Background:Optogenetics approaches, utilizing light-sensitive proteins, have emerged as unique experimental paradigms to modulate neuronal excitability. Here, we aimed to test the hypothesis that similar strategies can be used to develop optogenetics-based approaches for cardiac pacing and resynchronization in the
in vivo rat heart.
Methods:Fisher rats were injected intra-myocardialy with AAV encoding for Channelrhodopsin-2(ChR2) protein (at single/multiple sites). Two weeks later, the ability to optogentically pace the animals was evaluated either in the in vivo setting (using a mid-sternotomy open-chest approach) or using the isolated Langendorff-perfused rat heart model. Focused illumination was performed using a monochromic light at different flashing frequencies. A digital ECG data acquisition system was used to evaluate capture rates. Optical mapping technique was used to analyze the activation pattern and time by construction of isochronal activation maps.
Results:Illumination to the site of gene delivery resulted in pacing of the heart in both the open-chest setting as well as in the Langendorff configuration. We were able to vary the beating rate to rates as high as 500 bpm, and to continuously pace the heart for several hours without pacing failure. Optical mapping confirmed that during illumination the location of the pacing site shifted to the site of ChR2 transgene delivery. Importantly, diffuse illumination of hearts, in which the transgene was delivered to a number of sites, resulted in simultaneous activation of the ventricle from these multiple-sites and significant shortening of the total activation time (from 28.4±2.8ms to 16.9±2.3ms ;p=0.002 ;n=8).
Conclusions:This is the first report on light-based cardiac pacing in non-transgenic mammals in-vivo. We have demonstrated that optogenetics enable precise control of the cardiac beating rate with high efficacy, and for prolong periods. Importantly, optogenetics could be used for multi-site pacing, thereby inducing synchronized contraction.
