Immediate and Late Effects of Pulse Widths and Cycles on Bipolar, Gated Radiofrequency-Induced Tissue Reactions in in vivo Rat Skin

Abstract

Background Single to multiple pulse packs of bipolar, alternating current radiofrequency (RF) oscillations have been used for various medical purposes using invasive microneedle electrodes. This study was designed to evaluate the effects of pulse widths and cycles of RF pulse packs on immediate and delayed thermal tissue reactions in in vivo rat skin. Methods RF energy at the frequency of 1 MHz and power of 70 W was delivered at each experimental setting into in vivo rat skin at 1.5-mm microneedle penetration, and then, tissue samples were obtained after 1 h and 3, 7, 14, and 21 days and histologically analyzed. Results A single-pulse-pack RF treatment generated coagulative necrosis zones in the dermal peri-electrode area and zones of non-necrotic thermal reactions in the dermal inter-electrode area. Multiple pulse-pack, RF-treated rat skin specimens revealed that the number and size of peri-electrode coagulative necrosis were markedly decreased by increasing the number of pulse packs and accordingly decreasing the conduction time of each pulse pack. The microscopic changes in RF-induced non-necrotic thermal reaction in the inter-electrode area were more remarkable in specimens treated with RF of 7 or 10 pulse packs than in specimens treated with RF of 1–4 pulse packs. Conclusion The gated delivery of multiple RF pulse packs using a bipolar, alternating current, 1-MHz RF system using insulated microneedle electrodes efficiently generates non-necrotic thermal tissue reactions over the upper, mid, and deep dermis and subcutaneous fat in the inter-electrode areas.

Effects of Parallel Contact Cooling on Pulsed-Type, Bipolar Radiofrequency-Induced Tissue Reactions in an in vivo Porcine Model

“…Conversely, under multiple sub-pulse pack settings, increasing the number of sub-pulse packs reduced or eliminated the PECN zone. 5 Interestingly, with extended off-time settings between sub-pulse packs, we observed a more distinct inter-electrode non-necrotic thermal reaction (IENT) zone in the upper papillary, mid, deep dermis, and subcutaneous fat layers. Therein, IENT was histologically presented as a relatively ill-demarcated zone of eosinophilic cellular and stromal changes between the penetrating electrodes without remarkable tissue necrosis.…”

“…Specifically, we focused on peri-electrode and inter-electrode areas in the dermis under varying conduction times and numbers of sub-pulse packs. 5 We observed that increasing the total RF conduction time from 200 to 800 ms under a single pulse pack setting led to an expansion of peri-electrode coagulation necrosis (PECN), which was histologically presented as a relatively well-demarcated round to oval-shaped zone of tissue coagulation along the penetrating electrode. 5 The location and degree of coagulation necrosis were influenced by skin tissue impedance and adjacent adnexal structures.…”

“… 5 We observed that increasing the total RF conduction time from 200 to 800 ms under a single pulse pack setting led to an expansion of peri-electrode coagulation necrosis (PECN), which was histologically presented as a relatively well-demarcated round to oval-shaped zone of tissue coagulation along the penetrating electrode. 5 The location and degree of coagulation necrosis were influenced by skin tissue impedance and adjacent adnexal structures. Conversely, under multiple sub-pulse pack settings, increasing the number of sub-pulse packs reduced or eliminated the PECN zone.…”

Efficacy and safety of fractional microneedle radiofrequency for atrophic acne scars: A real‐world clinical study of 126 patients

“…Kim et al have reported that under the same needle length and energy level, a larger pulse width can result in wider thermal injury zones and increase collagen and elastic fiber production in mouse skin. 28 The histology after FMR has been found to be significantly influenced by the micro-needle length and radiofrequency delivery time (pulse width), a parameter affecting the volume (length and width) of the thermal coagulation zone, while this effect is not associated with energy level. 29 Higher energy levels can increase patient-reported pain during treatment and may increase the occurrence of adverse events, such as persistent erythema and pigmentation.…”

“…Therefore, a larger coagulation zone is followed by a higher production of new collagen tissue theoretically. Kim et al have reported that under the same needle length and energy level, a larger pulse width can result in wider thermal injury zones and increase collagen and elastic fiber production in mouse skin 28 . The histology after FMR has been found to be significantly influenced by the micro‐needle length and radiofrequency delivery time (pulse width), a parameter affecting the volume (length and width) of the thermal coagulation zone, while this effect is not associated with energy level 29 .…”