Assessment of the Relevant Field of View of Unipolar Electrodes Using In Vivo Imaging

Voltage mapping is integral to substrate assessment for ventricular tachycardia (VT) ablation; however, the spatial extent of myocardium contributing to a recorded electrogram signal remains poorly defined. Recent preclinical data assessed the relevant field of view (FOV) of 3.5 mm and 0.167 mm² electrodes using cardiac magnetic resonance to quantify extent of viable myocardium (VM) and found FOVs of 10 millimeters and 8 millimeters, respectively. However, this is yet to be investigated with clinical data.

This study sought to assess the FOV of 1-mm and 460-μm electrodes clinically and to evaluate the ability of cardiac magnetic resonance and cardiac computed tomography (CCT) to predict voltage amplitude.

Patients undergoing VT ablation received preprocedural late gadolinium-enhanced cardiac magnetic resonance (LGE-CMR) and CCT with extracellular volume (ECV) estimation. VM was identified using standard LGE-CMR thresholds, ECV maps were computed from CCT, and unipolar voltage was recorded during ablation procedure. VM volume and volume-weighted ECV within multisize spheres around each electrode recording site were correlated with local voltage amplitude.

A total of 16 patients were included; 15 had imaging-derived LGE-CMR/CCT-ECV analysis and 13 underwent left ventricular endocardial voltage mapping for FOV assessment. The FOV of both electrode sizes was determined to be 13 millimeters. Of the imaging modalities assessed, LGE-derived volume of VM produced the strongest correlations with voltage (1-mm electrode: r = 0.53; P < 0.001; 460-μm electrode: r = 0.49; P < 0.001). Volume-weighted ECV demonstrated weaker correlations (r = -0.34 and -0.24; P < 0.001).

Clinical evaluation of 1-mm and 460-μm electrodes suggests a larger FOV than preclinical investigations. This quantifies a larger scale across which myocardial viability can influence unipolar electrogram signals observed during ablation procedures and suggests that smaller electrodes can improve spatial sampling density but do not necessarily provide a distinctly more localized characterization of the electrophysiologic properties of the tissue. LGE-CMR best predicted unipolar voltage, whereas CCT-ECV performed less well. Correlations were lower than expected, indicating the need for electrophysiologic assessment alongside comprehensive imaging.