Radiofrequency Thermal Ablation: Current Data

First-Generation Device

In an industry-sponsored feasibility study (1) the Restore catheter (VNUS Medical Technologies, Inc., Sunnyvale, CA) induced a short subvalvular constriction to improve the competence of valve leaflets, and (2) the Closure catheter applied resistive heating over long vein lengths to cause maximum wall contraction for permanent obliteration. Treatment with Restore catheters resulted in recurrent or persistent reflux in 81% of patients followed up for 6 to 12 months. Treatment with Closure catheters resulted in a 6% recurrent reflux rate and a 4% incidence of recurrent varicosities at a mean follow-up of 4.7 months. The authors concluded that treatment with Closure catheters was an effective, less invasive option than saphenous stripping, with complications and early failures that could be mitigated through further procedural modifications.

In 1999, VNUS Medical Technologies, Inc. (Sunnyvale, CA) received approval from the US Food and Drug Administration to market and sell a new device for closure of incompetent saphenous veins. The first-generation device, known as the Closure Procedure, used bipolar electrodes mounted on the end of a catheter to deliver radiofrequency (RF) energy to the inner vein wall. The catheter's collapsible bipolar electrodes included a temperature sensor, which provided feedback to a dedicated RF generator. When deployed, the electrodes made direct contact with the endoluminal surface of the vein wall, and RF energy was delivered. The resistive effects of the vein wall tissue caused conversion of RF energy into heat. The principal mechanism of RF ablation has been demonstrated in animal studies. Vein wall collagen contraction, in response to thermal energy, causes immediate vein wall thickening and reduction in the lumen diameter. Endothelial destruction causes an inflammatory response, which results in fibrosis and permanent vein occlusion.

The thermal effect on the vein wall is directly related to both the treatment temperature and the treatment time, the latter being a function of catheter pullback speed. The treatment protocol called for a treatment temperature of 85°C at a pullback speed of 3 cm per minute. The thermal effect produces sufficient collagen contraction to occlude the lumen while limiting heat penetration to perivenous tissue. To assess the potential of perivenous tissue damage, the adventitial temperature was recorded in an in vitro model. With the standard treatment protocol, the average peak adventitial temperature was 64.4°C and usually lasted for approximately 10 seconds at any given position along the length of the vein. Peak adventitial temperature was decreased to 51.3°C in the presence of a 2-mm perivenous saline layer.

There are several different modes of endovenous radiofrequency (EVRF) ablation in commercial use around the world. These include the Celon RFITT (radiofrequency induced thermal therapy) procedure which uses bipolar RF, the monopolar FCare Systems EVRF procedure, and VNUS ClosureFast (now Medtronic Venefit) segmental ablation procedure ( Fig. 6.1 ).

Second-Generation Device (VNUS ClosureFast)

With the introduction of the ClosureFast RF ablation (RFA) catheter, the elimination of the slow pullback and the implementation of stationary (segmental) treatment at 120°C markedly improved the procedure. Controlled heating by conduction avoids vein perforations even with high dosing of thermal energy. The postprocedure inflammatory consequences often seen after endovenous laser ablation (EVLA) are relatively absent with ClosureFast.

The linear endovenous energy density (LEED) is frequently used to compare energy dosing in endovenous procedures. With the first-generation (bipolar) RF device, the catheter pullback velocity had to be slow enough to allow resistive heating of the vein wall to a target temperature of 85°C. Measurements of the delivered energy dose to the vein were not displayed to the operator because the power delivered by the generator was subject to regulation by a feedback loop to maintain a constant temperature of 85°C. With ClosureFast, the temperature is kept stable at 120°C during a 20-second treatment cycle. At the saphenofemoral junction (SFJ), two cycles of RF energy are delivered, averaging a LEED of 116.2 ± 11.6 J per cm for the first 7 cm of vein juxtaposed to the SFJ to ensure good vein closure at this critical site. Distal to the SFJ, 68.2 ± 17.5 J per cm is delivered to each 7-cm treatment site. Thus this aggressive double energy cycle at the zone of the SFJ is supported by Almeida and Raines' retrospective analysis.

Proebstle reported outcomes following ClosureFast in early 2008. The occlusion rate following segmental RFA was 99.6% at 2 years, and 70% of treated patients did not require any analgesia postprocedure.

Quality-of-Life Changes

Studies of quality of life are becoming more important; significant improvements in disease-specific quality-of-life following RFA were reported in the EVOLVeS (Endovenous Radiofrequency Obliteration [Closure] versus Ligation and Vein Stripping) study using the CIVIQ (Chronic Venous Insufficiency Quality of Life)-2 questionnaire. Moreover, these quality-of-life statistics were improved compared with patients treated with traditional venous surgery.