Abstract 3491: Endo-Epicardial Dissociation of Electrical Activity Increases During the Development of the Substrate for Atrial Fibrillation in the Goat
Background: The high incidence of transmural conduction of fibrillation waves (breakthroughs) in a complex substrate for atrial fibrillation (AF) implies the presence of electrical dissociation between the subepicardial layer (Epi) and the endocardial bundle network (Endo). The presence of this Endo/Epi dissociation (EED) in remodeled atria and its role in the progressive stabilization of AF over time has not been studied yet.
Methods: We developed a mapping tool for synchronous Endo/Epi mapping (spatial resolution 1.6mm) with 90 exactly opposing electrode pairs (open chest experiment). We included 3 groups of goats: C = Control (acute AF induced by 50Hz burst pacing, n=7), 3wk = 3weeks AF (n=7) and 6mo = 6months AF (n=7). Dissociated activity was postulated when either activation times differed by more than 12ms vertically or 8ms horizontally (indicating a local conduction velocity < 20cm/s) or local direction of propagation between Endo and Epi differed by more than 90 degrees. To monitor AF stability, repetitive in-vivo cardioversion experiments with class 1C drugs were performed in 6 of the 6mo goats at 2,6,10 and 14wk AF.
Results: Applying the time criterion, EED increased from 15±4% (C) to 22±11% (3wk) and 35±13% (6mo, p=0.002 vs. C). Also the differences in the direction of propagation significantly contributed to EED. Using the combined criterion, EED increased from 38±5% (C) to 46±10% (3wk) and 53±11% (6mo, p=0.007 vs. C). Dissociation within the epicardial and the endocardial layer (time criterion) increased to a comparable extent (19±8% vs. 27±14% vs. 37± 7%, p<0.001 C vs. 6mo). Mean Endo/Epi activation time differences were close to 0ms in all three groups (−1.0±15ms vs. −0.8±16ms vs. −0.3±20ms), ruling out preferential conduction from Endo to Epi or vice versa. Success rate of cardioversion experiments decreased from 83% (2w) to 33% (6wk) to 16% (10wk) to 0% (14wk) indicating increasing stability of AF over time.
Conclusion: During AF, pronounced EED occurs. EED (like dissociation within Endo and Epi) increases over time, contributing to the progressive stabilization of AF. Enhanced EED might explain the high incidence of transmural conduction (breakthroughs) in a complex substrate for AF.