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.

Endovascular laser treatment. Comparison of lasers and fibers of different generations: study of temperatures and tissue damage produced on a porcine liver model

The current international guidelines identify tumescent ablative techniques such as laser thermal ablation (EVLA) and radiofrequency (RFA) to be the gold standard in varicose vein surgery. New-generation lasers have been introduced, which have high wavelengths (1940 and 2000 nm) and therefore with a greater affinity for water than the old generation (980- and 1470-nm lasers). The purpose of the study was to evaluate the biological effect and the temperatures produced during the use of lasers with different wavelengths (980, 1470, and 1940 nm) and with optical fibers with different emission (radial diverging at 60° and radial with cylindrical mono-ring) on in vitro model. Porcine liver was used as an in vitro model. The laser control units used had 3 different wavelengths: 980, 1470, and 1940 nm. The optical fibers used were 2: the Corona 360 fiber (mono-ring radial fiber) and the infinite fiber (cylindrical mono-ring fiber). The laser operating parameters used included the delivery of 6 W in continuous wave (CW) mode with a standard 10 s/cm pull-back. Eleven measurements were made for each fiber and for each laser, for a total of 66 measurements. We performed measurements of the maximum transverse diameter produced with laser irradiation to evaluate the biological effectiveness of the treatment. During laser irradiation, we performed measurements of both of the temperatures reached on the external surface of the porcine tissue, near the tip of the laser catheter, and the temperatures reached inside the irradiated tissue by using a digital laser infrared thermometer with apposite probe. The calculation of the statistical significance (p-value) was obtained with the ANOVA method with two between factors. The comparison study of the maximum transverse diameter (DTM) of the lesion produced on the target tissue demonstrated the absence of statistically significant differences between the 1470-nm laser and the 1940-nm laser regardless of the type of fiber used. It was not possible to perform measurements of the maximum transverse diameter produced with the 980-nm laser as this produced no visible effect on the model. The comparison study of the temperatures developed during and immediately after the treatment instead showed higher maximum surface temperatures (TSM) and a higher thermal increase (IT) regardless of the type of fiber used in a statistically significant way (respectively, p 0.002 and 0.012) when using the 980-nm laser versus the 1940-nm laser. Comparing instead the 980-nm laser with 1470 nm, there were no differences in TI recorded during the procedure but a significantly higher VTI (p 0.029). The experiment conducted with the new generation laser, compared with those of the first and second generation, shows how this works overall at lower temperatures with the same effectiveness.

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.

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.

Characterization of the ablation zones produced by three commercially available systems from a single vendor for radiofrequency thermoablation in an ex vivo swine liver model

Background

Radiofrequency Ablation (RFA) is rarely performed in veterinary medicine. A rationale exists for its use in selected cases of canine liver tumours. RFA induces ablation zones of variable size and geometry depending on the technique used and on the impedance of the targeted organ.

Objectives

(a) to describe the geometry and reproducibility of the ablation zones produced by three commercially available systems from a single company, using isolated swine liver parenchyma as a model for future veterinary applications in vivo; (b) to study the effects of local saline perfusion into the ablated parenchyma through the electrode tip and of single versus double passage of the electrode on size, geometry and reproducibility of the ablation zones produced.

Methods

Size, and geometry of ablation zones reproduced in six livers with one cooled and perfused (saline) and two cooled and non‐perfused systems, after single or double passage (n = 6/condition), were assessed macroscopically on digitalized images by a blinded operator. Longitudinal and transverse diameters, equivalent diameter, estimated volume and roundness index were measured. Reproducibility was assessed as coefficient of variation.

Results and Conclusions

Ablation zone reproducibility was higher when expressed in terms of ablation zone diameters than estimated volume. Local saline perfusion of the parenchyma through the electrode tip during RFA increased the ablation zone longitudinal diameter. Ablation zone estimated volume increased with saline perfusion only when double passage was performed. These data may provide useful information for those clinicians who intend to include RFA as an additive tool in veterinary interventional radiology.

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.

RF-energised intracoronary guidewire to enhance bipolar ablation of the interventricular septum: in-silico feasibility study

PURPOSE

Although bipolar radiofrequency (RF) ablation (RFA) is broadly used to eliminate ventricular tachycardias in the interventricular septum wall, it can fail to create transmural lesions in thick ventricular walls. To solve this problem, we explored whether an RF-energised guidewire inserted into the ventricular wall would enhance bipolar RFA in the creation of transmural lesions through the ventricular wall.

METHODS

We built three-dimensional computational models including two irrigated electrodes placed on opposing sides of the interventricular septum and a metal guidewire inserted into the septum. Computer simulations were conducted to compare the temperature distributions obtained with two ablation modes: bipolar mode (RF power delivered between both irrigated electrode) and time-division multiplexing (TDM) technique, which consists of activating the bipolar mode for 90% of the time and applying RF power between the guidewire and both irrigated electrodes during the remaining time.

RESULTS

The TDM technique was the most suitable in terms of creating wider lesions through the entire ventricular wall, avoiding the hour-glass shape of thermal lesions associated with the bipolar mode. This was especially apparent in the case of thick walls (15 mm). Furthermore, the TDM technique was able to create transmural lesions even when the guidewire was displaced from the midplane of the wall.

CONCLUSIONS

An RF-energised guidewire could enhance bipolar RFA by allowing transmural lesions to be made through thick ventricular walls. However, the safety of this new approach must be assessed in future pre-clinical studies, especially in terms of the risk of stenosis and its clinical impact.

Radiofrequency Thermal Ablation Heat Energy Transfer in an Ex-Vivo Model

Little work has been done to consider the temperature changes and energy transfer that occur in the tissue outside the vein with ultrasound-guided vein ablation therapy. In this experiment, a ex-vivo model of the human calf was used to analyze heat transfer and energy degradation in tissue surrounding the vein during endovascular radiofrequency ablation (RFA). A clinical vein ablation protocol was used to determine the tissue temperature distribution in 10 per cent agar gel. Heat energy from the radiofrequency catheter was measured for 140 seconds at fixed points by four thermometer probes placed equidistant radially at 0.0025, 0.005, and 0.01 m away from the RFA catheter. The temperature rose 1.5°C at 0.0025 m, 0.6°C at 0.005 m, and 0.0°C at 0.01 m from the RFA catheter. There was a clinically insignificant heat transfer at the distances evaluated, 1.4 ± 0.2 J/s at 0.0025 m, 0.7 ± 0.3 J/s at 0.0050 m, and 0.3 ± 0.0 J/s at 0.01 m. Heat degradation occurred rapidly: 4.5 ± 0.5 J (at 0.0025 m), 4.0 ± 1.6 J (at 0.0050 m), and 3.9 ± 3.6 J (at 0.01 m). Tumescent anesthesia injected one centimeter around the vein would act as a heat sink to absorb the energy transferred outside the vein to minimize tissue and nerve damage and will help phlebologists strategize options for minimizing damage.

One-year results of the use of endovenous radiofrequency ablation utilising an optimised radiofrequency-induced thermotherapy protocol for the treatment of truncal superficial venous reflux

Background

In previous in vitro and ex vivo studies, we have shown increased thermal spread can be achieved with radiofrequency-induced thermotherapy when using a low power and slower, discontinuous pullback. We aimed to determine the clinical success rate of radiofrequency-induced thermotherapy using this optimised protocol for the treatment of superficial venous reflux in truncal veins.

Methods

Sixty-three patients were treated with radiofrequency-induced thermotherapy using the optimised protocol and were followed up after one year (mean 16.3 months). Thirty-five patients returned for audit, giving a response rate of 56%. Duplex ultrasonography was employed to check for truncal reflux and compared to initial scans.

Results

In the 35 patients studied, there were 48 legs, with 64 truncal veins treated by radiofrequency-induced thermotherapy (34 great saphenous, 15 small saphenous and 15 anterior accessory saphenous veins). One year post-treatment, complete closure of all previously refluxing truncal veins was demonstrated on ultrasound, giving a success rate of 100%.

Conclusions

Using a previously reported optimised, low power/slow pullback radiofrequency-induced thermotherapy protocol, we have shown it is possible to achieve a 100% ablation at one year. This compares favourably with results reported at one year post-procedure using the high power/fast pullback protocols that are currently recommended for this device.

Comparison of Endovenous Laser and Radiofrequency Ablation in Treating Varices in the Same Patient

Introduction: To compare endovenous laser ablation (EVLA) and radiofrequency ablation (RFA) in different legs in the same individual in patients with venous insufficiency. Methods: Sixty patients with bilateral saphenous vein insufficiency were included. EVLA or RFA was applied to one of the patient's legs and RFA or EVLA to the other leg. Results: EVLA and RFA complications were hyperemia at 20.7% and 31.0%, ecchymosis at 31.0% and 51.7% and edema at 27.6% and 65.5%, respectively. The rate of recanalization was 6.8% in the RFA group. No recanalization was observed in EVLA group. The level of patients satisfied with EVLA was 51.7%, compared to 31.0% for RFA, while 17.2% of patients were satisfied with both procedures. Times to return to daily activity were 0.9 days in the EVLA group and 1.3 days in the RFA group. Conclusion: EVLA procedure may be superior to RFA in certain respects.

Comparison of Endovenous Laser and Radiofrequency Ablation in Treating Varicose Veins in the Same Patient

Purpose:

To compare endovenous laser ablation (EVLA) and radiofrequency venous ablation (RFA) in different legs in the same patients with venous insufficiency.

Methods:

Sixty patients with bilateral saphenous vein insufficiency were included. Endovenous laser ablation or RFA was applied to one of the patient’s legs and the remaining procedure, RFA or EVLA, to the other leg.

Results:

Minor complications in EVLA and RFA were hyperemia at 20.7% and 31.0%, ecchymosis at 31.0% and 51.7% and edema at 27.6% and 65.5%, respectively. The rate of recanalization was 6.8% in the RFA group. No recanalization was observed in the EVLA group. The level of patients satisfied with EVLA was 51.7%, compared to 31.0% for RFA, while 17.2% of patients were satisfied with both the procedures. Times to return to daily activity were 0.9 days in the EVLA group and 1.3 days in the RFA group.

Conclusion:

The EVLA procedure may be superior to RFA in certain respects.

An amphiphilic block copolymer conjugated with carborane and a NIR fluorescent probe for potential imaging-guided BNCT therapy

A carborane-containing triblock copolymer conjugated with a near infrared (NIR) fluorescence probe has been synthesized via reversible addition fragmentation chain transfer (RAFT), ring open polymerization (ROP), and conjugations of a cyanine NIR dye.