Local Electrical Impedance Mapping of the Atria: Conclusions on Substrate Properties and Confounding Factors

The treatment of atrial fibrillation and other cardiac arrhythmias as a major cause of
cardiovascular hospitalization has remained a challenge predominantly for patients with
severely remodeled substrate. Individualized ablation strategies are extremely important
both for pulmonary vein isolation and subsequent ablations. Current approaches
to identifying arrhythmogenic regions rely on electrogram-based features such as
activation time and voltage. Novel technologies now enable clinical assessment
of the local impedance as tissue property. Previous studies demonstrated its use
for ablation monitoring and indicated its potential to differentiate healthy substrate,
scar, and pathological tissue. This study investigates the potential of local electrical
impedance-based substrate mapping of the atria for human in-vivo data. The presented
pipeline for impedance mapping particularly contains options for dealing with undesirable
effects originating fromcardiacmotion, cathetermotion, or proximity to other intracardiac
devices. Bloodpool impedance was automatically determined as a patient-specific
reference. Full-chamber, left atrial impedance maps were drawn up from interpolating
the measured impedances to the atrial endocardium. Finally, the origin and magnitude
of oscillations of the raw impedance recording were probed into. The most dominant
reason for exclusion of impedance samples was the loss of endocardial contact.
With median elevations above the bloodpool impedance between 29 and 46, the
impedance within the pulmonary veins significantly exceeded the remaining atrial walls
presenting median elevations above the bloodpool impedance between 16 and 20.
Previous ablation lesions were distinguished from their surroundings by a significant
drop in local impedance while the corresponding regions did not differ for the control
group. The raw impedance was found to oscillate with median amplitudes between 6
and 17 depending on the patient.Oscillations were traced back to an interplay of
atrial, ventricular, and respiratory motion. In summary, local impedance measurements
demonstrated their capability to distinguish pathological atrial tissue from physiological
substrate. Methods to limit the influence of confounding factors that still hinder
impedance mapping were presented. Measurements at different frequencies or the combination of multiple electrodes could lead to further improvement. The presented
examples indicate that electrogram- and impedance-based substrate mapping have the
potential to complement each other toward better patient outcomes in future.