccentric near the ablated area and smaller reflecting attenuated amplitude. Interestingly, near border zone locations large round loops are observed, suggesting curved or nonlinear wave propagation. Figure 2 shows that vector loops recorded from scar areas were diminished in size following ablation with a mean Vpp of 3.76 vs 2.18mV (p=0.0001) and exhibited less mean eccentricity, 0.925 vs 0.848 (p&lt;0.0001), with more round loops (eccentricity &lt; 0.7) found after ablation (12% of sites vs 4% pre-ablation, p &lt; 0.0001).

Conclusions
Significant changes in loop characteristics were observed even when ablation induced voltage attenuation was minimal. This suggests that vectorial loop eccentricity may provide information in addition to omnipolar Vpp. Wavefront propagation disruption near ablation border zones is thus potentially valuable to detect lesion gaps. This information along with wave amplitude and direction can now be integrated into a novel multi-modal map.