DEVELOPMENT AND EVALUATION OF A FIBER OPTIC TIP LASER CATHETER FOR CORONARY ANGIOPLASTY

A fiber-optic tip catheter has been developed for treating coronary and peripheral atherosclerosis percutaneously. The catheter is coupled to an ionised Argon laser emitting at an optical power of 1 to 7 Watts. It is designed to follow a guide wire and to perform tissue ablation by a new concept combining the effects of central vaporisation and peripheral thermal remodelling of the obstructed artery. This mode of function should considerably reduce the risks of false route previously encountered with laser angioplasty. The optical and thermic properties of the catheter prototypes were determined by physical methods. These experiments showed that the temperature of the metallic component of the catheter tip did not exceed 30-degrees-C at a continuous power of 6 laser Watts when the flush was functioning. It attained 400-degrees-C in the absence of the flush. The performances of the catheter were then tested in a number of in vitro experiments. First of all, the catheter tip was placed perpendicularly to atheromatous cadaver aortae to study the effect of vaporisation with respect to the laser power. The threshold of vaporisation was 1 Watt (irradiance : 110 Watts/cm2). The catheter was then introduced into plastic tubes obstructed by atheromatous plaques. This experiment demonstrated the mechanical solidity of the catheter and its flexibility in difficult operating conditions : diameter 2mm, 45-degrees angles, irregular calcified plaques. It also showed that the optimal safety-efficacy laser power was 3 laser Watts and that the exposure times varied with respect to the nature of the plaques tested. As there were no cases of perforation, an in vivo study was carried out on an animal experimental model (5 artificially atheromatous New Zealand rabbits). The catheter was introduced via the femoral artery and bursts of 1.5 to 3 Watts were emitted from the iliac artery towards the aorta for variable periods of time. No cases of perforation were observed during these experiments. At present, the catheter parts are being perfected. The implantation of various security devices should enable its use in clinical trials.