Dependence of damage within 10 min to myocardial cells by a photodynamic reaction with a high concentration of talaporfin sodium outside cells in vitro on parameters of laser irradiation

Background: To investigate the immediate occurrence of irreparable severe damage to myocardial cells up to 10 min after a photodynamic reaction with a high concentration of photosensitizer outside cells, we measured the damage response time and the parameters that govern the response time via rat myocardial Ca²⁺ concentration. In our proposed method for catheter ablation of tachyarrhythmia by photodynamic reaction, there are two components to the electrical conduction block: an immediate electrical conduction block of several tens of seconds to several minutes, and a permanent electrical conduction block. Methods: Rat myocardial intracellular Ca²⁺ concentration changes before, during and after the photodynamic reaction with a high concentration of photosensitizer outside myocardial cells were continuously observed using a Fluo-4 AM Ca²⁺ probe. Talaporfin sodium with 663-nm excitation was used to induce the photodynamic reaction. Talaporfin concentration was 10-30 μg/ml, radiant exposure was 10-40 J/cm², and irradiance was 30-290 mW/cm². We evaluated the response time of irreparable severe damage to myocardial cells, according to Ca²⁺ concentration. Results: The response time of the defined severe damage occurrence to myocardial cells ranged from 200 to 500 s. The response time decreased with increasing irradiance and photosensitizer concentration, but exhibited no significant change with total radiant exposure. Conclusions: We found that severe myocardial cell damage caused by a photodynamic reaction with a high concentration of photosensitizer outside cells occurred within a few minutes, which might be useful for catheter ablation for tachyarrhythmia that needs immediate response during the ablation procedure.