Sapphire and metal tip recanalisation: Implications for safety

Abstract

The characteristics of two modified fiber tips, the metal laser probe and the rounded sapphire contact probe, were examined in vitro and in vivo with respect to some of the risks of laser angioplasty.Both probes have an atraumatic, blunt shape. The laser beam prof'de of the sapphire contact probe looses its focussing properties in water. In vitro, we found a large temperature gradient from the front to the rim of the probe. Ablative temperatures were reached a t the tip whereas the temperature of the metal connector near the rim of the sapphire crystal rose only 30 C in blood when,15 W Nd-YAG was applied for 1 s. In contrast, the metal laser probe reached temperatures over 500 C in an in vitro tissue/blood environment when 10 W was applied for 5 s. The metal probe ablated both in the forward and the radial direction. In a rabbit model there was a large variation in temperature of the metal in vivo ( 70 -320 ~ The highest temperatures were associated with acute complications. However, in spite of transmural coagulation necrosis the artery wall remained functionally intact during a follow up period of up to 56 days.

Laser ablation and the need for intra-arterial imaging

“…The sapphire tip delivers its energy preferentially in the forward directien with limited heating of the lateral side of the sapphire [15,26]. The 'blind' tracking of the occluded artery on advancing these probes may be attributed to fatty plaque liquefaction, to some preferential thermal ablation of plaque vs normal wall [27] and to the relative resistance to heat of the internal elastic lamina [28].…”

“…In the femoropopliteal arteries, the low risk of mechanical or thermal perforation (about 10% or less) and the high primary success rate (about 80%) of the metal laser probe [24] and the sapphire contact probe in conjunction with a Nd:YAG laser [17,25] is to be attributed in part to the atraumatic, blunt shape of these modified fiber tips [5,15,23,26]. The sapphire tip delivers its energy preferentially in the forward directien with limited heating of the lateral side of the sapphire [15,26].…”

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty

“…5a and b). This is indicative of a high temperature gradient between the front and rim of the sapphire and corresponds to the changes seen a t the surface of the probe and tissue immediately after laser exposure [14]. The irregular surface of the SLT sapphires produces scattering and reflection of light such that absorption of energy is enhanced and heat production is concentrated and usefully localised 242 Ashley et al to the sapphire-tissue interface.…”

Femoropopliteal artery recanalization: Factors affecting clinical outcome of conventional and laser-assisted balloon angioplasty

“…The continuous-wave mode laser, coupled to a 2.2-mm hemispheric optical sapphire probe, achieved its goal through direct laser-tissue interaction [8][9][10][11]. The continuous-wave mode laser, coupled to a 2.2-mm hemispheric optical sapphire probe, achieved its goal through direct laser-tissue interaction [8][9][10][11].…”