Abstract 10814: Prolongation of the Refractory Period is a Key Mechanism of Optogenetic Termination of Atrial Fibrillation in Mouse Hearts

Abstract

Backgrounds: Optogenetics is a new technique that employs light-sensitive channels and manipulates the cell membrane potential. Although painless defibrillation of reentry arrhythmias such as atrial fibrillation (AF) using optogenetics has been reported, the mechanism has not been fully elucidated because of the difficulty to evaluate the action potential (AP) modification by in/ex-vivo light illumination. Purpose: Our aim is to clarify the mechanism of optogenetic defibrillation of AF in a mouse heart by voltage-sensitive optical mapping. For this purpose, we employed a novel approach using brief light illumination combined with a systematic electrical stimulation protocol. Methods and Results: Hearts from transgenic mice expressing channelrhodopsin-2 in atrial cardiomyocytes were explanted and perfused with tyrode’s solution containing low K + concentration (2.7mM) and K ACh -channel activator carbachol (2μM). Atrial tachyarrhythmia induced by burst pacing was terminated by blue light (470nm) illumination with a pulse duration of 10 ms and a light intensity of 16 mW/mm 2 with a probability of 64.7 ± 8.1% (n=9). The termination rate depended on the pulse duration and light intensity. Then, we examined whether brief light illumination (10 ms, 6mW/mm 2 ) at different time phases from the rise of the AP (phase 0) to the repolarization (phase 4) modify AP shape and prolong the effective refractory period (ERP) using voltage-sensitive optical mapping. Brief light illumination prolonged AP duration and ERP in all time phases. The degree of ERP prolongation was dependent on the pulse duration, but not on the light intensity above 1 mW/mm 2 . Finally, we measured the attenuation of blue light intensity through the atrial tissue and observed that the intensity decreased by 38.1 ± 3.5% at 10mW/mm 2 on 3 mm 2 circular area(n=6), suggesting that high-intensity light also modulates the APs of atrial cardiomyocytes in deeper layers. Conclusion: Our results directly demonstrated that brief light illumination prolonged the atrial refractory period depending on pulse duration in a perfused heart and suggests the prolongation of the refractory period is a key mechanism of optogenetic termination of AF.