Optical control of excitation waves in cardiac tissue

Abstract

In nature, macroscopic excitation waves^1,2 are found in a diverse range of settings including chemical reactions, metal rust, yeast, amoeba and the heart and brain. In the case of living biological tissue, the spatiotemporal patterns formed by these excitation waves are different in healthy and diseased states^2,3. Current electrical and pharmacological methods for wave modulation lack the spatiotemporal precision needed to control these patterns. Optical methods have the potential to overcome these limitations, but to date have only been demonstrated in simple systems, such as the Belousov-Zhabotinsky chemical reaction⁴. Here, we combine dye-free optical imaging with optogenetic actuation to achieve dynamic control of cardiac excitation waves. Illumination with patterned light is demonstrated to optically control the direction, speed and spiral chirality of such waves in cardiac tissue. This all-optical approach offers a new experimental platform for the study and control of pattern formation in complex biological excitable systems.

Figure 1. All-optical system for control of wave dynamics in biological media

a, Experimental set-up, including an actuation light source (LS1: 10WLED, 460 nm), a total-internal-reflection prism (TIR) and a computer-controlled digital micromirror device (DMD). Generated light patterns are projected via lenses and a dichroic mirror (DM, 510 nm) to the biological sample. A second light source (LS2: white LED, bandpass filtered at 580 ± 20 nm) provides oblique trans-illumination for dye-free imaging onto a scientific complementary metal-oxide semiconductor (sCMOS) camera through an objective lens (×1, 0.25 NA) and a long-pass emission filter (F, >580 nm). b, Example of minimally filtered images in response to optical line stimulation in cardiac monolayers. c,d, Intensity (I) versus time (t) trace from a single pixel (c) and activation maps (d) showing ongoing spontaneous activity (a spiral) pre-stimulus, terminated by a strong global optical stimulation (P1) and followed by periodic optical stimulation (P2) by a line stimulus. For b–d, see also Supplementary Movies 1 and 2.

Figure 2. Optical control of cardiac wave direction

a, Sample and applied light stimulus S, inducing bidirectional propagation. b–d, Schematic representation (b) of the applied light protocol in space and time (x–t) with pre-conditioning stimuli p1 and blocking stimuli bL and bR to set tissue refractoriness before stimulus S, resulting in a right-side (c) or a left-side (d) unidirectional block. Here p1 is 350 ms, bR and bL are 50 ms and S is 10 ms. Irradiance levels are high (1,200 W m⁻²) and medium (700 W m⁻²). Activation maps show isochrones at 100 ms spacing.

Figure 3. Optical control of cardiac wave conduction velocity

a, Schematic of applied optical stimulation protocol in space (x) and time (t). b,c, Activation maps of controlled left-side (b) and right-side (c) increase of conduction velocity by light, indicated by the larger spacing of the isochrones. d, Relationship between conduction velocity and irradiance, with linear regression best fit (dashed line) and 95% confidence intervals (dotted lines). Results from nine independent experiments are shown in Supplementary Fig. 6. iR and iL are 500 ms. Isochrones are 100 ms apart. Irradiance levels for the stimulating pulse (‘Med’ in a) are 700 W m⁻², with low irradiance varying between 0 and 80 W m⁻² applied as shown in b and c. For b and c, see also Supplementary Movie 3.

Figure 4. Optical control of spiral wave chirality in cardiac monolayer

a, Snapshots from an ongoing anticlockwise spiral wave (frames 2,000–2,160), an optically applied computer-generated clockwise spiral wave (frames 2,240–2,480) and the persisting spiral wave post-chirality reversal (frames 2,560–2,720). b, Activity traces from the red and blue pixels indicated in a, showing four light-controlled chirality reversals. Computer-generated spirals were imposed at random phases for less than two rotations, as seen in the four higher-intensity transients. Black arrows indicate the time period presented in a. Red and blue arrows indicate the switch of order of excitation at the chosen locations due to chirality reversal. c, Activation maps for the initial spiral wave and the four resultant spirals after each of the chirality reversals. See Supplementary Movies 4 and 5 for minimally processed and colourized data, respectively (for more details see Supplementary Fig. 3).