Vascular and Endovascular Surgery http://ves.sagepub.com Endovenous Laser Treatment of Saphenous Vein Reflux: How Much Energy Do We Need to Prevent Recanalizations? Marc Vuylsteke, Koen Liekens, Peter Moons and Serge Mordon Vasc Endovascular Surg 2008; 42; 141 originally published online Jan 31, 2008; DOI: 10.1177/1538574407311107 The online version of this article can be found at: http://ves.sagepub.com/cgi/content/abstract/42/2/141 Published by: http://www.sagepublications.com Additional services and information for Vascular and Endovascular Surgery can be found at: Email Alerts: http://ves.sagepub.com/cgi/alerts Subscriptions: http://ves.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsreprints.nav Permissions: http://www.sagepub.com/journalspermissions.nav Citations (this article cites 25 articles hosted on the SAGE Journals Online and HighWire Press platforms): http://ves.sagepub.com/cgi/content/refs/42/2/141
Endovenous Laser Treatment of Saphenous Vein Reflux: How Much Energy Do We Need to Prevent Recanalizations? Vascular and Endovascular Surgery Volume 42 Number 2 April/May 2008 141-149 2008 Sage Publications 10.1177/1538574407311107 http://ves.sagepub.com hosted at http://online.sagepub.com Marc Vuylsteke, MD, Koen Liekens, MD, Peter Moons, MD, and Serge Mordon The aim of this study was to report the results of highenergy endovenous laser treatment to measure the relationship between the fluence and the outcome in terms of recanalization. In 97 patients, 129 great saphenous veins were treated with endovenous laser treatment, using a 980-nm diode laser. Follow-up visits were done at 3 days, 1 month, and 6 months. The best results were noted 1 month postoperative, but at 6 months, control late recanalizations occured decreasing occlusion rate to 90.6%. Patients were divided into 2 groups according to the outcome (occlusion or recanalization) at 6 months, and statistical analysis was done. The authors found 52 J/cm 2 mean fluence in the occlusion group and 43.7 J/cm 2 in the nonocclusion group. This was a statistical significant difference (P <.01). The occlusion rate on long term is fluence dependent. But recanalizations might occur even in these higher fluence treatment groups. A fluence of 52J/cm 2 is advised. Keywords: varicose disease; endovenous laser treament Superficial venous incompetence is a common disorder affecting up to 15% of men and 25% of women afflicted with varicose veins. 1,2 Great saphenous vein (GSV) reflux is the underlying cause in 3 out of 4 cases. 3 The classical treatment of this disorder was a crossectomy at the sapheno-femoral junction (SFJ) and a stripping of the incompetent saphenous vein (SV). Unfortunately, this treatment has some disadvantages, such as postoperative pain, swelling, hematoma formation along the stripping traject, with possible lasting pigmentation of the skin, crossinfections, and paresthesia caused by saphenous or cutaneous nerve damage. 1,4-6 Because of this postoperative morbidity, there is a mean sick leave of 18 From the Department of Vascular Surgery (MV, KL), Department of Radiology (PM), Sint-Andries Hospital, Tielt, Belgium, and INSERM- IFR 114, Lille University Hospital (SM), 59037 Lille, France. Address correspondence to: Marc Vuylsteke, MD, Department of Vascular Surgery, Sint-Andries Hospital, Tielt, Belgium; e-mail: marc.vuylsteke@skynet.be. days after stripping 1 leg. 7 The most annoying inconvenience of this treatment is the high recurrence rate of 40% after 5 years and 70% after 10 years. 8 These disadvantages gave rise to new mini invasive alternative treatments, such as VNUS Closure and endovenous laser treatment (ELT). In these new treatments, a crossectomy is no longer performed, and the SV is obliterated in a percutaneous way. Because the closure technique is much more expensive, ELT has become a popular mini-invasive alternative to crossectomy and stripping and is proven to be safe and effective. 9,10 Several wavelengths, 810, 940, 980, 1064, and 1320 nm, 4,11-14 have been proposed, and the wavelengths 810, 940, and 980 nm are most commonly used. At these wavelengths, power is usually set between 10 and 15 W. The energy is administered endovenously, either in a pulsed fashion (pulse duration: 1-3 seconds with fiber pull back in 3-5 mm increments every 2 seconds) or continuously with a constant pullback of the laser fiber (pullback velocity ranging from 1-3 mm/s). 141
142 Vascular and Endovascular Surgery / Vol. 42, No. 2, April/May 2008 At these parameters, the average linear endovenous energy density (LEED), which is commonly used to report the dose, administered to the vein ranges from 20 to 140 J/cm. 15,16 These doses induce heating of the vein wall, which is necessary to cause contraction of the collagen and destruction of endothelium. This stimulates vein-wall thickening, leading to luminal contraction, venous thrombosis, and vein fibrosis. 17 Because tumescent anesthesia is always delivered, patients feel no pain during endovenous laser ablation at the suggested or commonly used laser parameters. This tumescent anesthesia has 2 functions: it compresses and reduces the diameter of the veins, and it acts as a protective barrier, minimizing the risk of heatrelated damage to adjacent tissues. 18,19 If blood is still present in the vessel lumen, 20 steam bubbles begin to form when the temperature at the tip reaches 100 C. The bubbles grow, and when they reach into cooler areas, they collapse. Therefore, the boiling zone is within the lumen of the blood vessel, and vapor bubbles have little effect on the vessel wall especially in the larger veins. Carbonization and tract within the vein wall seen by using histology methods following endovenous laser can only be the result of direct contact between the laser tip and the vein wall. Steam bubbles originating from boiling blood is not the only pathophysiological mechanism of action of ELT. Short-term efficacy to close the SV has been reported to be greater than 95%. 21 However, studies with a longer follow-up have provided evidence that a variable number of the post-elt occluded veins (2%- 20%) undergoes recanalization. Usually, all recurrences occur before 9 months, with the majority observed immediately or before 3 months. 9,22 These recanalizations can be the cause of clinical varicose recurrence and therefore have to be avoided if possible. Mathematical modeling of ELT 23 provides a better understanding of the ablation process and may determine the optimal dosage as a function of vein diameter. It confirms that thermal damage of the inner vein wall (tunica intima) is required to achieve the tissue alterations necessary to lead the vein to permanent occlusion. However, to obtain a high rate of success without adverse events, the knowledge of the vein diameter after tumescent anesthesia is recommended to use the optimal energy. Results showed that in pulsed mode, for a 3-mm vein diameter, a minimum fluence of 15 J/cm² was required to obtain a permanent damage of the intima. For a 5-mm vein diameter, 50 J/cm² was required. In a continuous mode, for a 3-mm and 5-mm vein diameter 65 J/cm² and 100 J/cm², respectively, were required to obtain a permanent damage of the vessel wall. The use of different wavelengths (810 nm or 980 nm) had minor influence on these results. An interesting observation in this model is that less amount of energy is required in pulsed mode than in continuous mode. Publications showed that nonocclusion and early reopening of the greater SV after ELT is fluence dependent. 15,21 In this prospective consecutiveenrollment study, we have treated 129 GSV in 97 patients. We used a high-energy treatment to prevent recanalizations, if possible. The purpose of this study was to report our results of high-energy laser treatment and to measure the relationship between fluence and outcome in terms of recanalization. Materials and Methods Patient Group From November 2005 to May 2006, 97 patients were scheduled for treatment of SV insufficiency at the Department of Vascular Surgery, Sint-Andries Hospital, Tielt, Belgium. In these 97 patients, 129 consecutive GSVs were treated with ELT. Seventy-two patients (74.2%) were female, 25 patients (25.8%) were male. Mean age was 50 years, with the youngest patient 23 and the oldest 79 years of age. According to the CEAP (clinical, etiology, anatomy, pathophysiology) clinical classification, 77% of the patients presented with visible varicose veins (C2) and 20% presented with edema (C3). One patient had skin changes due to venous disease (C4), another patient had a healed ulcer (C5), and 2 patients were suffering from an active ulcer (C6, Table 1). The ELT was performed in 68 left legs (53%) and 61 right legs (47%). Sixty-five patients (67%) underwent a unilateral treatment, and 32 patients (33%) had bilateral treatment. Patients who had arterial occlusive disease, patients with a known thrombotic or hemorrhagic tendency (also oral anticoagulation), women who were pregnant or planning to become pregnant were excluded as were patients with a venous diameter greater than 15 mm and dilatation from the SF junction with multiple insufficient side branches. In all patients, the diagnosis of venous incompetence with reflux was made by clinical evaluation and color Doppler studies.
Endovenous Laser Treatment of Saphenous Vein Reflux / Vuylsteke et al 143 Table 1. Patient Classification According to CEAP Clinical Classification Clinical Classification Characteristics % of Patients (n) Class 0 No visible or palpable sign of venous disease 0 Class 1 Telangiectasias or reticular veins 0 Class 2 Varicose veins 77 (99/129) Class 3 Edema 20 (26/129) Class 4 Venous disease and skin changes 0.7 (1/129) Class 5 Venous disease with healed ulceration 0.7 (1/129) Class 6 Skin changes with active ulceration 1.6 (2/129) Note: CEAP = clinical, etiology, anatomy, pathophysiology. Technique Before surgery, a detailed duplex mapping and grading of the superficial venous, deep venous, and perforator system was performed in standing position, including measuring the diameter of the incompetent SV at 3 referential points (at the SF junction, mid thigh, and knee). With these measurements, we calculated the average diameter of the vein. The incompetent side branches and perforating veins were marked on the skin. The most distal point of GSV insufficiency was preoperatively marked as appropriate laser fiber entry point. All the duplex scannings were performed by the same independent observer from the radiology department, in the morning of the operation day, using GE logic 9 ultrasound equipment. The SVs were catheterized at the distal point of reflux, and a guiding catheter (6-Fr Endocath) with bare fiber was introduced. The end point of a 600-µm fiber tip was localized 2 cm distal to the SF junction. Its position was verified by peroperative ultrasound and by visualization of the red aiming beam through the skin, which disappears when entering the common femoral vein. The catheter was retracted 2 cm from its tip. Attention was given to inject the tumescent anesthesia in the perivenous area, the so-called saphenous eye, around the wall of the GSV, under real-time ultrasound guidance. Large volumes of tumescent anesthesia were administered to patients receiving more than 250 ml/vein. The vein should be completely surrounded by liquid (Figure 1). This induces a spasm of the vein with a better apposition of the fiber tip to the vessel wall and a protection of the perivenous tissue. The injected fluid is a cocktail of 2 ampoules (10 ml) xylocaine 1% with 300 ml of saline. If necessary (bilateral treatment), the fluid is diluted up to more than 500 ml. The safe dose of xylocaine was never exceeded. The veins were treated Figure 1. Ultrasound-guided injection of tumescent anesthesia around the saphenous vein. with a pulsed pullback protocol using a 980-nm Diode laser (Intermedic Barcelona, Spain) with pulses of 10 W, 3 seconds and 3 to 4 shots every centimeter. Below the knee, the energy deliverance was reduced (pulses: 7 W-3 seconds). The mean diameter (average of the diameters measured at referential points with the patient in standing position) of the GSV in our patients was 6.9 cm ± 2.3 (pretreatment diameter). Mean energy applied per length (LEED) was 103 J/cm ± 22. Energy fluence, calculated separately for each patient, averaged 51 J/cm 2 ± 17. Peroperative manual compression was avoided because this compression facilitates the direct contact between the fiber tip and the vessel wall and thus increases the risk of perforation.
144 Vascular and Endovascular Surgery / Vol. 42, No. 2, April/May 2008 After the ELT, a foam sclerosis of incompetent side branches in combination with a limited Muller phlebectomy was performed. If necessary, a bilateral treatment was done. When the ELT was combined with an extended phlebectomy of the tributaries and if a bilateral treatment is performed, patients were treated under general or spinal anesthesia. Postoperative Care and Follow-up After surgery, a compressive bandage was applied until the first follow-up visit 3 days later. At that time, the patients were provided with compressive stockings (20-30 mm Hg) for another 3 weeks. All patients were given a prescription for a nonsteroidal analgetics. Patients were allowed to walk immediately postoperatively and encouraged to resume their usual occupational activities as soon as possible. Follow-up visits were scheduled at 3 days and 4 weeks postoperatively. An additional follow-up visit was planned after 6 months. Patients were examined by color duplex ultrasonography at their 4-week and 6-month follow-up visit. Study Endpoints and Definitions Duplex ultrasound criteria for the successful treatment were the following: at 1 month follow-up, an enlarged noncompressible vein, with an echogenic thickened vein wall, was observed, and there was no flow observed within the occluded vein lumen on color Doppler investigation, and at 6 months, an occluded vein with a substantial (>50%) reduction in diameter was observed. A proximal recanalization is a repermeabilization of the vein up to 10 cm from the SFJ with reflux when performing the Valsalva maneuver in standing position. We define a partial recanalization as a repermeabilisation of a treated vein up to 30 cm (Figure 2). Calculation of Energy Deposits For the energy amount in joules divided by the treated vein length in centimeters, we use the term LEED. 24 The LEED reflects the average amount of energy in joules administrated endovenously to a given length of treated vein in centimeters. To take into account the different diameters of the GSV with respect to the administrated laser energy, a cylindrical approximation of the inner vein Figure 2. Classification. A, complete occlusion. B, proximal recanalization. C, partial recanalization.
Endovenous Laser Treatment of Saphenous Vein Reflux / Vuylsteke et al 145 Table 2. Occlusion Rate of GSV at 1 and 6 Months Postoperatively GSV Day 1 1 Mo 6 Mo Number of controlled veins 129 129 118 (11 lost of FU) Complete occlusion 129 122 107 Proximal recanlization 0 5 4 Partial recanalization 0 2 7 Note: GSV = great saphenous vein; FU = follow-up. surface area was calculated using the average diameter of the vein (by calculating the mean diameter of the 3 referential diameters measured preoperatively with the patient in standing position). For the quotient of delivered energy in joules against the approximated inner vessel surface, we use the term endovenous fluence (EF). The advantage of using EF is that it makes it easy comparing energy used in treated veins with a different diameter because the diameter is included in calculating the fluence. Statistical Analysis Intergroup variances were evaluated by use of the t test for variance of means. Statistical analysis was performed using the SPSS statistical package. Results In the group of the GSV treatment, no major complication was observed. No deep-venous thrombosis or pulmonary embolism was noted. No skin burn was noted. The following minor complications were observed at 1 month. In the early postoperative period, 83 patients (86%) had no pain or mild pain. Fourteen patients (14%) complained of moderate to severe pain, and needed analgetics. Twelve patients developed periphlebitis with mild induration of the treated GSV, all of them resolved with the use of nonsteroidal anti-inflammatory drugs. On day 3, most patients developed ecchymoses along the treated GSV; possibly from direct laser ablation and perforation or needle punctures for tumescent anesthesia. These were self-limiting during the period of 1 week. At 1 month, there were 5 persistent ecchymoses and 8 small hematomas. Most of the hematomas were because of the associated phlebectomy and were punctured successfully. Six patients developed temporary paresthesia or hypoesthesia in the treated leg mostly related to the phlebectomies. These had all resolved at 6 months. Six patients had residual skin pigmentation. One infection was noted at a phlebectomy site. Two patients with an active venous ulcer reported healing of this ulcer at 1 month. The clinical success rate was 100%. At 1 month, we found 5 proximal recanalizations and 2 partial recanalizations. The total occlusion rate was 94.6%; at 6 months, there were 4 proximal recanalizations and 7 partial recanalizations (Table 2). All recanalized veins distally had a connection with an incompetent side branch. The total occlusion rate after 6 months was 90.7%, which was with a high-energy treatment (mean LEED = 103 J/cm; mean energy fluence = 51 J/cm 2 ). It is still an unsolved question if a recanalization will lead to clinical varicose recurrence. Nevertheless all recanalized veins were treated with echoguided foam sclerosis. Discussion Despite the high-energy treatment of the GSV, our recanalization rate at 6 months is still important. When we look carefully at the data, we see that the recanalizations occur preferentially in larger veins (mean diameter of recanalized veins: 8.18 vs 6.9 mm for all GSV). We divided the patient population in 2 groups: the first group with complete occluded veins and a second group with recanalized veins. Because we measured the mean diameter of each vein and the energy we used, we calculated the fluence of each treated vein (Figure 3). The mean fluence (EF) of the veins with total occlusion (n = 107) was 52 and 43.73 J/cm² in the group of recanalized veins (n = 11). When compared with the t test for variance of means, these 2 groups are statistically significantly different (P <.01). How much energy do we need to prevent recanalizations? Because a fluence of 52 J/cm 2 is the mean fluence of the occluded veins, we propose to
146 Vascular and Endovascular Surgery / Vol. 42, No. 2, April/May 2008 Figure 3. Occlusion versus recanalization as a function of fluence. deliver this energy for ELT of incompetent SV. The proposed energy used can be calculated using the following formula: E (J/cm) = 52 π vein diameter (cm) = 16.3 vein diameter (mm) If you have a vein with a mean diameter of 0.8 cm, the energy you need is: 52 3.14 0.8 = 130 J/cm. As already stated by Proebstle and based upon our own results, we can conclude that the recanalization rate is fluence dependent, but you can have a recanalization even with a high-energy treatment. So probably energy is not the only problem. If a recanalization occurs, the SV treated with ELT always has an incompetent side branch at the distal part of the refluxing segment. If we indicate this proximal incompetent side branch in the preoperative duplex mapping and eliminate this side branch with a Muller-phlebectomy during the intervention, it may be possible to avoid some recanalizations. Of course, this has to be confirmed by new prospective trials. In our series, the patients were treated in a horizontal position. A French study 17 proved that a Trendelenburg position of the patient treated with ELT has statistical superior results concerning the occlusion rate. Especially in veins with a diameter superior to 8 mm, where the amount of intravenous blood is very important even in the Trendelenburg position. In these cases, the laser irradiation is not sufficient to heat up the vessel wall, because the light energy is almost entirely absorbed by the blood, and the initial success rate is mainly due to a thrombotic effect as already stated by Proebstle et al. 11 However, the thrombus dissolution leads to a recanalization of those large GSV. On the technical point of view, ELT also has some imperfections; the bare fiber used for ELT is a rigid fiber. When this fiber is introduced in a SV, which usually has some small tortuosities and turnings, the fiber always has a tendency to stretch. As a consequence of this stretching, the fiber tip frequently hits the vessel wall (Figure 4). Examining the fiber localization on peroperative ultrasound
Endovenous Laser Treatment of Saphenous Vein Reflux / Vuylsteke et al 147 Figure 5. Uneven destruction of the vein wall. Figure 4. Eccentric fiber tip hits the vessel wall. control, we see the fiber tip mostly situated very eccentric in the vein, with the tip touching the vein wall. Tumescent anesthesia induces spasm of the vein around the fiber and can diminish this effect. But even then, especially in larger veins, the fiber tip stays eccentric. In such a situation, when the energy is delivered from the fiber tip, a direct contact between the fiber tip and the vessel wall results in a destruction and ulceration or a perforation of the vein. A consequence of this is a very uneven application of light energy. When we examine a specimen of vein which has been treated with ELT, we see a line of damaged vessel wall with carbonized vein wall and ulcerations and perforations, whereas the rest of the vessel wall stays unaffected (Figure 5). These perforations cause the postoperative appearance of ecchymosis and can also injure the perivenous tissue, especially when the tumescent fluid is not surrounding the vein. Other parts of the vein wall stay untouched. If the ulcerations are healing, we can get a recanalization of the treated vein. Endovenous laser treatment results in an incomplete circumferential destruction of vessel wall structures, and this may allow a regeneration of the vein. This problem has been studied in an ex vivo model. 25 It shows that using the bare fiber results in uneven application of light energy and necessitates the use of greater energy to ensure sufficient destruction of the vein wall to prevent recanalizations. By carbonizing the vein wall (direct contact
148 Vascular and Endovascular Surgery / Vol. 42, No. 2, April/May 2008 with vessel wall), a lot of energy is lost. This in turn increases the likelihood of vein perforation. So it may be possible that when we use a suitable guiding catheter, which prevents a direct contact between the fiber tip and the vessel wall, we could improve our results: with a more even application of light energy, we can obtain lower recanalization rate and prevent ulcerations and perforations of the vein wall. We can achieve this with lower energy deliverance. A new catheter design with a pullback system is presented in Figure 6. Conclusion Endovenous laser treatment is a safe and effective treatment of SV reflux and even high-energy treatment is well tolerated. The occlusion rate is fluence dependent and therefore a higher energy treatment is necessary. But even in these higher fluence treatment groups, recanalizations might occur especially 6 months postoperatively. We can possibly ameliorate our results by treating the patient in a Trendelenburg position, using an average fluence of 52 J/cm², eliminating the proximal incompetent side branches and by introducing a new catheter design. References Figure 6. New catheter design to prevent a direct contact between the fiber tip and the vessel wall. 1. Callam MJ. Epidemiology of varicose veins. Br J Surg. 1994;81:167-173. 2. Goldman MP, Weiss RA, Bergan JJ. Diagnosis and treatment of varicose veins: a review. J Am Acad Dermatol. 1994;31:393-416. 3. Parente EJ, Rosenblatt M. Endovenous laser treatment to promote venous occlusion. Lasers Surg Med. 2003; 33:115-118. 4. Oh CK, Jung DS, Jang HS, Kwon KS. Endovenous laser surgery of the incompetent greater saphenous vein with a 980-nm diode laser. Dermatol Surg. 2003;29:1135-1140. 5. Bergan JJ, Kumins NH, Owens EL, Sparks SR. Surgical and endovascular treatment of lower extremity venous insufficiency. J Vasc Interv Radiol. 2002;13:563-568. 6. Rautio T, Ohinmaa A, Perälä J, et al. Endovenous obliteration versus conventional stripping operation in the treatment of primary varicose veins: a randomised controlled trial with comparison of the costs. J Vasc Surg. 2002;35:958-965. 7. Vuylsteke M, Vanden Bussche D, Audenaert EA, et al. Endovenous laser obliteration for the treatment of primary varicose veins. Phlebology. 2006;21:80-87.
Endovenous Laser Treatment of Saphenous Vein Reflux / Vuylsteke et al 149 8. Cambell WB, Vijay Kumar A, Allington KL, Michaels JA. The outcome of varicose vein surgery at 10 years: clinical findings, symptoms and patient satisfaction. Ann R Coll Surg Engl. 2003;85:52-57. 9. Min R, Khilnani N, Zimmet S. Endovenous laser treatment of saphenous vein reflux: long-term results. J Vasc Interv Radiol. 2003;14:991-996. 10. Weiss RA. Endovenous techniques for elimination of saphenous reflux: a valuable treatment modality. Dermatol Surg. 2001;27:902-905. 11. Proebstle TM, Lehr HA, Kargl A, et al. Endovenous treatment of the greater saphenous vein with a 940-nm diode laser: thrombotic occlusion after endoluminal thermal damage by laser-generated steam bubbles. J Vasc Surg. 2002;35:729-736. 12. Chang CJ, Chua JJ. Endovenous laser photocoagulation (EVLP) for varicose veins. Lasers Surg Med. 2002;31: 257-262. 13. Goldman MP, Mauricio M, Rao J. Intravascular 1320-nm laser closure of the great saphenous vein: a 6 to 12 month follow-up study. Dermatol Surg. 2004;30:1380-1385. 14. Min RJ, Zimmet SE, Isaac MN, Forrestal MD. Endovenous blaser treatment of the incompetent greater saphenous vein. J Vasc Interv Radiol. 2001;12: 1167-1171. 15. Proebstle TM, Krummenauer F, Knop GJD, et al. Nonocclusion and early reopening of the great saphenous vein after endovenous laser treatment is fluence dependent. Dermatol Surg. 2004;30:174-178. 16. Mozes G, Kalra M, Camo M, Swenson L, Gloviczki P. Extension of saphenous thrombus into the femoral vein: a potential complication of new endovenous ablation techniques. J Vasc Surg. 2005;41:130-135. 17. Desmyttere J, Grard C, Mordon S. A 2 years follow-up study of endovenous 980nm laser treatment of the great saphenous vein: role of the blood content in the GSV. Med Laser Appl. 2005;20:283-289. 18. Van den Bussche D, Moreels N, De Letter J, Lanckneus M. Endovenous laser treatment for primary varicose veins. Acta Chir Belg. 2006;106:32-35. 19. Kalra M, Gloviczki P. Fifteen years ago laser was supposed to open arteries, now it is supposed to close veins: what is the reality behind the tool. Perspect Vasc Surg Endovasc Ther. 2006;18:3-8;discussion 9-10. 20. Proebstle TM, Sandhofer M, Kargl A, et al. Thermal damage of the inner vein wall during endovenous laser treatment: key role of energy absorption by intravascular blood. Dermatol Surg. 2002;28:596-600. 21. Timperman PE. Prospective evaluation of higher energy great sap henous vein endovenous laser treatment. J Vasc Interv Radiol. 2005;16:791-794. 22. Perkowski P, Ravi R, Gowda RC, et al. Endovenous laser ablation of the saphenous vein for treatment of venous insufficiency and varicose veins: early results from a large single-center experience. J Endovasc Ther. 2004;11: 132-138. 23. Mordon SR, Wassmer B, Zemmouri J. Mathematical modeling of endovenous laser treatment (ELT). Biomed Eng Online. 2006;25:5-26 24. Proebstle TM, Moehler T, Gûl D, Herdemann S. Endovenous treatment of the great saphenous vein using a 1320 nm Nd:YAG laser causes fewer side effects than using a 940 nm Diode laser. Dermatol Surg. 2005;31:1678-1684. 25. Schmedt CG, Sroka R, Steckmeier S, et al. Investigation on radiofrequency and laser (980 nm) effects after endoluminal treatment of saphneous vein insufficiency in an ex-vivo model. Eur J Endovasc Surg. 2006;32: 318-325.