Intravascular Approaches to the Treatment of Varicose Veins: Radiofrequency, Lasers and More

Introduction

For nearly a century, open surgical treatment has been considered the gold standard to treat uncomplicated varicose veins. Since the early 1990s, however, techniques have shifted toward minimally invasive approaches. Foremost among these techniques are endovenous thermal ablation using radiofrequency and endovenous laser therapy. Multiple randomized clinical trials have now established the equivalent efficacy of both radiofrequency ablation (RFA) and endovenous laser therapy (EVLA) techniques as compared with conventional open surgery. The cost effectiveness and economic impact of these minimally invasive procedures also appear to be comparable, and their associated adverse effects profiles are superior. As a result, many specialized surgical vein centers and dermatologic phlebologists have now adopted these minimally invasive approaches as first line treatment.

Other techniques reported in the literature include ultrasound-guided foam sclerotherapy (UGFS), in addition to less common approaches such as cyanoacrylate glue, mechanochemical ablation (MOCA) and steam ablation. The shift toward minimally invasive approaches is further highlighted by the United Kingdom's National Institute of Health and Care Excellence (NICE) guidelines, published in 2013, advising the use of endovenous treatments with RFA or EVLA, followed by UGFS, ahead of open surgery for the treatment of varicose veins. In the following sections, each of these intravascular approaches to the treatment of varicose veins will be discussed in detail.

Open Venous Surgery

Open venous surgery is a highly invasive procedure that involves ligation of the saphenofemoral junction (SFJ), with or without stripping/removal of the great saphenous vein (GSV). Unfortunately, ligation and stripping usually requires general or regional anesthesia, with the patient usually taking a week or more to return to normal activities.

The current debate surrounding the utility of open venous surgery, as compared with minimally invasive endovenous treatments, involves its high rates of postoperative morbidity, cost and vein recurrence. In general it is widely accepted that patients suffer less postoperative discomfort and resume daily activities sooner when undergoing endovenous treatments using RFA or EVLA. Furthermore, these treatments have the added benefit of being performed with tumescent anesthesia, without the need for general or regional anesthesia, which results in cost savings.

The meta-analysis by Murad et al. studied over 8000 patients undergoing all forms of treatment intervention for primary varicose veins including open surgery. The study showed that less invasive treatments were associated with less periprocedural disability and pain. As expected, open surgery was associated with an increase in complications including wound-related infection, hematoma formation and sensory nerve injury.

In addition, open surgery demonstrated a high degree of recurrence of varicose veins, upwards of 50% at 3 to 11 years. Specifically, Winterborn et al conducted a randomized trial of 100 patients (133 legs) who underwent SFJ ligation with or without GSV stripping. After an 11-year follow-up, a cumulative total of 83 legs (62%) had developed clinical recurrent varicose veins. There was no statistically significant difference between the ligation only and the ligation plus stripping groups. However, reoperation was required for 20 of the 60 legs that underwent ligation alone, as compared with 7 of the 64 legs that underwent SFJ ligation plus GSV stripping. Stripping of the GSV significantly reduced the risk of reoperation by 60% after 11 years, even though it did not reduce the rate of clinical recurrent varicose veins. Therefore, SFJ ligation plus GSV stripping was recommended as part of routine open varicose vein surgery.

The necessity for SFJ ligation plus GSV stripping led to a demand to develop minimally invasive alternatives resulting in the advent of endovenous techniques using intravascular lasers or radiofrequency devices to thermocoagulate endothelial cells and vein walls, thereby allowing for specific destruction of the targeted vessel without the necessity for ligation or stripping.

Radiofrequency Ablation

The first theories of endovenous ablation were based on the belief that specifically directing relatively omnidirectional radiofrequency energy into vein walls to cause their destruction was potentially safer, easier to engineer and more controllable than other mechanisms for doing so. Initial designs involved a mechanism by which radiofrequency current heated tissue by resistive (or ohmic) heating of a narrow rim (less than 1 mm) of tissue in direct contact with an electrode. Deeper tissue planes could be slowly heated by conduction from the small-volume region of heating, although heat was typically dissipated by conduction into surrounding normothermic tissue. By carefully regulating the degree of heating with microprocessor control, subtle gradations of either controlled collagen contraction or total thermocoagulation of the vein wall could be achieved.

The initial design was such that when the radiofrequency catheter was pulled back, a feedback-controlled loop regulated by readings from a thermocouple enabled the operator to heat a section of vein wall to a specified preset temperature. This produced relative safety because the temperature increase remained localized around the active electrode. This necessitated the maintenance of close, stable contact between the active electrode and the vessel wall without coagulum formation. It was believed by strictly limiting the temperature to 85°C, boiling, vaporization and carbonization of the tissues could be avoided. It was also believed that heating the endothelial wall to 85°C resulted in heating the vein media to no more than 65°C, the minimal temperature at which collagen contracts.

Ex vivo studies by Reich-Schupke et al investigated histological changes following RFA at various powers and application times. When low power (5 W) and an application time up to 400 ohms was applied histological changes were not uniform. Necrosis was limited to the endothelium in the majority of vein segments and rarely reached the media. This would not likely result in complete vein shrinkage and occlusion. At 20 W and an application time up to an impedance of 400 ohms, histological changes included widespread necrosis of the intima and media and collagen bundle coagulation. The authors concluded that with increased power and application time there was a more homogeneous and extensive heating of the vein wall, which was thought to lead to a more successful outcome.

Vessel wall ablation using electrode-mediated radiofrequency is a self-limiting process. As coagulation of tissue occurs there is a marked decrease in impedance that limits heat generation. Alternatively, if a clot builds up on the electrodes, blood is heated instead of tissue and there is a marked rise in impedance (resistance to radiofrequency). The radiofrequency generator can be programmed to rapidly shut down when impedance rises, thus assuring minimal heating of blood, but efficient heating of the vein wall. The problem is that the electrodes must be manually debrided of coagulum, which requires the removal of the catheter, cleaning by the operator and then reinsertion, which is problematic during tumescent anesthesia.

The initial system developed in part by Mitchel Goldman and Robert Weiss, introduced along with electrode-mediated RFA was the Closure system (VNUS Medical Technologies, Sunnyvale, CA, now Covidien, North Haven, CT). With the Closure catheter system bipolar electrodes are deployed by spring action and placed in contact with the vein wall. As the vein wall contracts, the electrodes are able to retract within the vein allowing vein wall narrowing. Selective insulation of the electrodes results in a preferential delivery of the radiofrequency energy to the vein wall and minimal heating of the blood within the vessel.

The initial catheter designs included collapsible catheter electrodes and a central lumen to allow a guidewire and/or fluid delivery structured within the 5-French (1.7-mm) catheter. This permits treatment of veins as small as 2 mm and as large as 8 mm. A larger 8-French catheter allowed treatment of saphenous veins up to 12 mm in diameter. Both catheters had thermocouples on the electrodes embedded in the vein wall, which measured temperature and provided feedback to the radiofrequency generator for temperature stabilization. The control unit displayed power, impedance, temperature and elapsed time so that precise control could be obtained. The unit delivered the minimum power necessary to maintain the desired electrode temperature. For safety, if a coagulum formed on the electrodes, the impedance rises would cut off the radiofrequency generator.

The initial experience dating back to 1998, demonstrated an efficacy equal to or better than that of ligation and stripping with few, if any, adverse sequelae. Early experience directly comparing with ligation and stripping procedures, even with RFA performed under general anesthesia, noted equal efficacy with less pain, shorter sick leave and faster return to normal activities.

When performed by us (MPG, RAW), the procedure was entirely under local tumescent anesthesia with over 90% of patients resuming normal activities 1 to 2 days postoperatively. Its main drawbacks were the high cost of single-use catheters, the necessity to withdraw the catheter manually at a speed of 2 to 3 cm per minute and frequent cleaning of coagulum on the electrodes, which made the procedure tedious at times. To speed up the procedure, Goldman recommended that only the most proximal 20 cm of the GSV be treated with RFA and the remaining varicose GSV be treated with ambulatory phlebectomy. Goldman believes that the addition of ambulatory phlebectomy minimizes the possibility of recurrence from distal perforators. Proebstle et al confirmed that up to 30% of tributary veins do not resolve with laser ablation of the GSV alone, thereby necessitating removal with ambulatory phlebectomy.

In addition, treatment of the GSV below the knee may not be entirely necessary, as others have shown that ligation and stripping procedures from the groin to the knee add little to the procedure's efficacy. Others have also demonstrated equal effectiveness with less than 2 years follow-up when only the proximal 30 to 40 cm of the GSV was treated without treating distal varicose tributaries.

Weiss and Weiss evaluated patients treated with a percutaneous approach allowing access of the Closure catheter to treat the proximal GSV. Patients (mean age, 47.2 ± 12.6 years; 76% female) had symptomatic saphenous reflux with a saphenous vein diameter of 2 to 12 mm (mean, 7.4 mm). Most of the veins treated were above-knee great saphenous (73%), some entire great saphenous (21%), and the remaining included below-knee great saphenous, small saphenous and accessory saphenous. Adjunctive procedures performed at the time of treatment were phlebectomy on more distal branches in 61% and high ligation in 21%, but the adjunctive procedures did not affect outcome.

Vein occlusion at 1 week was documented by duplex ultrasound in 300 out of 308 legs, or a success rate of 97%. Occlusion persisted at 6 weeks in 95% and at 6 months in 92%. In this report if the saphenous vein was closed at 6 months, it was noted by duplex ultrasound to remain closed to 12 months and beyond. Subsequent follow-up for up to a decade by duplex ultrasound indicates that any vein noted to have been eliminated at 12 months by RFA will not recur. Typically when the GSV is treated, there is closure or elimination of major tributaries at the SFJ except for the superior epigastric vein, which is intentionally not treated and continues to empty superiorly into the common femoral vein. We believe that there is a high margin of safety by maintaining flow through this tributary. The high flow rate appears to diminish the possibility of extension of any thrombus (in the unlikely event that this would occur) from the GSV and has the additional benefit of allowing normal venous flow from the lower abdominal wall into its proper drainage into the common femoral vein. By leaving the superior epigastric vein intact, thrombus in the GSV following this procedure has not been observed.

Long-term efficacy with the RFA has been documented by Merchant et al investigating 1222 limbs (great saphenous, small saphenous and accessory saphenous veins). Occlusion rates (evaluated via duplex ultrasound) of 96.8%, 89.2%, 87.1%, 88.2%, 83.5%, 84.9% and 87.2% were found at 1 week, 6 months, 1 year, 2 years, 3 years, 4 years and 5 years, respectively. Body mass index greater than 25 was associated with an increased incidence of nonocclusion, groin reflux and recanalization. A pullback speed above 3 cm/minute at 85°C was more likely to result in nonocclusion and recanalization. In the study by Vasquez et al, factors associated with improved occlusion rates included increasing age, female sex and volumes greater than 250 mL of tumescent anesthesia. The authors theorized that increased failure rates associated with male sex and younger age are secondary to variations in collagen and inflammation in these populations.

Regarding clinical symptoms, a successful radiofrequency (or laser) endovenous occlusion procedure rapidly reduces patient pain, fatigue and aching, correlating with a reduction in the CEAP (clinical, etiologic, anatomic, pathophysiologic) clinical class for symptoms and clinical severity of venous disease. When patients have had simultaneous surgical stripping on the opposite leg, the degree of pain, tenderness and bruising have been far greater on the leg treated by stripping. Side effects of this technique have included thrombus extension from the proximal GSV in 0.8% (with one case of pulmonary embolus), skin burn (before the tumescent anesthesia technique) in 2.5%, clinical phlebitis at 6 weeks in 5.7% and temporary 1–2 cm sized areas of paresthesia in 18%, with most of these occurring immediately above the knee and resolving within 6 months to a year. Compared with most techniques—but in particular, traditional ligation and stripping of similar size saphenous veins—the effectiveness of endovenous radiofrequency occlusion is quite high.

In a study by Goldman and Amiry, closure of the GSV with endoluminal radiofrequency thermal heating in combination with ambulatory phlebectomy was easily accomplished and efficacious. The first 47 sequential, nonrandomized patients having an incompetent GSV from an incompetent SFJ and painful varicosities in 50 legs were treated with the VNUS Closure procedure. The varicose veins were marked with the patient standing and again with the patient lying down in the operative position with a Venoscope transilluminator (LLC, Lafayette, LA) ( Fig. 11.1 ). After appropriate marking, the area surrounding the GSV and distal tributaries to be treated was infiltrated with 0.1% lidocaine tumescent anesthesia. The amount of tumescent fluid averaged 800 mL with a lidocaine dose of 8 mg/kg. The GSV was then accessed through a 2- to 3-mm incision in the medial mid thigh, usually 20 cm inferior to the SFJ. The proximal portion of the GSV was then treated with VNUS Closure and the distal portion, including all varicose tributaries, was removed with a standard ambulatory phlebectomy technique.

Thirty-nine patients with 41 treated legs were available for evaluation at the longest follow-up period. Six patients (9 treated legs) could not be located for re-evaluation after 6 months because of change in location (often out of the state).

The average time to access the GSV in the medial thigh with a phlebectomy hook was 7 minutes (range, 1–30 minutes). Twenty-seven patients had the GSV accessed in less than 1 minute. The average catheter pullback rate was 2.76 cm/minute over an average length of treated GSV of 19 cm (range, 6–42 cm). Complete surgical time, including the phlebectomy portion of the procedure, was approximately 20 minutes (range, 13–35 minutes).

Ninety-five percent of all patients could resume all preoperative activities within 24 hours. The other two patients could resume all activities within 48 hours. Every patient had complete elimination of leg pain and fatigue. Twenty-one of 22 patients who presented with ankle edema had resolution of ankle edema. All patients said that they would recommend this procedure to a friend.

Adverse sequelae were minimal, with four patients complaining of heat distal to the SFJ during the procedure which resolved with additional tumescent anesthesia. Twenty-eight of 50 treated legs had some degree of purpura lasting 1 to 2 weeks. Five patient legs developed mild erythema over the GSV closure site that lasted 2 to 3 days. Eight legs had an indurated fibrous cord over sites of ambulatory phlebectomy that lasted up to 6 months.

Clinical and duplex evaluation performed by an independent laboratory and/or physician at 6, 9, 12, 18 and 24 months disclosed 90% abolition of reflux. No new varicose veins were noted to appear in three patients with recurrent reflux in the GSV. One patient who developed reflux had the development of new veins at 1 year posttreatment.

Other surgeons have had a different experience with the use of VNUS Closure in the treatment of incompetent GSV. The reason for the difference in results is likely to be secondary to the anesthesia and technique used as described hereafter.

Three separate papers detail a similar cohort of patients treated in multicenter studies encompassing 16 to 31 clinics, 210 to 324 patients and 6 to 12 month follow-up. The vein occlusion rate at 1 year examination was 91.6% from nine centers and 81.9% from fourteen centers. Forty-nine patients were followed at 2 years with duplex scans and showed an 89.8% closure rate. There was a 3% incidence of paresthesia, which was decreased to 1.6% when treatment was confined to the thigh. Two limbs (0.8%) developed scarring from skin burns and three patients developed a deep vein thrombosis (DVT) with one embolism. The reason for the increase in adverse effects appears to be the use of general anesthesia instead of tumescent anesthesia by a majority of the surgeons.

Sybrandy and Wittens from Rotterdam reported 1-year follow-up of 26 patients treated with VNUS Closure. They reported five patients with postoperative paresthesia of the saphenous nerve and one with a cutaneous burn, for an overall complication rate of 23%. One patient (3.8%) had total recurrence of the GSV. One patient (3.8%) could not be treated because of a technical failure. Eight patients (30.8%) had closure of the GSV, but with persistent reflux of the SFJ. Thirteen patients (50%) had closure of both the GSV and SFJ. Overall 88% of patients had a totally occluded GSV.

One probable reason for the increase in adverse effects was the use of spinal anesthesia instead of the recommended tumescent anesthesia. In addition, they treated all patients from the ankle proximally, which exposed the GSV within the calf to heat from the radiofrequency catheter. The mean operating time was 67 minutes (range, 25–120 minutes).

Another report describes two episodes of DVTs in 29 patients treated with the RFA. Here the surgeons treated the patient with a groin incision and passage of the catheter from the groin downward. The authors do not report the type of anesthesia used or the length of vein treated. It is presumed that patients were not ambulatory and were treated under general anesthesia.

The important information to come out of a review of various treatments of the GSV is that the use of tumescent anesthesia in awake patients who can ambulate immediately after the procedure is important in preventing skin burns and DVTs. Treatment when limited to the GSV segment above the knee is also important in preventing paresthesia to the saphenous nerve.

In our experience using tumescent anesthesia in awake patients, two patients developed focal numbness 4 cm in diameter on the lower medial leg. These resolved within 6 months. Since adopting the principles outlined earlier with tumescent anesthesia and moving the catheter rapidly from any points of sharp pain, no paresthesia has been noted. No skin injury or thrombus has been observed in any of our patients. Unfortunately, with both endoluminal radiofrequency and laser procedures, complications in the form of DVTs, pulmonary embolism or angiogenesis have been reported if patients are not ambulatory after the procedure and/or if tumescent anesthesia is not given. Tumescent anesthesia or the placement of large volumes of dilute anesthesia in a perivascular position serves several purposes:

• To protect perivascular tissues from the thermal effects of intravascular energy such as radiofrequency

• To decrease the diameter of the treated vein that allows for better contact of the radiofrequency electrodes or laser fiber tip with the vein wall, and thus secondarily reduce intravascular blood for nonspecific coagulation

• To provide local anesthesia for patients so that they may be awake during the procedure with the ability to report any pain or discomfort and walk off the operating table and around the recovery room

Contrary to the report by Hingorani et al, we have never seen DVTs in any of our patients treated with intravascular laser or radiofrequency. We believe that the reason for our lack of adverse sequelae is the use of tumescent anesthesia in awake patients with immediate ambulation and avoidance of occlusion of the superior epigastric vein. Although we realize treating patients without general anesthesia is not standard practice for general or vascular surgeons, some vascular surgeons who perform tumescent anesthesia on awake patients with immediate ambulation have reported similar results with virtually no DVTs. A DVT was noted in a female patient treated using tumescent anesthesia while awake, but she weighed more than 350 pounds and did not ambulate after the endoluminal radiofrequency procedure.

Salles-Cunha et al reported on the development of angiogenesis and fibrotic tissue along the course of the GSV treated with RFA under general anesthesia. Contrary to this report, our experience with tumescent anesthesia is a complete lack of detection of small vessel networks (angiogenesis) by duplex ultrasound. We believe that the reason for our lack in detecting small vessel networks is not from a lack of trying to see them, but from the minimization of inflammation that occurs with tumescent anesthesia placed in the perivascular space during either RFA or EVLA.

We have not performed ligation of the SFJ in any of our over 2000 patients (to date, January 2016) and question the accuracy of the findings of Salles-Cunha et al, who found a decreased incidence of small vessel networks in patients undergoing RFA with SFJ ligation. We suspect that the small number of patients who were treated without ligation (6 out the 13 patients or 46%) as compared with the those who were treated with ligation (13 out of the 93 patients or 14%), produced falsely positive statistical significance. We question if inflammation is the most likely cause for small vessel networks because ligation should not increase or decrease the extent or time of inflammation.

Closurefast Catheter

In 2006 VNUS introduced the ClosureFAST catheter. This new device promised increased efficiency with ablation of incompetent veins of any size. The 7F ClosureFAST catheter allows 7 cm segments of vein to be uniformly heated for 20 seconds at 120°C ( Fig. 11.2 ). The temperature is maintained by a radiofrequency generator through a feedback loop, and vein segments are treated serially with continuous pullback not needed. Although treatment with the Closure system was limited to veins of less than 12 mm, no diameter restrictions are indicated with the ClosureFAST catheter. The manufacturer recommends the initial and most proximal 7 cm of GSV to be treated with two consecutive cycles, whereas the remaining vein segments may be treated with a single cycle.

Proebstle et al treated 252 GSVs with ClosureFAST and either adjuvant ambulatory phlebectomy (in 71.6%) or foam sclerotherapy (in 13.9%). Mean treatment time (spanning the time between catheter insertion and removal) was 16.4 ± 8.2 minutes and 6.7 ± 1.7 treatment cycles. The linear endovenous energy density was 116.2 ± 11.6 J/cm for the initial 7 cm of GSV, and 68.2 ± 17.5 J/cm for the subsequent 7 cm. Patients were followed at 3 days, 3 weeks, 3 months and 6 months postprocedure. All patients had successful occlusion of their GSV. Life-table analysis indicated that occlusion rates were 99.6%. Seventy percent of patients experienced no post procedural pain. No DVTs or skin burns were seen. Side effects were infrequent with 3.2% paresthesia, 0.8% phlebitis, 1.6% hematomas, 2% hyperpigmentation and ecchymosis in 6.4%. Mean patient down time was 1.0 ± 1.9 days. Finally 99% of treated patients would recommend the ClosureFAST system to their friends.

Calcagno et al investigated the relationship of size to efficacy in 338 great and small saphenous veins following ClosureFAST treatment. Initial occlusion rates evaluated between 2 to 5 postoperative days were not significant (94% in veins ≤12 mm and 96% in those >12 mm). At 6 months, complete occlusion rates in veins less than or equal to 12 mm or greater than 12 mm were similar (98% and 100%, respectively). Interestingly, veins partially occluded in the immediate postoperative period developed complete occlusion at 6 months follow-up. Diameter did not affect the outcome for successful treatment of incompetent saphenous veins with ClosureFAST.

The Recovery Study by Almeida et al compared 87 GSVs treated with either ClosureFAST or 980-nm diode endovenous laser. This small, short term follow-up study of only 1 month, demonstrated increased incidence of ecchymosis, pain, phlebitis and tenderness in the 980-nm laser group during the initial postoperative 2 weeks. These increased side effects were attributed to microperforations caused by the 98-nm diode. Although quality of life and venous severity scores were more favorable in the initial 2 weeks in the ClosureFAST group, no difference was seen at 1 month follow-up. No comparisons of efficacy were provided in this short-term study.

Long-term studies are necessary to assess prolonged efficacy of the ClosureFAST system. Radiofrequency and 1320-nm Nd:YAG laser both stimulate collagen contraction, have negligible development of thrombi and show decreased incidence of side effects because of a lack of perforations in the vein wall. We feel a randomized blinded trial comparing the efficacy and safety of these two technologies is justified.

Endovenous Laser Ablation

Use of lasers with this application began with only a slight delay following the development of RFA. Various lasers have proven to effectively close axial veins through thermal damage to endothelium with subsequent thrombosis and resorption of the damaged vein. Endoluminal laser closure is less costly because fiber optics are less expensive than more complex and more engineered radiofrequency fibers. Before the development of ClosureFAST, lasers performed more quickly with the speed of pullback typically 10 to 20 cm/minute for 810- to 980-nm lasers and 6 cm/minute for the 1320-nm laser. By increasing the energy of the 1320-nm laser from 6 W to 10 to 12 W, the pullback rate can be increased to 2 mm/second, which doubles the speed of this endoluminal laser.

EVLA allows delivery of laser energy directly into the blood vessel lumen to produce endothelial and vein wall damage with subsequent fibrosis ( Fig. 11.3 ). It is presumed that destruction of the GSV with laser is a function of thermal damage to the endothelium and/or vessel wall. The presumed target for lasers with wavelengths of 810, 940, 980 and 1064 nm is intravascular red blood cell absorption of laser energy. However, thermal damage with resorption of the GSV has also been seen in veins believed to be “emptied” of blood, although it is virtually impossible to completely eliminate hemoglobin as a chromophore by maneuvers such as leg elevation. Although direct thermal effects on the vein wall probably occur, absorption by blood usually plays a significant role.

Some authors advocate emptying the vein of blood via manual compression, leg elevation and tumescent anesthesia immediately before the procedure. The presence of blood has several drawbacks including decreased transmission of laser energy to the vein wall, potential of complete laser energy absorption by blood resulting in thrombosis and recanalization, melting of the laser tip via carbonization and when the laser energy is given continuously and not pulsed, carbonization of the laser fiber tip with excessive thermal effects. However, the presence of blood leads to steam bubble production, which may contribute as a secondary mechanism to EVLA efficacy.

The extent of thermal injury to tissue is strongly dependent on the amount and duration of heat to which the tissue is exposed. Linear endovenous energy density (LEED) is defined as the total joules delivered divided by total centimeters of treated vein. On the one hand some authors recommend a LEED above 70 J/cm to reduce the incidence of recanalization and recurrence, whereas on the other hand, others have shown no statistical difference in failure rates based on LEED. In addition, because each laser wavelength has a unique effect on the endothelial cells, water content of the blood and/or red blood cells, the total energy of one laser wavelength may not have the same efficacy as another wavelength and cannot be casually compared. Moritz and Henriques investigated the time–temperature response for tissue exposed to up to 70°C. They found that skin can withstand temperature rises for very short exposure times and that the response appears to be logarithmic as the exposure times become shorter. For example, an increase in body temperature to 58°C will produce cell destruction if the exposure is longer than 10 seconds. Tissues, however, can withstand temperatures up to 70°C if the duration of exposure is less than 1 second. Any tissue injury from brief exposure to temperatures less than 50°C would likely be reversible.

One in vitro study model has predicted that thermal gas production by laser heating of blood in a 6-mm tube results in 6 mm of thermal damage. These authors used 810-, 940- and 980-nm diode lasers with multiple 15 J, 1-second pulses to treat the GSV. A median of 80 pulses (range, 22–116) were applied along the treated vein every 5 to 7 mm. Histologic examination of excised veins demonstrated thermal damage along the entire treated vein with evidence of perforations at the point of laser application described as ‘explosive-like’ photodisruption of the vein wall. This produced the homogeneous thrombotic occlusion of the vessel. This effect occurred only with blood-filled veins, not with saline-filled veins, attesting to the absorption of laser energy by hemoglobin (Hb) and HbO ₂ at these wavelengths. Because a 940-nm laser beam can only penetrate 0.3 mm in blood, the formation of steam bubbles may contribute to the mechanism of action. Multiple in vitro and animal models were performed to delineate the mechanism of action for vein closure. A consecutive series of events occur in endovenous ablation:

• 1.

  Laser energy absorption by blood

• 2.

  Coagulum formation at the fiber tip

• 3.

  Steam bubble formation and integration into the coagulum

• 4.

  Carbonization of the laser tip

Carbonization seen histologically on the vein wall indicates a direct contact with the laser fiber. This interaction leads to fibrosis and is believed by some to be the primary mechanism of vein wall closure. Thrombus formation results from steam bubble production at the laser tip and is thought to contribute to vein closure. However, the volume of steam produced in EVLA is not enough to result in significant collagen damage. Of note in the experiments of Disselhoff et al, continuous mode resulted in more carbonization, steam bubble formation and higher and more persistent endovenous temperatures than was found with an intermittent (pulsed) mode. It is interesting to note that Der Kinderen found no histological differences were seen between veins treated with continuous or intermittent modes.

Another possibility for the mechanism of action of EVLA is similar to that of RFA closure–collagen contraction. Collagen has been noted to contract at about 50°C, whereas necrosis occurs at between 70°C and 100°C. Whether collagen contraction, thermal damage or a combination of the two effects is responsible for destruction and resorption of the GSV is unknown and remains controversial.

A meta-analysis by van den Bos and colleagues compared occlusion rates following EVLA (all wavelengths included), RFA, UGFS and high ligation with stripping from 64 studies and 12,320 limbs. At 3 years, success rates were 94.5% for laser ablation, 84.2% for RFA, 77.4% for UGFS and 77.8% for high ligation with stripping. After 5 years treatment success was seen in 95.4%, 79.9%, 73.5% and 75.7% for laser ablation, RFA, UGFS and high ligation and stripping, respectively. The authors found efficacy for high ligation and stripping, RFA and UGFS were equal, but EVLA was more effective than the other three regimens. The incidence of DVTs were less than 1% in both the radiofrequency and laser ablation, and less than 2% in conventional surgery. Risk factors for the development of DVTs following EVLA include general or epidural anesthesia, presence of a coagulation disorder or incorrect placement of the laser fiber tip.

Ultimately the mechanism of action in EVLA is dependent on the wavelength of laser used ( Table 11.1 ). The wavelengths that primarily target tissue water (such as, the 1320-nm Nd:YAG laser) have proven to be superior to those that primarily target Hb (810–1064 nm), as described subsequently.