Abstract Body (Do not enter title and authors here): Background: Epicardial adipose tissue (EAT) is increasingly recognized as a key factor in the development of atrial fibrillation (AF). In addition to direct myocardial infiltration by adipocytes affecting conduction properties, EAT may also promote an arrhythmogenic substrate through paracrine and endocrine effects. EAT was shown to preferentially generate oxidase-dependent reactive oxygen species (ROS) when compared to subcutaneous fat. While a role for myocardial ROS in the development of AF is well established, a separate role for EAT oxidative stress remains unexplored.

Hypothesis: Oxidative stress in the EAT contributes to atrial electrical remodeling and development of AF.

Aims: Determine the effect of EAT-restricted gene therapy with NOX2 shRNA on atrial electrical remodeling in the short-term canine atrial tachypacing (ATP) model of AF.

Methods: A single-chamber pacemaker was inserted for the ATP model. Animals developed persistent AF after 4-6 weeks, after which the atria were harvested. Unpaced animals were used as controls. Expression of NOX2 in the EAT was assessed by qPCR. EAT oxidative stress was determined by IHC for 8-OHdG, a marker of DNA oxidative damage. A subset of animals underwent an open-chest gene injection procedure restricted to the EAT (with a plasmid expressing NOX2 shRNA or a scrambled sequence) prior to initiation of ATP for 9 days. A terminal EP study determined regional atrial ERP and AF inducibility.

Results: NOX2 expression was significantly increased in the EAT of animals with ATP-induced AF when compared to unpaced controls (Panel A, p<0.05 by t-test). IHC for 8-OHdG showed that in addition to the atrial myocardium, DNA oxidative damage was also extensively present in the EAT (Panel B, 8-OHdG+ nuclei marked with arrows). Animals having received NOX2 shRNA-expressing plasmids in the EAT had attenuated AF inducibility after short-term ATP when compared to controls (Panel C, p<0.001 by Chi-squared test). This was associated with an attenuation of ERP shortening (panel D, two-way ANOVA p<0.001). Importantly, this effect was not only observed in the posterior left atrium (PLA) but also in the left atrial appendage (LAA), which is devoid of EAT.

Conclusion: Expression of NOX2 is increased in the EAT of the canine ATP-model of AF. EAT-restricted NOX2 inhibition globally attenuates left atrial electrical remodeling, consistent with an at-a-distance effect of EAT oxidative stress on the formation of an atrial arrhythmogenic substrate.