Combination of lead-field theory with cardiac vector direction: ECG imaging of septal ventricular activation.

Background: Despite the tremendous progress recently reported in ECG imaging (ECGI), some fundamental challenges are still hindering this non-invasive technology from meeting rising clinical expectations. In the present work, we address one of the major ECGI shortcomings in reconstruction of ventricular activation - the limited accuracy of endocardial and particularly septal mapping.

Methods: Ten CRT patients (five female, median (min-max) age - 61 (27-78) years) with previously implanted CRT devices underwent ECGI with isolated right ventricular (RV) pacing. In eight patients, the RV pacemaker lead was placed in the middle septal area of the posterior RV wall. Two subjects had a pacing lead in the anteroseptal apical segment, two at septal RVOT, two at septal junction with posterior wall and six in anterolateral segments. Lead positions were exactly known from CT scans, making the respective paced ECG sequences ideal for validation of ECGI endocardial accuracy. Non-invasive mapping was performed for single RV paced beats using original parameters of the CRT device. For non-invasive estimation of the focal origins, we considered the lead-field based fastest route algorithm (FRA) and its combination with the cardiac vector fit (FRA-V). Furthermore, we extended the resulting combined map by incorporating cardiac activation direction (FRA-V-D) provided by the cardiac dipole.

Results: The median (min-max) localization errors were 14 mm (7-27), 9 mm (7-28) and 11 mm (8-24) for FRA, FRA-V and FRA-V-D, respectively. Notably, in all cases at least one of the considered ECGI methods was able to correctly localize the found excitation origin on the endocardium.

Conclusions: This preliminary study investigates combination of the rule-based fastest route algorithm with cardiac vector fit and direction for non-invasive imaging of septal ventricular sources. The developed ECGI methodology delivers reasonable reconstruction accuracy with the 10 mm median localization error. These findings suggest potential use of ECGI for challenging clinical cases, where catheter access to the correct cardiac anatomical region plays a crucial role in the execution of the electrophysiological procedure.