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In the context of dermatology, three fundamental types of RF devices exist: monopolar, unipolar and bipolar, which are differentiated by the configuration of electrodes and corresponding electromagnetic fields.
The clinical utility of radiofrequency (RF) devices is to deliver various morphologies of energy to biologic tissue, with objectives ranging from destruction to denaturing and rejuvenation.
In the context of dermatology, three fundamental types of RF devices exist: monopolar, unipolar and bipolar. These are differentiated by the configuration of electrodes and corresponding electromagnetic fields.
Fractionated RF is a variant of bipolar RF, wherein an electrode array is patterned to divide the treatment field into multiple RF thermal zones (RFTZs) with intervening areas of untreated tissue. The application of these technologies include tightening of the skin, rhytid reduction, striae reduction, as well as heating of adipose tissue used in body contouring and cellulite reduction.
Fractionated bipolar RF creates superficial RFTZs, and it is most commonly used today for rejuvenation of the skin. Because RF devices function independent of chromophores, they can be used on all skin types with little to no risk of pigment alteration.
Radiofrequency refers to oscillating electromagnetic waves within the range of 3 kHz to 300 GHz. To provide perspective, cellular telephone signals operate from 800 MHz to 2.69 GHz, and there is rarely a moment a person in the industrialized world is not being infinitesimally irradiated by one source or another such as these cellular carrier signals, WiFi or Bluetooth. These signals are typically distant from the transmitter and have low power density, and thus a presumed negligible biological effect. At higher power densities, achieved adjacent to an RF emitter, plentiful physical interactions can occur.
In dermatological applications, RF devices produce dielectric heating of organic matter; at higher frequencies the dominant mechanism may be due to molecular dipole rotation of water, which rotates rapidly to align itself with the rapidly alternating electromagnetic field (EMF). These rotating molecules in turn locally impart electric forces to neighboring molecules generating collisions that translate to kinetic energy, or heat. At lower frequencies, alternate mechanisms such as ion drag may be the predominant mechanism translating the EMF energy into thermal energy.
The conductivity of the material determines the response; for example, in RF devices the dry epidermis might be vaporized while the dermis experiences a lesser degree of heating, which is one reason cooling devices are needed. The EMF pattern is determined by the geometry of the electrodes, their size, shape, placement and metal can be designed to optimize fields for a specific application, and the voltage, current, frequency are parameters which modify the effect on tissue.
Monopolar RF devices use a single electrode with a distant ground pad or plate connected to the patient. The most common use in dermatology historically has been electrosurgery; however, in recent years devices with cosmetic applications have been cleared for tightening of lax skin, wrinkle reduction, improvement in the appearance of cellulite, and body contouring via thermal effects on adipocytes.
Thermage (Solta Medical) was the first device the Food and Drug Administration cleared for RF skin contraction in 2002, followed by periocular wrinkles (2004), and body contouring (2006). Exilis (BTL), Cutera (Trusculpt) and Ellman (Pelleve) are other monopolar RF devices. What these devices have in common is the capacity to treat a range of depths from superficial dermis to subcutaneous fat.
Unipolar RF devices have a single electrode without a ground, wherein current is driven solely by the voltage difference between the electrode and the organic tissue. These devices radiate omnidirectionally, much the way a light bulb does, and may also reach the subcutaneous tissue similar to monopolar devices. Common applications include noninvasive skin-tightening treatment of larger tissue areas such as abdomen, thighs, arms, cellulite reduction, and body contouring. These devices can also be used for sagging jowls and wrinkle reduction. The Accent (Alma Lasers) uses both unipolar RF for volumetric heating of adipose tissue, and bipolar RF for more superficial, non-volumetric heating.
The bipolar modality of RF delivery utilizes two electrodes, a positive and negative; alternating current flows back and forth between these points. The effective field depth, and thus the depth of tissue heated is determined by the distance of electrodes in relation to one another, although the degree of heating is still determined by the electrical parameters of the EMF.
Several incarnations of this modality are seen in clinical use: arrays of flat electrodes placed on the epidermis (eMatrix, e2, Syneron); needle electrodes mechanically inserted into the skin (ePrime, Syneron), (Infini, Lutronic) an array with electrodes at varied distances to achieve different depths of penetration (Endymed PRO, Endymed), and bipolar devices combined with other optical energy delivery modalities such as diode laser, or intense pulsed light (IPL; Polaris, Syneron).
Some bipolar devices utilize vacuum technology, which may enhance the depth of heating achieved. These include TiteFx (Invasix), Reaction, and Vtouch (Viora). Velashape II (Syneron) combines bipolar RF with vacuum as well as infrared light. Venus Freeze (Venus Concept) uses an array of bipolar electrodes they call “multipolar,” along with a magnetic pulse. Other bipolar devices on the market include Accent Elite (Alma) and Apollo-Tripolar (Pollagen).
Fractionated bipolar RF techniques migrate the concept of fractional photothermolysis (FP) from lasers to RF technologies, with some practical differences. Fractional photothermolysis was initially introduced in 2003 based on a conceptual shift from treating a continuous plane of tissue to using an array of microscopic columns of spatially confined thermal injury.1The concept that untreated areas of tissue provide reservoirs which fuel a more rapid dermal remodeling process was later demonstrated histologically.2, 3
The observation of skin tightening in fractionated bipolar RF was strongly supported by a histological study of fractionated RF (FRF), which demonstrated significant neoelastogenesis and neocollagenesis.4 This study used microneedle electrodes implanted in abdominal skin; tissue temperature was held at 72 degrees Celsius for four seconds. Analysis demonstrated in the reticular dermis zones of denatured collagen they termed RF thermal zones (RFTZ) with interspersed unaltered dermis. RFTZs persisted at 28 days, but had been replaced by new tissue at 10 weeks.
The reticular dermis demonstrated increased volume, cellularity, hyaluronic acid and elastin content. Immediate increases in IL-1B, TNF-A and MMP-13 were noted, and followed by increases in MMP-1, HSP72, HSP47, and TGF-B by two days. There were marked increases in tropoelastin, fibrillin, and procollagen 1 and 3 by day 28.
A major difference between bipolar FRF tissue injury patterns and those created from FP is the shape of the RFTZ. Where FP creates thermal injury in dermal columns that taper as they descend; FRF creates a different pattern that depends on the electrode configuration. Arrays of surface electrodes create zones of dermal injury narrowest at the epidermis, which enlarge conically as they descend until the pattern is truncated by attenuation.
Using fixed electrode placement, the depth of penetration is energy dependent, with maximal depths of 450 µm attained by 10 J to 20 J power setting with a bipolar device.5 This pattern of thermal injury has been termed by some as “sublative” referring to its effect beneath the ablated zone at the epidermis, with only 5% of the epidermis affected (using eMatrix 64 electrode array). In contrast, microneedle FRF systems generate ovoid or cocoon-shaped areas of dermal coagulation. Depth of injury in these systems is reported to depend on microneedle depth and RF conduction times, but not energy levels, while the width of these RFTZs was dependent on conduction times6.
The majority of studies using bipolar FRF devices report clinical improvement in photoaging, skin laxity and rhytids, gauged by photographic assessment after three treatments, and patient satisfaction, assessed by periodic questionnaire. Hruza et al found greater than half of 33 patients, skin types II-IV, experienced more than 40 percent improvement in texture and 80 percent of patients were satisfied.5 Seung Lee et al reported moderate (26-50 percent) and incremental improvement in 26 Asian women in skin tightness, brightness and overall appearance.7 Man and Goldberg reported significant improvement in most of 15 patients with darker skin types V-VI, without any postinflammatory pigmentary alteration.8
Numerous other small studies not detailed here echo the findings of moderate clinical improvement following a regimen of three treatments, majority patient satisfaction, safety in Asian and African-American patients, and no significant adverse events. The 50 W bipolar RF system (Infini, Lutronic) with 49 proximally insulated needles was found in a pig model to induce cocoon-shaped zones of thermal coagulation, which increased in volume with increasing energy levels and increasing RF conduction times.6 Another study utilizing this same device found a sebosuppressive effect of a single treatment at 1.5 mm depth on Korean patients.7
Acne scars have also been the target of research. Ramesh et al found 10-50% and 20-70% improvement in acne scars at the end of two and six, months respectively.9 Gold and Biron reported improvement in acne scars in 10 patients, skin types I-V, accompanied by high patient satisfaction.10 Particularly regarding acne scarring, several efforts to utilize this modality synergistically with laser and light devices have been reported.
Radiofrequency devices have become an important contributor to the armamentarium of devices available for the treatment of photoaging. The possibility for skin tightening and rejuvenation both on and off the face, in all skin types, ensures a prominent position for these devices in the aesthetic arena.
Disclosures: Drs. Kaufman and Green have served as consultants for Lutronic.
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