Time dependence of myocardial cell necrosis during photodynamic therapy with various photosensitizer contact time

We studied how the photosensitizer contact time affects the myocardial necrosis time during photodynamic therapy under a confocal microscopic system. Electrical conduction block by photodynamic reaction would be utilized as new catheter ablation for tachyarrhythmia to reduce complications. Photodynamic therapy with a short drug-light interval, which induces the oxidation mainly on the cell membrane is profitable to induce immediate myocardial cell necrosis. The necessary time to induce necrosis is important in the catheter ablation since the real-time electrocardiogram diagnosis is used to judge the treatment effect in clinical. The photosensitizer distribution changes from moment to moment during the therapy in vivo. It is necessary to investigate the time dependence of myocardial cell necrosis with various photosensitizer contact time in vitro. We measured the intracellular Ca²⁺ using fluo-4 AM during and after the photosensitization reaction. Talaporfin sodium was used as the photosensitizer, a CW red diode laser of 664 nm in wavelength was used for the photosensitizer excitation. Irradiance was 120 mW/cm². The necrosis occurrence time was analyzed as the sufficient intracellular Ca²⁺ decrease after the membrane rupture. The photosensitizer contact time was varied up to 60 min. The necessary time for the myocardial cell necrosis decreased with photosensitizer contact time increasing and the necessary time for the myocardial cell necrosis reached a minimum value of 150 s when photosensitizer contact time was 15 min. After 15 min of photosensitizer contact time, the necessary time for the myocardial cell necrosis increased as photosensitizer contact time increased.