Análisis de correlación entre variables

The exact mechanism of action of endovenous laser is not fully understood however several theories exist such as the “steam bubble theory,” the “direct contact theory,” the “heat pipe,” and “direct light energy absorption” hypotheses.186 Obviously several factors play an important role in the mechanism of endovenous laser ablation. Direct energy absorption by the vein wall appears the most efficient mechanism.186 With a view to extrapolating the potential ablative action of intravascular “steam bubbles”, steam itself has been used as an ablatant in a new method of thermal vein ablation. Its objective is to achieve a potentially safer and easier method of thermal ablation that has fewer side effects. Only one study has been reported thus far with histological reports from animal studies on sheep and a pilot study in humans. The Steam Vein Sclerosis (SVS) system (CERMA SA, Archamps France) was used. The SVS system consists of a steam generator and a hand-piece that injects micropulses of steam into a catheter that delivers the steam into the vein to be treated. They calculated that approximately 2258 J is released when 1 gram of steam condenses. In EVLA, it is considered consensus to apply about 50 to 60

Joules/cm. To occlude 30 cm of vein with steam ablation, theoretically, 1 to 1.5 mL of water is needed. In practice, 2 to 5mLof water is likely to be required, because not all steam condenses at the vein wall. The steam is produced by means of piston pressing a fixed amount of water (76µL=diameter piston x stroke) through a heated element located just before the catheter. By keeping the lumen diameters very small and the exit holes even smaller, pressure is maintained and loss of energy is limited. The volume of the steam depends on the pressure and temperature. As the energy is transferred to the vein, the steam cools and condenses to the same volume of water used to produce the steam. The steam starts to cool and condense when it leaves the catheter due to the drop in pressure and the exchange of energy with the surroundings. This process is dynamic. The theoretic amount of energy of one pulse of steam is 174 J. The measured amount released at the tip of the catheter is 60 J per pulse. Results in sheep veins treated with steam ablation displayed fibrosis and destruction of the vein was confirmed by histology, and ongoing fibrotic contraction was confirmed by shrinking of vein diameter on US imaging. The similar histological changes found after heating using the RFA technique are stated by the authors to show that their study design was valid and in line with other minimally invasive thermal ablation modalities. The human pilot study comprised 19 patients treating 20 veins. The mean treated length of the veins was 25 cm, with an average of 50 pulses of steam were administered per treated vein. All treated veins were occluded on US examination at 1 week. At 3 months, 1 of the 20 treated varicose veins showed a small segment of several centimetres with minimal blood flow. At 6 months, flow was observed on US examination in 7 of 20 treated saphenous veins, but this was segmental (<10 cm). Subsequent work by this team has led them to recommend an increase

dose of steam to induce veins i.e. 2 instead of 1 steam pulse/cm.187 Though this potential treatment modality is very much in its infancy, it appears to show promise.

1.8.2.3.2 CYANOACRYLATE

Cyanoacrylate (CA), commonly referred to as ‘‘superglue,’’ has gained momentum in recent years for intravascular use to treat conditions such as arteriovenous malformations (AVMs),

varicoceles among other pathologies.188 189-191 Although its use is off patent for peripheral applications, the properties of CA make it potentially useful for a number of vascular occlusion procedures. When used intravascularly, CA triggers a robust inflammatory reaction in the vessel wall. Anionic substances such as plasma, blood, or saline stimulate polymerisation of the CA adhesive upon contact, leading to occlusion. The resultant polymerisation damages the vascular intima and induces an acute immunological response.192 After polymerisation is complete, gradual resorption of the occlusive polymer takes place. Within approximately one month, the response progresses to granuloma formation with giant cells and eventually fibrosis.193 194 Preliminary studies have been carried out in animal models and a small number of human subjects though the later has not yet been reported. These studies have employed the Sapheon® CA adhesive delivery catheter (Sapheon, Santa Rosa, California). The dispenser gun delivers a fixed volume (0.16mL) of glue per trigger pull, which is repeated every 3cm. Animal studies using a porcine model report endpoints of histological findings at 30 and 60 days as being, venous closure, segmental wall thickening and fibrosis. They state that intravascular injection of CA is feasible for closure of superficial veins in animal models and clarify that these findings warrant further animal studies of this proprietary CA to assess efficacy, safety and its effects on perivenous structures. They have already

conducted human trials on eight subjects with incompetent GSVs and signs or symptoms of chronic venous disease. They report that the mean treatment time was 17 minutes, the mean treatment length was 31 cm, and the mean CA injected volume was 1.58 mL. Results declared are that all veins were closed at 1 month and there were apparently no serious adverse events. The authors conclude that CA adhesive is a feasible alternative treatment for incompetent saphenous veins and state that a more robust study began in March 2011.195 Human studies have begun in other units.196