Use of Atrial Fibrillation Electrograms and T1/T2 Magnetic Resonance Imaging to Define the Progressive Nature of Molecular and Structural Remodeling - A New Paradigm Underlying the Emergence of Persistent Atrial Fibrillation

Background The temporal progression states of the molecular and structural substrate in atrial fibrillation (AF) are not well understood. We hypothesized that these can be detected by AF electrograms and magnetic resonance imaging (MRI) parametric mapping. Methods and Results AF was induced in 43 dogs (25-35 kg, ≥1 year) by rapid atrial pacing (RAP) (3-33 weeks, 600 beats/min), and 4 controls were used. We performed high-resolution epicardial mapping (UneMap, 6 atrial regions, both atria, 130 electrodes, distance 2.5mm) and analyzed electrogram cycle length (CL), dominant frequency (DF), organization index (OI) and peak-to-peak bipolar voltage (Vbip). Implantable telemetry recordings (DSI) were used to quantify parasympathetic nerve activity (PNA) over RAP time. MRI native T1, post-contrast T1, T2 mapping, and extracellular volume fraction (ECV) were assessed (1.5T, Siemens) at baseline and AF. In explanted atrial tissue, DNA oxidative damage (8-OHdG staining) and % fibro-fatty tissue were quantified. CL, OI decreased (R=0.5, P<0.05), (R=0.5, P<0.05) and DF increased (R=0.3, P n.s.) until 80 days of RAP, but not thereafter. In contrast, voltage continued to decrease throughout the duration of RAP (R=0.6, P<0.05). PNA increased post-RAP and plateaued at 80 days. MRI native T1 and T2 times increased with RAP days (R=0.5, P<0.05), (R=0.6, P<0.05) in PLA throughout RAP. Increased RAP days correlated with increasing 8-OHdG levels and with fibrosis % (R=0.5, P<0.05 for both). Conclusions A combination of AF electrogram characteristics and T1/T2 MRI can detect early-stage AF remodeling (autonomic remodeling, oxidative stress (OS)) and advanced AF remodeling due to OS and fibrosis.