Defining the Parameters for Endovenous Microwave Ablation to Achieve Equivalence With Endovenous Laser Ablation, Using the Porcine Liver Model

AIMS

Endovenous microwave ablation (EMWA) is an endovenous thermoablation (EVTA) system to ablate incompetent truncal veins. Early results suggest that EMWA uses more power than endovenous laser ablation (EVLA) to get the same results. We aimed to define the parameters for EMWA, which give the same tissue ablation as EVLA, using the validated porcine liver model.

METHODS

EVLA (1470 nm 600 micron radial fibre) treatments were performed at 6 W, 8 W and 10 W, at pullback speeds of 6, 7, 8 and 9 s/cm, giving Linear Endovenous Energy Densities (LEEDs) between 36 - 90 J/cm. Each combination of power and pullback was repeated 5 times. We then used EMWA in the same model. Powers of 35-75 W and pullback speeds of 4-9 s/cm were used (LEEDs 140-675 J/cm). Ablation tracts from both devices were analysed by 2 blinded observers, noting thermal spread and carbonisation.

RESULTS

For each commonly used parameter for EVLA, we identified a range of parameters for EMWA that produced similar tissue ablation in the porcine liver model. To keep the pullback speeds within the usual range, powers of 35-75 W were needed with EMWA, with mean EMWA LEEDs 3.9 - 5.8 times higher than EVLA LEEDs. We found the quicker the pullback speed, the higher the multiple of EMWA LEED we needed to get the same effect.

CONCLUSION

We have identified parameters for EMWA that gave equivalent tissue ablation in the porcine liver model to commonly used parameters used for EVLA. These need to be validated clinically, but as the model used has already been validated against clinical outcome in endovenous thermal ablation, there is little reason to suspect that these results would not be valid. As the power during EMWA is higher than EVLA, EVMA LEEDs are approximately 4-6 times higher than EVLA LEEDs to achieve the same thermal effect on the tissues.

A systematic review of endovenous ablation for the treatment of small saphenous varicose veins

Insufficiency of the small saphenous vein causes 15% of varicose veins in the lower extremities. Endovenous ablation for the treatment of small saphenous vein varices has become a trend, and an increasing number of studies have reported the effects of different types of endovenous ablation in patients with small saphenous varicose veins. The purpose of this systematic review is to summarize the results of existing studies on endovenous ablation for the treatment of small saphenous varicose veins, compare its role and efficacy, and provide insights into the future development of endovenous ablation for treating small saphenous varicose veins. A systematic review of literature published from January 1, 2002 to January 1, 2022 was conducted from PubMed, Embase, and China Academic Journals full-text databases. The pre-determined inclusion criteria were clinical literature of endovenous ablation for treating small saphenous varicose veins. Keywords included "ablation", "small saphenous vein", "lesser saphenous vein", "short saphenous vein", "xiaoyinjingmai" and "xiaorong". Of the 506 articles screened, 33 articles were included in this review: 19 articles were related to endovenous laser ablation, five were related to mechanochemical ablation, seven were related to radiofrequency ablation, and two were related to both endovenous laser ablation and radiofrequency ablation. The anatomical success rate of endovenous laser ablation, radiofrequency ablation, and mechanochemical ablation were 94.3%, 96.0%, and 88.1%, respectively, and the heterogeneities were all moderate. Most of the current studies are of a low-quality level of research. Hence, long-term follow-up studies and large-scale randomized controlled trials are required to obtain high-quality evidence. Although the gold standard for the treatment of small saphenous vein insufficiency remains unclear, endovenous ablation is still the recommended method.

One Year Follow-Up of Endovascular Microwave Ablation and Concomitant Foam Sclerotherapy in the Treatment of Primary Small Saphenous Vein Insufficiency

BACKGROUND

In the last decade, the microwave ablation catheter specifically for treating lower extremity varicose veins has become popular. However, imited data is available on the efficacy, analysis, and evaluation of endovenous microwave ablation (EMWA) in treating SSV insufficiency. Our objective is to evaluated the feasibility, safety, and 1-year outcomes of EMWA and concomitant foam sclerotherapy of primary small saphenous vein (SSV) insufficiency.

METHODS

Our team carried out a single-center, retrospective analysis of 24 patients treated with EMWAand concomitant foam sclerotherapy for primary SSV insufficiency. All operations were performed using a MWA catheter and polidocanol for the trunk and branches of the SSV, respectively. The SSV occlusion rate was assessed at the 6- and 12-month follow-up examinations using duplex ultrasound. Secondary outcomes included the Clinical, Etiological, Anatomical, Pathophysiological (CEAP) clinical class; Venous Clinical Severity Score (VCSS); Aberdeen Varicose Vein Questionnaire (AVVQ); periprocedural pain; and complications.

RESULTS

100% of the cases have been technically successful. At the 6-month follow-up, all treated SSVs were occluded. The 12-month assessment duplex doppler showed anatomical success in patients with 95.8% (95% confidence interval, 0.756-0.994). The CEAP clinical class, VCSS, and the AVVQ had decreased significantly at the 6- and 12-month follow-up, respectively.

CONCLUSIONS

EMWA and concomitant foam sclerotherapy is a feasible and effective technique for treating SSV insufficiency.

Linear endovenous energy density (LEED) should always be quoted with the power used in endovenous thermal ablation - results from an in-vitro porcine liver model study

BACKGROUND

Linear Endovenous Energy Density (LEED) is the energy used per cm of vein in endovenous thermal ablation (EVTA) but does not include time. This study examines the effect of time during EVTA.

METHOD

EVTA was performed in a previously validated porcine liver model. LEEDs of 40, 60, 80 and 100 J/cm, using different powers were repeated 5 times each. Thermal spread, tissue carbonisation and device-tissue sticking during treatment were recorded.

RESULT

LEED positively correlated to thermal spread and carbonisation of the tissue. Power was correlated with carbonisation but not thermal spread. Pullback had no correlations with thermal spread or carbonisation. Catheter sticking found occurred in powers >= 15 W or LEED >= 80 J/cm.

CONCLUSION

LEED is a good measure of EVTA but does not include time. Power, which does include time, correlates with carbonisation and with device-tissue sticking. The power used must be quoted with the LEED.

A systematic review and meta-analysis of treatment modalities for anterior accessory saphenous vein insufficiency

OBJECTIVE

To investigate and compare the outcomes of the available treatment modalities for anterior accessory saphenous vein (AASV) incompetence.

METHODS

A systematic literature search was performed in MEDLINE, Embase, and the Cochrane Library. Studies reporting the outcomes of patients who were treated for primary AASV incompetence were included. The methodologic quality of the articles was assessed using the Methodological Index for Non-Randomized Studies (MINORS). A random-effects model was used to estimate anatomic success, defined as AASV occlusion. The secondary outcomes were pain during and after treatment, venous clinical severity score, quality of life, esthetic result, time to return to daily activities, and complications.

RESULTS

The search identified 860 articles, of which 16 met the inclusion criteria. A total of 609 AASVs were reported. The included studies were of poor or moderate quality according to MINORS score. The pooled anatomic success rates were 91.8% after endovenous laser ablation and radiofrequency ablation (EVLA, RFA, 11 studies), 93.6% after cyanoacrylate closure (3 studies), and 79.8% after sclerotherapy (2 studies). The non-pooled anatomic success rate was 97.9% after phlebectomy and 82% after CHIVA. Paresthesia was seen after EVLA in 0.7% of patients (6 studies). Phlebitis was seen in 2.6% of patients after RFA (2 studies), 27% after sclerotherapy (1 study), and 12% after the phlebectomy (1 study). Deep venous thrombosis and skin burn did not occur.

CONCLUSION

Treatment of AASV incompetence is safe and effective. Despite limited evidence, occlusion of the AASV can be achieved with endovenous thermal ablation and cyanoacrylate. There does not appear to be a benefit of EVLA compared to RFA regarding treatment efficacy. Phlebectomy shows promising results if the saphenofemoral junction is competent. Lower results are seen after sclerotherapy and CHIVA. However, studies with sufficient sample sizes of solely treatment of AASV incompetence are needed to draw firm conclusions.

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.

Endovenous Thermal Ablation of Prominent Central Forehead Veins (Supratrochlear Veins)

BACKGROUND

Many patients complain of prominent vertical veins in the center of their forehead, worse when smiling, wrinkling the forehead in bright light, leaning forward, and when vasodilated in heat, when exercising, or with alcohol. Previous attempts to treat these with external laser, sclerotherapy, and phlebectomy have not been successful.

OBJECTIVE

To describe a new method of treating prominent vertical forehead veins and to report the early results.

MATERIALS AND METHODS

We used endovenous laser ablation with a 1470 nm diode laser in 15 patients (F:M 12:3; mean age 38.4 years range 24-69). A bare fiber was used once and a 400-μm single ring radial fiber (Biolitec, Vienna, Austria) in all other cases. Tumescence was placed around the vein and a power of 2 to 3 W with a pullback of 7 to 10 seconds per centimeter.

RESULTS

Twelve of the 15 patients (80%) ended up with a good cosmetic result and were satisfied, although 2 needed redo treatment. One patient had minor skin tethering, and 2 (13%) suffered burns-one was the only bare fiber case and the other, the only one where 4 W was used.

CONCLUSION

We present a novel technique to treat prominent vertical forehead veins, with apparently good early results.

Pattern of thermal damage and tissue carbonisation from endovenous radiofrequency ablation catheter - Using an in vitro porcine liver model

BACKGROUND

Successful endovenous thermoablation relies on transmural vein wall ablation. We investigated the pattern of thermal spread and tissue carbonisation from RadioFrequency-induced ThermoTherapy (RFiTT) at different powers and pull back methods, using a porcine liver model.

METHODS

We used a previously validated in-vitro porcine liver model. Different powers from 5-25 W were used to administer 150 J. We compared continuous and pulsed energy delivery. Length, lateral spread, and total area of thermal damage, together with any tissue carbonisation, was measured using digital analysis software.

RESULTS

All experiments used 150 J total energy. Total thermal damage area was smaller with lower power and pulsed energy. Continuous energy caused more tissue carbonisation than pulsed except at 25 W.

CONCLUSION

Reduced thermal damage with lower power or pulsed energy results from cooling due to increased time of treatment. Increasing the power increases tissue carbonisation. Optimal treatment is determined by the highest power used continuously that does not cause tissue carbonisation.

Monopolar Radiofrequency Energy Delivered by a Conductive Endovascular Basket or Guidewire Leads to Thermal Occlusion in a Swine Model

PURPOSE

To assess the feasibility of inducing vascular occlusion by application of radiofrequency (RF) energy via conductive endovascular wires or baskets.

MATERIALS AND METHODS

A retrievable nitinol basket and stainless steel guidewire with a platinum tip were evaluated as conductors for endovascular application of RF energy. Tissue-mimicking thermochromic gel phantoms that change color with heating were cast with 2-, 5-, and 7-mm-diameter lumens and filled with 37 ^oC saline. After ablation, the phantoms were sectioned, and the thermal footprints were evaluated. Six castrated male domestic swine underwent endovascular ablation using the basket in iliac arteries and guidewires in renal arteries. Post-procedural angiography was performed, and postmortem arterial segments were resected for histopathologic analysis.

RESULTS

In the phantom, the depth of thermal change in the 5- and 7-mm lumens averaged 6.3 and 6.0 mm along the basket, respectively, and in the 2- and 5-mm lumens, the depth of thermal change averaged 1.9 and 0.5 mm along the wire, respectively. In the swine, RF energy delivery led to angiographic occlusion at 12 of 13 sites. Thermal injury and occlusion were similar at the proximal, middle, and distal basket treatment zone, whereas injury and occlusion decreased from the proximal to the distal end of the 5-cm wire treatment zone.

CONCLUSIONS

Endovascular delivery of RF energy via a conductive basket in medium-sized arteries or a guidewire in small arteries led to acute angiographic and histologic occlusion. The potential to induce stasis might be useful in settings where rapid occlusion is desirable.

Histopathologic differences in the endovenous laser ablation between jacketed and radial fibers, in an ex vivo dominant extrafascial tributary of the great saphenous vein in an in vitro model, using histology and immunohistochemistry

OBJECTIVE

The study aimed to investigate the biologic effects of the 1470-nm endovenous laser (EVL), with a jacketed fiber and a radial fiber, during EVL ablation of an ex vivo dominant extrafascial tributary of the great saphenous vein in our in vitro model by histology and immunohistochemistry.

METHODS

Ten segments of the dominant extrafascial tributary of the great saphenous vein were harvested by a consultant vascular surgeon from patients during routine varicose vein surgery. Six segments were treated using an ex vivo model of our design by a 1470-nm EVL with a jacketed fiber. The other four segments were also treated by a 1470-nm EVL but with a radial-firing fiber. Each segment was split into five sections and treated at five different linear endovenous energy densities (LEEDs) at 10 W: 0, 20, 40, 60, and 80 J/cm. The veins were incubated and subsections collected at 6 and 24 hours after treatment. Subsections were immersed in buffered formalin and taken for histologic and immunohistochemical analysis. Histopathologic analysis was then performed.

RESULTS

Treatment with the radial fiber led to a pattern of damage that was more homogeneous than with the jacketed fiber, with no carbonization of tissue present. Significant transmural damage and necrosis were observed at LEEDs of 60 and 80 J/cm in both treatment groups. At the same LEEDs, p53 and caspase 3 analysis showed that transmural cell wall vein death (necrosis or apoptosis) occurred by 6 hours after treatment with both fibers.

CONCLUSIONS

There was a significant difference in the effects of treatment with a jacketed fiber and a radial fiber in EVL ablation in vitro. Although both fibers caused transmural vein wall cell death at similar LEEDs, the pattern of damage with the radial fiber was more homogeneous. There was no overtreatment of tissue in terms of carbonization after treatment with the radial fiber. Treatment with the jacketed fiber showed carbonization of tissue at the same LEEDs.

Development of a catheter-based technique for endoluminal radiofrequency sealing of pancreatic duct

Introduction: Endoluminal sealing of the pancreatic duct by glue or sutures facilitates the management of the pancreatic stump. Our objective was to develop a catheter-based alternative for endoluminal radiofrequency (RF) sealing of the pancreatic duct. Materials and methods: We devised a novel RF ablation technique based on impedance-guided catheter pullback. First, bench tests were performed on ex vivo models to tune up the technique before the in vivo study, after which endoluminal RF sealing of a ∼10 cm non-transected pancreatic duct was conducted on porcine models using a 3 Fr catheter. After 30 days, sealing effectiveness was assessed by a permeability test and a histological analysis. Results: The RF technique was feasible in all cases and delivered ∼5 W of power on an initial impedance of 308 ± 60 Ω. Electrical impedance evolution was similar in all cases and provided guidance for modulating the pullback speed to avoid tissue sticking and achieve a continuous lesion. During the follow-up the animals rate of weight gain was significantly reduced (p < 0.05). Apart from signs of exocrine atrophy, no other postoperative complications were found. At necropsy, the permeability test failed and the catheter could not be reintroduced endoluminally, confirming that sealing had been successful. The histological analysis revealed a homogeneous exocrine atrophy along the ablated segment in all the animals. Conclusions: Catheter-based RF ablation could be used effectively and safely for endoluminal sealing of the pancreatic duct. The findings suggest that a fully continuous lesion may not be required to obtain complete exocrine atrophy.