Nd:YAG laser-assisted angioplasty in femoropopliteal artery occlusions: "hot" versus "cold" recanalization with transparent contact probe.

Abstract

Percutaneous recanalization of femoropopliteal artery occlusions (1-21 cm; median, 8 cm) was attempted in 50 patients. A 2.2-mm-diameter contact probe catheter connected to a continuous-wave neodymium yttrium aluminum garnet (Nd:YAG) laser was used. The laser was activated (15 W, 1-second pulses) only if too much resistance was met. Balloon angioplasty was performed after successful traversal of the occlusion. Primary success was achieved in 40 of 50 patients (80%). In 20 cases, recanalization was achieved mechanically (cold group). In the other 20 cases, recanalization was achieved with the help of laser irradiation (hot group: 15-405 J; median, 90 J). Except for the length of the obstruction (longer in the cold group), the two groups did not differ in baseline characteristics. Neither the length of the occlusion nor the duration of symptoms correlated with failure or success or with the delivered laser energy. Cold and hot groups did not differ with regard to functional improvement and angiographic patency at 3 and 12 months (94% +/- 4). Thus, brief laser activation doubled the cold primary success rate, but the major action of the laser contact probe is mechanical remodeling of the obstruction.

Laser light delivery systems for medical applications

“…Mechanical interaction: CW lasers. When using a fibre tip in contact with tissue, is has been demonstrated both clinically and experimentally that tissue ablation or probe penetration is dependent on the force exerted by the probes on the tissue (Berengoltz et al 1992).…”

Study of the interaction of silica-based Nd: YAG laser optical fibers with tissue

“…Bond stress would cause the index of refi'action to change waich would reflect the laser light causing local points of high power densities inside the fiber tip. Note the equation: An = Ra (16) where An is the change in index of refraction, R is the stress optical coefficient, and o is the stress applied [185]. Equation (16) shows that as stress increases, the index of refraction changes.…”

“…Note the equation: An = Ra (16) where An is the change in index of refraction, R is the stress optical coefficient, and o is the stress applied [185]. Equation (16) shows that as stress increases, the index of refraction changes. This results in an inhomogeneous fiber tip which would cause internal reflections and possible heating at the tip.…”