Entrance and propagation pattern of high-frequency electrical currents in biological tissues as applied to fractional skin rejuvenation using penetrating electrodes.

BACKGROUND: Fractional resurfacing of the skin using radiofrequency devices has been used for collagen remodeling and rejuvenation. OBJECTIVES: To determine how radiofrequency current enters and propagates through tissue, and the pattern of the resulting effect. MATERIALS AND METHODS: An electrosurgical device with a 0.4 MHz frequency output was used as the source of radiofrequency current. Current was applied via a metallic needle introduced into a large piece of cow liver, with different amounts of energy delivered at multiple points. Cross-sections of the liver were then studied for tissue effect. RESULTS: Thermal coagulation of tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed around the entire length of the needle. This rim of coagulated tissue was thicker around the tip of the electrode. CONCLUSION: Radiofrequency currents have a tendency to move toward the center of the bulk of tissue. When an electrode of a fractional radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in the dermis. This phenomenon can preserve epidermis from injury during dermal heating, reducing post-procedural skin surface side effects seen with many skin rejuvenation procedures.