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.

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.

Periprocedural prophylactic antithrombotic strategies in interventional radiology: current practice in the Netherlands and comparison with the United kingdom.

PURPOSE: The use of prophylactic antithrombotic drugs to prevent arterial thrombosis during the periprocedural period during (percutaneous) peripheral arterial interventions (PAIs) is still a matter of dispute, and clear evidence-based guidelines are lacking. To create those guidelines, a study group was formed in the Netherlands in cooperation with the Dutch Society of Vascular Surgery and the Society of Interventional Radiology. The study group is called "Consensus on Arterial PeriProcedural Anticoagulation (CAPPA)." MATERIALS AND METHODS: The CAPPA study group devised and distributed a comprehensive questionnaire amongst Dutch interventional radiologists (IRs). RESULTS: One hundred forty-two IRs responded (68 %) to the questionnaire. Almost no IR stopped acetyl salicylic acid before interventions, and 40 % stopped clopidogrel before PAI but not before carotid artery stenting (CAS). A flushing solution on the sideport of the sheath was used routinely by 30 % of IRs in PAI and by 50 % of IRs during CAS. A minority of IRs used a heparinised flushing solution (28 %). Unfractionated heparin was used by 95 % of IRs as bolus; 5000 IU was the most used dosage. Timing of administration varied widely. A majority of IRs (75 %) repeated heparin administration after 1 h. CONCLUSION: A substantial variety exists amongst IRs in the Netherlands regarding the use of prophylactic periprocedural antithrombotic drugs to prevent arterial thrombosis during PAI. When compared with varying results regarding the use of heparin in the United Kingdom, the variety in the Netherlands showed a different pattern. The proven variety in these countries, and also between these countries, emphasises the need for authoritative studies to develop evidence-based practical guidelines.

[Aneurysms of the popliteal vein; treat early]. / Aneurysmata van de V. poplitea: tijdig behandelen.

BACKGROUND: Venous aneurysms are uncommon and of little clinical significance. However aneurysms of the popliteal vein may be a source of potentially lethal recurrent pulmonary emboli and deep venous thrombosis. This is also possible in asymptomatic aneurysms without thrombus. CASE DESCRIPTION: A 67-year-old hairdresser saw a vascular surgeon with a swelling in the left popliteal space that was mildly painful. Further investigations revealed an aneurysm of the popliteal vein without accompanying thrombus. She underwent surgery to remove the aneurysm and maintain the patency of the popliteal vein. Postoperatively the patient was treated with oral anticoagulation therapy for 6 months. Postoperative duplex tests showed the popliteal vein to be patent and without thrombus. The patient continued to have minor oedema after a day of standing at work. CONCLUSION: Aneurysms of the popliteal vein are rare and are often accidental findings during duplex examination for varicose veins. They can also present as recurrent pulmonary embolisms or deep venous thrombosis. Vascular surgery is the treatment of choice due to the risk of thrombo-embolic complications of the aneurysm, also in asymptomatic patients.

A brain symmetry index (BSI) for online EEG monitoring in carotid endarterectomy.

INTRODUCTION: Carotid endarterectomy is a common procedure as a secondary prevention of stroke, and one of the early controversies in carotid surgery is centered around whether a shunt should be used during this procedure. Although various EEG parameters have been proposed to determine if the brain is at risk during carotid artery clamping, the common procedure is still the visual assessment of the EEG. We propose a brain symmetry index (BSI), that has been implemented as an on-line quantitative EEG parameter, as an additional criterion for shunt need in carotid endarterectomy. METHODS: The BSI captures a particular asymmetry in spectral power between the two cerebral hemispheres, and is normalized between 0 (perfect symmetry) and 1 (maximal asymmetry). The index was evaluated retrospectively in a group of 57 operations in which the EEG and the transcranial Doppler were used as criteria for shunt insertion. In addition, after online implementation of the algorithm, several patients have been evaluated prospectively. RESULTS: If no visual EEG changes were detected, it was found that the change in BSI from baseline, DeltaBSIor=0.06. In this group, one patient suffered from intraoperative stroke and one patient died, most likely from a hyperperfusion syndrome. CONCLUSIONS: The BSI may assist in the visual EEG analysis during carotid endarterectomy and provides a quantitative measure for electroencephalographic asymmetry due to cerebral hypo-perfusion. In patients with a change in the BSI (DeltaBSI) smaller than 0.03 during test clamping, visual EEG analysis showed no changes, whereas if visual EEG analysis did warrant shunting, it was found that DeltaBSI>or=0.06.