The invention provides a catheter for optical ablation of tissue in a living body, the catheter including: a distal end; a proximal end; an elongate catheter body coupled between the distal end and the proximal end; a light emission device at the distal end and configured to emit an ablation light having characteristics selected to regulate an optically regulatable transcription control element operably linked to a nucleic acid sequence for a gene product, the expression of which gene product in cells directly or indirectly kills cells; and a projection control mechanism coupled to the light emission device and configured to control an effectively illuminated area where the optically regulatable transcription control element is effectively regulatable by the ablation light projected from the light emission device. Also provided is a system which includes the catheter, and methods to prevent, inhibit or treat AF which employ an expression cassette and/or one or more selected wavelengths of light.