Enhanced ablation of human atheroma using a copper vapor laser

Abstract

The most suitable type of laser and delivery system for arterial recanalisation remains a matter of controversy. Atheroma demonstrates preferential absorption of laser light relative to normal vessel wall at wavelengths in the region of SOOnm. This phenomenon may be useful in laser angioplasty. A low power commercial quasi-continuous-wave copper vapour laser (CVL) licensed for photodynamic therapy (Oxford Lasers model CUb-A, Oxford, U.K.), emits light at 2 wavelengths - 51mm (green) and 578nm (yellow) [green/yellow ratio 2:1]. This laser may also be used to pump a dye laser producing a tunable output from 530-900nm. The output was coupled to a 1 mm diameter bare quartz optical fiber, and the effects of these wavelengths on atheroma were studied. Perforation thresholds in normal vessel were determined initially. Subsequently, tissue craters were created in sections of normal human femoral artery and in white fibrous atheromatous artery, using a total of 8 J of laser energy delivered with the fiber in contact and perpendicular to the tissue. Crater dimensions were determined histologically in 10 sections from each group, using an optical graticule. Results:- The dye laser pumping produced insufficient power output to achieve tissue ablation. The crater depth, width, and volume, in normal (N) and atheromatous (A) arterial wall achieved with the CVL were statistically compared using a Paired Student's t-test. Crater depth (mm) [mean (s.e.)]: N 0.91 (0.06), A 0.69 (0.05), p<O.O5. Crater width (mm): N 0.74 (0.08), A 1.43 (0.04), p<O.OOl. Crater volume (mm3): N 0.40 (0.08), A 1.14 (0.11), (ratio A/N=2.9), p<O.OOl. A narrow zone of vacuolisation and coagulative thermal damage lined the crater margins. In conclusion, selective ablation of atheroma using low power copper vapour laser light is possible. The CVL is an attractive alternative to argon ion laser and its potential application to laser angioplasty merits further study, preferably using a modified optical fibertip delivery system.