The accuracy of ECG imaging (ECGI) in structural heart disease remains uncertain. This study aimed to provide a detailed comparison of ECGI and contact-mapping system (CARTO) electrograms.

Simultaneous epicardial mapping using CARTO (Biosense-Webster, CA) and ECGI (CardioInsight) in 8 patients was performed to compare electrogram morphology, activation time (AT), and repolarization time (RT). Agreement between AT and RT from CARTO and ECGI was assessed using Pearson correlation coefficient, ρ_AT and ρ_RT, root mean square error, E_AT and E_RT, and Bland-Altman plots.

After geometric coregistration, 711 (439–905; median, first-third quartiles) ECGI and CARTO points were paired per patient. AT maps showed ρ_AT=0.66 (0.53–0.73) and E_AT=24 (21–32) ms, RT maps showed ρ_RT=0.55 (0.41–0.71) and E_RT=51 (38–70) ms. The median correlation coefficient measuring the morphological similarity between the unipolar electrograms was equal to 0.71 (0.65–0.74) for the entire signal, 0.67 (0.59–0.76) for QRS complexes, and 0.57 (0.35–0.76) for T waves. Local activation map correlation, ρ_AT, was lower when default filters were used (0.60 (0.30–0.71), P=0.053). Small misalignment of the ECGI and CARTO geometries (below ±4 mm and ±4°) could introduce variations in the median ρ_AT up to ±25%. Minimum distance between epicardial pacing sites and the region of earliest activation in ECGI was 13.2 (0.0–28.3) mm from 25 pacing sites with stimulation to QRS interval <40 ms.

This simultaneous assessment demonstrates that ECGI maps activation and repolarization parameters with moderate accuracy. ECGI and contact electrogram correlation is sensitive to electrode apposition and geometric alignment. Further technological developments may improve spatial resolution.