Optimal control of spiral waves in heterogeneous excitable media: non-monotonic efficacy of localized optogenetic inhibition

Structural heterogeneity stabilizes spiral waves in excitable media, yet how its spatial architecture, ranging from diffuse interstitial deposition to focal scar patterns, modulates the efficacy of localized optogenetic control remains poorly understood. Using a two-dimensional computational model of human atrial tissue expressing the inhibitory opsin GtACR1, we systematically evaluated spiral wave termination across fibrosis coverage from 0 to 100%, two distinct spatial patterns, and various illumination strategies, including varied coverage, intensity profiles and low-intensity periodic stimulation. We identify a robust non-monotonic dependence of termination efficacy on illuminated area, with distinct dynamical origins for diffuse and focal fibrosis. Diffuse heterogeneity promotes efficient termination via drift toward tissue boundaries, while focal fibrosis strongly anchors the spiral core and requires substantially broader illumination for effective suppression. An optimal window covering 40-70% of the domain maximizes annihilation efficiency by reshaping the functional excitable domain and shortening the spiral core's drift path to the boundary. Excessive sub-global coverage paradoxically prolongs persistence via narrow-strip geometric confinement. Wavefront fragment collisions in focal fibrosis make only a minor, non-essential contribution to this non-monotonic response. This optimal window remains robust across varied biophysical, conduction and structural parameters, revealing a general principle for low-energy pattern control in disordered excitable media.