Concerning the publication: “Histological difference between pulsed wave laser and continuous wave laser in endovenous laser ablation” by Kansaku R,Sakakibara N,Amano A,Endo H,Shimabukuro T,Sueishi M. Phlebology 2015;30: 429–434

Dear Editor,

We read this article in Phlebology with great interest. ¹ This is a very important subject and concerns the use of endovenous laser ablation.

However, we do have some comments.

Vein wall ulcerations and perforations after endovenous laser ablation are mostly due to the direct contact between the laser fibre and the vein wall. ² This can be noticed especially when a bare fibre is used. Another possible cause of perforation is an overdosage of energy administered to the vein wall when the used energy deposits are too high. ³

The conclusion of the trial, however, is that the use of pulsed wave energy deliverance avoids the vein wall perforations.

The use of different wavelength lasers was compared in this study, but also simultaneously different energy settings and different fibres were used. This can include a major bias. In the veins treated with 1320 nm laser (pulsed wave), the authors used a different fibre type compared to the veins treated with a 980 nm and 1470 nm laser (continuous wave).

This fibre type is covered with Teflon®. So the direct contact between the fibre tip and vein wall is avoided. This might also explain why there were no ulcerations and perforations in the veins treated with the 1320 nm laser (pulsed wave). Why was a similar wavelength, equal energy and fibre type not used and only one variable included (continuous wave versus pulsed wave)?

Also the used energy delivered in the consecutive veins differed. A LEED of 120 J/cm (1470 nm) for treating a saphenous vein is much too high, resulting in vein wall perforation. On the other hand, in the group 8 (1320 nm, 90 J/cm), the author's could not find any ulceration or perforation. But the number of specimens was very low in that group (n = 2). How many sections have been taken from those veins? There is also no information about the diameters of the different veins.

The author's suggest that clot formation inside the vein after EVLA is due to the use of continuous wave energy deliverance. However, during EVLA, clot formation starts when the emitted light energy is absorbed by the blood. This occurs at all wavelengths. The difference between the different wavelengths is due to the fact that the energy is more specifically absorbed by the blood (and also by the vein wall and the pervious tissue) at the higher wavelength (Table 1). ⁴

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Table 1.

Extinction coefficients (red) related to wavelength and different biological tissues.

		810	940	980	1320	1500
Blood	µa(mm−1)	0.16	0.25	0.28	0.38	3.0
	µ′s(mm−1)	0.73	0.64	0.6	0.54	0.52
	µeff(mm−1)	0.65	0.82	0.86	1.02	5.63
Vessel wall	µa(mm−1)	0.2	0.12	0.1	0.3	2.4
	µ′s(mm−1)	2.4	2.13	2.0	1.8	1.7
	µeff(mm−1)	1.25	0.9	0.79	1.37	5.43
Perivenous Tissue	µa(mm−1)	0.017	0.027	0.030	0.045	0.35
	µ′s(mm−1)	1.2	1.1	1.0	0.9	0.84
	µeff(mm−1)	0.25	0.3	0.3	0.36	1.12

An important question to ask would be; “is a vein filled with blood a good model to study endovenous laser ablation?” ⁴ It has been shown that more vein wall destruction can be achieved with a similar amount of energy, when the vein is emptied of its intraluminal blood.^3–6

In our opinion, clot formation also depends on the amount of intraluminal blood. Treating the patient in a Trendelenburg position and injecting sufficient tumescent liquid around the target vein is very important to achieve optimal results in EVLA. In the trial, it was found that more clot formation around the fibre was seen using continuous wave. However, maybe the adherence of the clot to the fibre in the pulsed mode might be influenced by the fact that the fibre tip was covered with Teflon. There is also no information about the intraluminal position of the fibre tip during the tests.

The different fibre types (jacket fibres, radial fibres and tulip fibres) have been developed to increase the illuminated inner surface of the vein wall and so locally decrease the energy density. ⁷ The aim is to have a more even energy distribution to the vein wall and avoid vein wall perforations. This has very little to do, as suggested, with the use of different wavelengths. Once again, especially when using higher laser wavelengths (1470–1500 nm) and the new fibres described above, it is very important to empty the vein of its intraluminal blood during EVLA.

This is an ex vivo study. When the vein wall destruction was measured (including ulcerations and perforations) due to thermal ablation, the authors should have considered the fact that tissues show a delayed reaction to high temperature. When a vein is examined, immediately after it has been removed, post treatment, the vein can look untouched. However, if a similar vein is removed, several days or weeks after EVLA, this vein can show transmural necrosis.^2,3,8,9

So in our opinion, an ex vivo model is not a good model to measure vein wall destruction after thermal ablation. Also in this ex vivo model, no tumescence was used.

In conclusion, we believe that this study includes major limitations and the conclusions should be put in perspective.