Endovenous laser ablation: a review of mechanisms of action

Comparative study between endovenous laser ablation (EVLA) with 1940 nm versus EVLA with 1470 nm for treatment of incompetent great saphenous vein and short saphenous vein: a randomized controlled trial

BACKGROUND

To date, the most commonly used endothermal ablation method is endovenous laser ablation (EVLA). The objective of this work is to assess the initial and short-term outcomes of a 1940 nm diode laser compared with 1470 nm diode laser utilization for the treatment of lower limb varicose veins.

METHODS

This is a randomized controlled prospective study that included patients with varicose veins. The allocated patients were randomized according to the technique used: group I, which was treated using EVLA with a 1940 nm diode laser, and group II, which was treated using EVLA with a 1470 nm diode laser.

RESULTS

This study initially included 216 patients. After the exclusion of patients lost during follow-up, group I consisted of 105 patients, and group II consisted of 101 patients. There were high rates of anatomical success in the two groups with obliteration of the treated vessels at the 1-month follow-up (100% and 99%, respectively) and the 6-month follow-up (100% and 99%, respectively). A very low rate of adverse events was encountered (1%). Group II showed obviously longer median days to return for usual activities (11.5 compared with 7 days). They showed significantly higher pain scores, which was evident at the 7-day and 1-month follow-ups (P < .001).

CONCLUSIONS

Both lasers provided excellent outcomes in terms of anatomical success and low rates of adverse events. The 1940 nm diode laser was associated with lower median days to return for usual activities and significantly lower pain scores. Evidently, lower power and linear endovenous energy density were required for this laser.

An in vitro feasibility study of 355 nm laser atherectomy for the treatment of peripheral atherosclerotic lesions

In this study, we utilized a novel 355 nm laser to ablate porcine aortas in the presence of physiological saline and contrast agent. Subsequently, we investigated the shape and depth of the resulting injuries. After ablating bovine tendons and aortas with the laser, we analyzed the size and quantity of particles postablation. Finally, we conducted ablation experiments using human ex vivo plaques. The analysis revealed minimal damage to porcine aortas within 2 s of exposure to the 355 nm laser. The degree of injury in the presence of contrast agent was higher than that in the presence of physiological saline but significantly lower than the damage caused by 308 nm laser. Regardless of whether it was bovine tendon or porcine aorta tissue, the proportion of particles <25 μm postlaser ablation exceeded 99%. Lastly, the 355 nm laser successfully opened three types of plaques: chronically occluded, stent restenosis, and stale thrombosis.

Endovenous laser ablation (EVLA) 980 nm versus 1470 nm and the impact of fiber type: a systematic review and meta-analysis

We sought to assess the efficacy and safety of endovenous laser ablation utilizing a 980 nm device versus a 1470 nm device in the treatment of lower limb venous insufficiency. We performed a systematic review adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement. A research on PubMed, Scopus and Web of science for articles published by January 2024 was conducted. The primary endpoint was great saphenous vein (GSV) and truncal vein occlusion. Eleven studies encompassing 3061 patients and 3193 truncal veins, were included. The 1470 nm device demonstrated superior truncal vein and GSV occlusion outcomes compared to the 980 nm device at the early, one-year, and medium to long-term follow-up intervals. Odds ratios (OR) were 2.79(95%CI:1.31-5.94), 2.22(95%CI:1.21-4.07), and 2.02(95%CI:1.24-3.29) for truncal veins and 2.54(95%CI:1.119-5.41), 2.06(95%CI:1.07-3.95) and 2.04(95%CI:1.25-3.33) for GSV, across the respective intervals. While both devices demonstrated minimal, deep vein thrombosis (DVT), endovenous heat-induced thrombosis (EHIT) ≥ 2, and burn estimates, the 1470 nm device exhibited improved paresthesia, risk ratio (RR), 0.51(95%CI:0.34-0.77) and pain outcomes, standardized mean difference (SMD), -0.62(95%CI:-0.99to-0.25). Subgroup analysis displayed enhanced occlusion outcomes with the 1470 nm device for the six-month and one-year intervals, irrespective of fiber type. Radial fibers were associated with improved paresthesia outcomes (β=-0.9520,p = 0.03). This review emphasized the enhanced efficacy of the 1470 nm device over the 980 nm device, regardless of fiber type. Radial fibers showed promise for improved paresthesia outcomes, suggesting similar safety profiles for both systems. Conclusive remarks on pain outcomes were impeded by data limitations.

Third generation of laser (>1900) for endovenous thermoablation (EVLA) of varicose veins: A systematic review and meta-analysis

OBJECTIVES

Third generation lasers with longer wavelengths (>1900 nm) have been introduced, in recent years, for the treatment of varicose veins. The possible advantage of the new generation lasers is that they allow complete damage to the vein wall using a lower Power in Watts (W: J/sec) and a lower linear energy density (LEED: J/cm). The aim of this work is to evaluate the results present in the literature regarding efficacy and safeness of the new generation lasers for the treatment of varicose veins.

METHODS

Published articles were searched on PubMed database and on Cochrane Library, entering the keywords "1940 nm or 1920 nm laser AND varicose veins laser thermoablation (EVLA)." The primary endpoint of the study was to value rate of occlusion and adverse events at the short term follow-up. The search yielded a total of 14 studies. In the end, only six studies were judge eligibility.

RESULTS

The studies were heterogenous in their documentation, EVLA, duplex ultrasound protocol and result reporting. A total of 540 limbs of 377 patients were treated with endovenous laser ablation (EVLA) with laser 1920-1940 nm. The treated veins had a mean diameter of 0.74 ± 0.17 cm and a mean length of 27.87 ± 20.63 cm. The pooled estimates of immediate occlusion rate was of 99.8% (95% CI: 97.9% to 100.0) with high heterogeneity (I2 = 60%; 95% PI: 89.7% to 100%), while at short-term follow-up was of 98.2% (95% CI: 94.0% to 100.0%) with higher heterogeneity (I2:79%; 95% PI: 77.1% to 100.0%). EHIT occurred in 7 cases (pooled estimate: 0.7%). The other adverse events rate reported were 1% of hyperpigmentation, 2.8% of neurological complications, 0.6% thrombophlebitis and 1.9% of bruising/hematoma. The pooled mean estimates of LEED was equal to 38.2 J/cm (95% CI: 26.3 to 50.1 J/cm) although with a very large heterogeneity (I2 = 100%).

CONCLUSIONS

The overall success rate of EVLA was high. The analysis of these studies suggests that using lower parameters (Power and linear administered energy) may have no effect on the treatment success rate. Short-term results demonstrate comparable occlusion rates respect the second-generation lasers. Instead, data suggest a low complication rates. Short-term results demonstrate comparable complications rates respect the second-generation lasers (1300-1470 nm). Randomized studies with longer follow-up are required to evaluate the EVLA 1900 nm procedure further.

Ultrasound and Photoacoustic Imaging for the Guidance of Laser Ablation Procedures

The accuracy and efficacy of laser ablation procedures depend on the accurate placement of the laser applicator within the diseased tissue, monitoring the real-time temperature during the ablation procedure, and mapping the extent of the ablated region. Ultrasound (US) imaging has been widely used to guide ablation procedures. While US imaging offers significant advantages for guiding ablation procedures, its limitations include low imaging contrast, angular dependency, and limited ability to monitor the temperature. Photoacoustic (PA) imaging is a relatively new imaging modality that inherits the advantages of US imaging and offers enhanced capabilities for laser-guided ablations, such as accurate, angle-independent tracking of ablation catheters, the potential for quantitative thermometry, and monitoring thermal lesion formation. This work provides an overview of ultrasound-guided procedures and how different US-related artifacts limit their utility, followed by introducing PA as complementary to US as a solution to address the existing limitations and improve ablation outcomes. Furthermore, we highlight the integration of PA-driven features into existing US-guided laser ablation systems, along with their limitations and future outlooks. Integrated US/PA-guided laser ablation procedures can lead to safer and more precise treatment outcomes.

Laser ablation on vascular diseases: mechanisms and influencing factors

Vascular diseases, such as venous insufficiency and coronary artery diseases, have been threatening the health of people. Efficient treatment with proper postoperative care is required to relieve the pain of the patients. Traditionally, venous insufficiency is treated with ligation and stripping, an open surgery whose complication rate cannot be ignored. Coronary artery disease is often treated with balloon angioplasty during which undilatable lesions may be encountered, limiting the efficacy of this approach. With advances in laser photonics and percutaneous coronary intervention procedure, laser ablation is emerging as an alternative and adjunctive therapy for these diseases. Endovenous laser ablation has the advantages of high success rate, low complication risk, and fast postoperative recovery. Laser ablation in arteries can handle uncrossable or undilatable lesions with a low incidence of serious complications. In this review, previously published research concerning vascular diseases and their therapies are analyzed in order to provide a clear explanation of the mechanisms and merits of laser ablation. For endovenous laser ablation, the main mechanisms are steam bubbles, heat conduction, and heat pipe, and three main influencing factors are wavelength, fiber types, and laser energy density. For excimer laser coronary atherectomy, the main mechanisms are photochemical, photothermal, and photomechanical effects, and three main influencing factors are catheter, medium, and laser parameters.

A cyanoacrylate/triethyl citrate/nanosilica-based closure glue with wet-adhesion capability for treatment of superficial varicose veins

Varicose veins in legs are common in clinics. Currently, medical adhesive-based, minimally invasive endovenous occlusion is used to treat them. However, the most common cyanoacrylate medical adhesives do not perform well when used under blood/wet conditions. In particular, poor adhesion, short curing time, and high heat release greatly limit their clinical use. In this paper, we demonstrate the use of a composite system composed of butyl-cyanoacrylate, triethyl citrate, and nanosilica that exhibits a blood/wet-adhesion capability to serve as a new sealing glue. Hydrophobic triethyl citrate groups displace boundary waters while also protecting cyanoacrylate monomers from undergoing rapid polymerization. Nanosilica increases viscosity, which contributes to in situ extrusion molding and retention. An optimal formulation, FAL-006, exhibited good physical and chemical properties in vitro. The performed additional safety assays indicated that FAL-006 has good biocompatibility. The closure efficiency of FAL-006 in vivo was evaluated in both a rat abdominal aortic closure model and in a sheep lower limb venous closure model. Taken together, these results indicate that FAL-006 exhibits promising potential for use in clinical applications. Furthermore, this study provides a new strategy for designing underwater adhesive agents for additional clinical applications, and a strategy for constructing other biomaterials needed for use under wet conditions.

Varicose Veins of the Lower Extremity: Doppler US Evaluation Protocols, Patterns, and Pitfalls

Venous insufficiency is a cause of substantial morbidity and medical expenditures. Diagnostic US evaluation of venous insufficiency requires a thorough understanding of the venous anatomy, including the deep, superficial, and perforator veins. The highly variable venous anatomy requires that operators use sound judgment to expand on protocol images and thus avoid missing important sources of reflux. The US examination requires specific patient positioning and use of provocative maneuvers. A basic understanding of the pathophysiology of venous insufficiency and the various treatment methods helps to identify key observations so that ineffective treatment methods are not pursued. The examination reports should have greater detail than those for the more common lower extremity deep venous thrombosis evaluation, requiring numeric and narrative descriptions of deep and superficial venous patency, reflux, diameter, and pathways. Potential pitfalls include not recognizing or detecting deep venous reflux, misidentifying common femoral vein reflux as deep venous reflux when the reflux is isolated or related to saphenofemoral insufficiency, not recognizing anterior accessory great saphenous vein (AAGSV) involvement in saphenofemoral insufficiency, not recognizing or reporting great saphenous vein or AAGSV superficialization, not suspecting central venous obstruction, and not realizing when provocative maneuvers were ineffective. With knowledge of the lower extremity venous anatomy, venous insufficiency pathophysiology, basic treatment strategies, protocol best practices, patterns of observation, and diagnostic pitfalls, those who interpret venous insufficiency US studies can perform examinations and deliver reports that help patients receive appropriate treatment. Online supplemental material is available for this article. ^©RSNA, 2022.

A Novel Laser Energy Ablation Catheter for Endocardial Cavo-Tricuspid Isthmus Ablation and Epicardial Ventricular Lesion Formation: An in vivo Proof-of-Concept Study

Aim

This proof-of-concept study aimed to investigate atrial and ventricular lesion formation by a 20-mm linear laser ablation catheter, regarding lesion depth and tissue damage.

Methods

In total, 6 female swines underwent standard femoral vein access to introduce a novel 20-mm linear laser ablation catheter in the right atrium to perform endocardial cavotricuspid isthmus (CTI) ablations. The navigation took place under fluoroscopy with additional visualization by intracardiac echocardiograph. Via a sternotomy, epicardial ablations were performed on the surface of the left ventricle (LV), right ventricle (RV), and right atrial appendage (RAA). Procedural safety was assessed by registration of intraprocedural adverse events and by macroscopic examination of the excised hearts for the presence of charring or tissue disruption at the lesion site.

Results

Altogether 39 lesions were created, including 8 endocardial CTI (mean lesion length 20.6 ± 1.65 mm), 26 epicardial ventricle (mean lesion length LV: 25.3 ± 1.35 mm, RV: 24.9 ± 2.40 mm), and 5 epicardial appendage ablations (mean lesion length RAA: 26.0 ± 3.16 mm). Transmurality was achieved in all CTI and atrial appendage ablations, in 62% of the RV ablations and in none of the LV ablations. No perforation or steam pop occurred, and no animal died during the procedure.

Conclusion

In this porcine study, the 20-mm linear laser ablation catheter has shown excellent results for endocardial cavotricuspid isthmus ablation, and it resulted in acceptable lesion depth during atrial and ventricular epicardial ablation. The absence of tissue charring, steam pops, or microbubbles under the experimental conditions suggests a high degree of procedural safety.

Review on Laser Technology in Intravascular Imaging and Treatment

Blood vessels are one of the most essential organs, which nourish all tissues in our body. Once there are intravascular plaques or vascular occlusion, other organs and circulatory systems will not work properly. Therefore, it is necessary to detect abnormal blood vessels by intravascular imaging technologies for subsequent vascular treatment. The emergence of lasers and fiber optics promotes the development of intravascular imaging and treatment. Laser imaging techniques can obtain deep vascular images owing to light scattering and absorption properties. Moreover, photothermal and photomechanical effects of laser make it possible to treat vascular diseases accurately. In this review, we present the research progress and applications of laser techniques in intravascular imaging and treatment. Firstly, we introduce intravascular optical coherent tomography and intravascular photoacoustic imaging, which can obtain various information of plaques. Multimodal intravascular imaging techniques provide more information about intravascular plaques, which have an essential influence on intravascular imaging. Secondly, two laser techniques including laser angioplasty and endovenous laser ablation are discussed for the treatment of arterial and venous diseases, respectively. Finally, the outlook of laser techniques in blood vessels, as well as the integration of laser imaging and treatment are prospected in the section of discussions.

No significant difference between 1940 and 1470 nm in endovenous laser ablation using an in vitro porcine liver model

Current endovenous laser ablation (EVLA) practice favours 1470 nm, as water is a major chromophore for this wavelength. Water has a greater affinity for 1940 nm, leading to claims that lower powers or linear endovenous energy densities (LEEDs) are needed. We compared the thermal spread and carbonisation of EVLA using these two wavelengths, in the porcine liver model. Using the previously validated porcine liver model, we performed 5 treatments, at each power: 2 W, 4 W, 6 W, 8 W and 10 W using a standard pullback of 8 s/cm. This gave LEEDs for each wavelength of 16, 32, 48, 64 and 80 J/cm. Digital images were given random codes and analysed by two blinded observers. Thermal spread was measured using "SketchandCalc" online software and graded carbonisation from 0 (none) to 3 (black carbon tract). There was no significant difference in thermal spread between the two wavelengths at 6 W, 8 W and 10 W. At 2 W, the 1470-nm laser had a significantly increased thermal spread over the 1940 nm. Significantly more carbonisation was found with the 1940-nm laser compared to 1470 nm. In this model, there was no significant difference in thermal spread at powers of 6 W and more. At 2 W and potentially 4 W, 1470 nm showed spread than 1940 nm, due to increased absorption at the device/tissue interface. At powers and LEEDs used for saphenous ablation, we found no evidence to support reduced power or LEED when using 1940 nm. However, 1940 nm may be more advantageous than 1470 nm when ablating small thin-walled veins, near to the skin.

What is the optimal treatment technique for great saphenous vein diameter of ≥10 mm? Comparison of five different approaches

OBJECTIVE

We aimed to investigate the efficacy and safety of five different treatment approaches in patients with a great saphenous vein (GSV) diameter of ≥10 mm.

METHODS

A total of 697 extremities of 671 patients who were diagnosed with a GSV diameter of ≥10 mm underwent conventional surgery or endovenous therapy for symptomatic varicose veins between January 2012 and January 2017 were included in this retrospective study. All extremities included in the study were divided into five groups as follows: high ligation + stripping (HLS), radiofrequency ablation (RFA), cyanoacrylate closure (CAC), endovenous laser ablation (EVLA) procedures at 980 nm and 1,470 nm wavelengths.

RESULTS

Among all groups, despite lower recurrence rates in HLS group than the other groups, there was no significant difference at 6 months and 1 year among the HLS, EVLA at 1,470 nm wavelength, and RFA groups. The recurrence rates of EVLA at 980 nm wavelength and CAC groups were found higher than other groups.

CONCLUSIONS

In conclusion, our study results show that although HLS seems to be an effective method for the treatment of a GSV diameter of ≥10 mm with a low recurrence rate, it does not statistically significantly differ from EVLA at 1,470 nm wavelength and RFA. Therefore, we believe that EVLA at 1,470 nm wavelength and RFA can be preferred over HLS with low pain scores in this patient population.

Comparison of Short-Term Outcomes Between Endovenous 1,940-nm Laser Ablation and Radiofrequency Ablation for Incompetent Saphenous Veins

Background: Radiofrequency ablation (RFA) has shown faster recovery and lower pain scores compared to Endovenous laser ablation (EVLA) for treatment of varicose veins. However, a comparison of 1,940-nm EVLA and RFA has not been reported. This study compared short-term outcomes using 1,940-nm EVLA and RFA for varicose veins. Methods: Between April 2018 and June 2018, 43 patients (83 incompetent saphenous veins) were treated with 1,940-nm EVLA and 37 patients (64 incompetent saphenous veins) with RFA. Follow-up duplex was checked at 1 month and 3 months. Results: Baseline characteristics showed no significant differences between both groups except for age. Pain scores at 6 h, and at 1, 10, and 30 days after treatment showed no differences. Complications and time to return to normal activity showed no differences. The 100% closure rate was checked in both groups at 1 month and 3 months follow-up. Conclusion: Short-term outcomes showed no significant differences between 1,940-nm EVLA and RFA treatment.

Homogeneously Emitting, Mechanically Stable, and Efficient fs-Laser-Machined Fiber Diffusers for Medical Applications

BACKGROUND AND OBJECTIVES

Light delivery is an essential part of therapy forms like photodynamic therapy (PDT), laser-induced thermotherapy, and endovenous laser therapy. While there are approaches to the light application for all three therapies, there is no diffuser that can be used for all three approaches. This diffuser must meet the following criteria: Homogeneous radiation profile over a length of 40 mm, efficient light extraction in the diffuser area, mechanical breakage resistance as well as thermal stability when applying high power.

STUDY DESIGN/MATERIALS AND METHODS

An ultrashort pulse laser was used to inscribe inhomogeneities into the core of a fused-silica fiber core while scanning the laser focus within a linear arrangement of cuboids centered around the fiber axis. The manufactured diffuser was optically and mechanically characterized and examined to determine the maximum power that can be applied in a tissue environment.

RESULTS

Based on the analysis of all examined diffusers, the manufactured diffuser exhibits an emission efficiency ε = (81.5 ± 5.9)%, an intensity variability of (19 ± 5)% between distal and proximal diffuser end, and a minimum bending radius R_b = (15.4 ± 1.5) mm. It was taken advantage of the fact that the outer areas of the fiber core do not undergo any structural changes due to the machining and therefore do not suffer a major loss of stability. Tissue experiments revealed that a maximal power of 15 W was deliverable from the diffuser without harming the diffuser itself.

CONCLUSIONS

It could be shown that a diffuser manufactured by ultrafast-laser processing can be used for low power applications as well as for high power applications. Further tests have to show whether the mechanical stability is still maintained after the application of high power in a tissue environment. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Ten years of experience with first-visit foam sclerotherapy to initiate venous ulcer healing

OBJECTIVE

We evaluated the effect of first-visit foam sclerotherapy compared with scheduled treatment for patients with venous ulceration.

METHODS

The study design was a retrospective comparative study. From December 2009 to October 2019, a total of 245 venous ulcers in 214 patients (including recurrent ulcers) were treated at Oulu University Hospital. Of these 245 venous ulcers, 143 were treated with first-visit foam sclerotherapy (group A) and 102 with scheduled treatment (group B). All patients received endovenous ablation (foam sclerotherapy and/or endothermal ablation) and compression therapy to promote venous ulcer healing. The primary outcome was the interval to ulcer healing, determined by Kaplan-Meier survival analysis. The secondary outcomes included the time to ulcer healing from the receipt of referral and ulcer recurrence.

RESULTS

The median time to ulcer healing was 2.3 months for group A and 3.2 months for group B (P = .002). The estimated median ulcer healing times after referral for a first session of endovenous ablation were 2.7 months with a delay of <1 month from the referral, 3.3 months with a delay of 1 to 2 months, and 5.0 months with a delay of >2 months (P = .002). In group A, recurrent ulcers were recorded for 11 patients (7.7%). In group B, recurrent ulcers were recorded for 12 patients (11.8%; P = .281).

CONCLUSIONS

The results of the present retrospective comparative study support first-visit foam sclerotherapy as an effective method to initiate endovenous ablation to promote venous ulcer healing. In venous ulcers, delays to endovenous ablation should be avoided whenever possible.

Efficacy and safety assessment of an ultrasound-based thermal treatment of varicose veins in a sheep model

Purpose: Varicose veins are a common pathology that can be treated by endovenous thermal procedures like radiofrequency ablation (RFA). Such catheter-based techniques consist in raising the temperature of the vein wall to 70 to 120 °C to induce vein wall coagulation. Although effective, this treatment option is not suited for all types of veins and can be technically challenging.Materials and methods: In this study, we used High-Intensity Focused Ultrasound (HIFU) as a non-invasive thermal ablation procedure to treat varicose veins and we assessed the long-term efficacy and safety of the procedure in a sheep model. In vivo experiments were first conducted on two saphenous veins to measure the temperature rise induced at the vein wall during HIFU ablation and were compared with reported RFA-induced thermal rise. Thermocouples were inserted in situ to perform 20 measurements during 8-s ultrasound pulses at 3 MHz. Eighteen saphenous veins of nine anesthetized sheep (2-2.5 % Isoflurane) were then exposed to similar pulses (85 W acoustic, 8 s). After treatments, animals recovered from anesthesia and were followed up 30, 60 and 90 days post-treatment (n = 3 animals per group). At the end of the follow-up, vein segments and perivenous tissues were harvested and histologically examined.Results: Temperatures induced by HIFU pulses were found to be comparable to reported RFA treatments. Likewise, histological findings were similar to the ones reported after RFA and laser-based coagulation necrosis of the vein wall, thrombotic occlusions and vein wall fibrosis.Conclusion: These results support strongly the effectiveness and safety of HIFU for ablating non-invasively veins.

Post-procedural Compression vs. No Compression After Radiofrequency Ablation and Concomitant Foam Sclerotherapy of Varicose Veins: A Randomised Controlled Non-inferiority Trial

OBJECTIVE

To compare post-operative compression with no compression, after radiofrequency endothermal ablation (RFA) of a truncal varicose vein and concomitant foam sclerotherapy of the tributaries.

METHODS

This prospective randomised controlled, non-inferiority trial recruited patients from two centres in Northern Ostrobothnia, Finland. Patients with clinical class C2-C4 chronic venous disease were randomised to receive no compression after the operation, or to receive compression stockings continuously for two days, and then, during the daytime for five days. In follow up visits, additional foam sclerotherapy was performed for symptoms of distal incompetence. Patients were followed up for six months. The primary outcome was occlusion of the RFA treated truncal vein at six months. Secondary outcomes were return to full activity within 14 days, Aberdeen Varicose Vein Questionnaire (AVVQ) score, post-operative pain, need for painkillers, and postprocedural complications.

RESULTS

Of 177 included patients, 90 were allocated to post-operative compression and 87 to no compression. At six months, both groups showed 100% occlusion rates in RFA treated truncal veins (95% confidence interval -0.043-0.042). Within 14 days of treatment, full physical activity was achieved by 87% of the compression group and 81% of the no compression group, (p = .29). At six months, the AVVQ scores were comparable and significantly improved in both groups, compared with baseline. Pain scores were comparable between groups, in day to day analyses, and they were significantly lower in both groups on day 10, compared with pre-operative pain caused by varicose veins. On average, post-operative pain medication was used for 2.3 days and for 2.8 days in the compression and no compression groups, respectively (p = .28). Complications throughout the six month follow up were comparable between groups, although skin rash/blisters occurred more often in the compression group (p = .01).

CONCLUSION

After treating C2-C4 varicose veins with RFA and concomitant foam sclerotherapy, no post-operative compression was non-inferior to post-operative compression, in terms of safety and efficacy. ClinicalTrials.gov Identifier: NCT02890563.

European College of Phlebology guideline for truncal ablation

Background

The purpose of the guideline was to achieve consensus in the care and treatment of patients with chronic venous disease, based on current evidence.

Method

A systematic literature search was performed in PubMed, Embase, Cinahl, and the Cochrane library up until 1 February 2019. Additional relevant literature were added through checking of references. Level of evidence was graded through the GRADE scale and recommendations were concluded.

Results

For the treatment of great and small saphenous vein reflux, endovenous ablation with laser or radiofrequency was recommended in preference to surgery or foam sclerotherapy. If tributaries are to be treated it should be done in the same procedure. Treatment with mecanicochemical ablation and glue can be used but we still need long term follow up results.

Conclusion

For the treatment of truncal varicosities, endovenous ablation with laser or radiofrequency combined with phlebectomies is recommended before surgery or foam.

Influência da densidade de energia endovenosa linear no sucesso da termoablação endovenosa a laser como tratamento da insuficiência venosa crônica

Background

It is relevant to elucidate the influence that mean linear endovenous energy density (LEED) has on the success of endovenous laser ablation treatment for chronic venous insufficiency, in order to reduce the method’s adverse effects.

Objectives

To evaluate the influence of mean LEED on the prevalence of saphenous closure 30 days after the laser ablation procedure.

Methods

153 lower limbs from 118 patients seen at a tertiary hospital and treated for chronic venous insufficiency with endovenous 1470 nm laser ablation under local anesthesia were evaluated. The mean LEED used to treat patients was calculated to determine whether greater than average LEED was required for treatment success.

Results

A significant difference (p = 0.021) in saphenofemoral junction closure was associated with mean LEED used above the knee. Conversely, there was no significant difference in the thigh segment.

Conclusions

Linear intravenous energy density greater than the mean of 70.57 J/cm was associated with a higher rate of closure at the saphenofemoral junction. However, density did not have an influence on the result for the thigh segment, showing that an energy density exceeding 70.57 J/cm tends not to be required for treatment of this segment.

Initial outcomes of endovenous laser ablation with 1940 nm diode laser in the treatment of incompetent saphenous veins

OBJECTIVES

To investigate the initial outcomes of 1940 nm diode laser in the treatment of incompetent saphenous veins.

METHODS

This was a prospective observational study. We treated 89 patients with 160 incompetent saphenous veins using a 1940 nm diode laser and bare fiber. The laser's power was set to 4.5 W with a mean linear endovenous energy density of 50.4 J/cm.

RESULTS

The one-month closure rate was 100%. The post-procedural pain score at 6 h, 1 day, 10 days, and 1 month was 0.85 ± 1.04, 0.65 ± 1.01, 0.82 ± 1.25, and 0.47 ± 0.82, respectively. Complications encountered included paresthesia (3.8%) and thrombophlebitis (4.4%), whereas no cases of endovenous heat-induced thrombosis were observed.

CONCLUSION

The 1940 nm laser and bare fiber at 50.4 J/cm showed satisfactory initial outcomes with less pain and fewer complications, in the treatment of incompetent saphenous veins.

Endovenous Thermal Ablation of Recurrent Varicose Veins due to Residual Great Saphenous Venous Insufficiency After Saphenous Venous Surgery: A Comparative Study

BACKGROUND

Redo surgery for recurrent varicose veins of the great saphenous vein (GSV) is technically more challenging than the initial surgery.

OBJECTIVE

To compare 980 and 1,470-nm endovenous laser ablation (EVLA) and radiofrequency ablation (RFA) for the treatment of residual GSV insufficiency after saphenofemoral ligation ± stripping.

MATERIALS AND METHODS

Thirty-seven limbs in 29 patients with recurrent varicose veins were retrospectively evaluated. Patients were divided into 3 groups: 980-nm EVLA (group A), 1,470-nm EVLA (group B), and RFA (group C). Duplex ultrasonography, Venous Clinical Severity Score (VCSS), and adverse events were examined at intervals of 1 week, 1, 3, 6, and 12 months.

RESULTS

Complete closure was achieved in 35 (94.6%) limbs at 12 months. Venous Clinical Severity Score decrease in group C (3.6 ± 0.5) was significantly (p < .017) greater compared with that of group A (2.6 ± 0.9). Ecchymosis grade was significantly (p < .017) lower in group C (0.1 ± 0.3) than that in group A (1.6 ± 1.5).

CONCLUSION

Endovenous thermal ablation using EVLA or RFA is safe and effective for treatment of recurrent varicose veins resulting from residual GSV insufficiency after saphenous venous surgery. The RFA is superior to 980-nm EVLA in terms of postprocedural ecchymosis and improvement in VCSS.

Endovenous Laser Application

Introduction: Endoluminal vein treatment is a promising minimal invasive treatment option for peoples suffering from varicose veins. The basic mechanism underlying this procedure is to selectively induce heat in the vessel wall with the result of denaturation of proteins and shrinkage of collagen fibers due to energy application. So far energy could be applied either as RF-current, laser light or water steam. The different approaches to deliver such forms of energies are described.

Methods: Investigations on heat dependent vein tissue effects were performed. The degree of shrinkage and wall thickening due to heat induction was calculated. Tensile test on vein tissue were performed. Investigation using the radial emitting laser fibre in the ox-foot-model under reproducible condition were done and wavelengths dependent tissue reaction were explored.

Results: The experiments clearly demonstrate the degree of the shrinkage of length and diameter, the thickening of the vein wall, as well as the decrease of the elasticity of the tissue. The optical irradiation pattern of the radial emitting laser fiber serves for safe and reproducible energy application directly to the vein wall. Using a laser wavelength with high absorption by the tissue water needs reduced irradiation and irradiance compared to wavelengths with less water absorption. Conclusion: An experimental approach to improve laser application for endovenous varicose treatment is described. Laser parameters and treatment parameters were found which are now under clinical testing. The demonstrated tissue effects may help to find further arguments for clinical findings and sensations described by the patients during follow-up.

Endoluminal application of glass-capped diffuser for ex vivo endovenous photocoagulation

Endovenous laser ablation (EVLA) has frequently been used to treat varicose veins for 20 years. In spite of 90˜95% occlusion rates, clinical complications such as burn and ecchymosis still occur due to excessive thermal injury to perivenous tissue. In the current study, a glass-capped diffusing applicator is designed to validate the feasibility of EVLA as an effective therapeutic device by applying circumferential light distribution. The proposed device is evaluated with a flat fiber as a reference in terms of temperature elevation, fiber degradation, and degree of coagulative necrosis after 532 nm-assisted EVLA at 100 J/cm. The diffusing fiber generates a 40% lower maximum temperature with a 90% lower transient temperature change in blood, compared to the flat fiber. Due to low irradiance (13.5 kW/cm² ) and wide light distribution, the diffuser tip experiences no significant thermal degradation while severe carbonization occurs at the flat fiber tip. Ex vivo tissue tests verify that the diffusing fiber induces circumferential and consistent tissue denaturation to the vein wall (107.8 ± 7.8 µm) along with 19% vessel shrinkage. The proposed glass-capped diffusing applicator can be a feasible therapeutic device for EVLA with minimal complications by entailing low maximum temperatures and uniform tissue denaturation in the venous tissue.

Prevention of Surgical Site Infections and Biofilms: Pharmacokinetics of Subcutaneous Cefazolin and Metronidazole in a Tumescent Lidocaine Solution

BACKGROUND

Tumescent anesthesia antibiotic delivery (TAAD) consists of subcutaneous infiltration of antibiotic(s) dissolved tumescent lidocaine anesthesia. Tumescent lidocaine anesthesia contains lidocaine (≤ 1 g/L), epinephrine (≤ 1 mg/L), sodium bicarbonate (10 mEq/L) in 0.9% saline. Our aim was to measure cefazolin and metronidazole concentrations over time in subcutaneous tumescent interstitial fluid (TISF) after TAAD, in serum after TAAD and after intravenous antibiotic delivery (IVAD). We hypothesize that the pharmacokinetic/pharmacodynamic profiles of TAAD + IVAD are superior to IVAD alone for the prevention of surgical site infections and biofilms.

METHODS

Concentrations of cefazolin and metronidazole in TISF and serum following TAAD and in serum following IVAD were compared in 5 female volunteers. Subjects received cefazolin or cefazolin plus metronidazole by IVAD alone and by TAAD alone. One subject also received concomitant IVAD and TAAD of these 2 antibiotics. Sequential samples of serum or subcutaneous TISF were assayed for antibiotic concentration.

RESULTS

Cefazolin (1 g) by TAAD resulted in an area under the curve of the concentration-time profile and a maximum concentration (Cmax) in subcutaneous tissue that were 16.5 and 5.6 times greater than in serum following 1 g by IVAD. Metronidazole (500 mg) by TAAD resulted in an area under the curve and Cmax that were 8.1 and 24.7 times greater in TISF, than in serum after 500 mg by intravenous delivery. IVAD + TAAD resulted in superior antibiotic concentrations to IVAD alone.

CONCLUSIONS

TAAD + IVAD produced superior antibiotic bioavailability in both subcutaneous interstitial fluid and serum compared with IVAD alone. There was no evidence that TAAD of cefazolin and metronidazole poses a significant risk of harm to patients.

Nanosecond laser ablation enhances cellular infiltration in a hybrid tissue scaffold

Hybrid tissue engineered (HTE) scaffolds constituting polymeric nanofibers and biological tissues have attractive bio-mechanical properties. However, they suffer from small pore size due to dense overlapping nanofibers resulting in poor cellular infiltration. In this study, using nanosecond (ns) laser, we fabricated micro-scale features on Polycaprolactone (PCL)-Chitosan (CH) nanofiber layered bovine pericardium based Bio-Hybrid scaffold to achieve enhanced cellular adhesion and infiltration. The laser energy parameters such as fluence of 25J/cm², 0.1mm instep and 15 mark time were optimized to get structured microchannels on the Bio-Hybrid scaffolds. Laser irradiation time of 40μs along with these parameters resulted in microchannel width of ~50μm and spacing of ~35μm between adjacent lines. The biochemical, thermal, hydrophilic and uniaxial mechanical properties of the Bio-Hybrid scaffolds remained comparable after laser ablation reflecting extracellular matrix (ECM) stability. Human umbilical cord mesenchymal stem cells and mouse cardiac fibroblasts seeded on these laser-ablated Bio-Hybrid scaffolds exhibited biocompatibility and increased cellular adhesion in microchannels when compared to non-ablated Bio-Hybrid scaffolds. These findings suggest the feasibility to selectively ablate polymer layer in the HTE scaffolds without affecting their bio-mechanical properties and also describe a new approach to enhance cellular infiltration in the HTE scaffolds.

Resultados de médio e longo prazo do tratamento endovenoso de varizes com laser de diodo em 1940 nm: análise crítica e considerações técnicas

Contexto

Desde a introdução do laser endovenoso para tratamento das varizes, há uma busca pelo comprimento de onda ideal, capaz de produzir o maior dano seletivo possível com maior segurança e menor incidência de efeitos adversos.

Objetivos

Avaliar os resultados de médio e longo prazo do laser de diodo de 1940 nm no tratamento de varizes, correlacionando os parâmetros utilizados com a durabilidade do desfecho anatômico.

Métodos

Revisão retrospectiva de pacientes diagnosticados com insuficiência venosa crônica em estágio clínico baseado em clínica, etiologia, anatomia e patofisiologia (CEAP) C2 a C6, submetidos ao tratamento termoablativo endovenoso de varizes tronculares, com laser com comprimento de onda em 1940 nm com fibra óptica de emissão radial, no período de abril de 2012 a julho de 2015. Uma revisão sistemática dos registros médicos eletrônicos foi realizada para obter dados demográficos e dados clínicos, incluindo dados de ultrassom dúplex, durante o período de seguimento pós-operatório.

Resultados

A média de idade dos pacientes foi de 53,3 anos; 37 eram mulheres (90,2%). O tempo médio de seguimento foi de 803 dias. O calibre médio das veias tratadas foi de 7,8 mm. A taxa de sucesso imediato foi de 100%, com densidade de energia endovenosa linear (linear endovenous energy density, LEED) média de 45,3 J/cm. A taxa de sucesso tardio foi de 95,1%, com duas recanalizações por volta de 12 meses pós-ablação. Não houve nenhuma recanalização nas veias tratadas com LEED superior a 30 J/cm.

Conclusões

O laser 1940 nm mostrou-se seguro e efetivo, em médio e longo prazo, para os parâmetros propostos, em segmentos venosos com até 10 mm de diâmetro.

Estimated Maximal Safe Dosages of Tumescent Lidocaine

Supplemental Digital Content is available in the text.

Published ahead of print February 18, 2016

BACKGROUND:

Tumescent lidocaine anesthesia consists of subcutaneous injection of relatively large volumes (up to 4 L or more) of dilute lidocaine (≤1 g/L) and epinephrine (≤1 mg/L). Although tumescent lidocaine anesthesia is used for an increasing variety of surgical procedures, the maximum safe dosage is unknown. Our primary aim in this study was to measure serum lidocaine concentrations after subcutaneous administration of tumescent lidocaine with and without liposuction. Our hypotheses were that even with large doses (i.e., >30 mg/kg), serum lidocaine concentrations would be below levels associated with mild toxicity and that the concentration-time profile would be lower after liposuction than without liposuction.

METHODS:

Volunteers participated in 1 to 2 infiltration studies without liposuction and then one study with tumescent liposuction totally by local anesthesia. Serum lidocaine concentrations were measured at 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 24 hours after each tumescent lidocaine infiltration. Area under the curve (AUC∞) of the serum lidocaine concentration-time profiles and peak serum lidocaine concentrations (Cmax) were determined with and without liposuction. For any given milligram per kilogram dosage, the probability that Cmax >6 μg/mL, the threshold for mild lidocaine toxicity was estimated using tolerance interval analysis.

RESULTS:

In 41 tumescent infiltration procedures among 14 volunteer subjects, tumescent lidocaine dosages ranged from 19.2 to 52 mg/kg. Measured serum lidocaine concentrations were all <6 μg/mL over the 24-hour study period. AUC∞s with liposuction were significantly less than those without liposuction (P = 0.001). The estimated risk of lidocaine toxicity without liposuction at a dose of 28 mg/kg and with liposuction at a dose of 45 mg/kg was ≤1 per 2000.

CONCLUSIONS:

Preliminary estimates for maximum safe dosages of tumescent lidocaine are 28 mg/kg without liposuction and 45 mg/kg with liposuction. As a result of delayed systemic absorption, these dosages yield serum lidocaine concentrations below levels associated with mild toxicity and are a nonsignificant risk of harm to patients.

Investigation of endovenous laser ablation of varicose veins in vitro using 1.885-μm laser radiation

This paper presents the results of endovenous laser ablation (EVLA) of varicose veins in vitro using radiation of a solid-state laser based on the crystal LiYF4:Tm, with a wavelength of 1.885 μm and power output of around 3 W. An experimental series with saline solution and red blood cell (RBC) suspension in the venous lumen was performed to identify the impact of a heated carbonized layer precipitated on the fiber end face versus the efficiency of EVLA. Results of these experiments confirmed that the presence of a heated carbonized layer on the fiber end face increases the efficiency of EVLA.

The Histological Changes of the Great Saphenous Vein at 2 Years after Cryosclerosis

Cryosclerosis was developed at the end of the last decade. It is the endovenous cryoablation of the great saphenous vein and has been forgotten before the era of the endovenous ablation techniques began. The caused histomorphological changes of the vein weren’t described before, especially, years after the procedure. A 31-year-old female patient underwent cryosclerosis 2 years ago. Because of the recanalization of the great saphenous vein and recurrent varicosity, high ligation, cryostripping and phlebectomy of varices were performed. During surgery, a saphenous vein piece was harvested to investigate the histomorphological effect of cryosclerosis. Histological findings verified that recanalization had occurred, the vein wall had undergone remodeling, and the picro-sirius red stain showed collagen deposition in the whole vein wall. Cryosclerosis seems to result in the remodeling of the vein wall.

Low Reactive Level Laser Therapy for Mesenchymal Stromal Cells Therapies

Low reactive level laser therapy (LLLT) is mainly focused on the activation of intracellular or extracellular chromophore and the initiation of cellular signaling by using low power lasers. Over the past forty years, it was realized that the laser therapy had the potential to improve wound healing and reduce pain and inflammation. In recent years, the term LLLT has become widely recognized in the field of regenerative medicine. In this review, we will describe the mechanisms of action of LLLT at a cellular level and introduce the application to mesenchymal stem cells and mesenchymal stromal cells (MSCs) therapies. Finally, our recent research results that LLLT enhanced the MSCs differentiation to osteoblast will also be described.

A randomised controlled trial comparing compression therapy after radiofrequency ablation for primary great saphenous vein incompetence

BACKGROUND

Optimal duration of leg compression after venous ablation remains unclear. This randomised controlled trial evaluates 4 h compared to 72 h of leg compression.

METHODS

Patients were randomised to 4 or 72 h of leg compression after radiofrequency ablation of the great saphenous vein. Primary outcome was change in leg volume after 14 days. Secondary outcomes were postoperative pain, complications and time to full recovery.

RESULTS

Patients wearing compression stockings for 4 h after treatment had a 64 mL (95%CI: - 23 to + 193) reduction in leg volume, compared to an increase of 21 mL (95%CI: 8.33-34.5) in patients wearing compression stockings for 72 h (P = 0.12). Patients wearing compression stockings for 4 h experienced fewer complications (16% vs. 33%, P = 0.05). Postoperative pain and time to full recovery did not differ significantly.

CONCLUSION

Wearing compression stockings for 4 h is non-inferior in preventing leg oedema as wearing compression stockings for 72 h.

Comparison of Bare-Tip and Radial Fiber in Endovenous Laser Ablation with 1470 nm Diode Laser

OBJECTIVE

Major side effects after endovenous laser ablation (EVLA) are pain and bruising. The aim of this study was to compare outcome and side effects after EVLA for primary varicose veins with 1470 nm diode laser using bare-tip orradial fiber.

METHODS

From October 2007 to December 2010, 385 patients (453 limbs) with primary varicose veins treated with 1470 nm laser were studied. Bare-tip fiber was used in 215 patients (242 limbs) (BF group) and radial fiber (ELVeS(TM)Radial, Biolitec AG, Germany) was used in 177 patients (211 limbs) (RF group). This study is a retrospective study and radial fiber was started for use from November 2008. Laser energy was administered at 6-12 W of power in the BF group and 10 W of power in the RF group with constant pullback of laser fiber under tumescent local anesthesia. The patients were assessed by clinical examination and venous duplex ultrasonography at 24-48 h, one week, one month, 4 months and one year follow-up postoperatively.

RESULTS

Mean operating time, length of treated vein and linear endovenous laser energy of all cases were 42.6 min, 36.2 cm and 83.4 J/cm, respectively. Major complications such as deep vein thrombosis and skin burns were not noted. Bruising (1.9% vs. 19.4%) and pain (0.9% vs. 7.4%) were significantly lower in the RF group. Cumulative occlusion rates by Kaplan-Meier method were 100% at 32 months in the RF group and 99.5% at 4 years in the BF group.

CONCLUSION

EVLA using 1470 nm laser with the radial fiber minimized adverse effects compared with bare-tip laser fiber. (English translation of Jpn J Vasc Surg 2013; 22: 615-621).

Role of endovenous laser therapy in large and very large diameter great saphenous veins

BACKGROUND

The literature suggests that endovenous laser is less efficacious in great saphenous veins (GSVs) with a diameter of greater than 1 cm. This paper describes the efficacy of endovenous laser therapy (EVLT) in ablating GSV with a diameter greater than 1.0 cm.

METHODS

Retrospective review of consecutive patients undergoing GSV EVLT between 15 November 2012 and 25 July 2013 was performed. GSV with a maximum diameter of ≥1.0 cm were defined as large, those with a maximum diameter of ≥2.0 cm were defined as very large.

RESULTS

A total of 38 ablations were reviewed; two patients had bilateral GSV vein ablations. All underwent a 6-week post-procedural duplex. There were 20 ablations on veins >1 cm and 4 ablations on veins ≥2.0 cm. Median GSV length was 21.5 cm (16.5 cm for <1 cm, 24.5 cm for 1-2 cm and 24.5 cm for >2 cm). When correcting for length of vein treated, the energy deposited was stable for all patients at 80 J/cm. Tumescent volumes per centimetre were 3.7 mL/cm for veins <1.0 cm and 4.6 mL/cm for veins >1.0 cm. Successful ablation was achieved in 100% of veins independent of size.

CONCLUSION

Ablation rates for large and very large GSVs in our series do not differ from the cohort of patients with GSV < 1.0 cm and from published results for GSVs < 1.0 cm. This supports the use of EVLT for venous insufficiency in the larger diameter GSV typically found in patients on public hospital waiting lists.

Ins and outs of endovenous laser ablation: afterthoughts

Physicists and medical doctors "speak" different languages. Endovenous laser ablation (EVLA) is a good example in which technology is essential to guide the doctor to the final result: optimal treatment. However, for the doctor, it is by far insufficient just to turn on the knobs of the laser. He should understand what is going on in the varicose vein. On the other hand, the physicist is usually not aware what problems the doctor finds on his road towards improving a new technique. We have tried to bring both languages together in the special on Ins and outs of endovenous laser ablation published in this issue of Lasers in Medical Science. The 13 articles include endovenous related clinical (de Roos 2014; Kockaert and Nijsten 2014; van den Bos and Proebstle 2014) and socioeconomical articles (Kelleher et al 2014), the first paper on the molecular pathophysiologic mechanisms (Heger et al 2014), fiber tips (Stokbroekx et al 2014), the future of EVLA (Rabe 2014), a review of EVLA with some important issues for debate (Malskat et al 2014), an excellent paper on transcutaneous laser therapies of spider and small varicose veins (Meesters et al 2014), as well as several scientific modeling articles, varying from a mathematical model of EVLA that includes the carbonized blood layer on the fiber tip (van Ruijven et al 2014) and its application to the simulation of clinical conditions (Poluektova et al 2014) via experimental measurements of temperature profiles in response to EVLA, radiofrequency waves, and steam injections (Malskat et al 2014) to a literature review and novel physics approach of the absorption and particularly scattering properties of whole blood also including the infrared wavelengths used by EVLA (Bosschaart et al 2014). The aim of our afterthoughts, the 14th article in this special, is to try to amalgamate the clinical and physical contents of these contributions, providing the reader with the bridge that overlaps these different backgrounds.

Endovenous laser ablation (EVLA): a review of mechanisms, modeling outcomes, and issues for debate

Endovenous laser ablation (EVLA) is a commonly used and very effective minimally invasive therapy to manage leg varicosities. Yet, and despite a clinical history of 16 years, no international consensus on a best treatment protocol has been reached so far. Evidence presented in this paper supports the opinion that insufficient knowledge of the underlying physics amongst frequent users could explain this shortcoming. In this review, we will examine the possible modes of action of EVLA, hoping that better understanding of EVLA-related physics stimulates critical appraisal of claims made concerning the efficacy of EVLA devices, and may advance identifying a best possible treatment protocol. Finally, physical arguments are presented to debate on long-standing, but often unfounded, clinical opinions and habits. This includes issues such as (1) the importance of laser power versus the lack of clinical relevance of laser energy (Joule) as used in Joule per centimeter vein length, i.e., in linear endovenous energy density (LEED), and Joule per square centimeter vein wall area, (2) the predicted effectiveness of a higher power and faster pullback velocity, (3) the irrelevance of whether laser light is absorbed by hemoglobin or water, and (4) the effectiveness of reducing the vein diameter during EVLA therapy.

Some controversies in endovenous laser ablation of varicose veins addressed by optical-thermal mathematical modeling

Minimally invasive treatment of varicose veins by endovenous laser ablation (EVLA) becomes more and more popular. However, despite significant research efforts performed during the last years, there is still a lack of agreement regarding EVLA mechanisms and therapeutic strategies. The aim of this article is to address some of these controversies by utilizing optical-thermal mathematical modeling. Our model combines Mordon's light absorption-based optical-thermal model with the thermal consequences of the thin carbonized blood layer on the laser fiber tip that is heated up to temperatures of around 1,000 °C due to the absorption of about 45% of the laser light. Computations were made in MATLAB. Laser wavelengths included were 810, 840, 940, 980, 1,064, 1,320, 1,470, and 1,950 nm. We addressed (a) the effect of direct light absorption by the vein wall on temperature behavior, comparing computations by using normal and zero wall absorption; (b) the prediction of the influence of wavelength on the temperature behavior; (c) the effect of the hot carbonized blood layer surrounding the fiber tip on temperature behavior, comparing wall temperatures from using a hot fiber tip and one kept at room temperature; (d) the effect of blood emptying the vein, simulated by reducing the inside vein diameter from 3 down to 0.8 mm; (e) the contribution of absorbed light energy to the increase in total energy at the inner vein wall in the time period where the highest inner wall temperature was reached; (f) the effect of laser power and pullback velocity on wall temperature of a 2-mm inner diameter vein, at a power/velocity ratio of 30 J/cm at 1,470 nm; (g) a comparison of model outcomes and clinical findings of EVLA procedures at 810 nm, 11 W, and 1.25 mm/s, and 1,470 nm, 6 W, and 1 mm/s, respectively. Interestingly, our model predicts that the dominating mechanism for heating up the vein wall is not direct absorption of the laser light by the vein wall but, rather, heat flow to the vein wall and its subsequent temperature increase from two independent heat sources. The first is the exceedingly hot carbonized layer covering the fiber tip; the second is the hot blood surrounding the fiber tip, heated up by direct absorption of the laser light. Both mechanisms are about equally effective for all laser wavelengths. Therefore, our model concurs the finding of Vuylsteke and Mordon (Ann Vasc Surg 26:424-433, 2012) of more circumferential vein wall injury in veins (nearly) devoid of blood, but it does not support their proposed explanation of direct light absorption by the vein wall. Furthermore, EVLA appears to be a more efficient therapy by the combination of higher laser power and faster pullback velocity than by the inverse combination. Our findings suggest that 1,470 nm achieves the highest EVLA efficacy compared to the shorter wavelengths at all vein diameters considered. However, 1,950 nm of EVLA is more efficacious than 1,470 nm albeit only at very small inner vein diameters (smaller than about 1 mm, i.e., veins quite devoid of blood). Our model confirms the efficacy of both clinical procedures at 810 and 1,470 nm. In conclusion, our model simulations suggest that direct light absorption by the vein wall is relatively unimportant, despite being the supposed mechanism of action of EVLA that drove the introduction of new lasers with different wavelengths. Consequently, the presumed advantage of wavelengths targeting water rather than hemoglobin is flawed. Finally, the model predicts that EVLA therapy may be optimized by using 1,470 nm of laser light, emptying of the vein before treatment, and combining a higher laser power with a greater fiber tip pullback velocity.

Optical-thermal mathematical model for endovenous laser ablation of varicose veins

Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45% of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95 °C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104 °C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures.

Regulation of miRNA expression by low-level laser therapy (LLLT) and photodynamic therapy (PDT)

Applications of laser therapy, including low-level laser therapy (LLLT), phototherapy and photodynamic therapy (PDT), have been proven to be beneficial and relatively less invasive therapeutic modalities for numerous diseases and disease conditions. Using specific types of laser irradiation, specific cellular activities can be induced. Because multiple cellular signaling cascades are simultaneously activated in cells exposed to lasers, understanding the molecular responses within cells will aid in the development of laser therapies. In order to understand in detail the molecular mechanisms of LLLT and PDT-related responses, it will be useful to characterize the specific expression of miRNAs and proteins. Such analyses will provide an important source for new applications of laser therapy, as well as for the development of individualized treatments. Although several miRNAs should be up- or down-regulated upon stimulation by LLLT, phototherapy and PDT, very few published studies address the effect of laser therapy on miRNA expression. In this review, we focus on LLLT, phototherapy and PDT as representative laser therapies and discuss the effects of these therapies on miRNA expression.