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

Abstract

BACKGROUND: 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. METHODS: Dogs (n&#xa0;=&#xa0;6) were implanted with a neurostimulator in the right atrium (AF group). No implantation was done in the Control group (n&#xa0;=&#xa0;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. RESULTS: A significant increase was seen in the left atrial (LA) volume among all AF animals (22.25 &#xb1; 12.60 cmvs 34.00 &#xb1; 12.23 cm, P&#xa0;=&#xa0;.01). Also, mean bipolar amplitude in the LA significantly decreased from 5.96 &#xb1; 2.17&#xa0;mV at baseline to 3.23 &#xb1; 1.51&#xa0;mV (P&#xa0;<&#xa0;.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 &#xb1; 0.37&#xa0;Hz to 10.12 &#xb1; 0.28&#xa0;Hz at chronic AF (P&#xa0;<&#xa0;.01). Moreover, the percentage of fibrosis in chronic AF animals was significantly larger than that of control animals in each location (P&#xa0;<&#xa0;.01). CONCLUSIONS: 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.