Changes in atrial electrophysiological and structural substrate and their relationship to histology in a long-term chronic canine atrial fibrillation model.

Abstract

Atrial fibrillation (AF) is related to numerous electrophysiological changes; however, the extent of structural and electrophysiological remodeling with long-term AF is not well characterized. Dogs (n=6) were implanted with a neurostimulator in the right atrium (AF group). No implantation was done in the Control group (n=3). Electroanatomical mapping was done prior to and following more than 6 months of AF. Magnetic resonance imaging was also done to assess structural remodeling. Animals were euthanized and tissue samples were acquired for histological analysis. A significant increase was seen in the left atrial (LA) volume among all AF animals (22.25 ± 12.60 cm3 vs 34.00 ± 12.23 cm3 , P=.01). Also, mean bipolar amplitude in the LA significantly decreased from 5.96 ± 2.17mV at baseline to 3.23 ± 1.51mV (P<.01) after chronic AF. Those significant changes occurred in each anterior, lateral, posterior, septal, and roof regions as well. Additionally, the dominant frequency (DF) in the LA increased from 7.02 ± 0.37Hz to 10.12 ± 0.28Hz at chronic AF (P<.01). Moreover, the percentage of fibrosis in chronic AF animals was significantly larger than that of control animals in each location (P<.01). Canine chronic AF is accompanied by a significant decrease in intracardiac bipolar amplitudes. These decreased electrogram amplitude values are still higher than traditional cut-off values used for diseased myocardial tissue. Despite these "normal" bipolar amplitudes, there is a significant increase in DF and tissue fibrosis.