Cath Lab Digest

Introduction

Since the introduction of endovenous lasers (EVL) in the early 2000s, procedure methodologies, as well as device technologies, have evolved extensively in the endeavor to improve treatment outcomes. As each novel parameter has been studied, new data have enabled the venous ablation community to acquire an enhanced understanding of the laser’s mechanism of action. The primary subject matter in EVL studies has routinely included one or a combination of the following: laser fiber vein-wall contact,^1,2 linear endovenous energy density (LEED),  ^3,4 laser power settings,⁵ variable laser wavelengths,^6,7 and most recently, covered laser fibers.^8,9 This article aims to provide a succinct review of these major topics, from EVL inception to the latest methodologies employed by thought leaders.

Evolution of EVL Technology

The shift from pulsed energy to continuous laser energy. Initial investigators of endovenous lasers employed methodologies that involved laser fiber vein-wall contact and bare-tip fibers to deliver pulsed energy. Users combined manual compression with a slow pullback of the fiber.^1,2,10 At this early juncture, it was believed that the primary mechanism of action for vein obliteration was direct contact with the vessel wall.¹⁵ The pulsed method with applied compression produced several perforations at the site of contact of the bare-tip fiber with the vessel wall, resulting in high rates of post-operative pain and bruising.^1,2,10–12 Ensuing these early adverse findings, investigators began utilizing continuous energy instead of pulsed energy, and discontinued the use of manual compression.^2,10

Other early researchers postulated that laser-induced steam bubble formation, similar to direct fiber-tip contact, caused perforations of adjacent wall areas.^11,12 Proebstle¹³ and Perkowski¹⁴ both proposed that the primary mechanism of action for 940 nm EVL was the formation of steam bubbles via delivery of laser energy, causing thermal injury to the vein endothelium, resulting in thrombotic occlusion. This mechanism was further defined by Proebstle et al¹⁸ using in vitro generation of steam bubbles with 810, 940 and 980-nm lasers. Each laser was examined in saline, plasma and hemolytic blood.¹⁸ None of the lasers were able to produce steam bubbles in saline or plasma alone, but did create perforations at sites of direct laser-tip contact.¹⁸ However, all lasers did produce steam bubbles in hemolytic blood, indicating that hemoglobin plays a key role in inflicting thermal damage to the vein wall.¹⁸ Original data from these studies helped to form the opinion that vein-wall perforations and extravasation of blood into surrounding tissues are the culprits in causing EVL post-operative pain and bruising.⁸ Procedurally, it is now largely accepted that the use of manual compression to achieve direct laser fiber-tip contact actually exacerbates the incidence of perforation and extravasation, and hence the incidence of pain and bruising.

Linear endovenous energy density (LEED). Subsequent to the steam-bubble mechanism of action premise, several researchers began to evaluate LEED for its effect on treatment outcomes. LEED is best defined as the number of joules delivered per centimeter of the target vein during an EVL procedure.¹⁷ Efficacy has been the primary endpoint of LEED studies, evaluating low LEED versus high LEED. In initial studies, Timperman et al^3,4 determined that energy doses > 80 J/cm produced more efficacious results than LEED < 80 J/cm, with no difference in side effects. Similarly, another study concluded that LEED was the main determinant in the success of EVL, with the greatest efficacy occurring at an LEED > 60 J/cm.¹⁶ Pannier et al²¹ evaluated a 1470 nm laser, reporting a 100% success rate with an average LEED of 107 J/cm for great saphenous vein treatment. It was noted that in the limbs which received a LEED > 100 J/cm, there was a considerably higher incidence of paresthesia (15.5%) than limbs receiving < 100 J/cm (2.3%).²¹ The data from these studies suggest that the optimal LEED is in the range of 60 J/cm to 100 J/cm.^3,4,16,21 LEED in these studies below the target range led to failure, whereas, high LEED demonstrated increased side effects.^3,4,16,21