The effects of pulse dye laser double-pass treatment intervals on depth of vessel coagulation

Background and Objective: Multi-pass treatments with pulse dye lasers (PDLs) are avoided due to perceived side effects. Proper multi-pass techniques allow for deeper vascular injury. New extended PDLs allow use of multipass procedures. This study evaluates how the time between pulses, inter-pulse interval [IPI] affect extent of vascular treatment. Study Design/Materials and Methods: Sixteen subjects were exposed to a series of exposures on normal skin to determine depth of injury for various IPI. Subjects were exposed to single pass, and 4 double-pass intervals. Tests included exposures at 0.5 milliseconds, 2-7 j/cm(2). Exposures included one and two passes, IPI of 1, 10, 30, and 60 seconds; 5 and 30 minutes. Treatments were done with PhotoGenica V-Star (595-nm), SmartCool air cooling. Biopsies were taken: single pass and double pass purpuric thresholds; and at 7 j/cm(2) to determine depth of vascular coagulation. Results: Histology revealed increased vascular coagulation depth at purpura threshold for intervals of 1, 10, 30, and 60 seconds between passes compared to single pass treatment, and a significant monotonic increase in depth of vascular injury at 7 j/cm(2) with increasing IPI. Conclusions: The use of multiple passes increases depth of vascular injury, which may increase the efficacy of treatment without significant increase in purpura or risk of scarring for treatments at purpura threshold. At purpura threshold, the depth of vascular injury increases with increasing IPI up to 60 seconds. Above purpura threshold, there is a monotonic increase in depth of vascular injury for IPI up to 30 minutes. These observations suggest multipass treatment methods may be beneficial when employed with PDLs.