Temperature changes using excimer laser irradiation in a cochlear model

The excimer laser-ArF has certain characteristics that render it ideal for the performance of stapedotomy. These include the short wavelength of the emitted laser beam (193 nm), its high water absorption rate, the ability of pin-point focusing and its capability of operating in a pulse mode. In an effort to measure the temperature changes of the labyrinthine fluids in the inner ear during excimer laser irradiation, a cochlear model with the dimensions of the normal vestibule was designed. In this model cerebrospinal fluid (CSF) was used as a substitute for the labyrinthine fluids. Our study showed that the number of pulses needed to created the stapedotomy fenestra to the bony plate were 112–132. The temperature elevation of the CSF during laser irradiation showed only a slight increase of 0.1–0.4°C. The results of this study are very encouraging for the future use of the excimer laser in clinical situations. Part of this paper was presented at the ‘Lasers in Medicine Facing 1992’ Congress, Amsterdam, Netherlands, 1991.     

Excimer laser irradiation of non-calcified and calcified human atheroma (248 and 308nm wavelengths)

In order to develop a system of peripheral arterial angioplasty, we carried out an in vitro study to define the quantitative, thermal and morphological characteristics of human-atheroma ablation by excimer laser. A multigas ‘Sopra’ laser was used. The study was performed by using 248nm, krypton fluoride (KrF), then 308nm, xenon chloride (XeCl) wavelengths. The delivered energy was up to 150 mJ pulse⁻¹, pulse duration was 25ns, and the repetition rate could be adjusted to up to 20Hz. Irradiated tissue segments of the superficial femoral and external iliac arteries were obtained in man during surgical procedures and were both calcified and non-calcified atherosclerotic lesions. Quantitative measurements showed a linear increase of ablated tissue mass depending on the energy delivered. For the same energy, the loss of mass was greater with the 248nm wavelength than with the 308nm. The maximum temperature rise measured at the site of irradiation was 6°C at 248nm and 25°C at 308nm. Histological analysis of the irradiated segments revealed neat and precise ablation without thermal injury of adjacent tissue. At 248nm, this phenomenon was observed for calcified as well as non-calcified atheromas. It is concluded that quantitative, thermal and morphological characteristics of in vitro ablation of calcified and non-calcified human atheroma by excimer laser are compatible to clinical requirements. The results observed at 248nm were experimentally more satisfactory.     

Assessing argon laser therapy of port-wine stains

The outcome of argon laser therapy of port-wine stains (PWS), treated over an 8-year period, has been investigated. Of 571 patients that have attended a clinic between 1984 and 1992, a definite outcome of treatment has been derived for 417 patients. Outcome was assessed clinically in terms of lightening of colour and quality of skin surface after therapy. Transcutaneous microscopy (TCM) was also used to provide an initial classification of the nature of the PWS abnormality and to assist in the assessment of the outcome. Good to excellent results were achieved in 44% of the older patients, aged above 18 years. This result was achieved in 23% of children, aged 18 years and below. The outcome of treatment may related to the classification of the lesion. The majority of the lesions in children were classified as the types containing relatively normal blood vessels, whereas many of the older patients had lesion types containing dilated ectatic vessels.     

Occurrence,extent, and implications of pressure waves during excimer laser ablation of normal arterial wall and atherosclerotic plaque

Ablation of atherosclerotic plaque and normal arterial wall was performed using a Xenon-Chloride Excimer laser with a wavelength of 308 nm and a pulse duration of 115 ns. The light was transmitted via a 600 μm bare fibre and adjusted to an energy density of 3.5J/cm². The acoustic signals generated by the laser pulse were measured with two types of hydrophones consisting of polyvinylidenefluoride with active diameters of 0.3 mm and 0.5 mm and recorded on a dual channel digital storage oscilloscope using either a 0.5 m coaxial cable or a broadband fibre-optic transmission system. Tissue was retrieved from nine cadaver human aortas and macroscopically classified as either normal or calcified atherosclerotic plaque. Histological analysis (Haematoxylin eosin, elastica van Gieson, and immunohistochemical staining) was carried out after the experiments to verify the macroscopic diagnosis and to correlate the acoustic responses with the tissue characteristics. For normal arterial wall, maximum peak pressure was 1.28 MPa ± 0.85 MPa, rise time 163 ns ± 43 ns, and pressure increase 8,2k Pa ± 5,4k Pa/ns. For calcified, atheromatous segments, a maximum peak pressure of 2,02 MPa ± 1,16 MPa, a rise time of 69,9 ns ± 25,8 ns, and a pressure increase of 32,3 kPa ± 21,3 kPa/ns was found. Statistical analysis showed a significant shorter rise time (P < 0.0001) and a higher pressure increase (P < 0.0001) for calcified tissue in comparison to normal arterial wall, whereas maximum pressures alone did not allow a differentiation of tissue characteristics. Several hundred kPa are generated during Excimer laser ablation. The results suggest that focal tissue fragmentation is one mechanism of plaque ablation. A differentiation of tissue characteristics is possible by analysis of rise time and pressure increase, potentially providing the possibility of acoustic ablation control. © 1993 Wiley-Liss, Inc.     

Responses of atherosclerotic aorta to argon laser

Lasers have been advocated to resect atherosclerotic plaques in the cardiovascular system, yet little information is available regarding the effects of laser on the range of occlusive lesions seen in the peripheral arterial tree. This study was conducted to assess the risk of perforation in human cadaveric aorta involved with variable degrees of atherosclerosis. Ten fresh segments of atherosclerotic human aorta were graded for extent of atherosclerosis, then subjected to argon laser energy within 48 hours. Using air as the conduction medium and with the fiber tip 2 or 5 mm from the vessel wall, the argon laser was applied to matched calcified and non-calcified arteries at 3.0-7.0 W and 10.0–13.5 W with energy density identical for matched pairs. Results were compared among segments which were normal in appearance or had only fatty streaks grossly with those with gross regional wall calcification. The mean penetration time (T) for calcified and non-calcified lesions at low and high power outputs was compared. Mean time to perforation and range of time necessary to produce perforation were greater in calcified than non-calcified segments at all power levels employed. These data suggest that atherosclerotic lesions vary in their response to argon laser. The presence of calcium may preclude resection of some plaques and protect against wall perforation.     

Dose response of rat brains interstitially irradiated by argon laser light

The dose-response curve is reported of healthy rat brains exposed interstitially to argon laser light. By means of a 0.4 mm diameter optical fibre, doses of 1 W and 0.25 W were administered, for periods from 0 to 60 s. Well circumscribed oval lesions were obtained, sometimes with unexpected extensions towards a ventricle and even at distances from the main lesion.     

Current multicentre studies with the excimer laser: design and aims

. Excimer laser ablation to remove atherosclerotic plaque has been used for over a decade as a methodology to treat cardiovascular disease. Improvements in the technique and technology of excimer laser angioplasty, coupled with the recognition of new clinical opportunities for this treatment modality, have resulted in a resurgence of interest in the laser. Three clinical trials are now being conducted to explore potential applications, including the LARS trial of excimer laser versus balloon angioplasty to treat in-stent restenosis, the PELA trial of excimer laser angioplasty in occluded superficial femoral artery disease, and the LACI trial of excimer laser angioplasty in limb-threatening ischaemia. This article describes the rationale and objectives of these new approaches to some of the more challenging problems in cardiovascular disease.     

French experience in intra-operative XeCl excimer laser coronary artery endarterectomy

We present the results of 15 XeCl laser coronary artery endarterectomies performed in 13 patients during CABG surgery. The results are very encouraging but they show that the development of new and more efficient laser catheter delivery systems with a better proportion of optical active surface at the distal tip of the multifibre catheters is necessary to reduce the longterm and mid-term rates of restenosis.     

Smooth excimer laser coronary angioplasty (SELCA) and conventional excimer laser angioplasty: Comparison of vascular injury and smooth muscle cell proliferation

Although the excimer laser, which utilizes ‘non-thermal ablation effects’, has achieved encouraging results in early clinical trials, the long-term results have failed to show any advantage over conventional percutaneous transluminal coronary angioplasty (PTCA). A new system, Smooth Excimer Laser Coronary Angioplasty (SELCA), has been developed to reduce the tissue damage in the vessel wall caused by shock waves and vapour bubbles.SELCA (wavelength 308 nm, pulse duration 115 ns, repetition rate 150 Hz and energy density 50 mJ mm^-2) lowers the amount of shock wave formation and pressure peak amplitude in the surrounding tissue by about eight times when compared to the conventional 308 nm excimer laser (ELCA). In this preclinical evaluation, this new system was compared to ELCA. Fifty New Zealand White rabbits were stimulated by repeated weak DC impulses for a period of 28 days in order to form an atherosclerotic plaque in the right carotid artery. The vessels were excised 3, 7,14 and 28 days after laser irradiation for immunohistochemical analysis. SELCA and ELCA laser treatment lead to a decrease in maximal intimal wall thickness 3 days after intervention (control: 177±4 μm; SELCA: 131±22μm; ELCA: 120 ±33μm). In the period between 3 and 28 days, a moderate increase in intimal wall thickness was observed after SELCA treatment compared to a significant increase after ELCA (28 days after intervention: SELCA: 157±22μm; ELCA: 274 ±28μm). Bromodeoxyuridine (BrdU) was applied 18 and 12 h before excision of the vessels in order to determine the percent of cells undergoing DNA synthesis. The percent of BrdU labelled SMC in the intima (control: 13 ± 2 cells mm_-2) increased in both groups after 3 days (SELCA: 248 ± 107 cells mm^-2; ELCA: 162 ± 41 cells mm^-2) and 7 days (SELCA: 162± 55 cells mm^-2; ELCA: 279 ± 119 cells mm^-2). The present results demonstrate that vascular wall injury and increase in intimal wall thickness following SELCA are reduced in comparison to the results achieved with the conventional technique. Further trials are necessary to assess whether these improvements will lead to more favourable long-term results after excimer laser angioplasty.     

Factors influencing the ablation of atherosclerotic plaque with the argon laser

This paper describes the ablative effect of argon laser light, delivered fibre optically in vitro, on 234 segments of atherosclerotic human aorta. Variables such as energy density, type of atheroma and immersion media were taken into account. All irradiated specimens were subsequently submitted to histological examination and crater volumes in mm³ were derived from micrometer measurements made at light microscopy. Results showed: (1) a linear relationship between energy dose and crater volume in fibrous atheroma; (2) significantly greater surrounding tissue damage in the higher energy dose groups; (3) a lower dose response in calcified tissue than in fatty streaks or fibrous atheroma; (4) immersion of tissue in blood during ablation resulted in a significantly greater dose response than immersion in plasma or saline, and the corresponding surrounding tissue damage was greatest under blood. Thus, argon laser light is both effective and predictable in response when ablating atheromatous tissue, and the efficiency of the process depends on the immersion medium. The degree of surrounding tissue damage depends on the energy dose.     

Acute biological response to laser balloon angioplasty in the atherosclerotic rabbit

Laser balloon angioplasty with Nd:YAG energy has been proposed as a method to seal intimal dissection and prevent elastic recoil after balloon angioplasty. To better define the vessel response to laser balloon angioplasty, its effects on luminal diameter, Indium-111 labelled platelet deposition, and histology were studied in 10 atherosclerotic rabbits. Balloon angioplasty was performed in both iliac arteries and was followed by laser balloon angioplasty in only one iliac artery. The nonlased artery served as a control. Single (15–35 W for 20 sec) or repetitive laser pulses (12–25 W for 20 sec × 3) were used. Platelet deposition was quantified 2 hr after the intervention. Lumen diameter (mm) increased following balloon angioplasty from 0.99 ± 0.47 (mean ± SD) to 1.92 ± 0.43 and 0.89 ± 0.46 to 1.99 ± 0.57 in the balloon and laser-treated arteries, respectively (P < 0.001 for both groups for comparisons to baseline, P = NS for between groups comparison). Laser balloon angioplasty resulted in a further increase in luminal diameter to 2.42 ± 0.53 (P < 0.02) when compared to the post balloon angioplasty diameter. Platelet deposition (10⁶/cm vessel) was higher following laser balloon angioplasty (26.9, 10.2–189; median range) than after balloon angioplasty (10.6, 3.4–30), P < 0.001. Histologic evidence of laser “sealing” was present in only one artery. Thus although laser balloon angioplasty results in an improved lumen diameter, it is accompanied by increased platelet deposition. In the atherosclerotic rabbit model, abolition of vascular recoil rather than “sealing” seems to be the most important advantage of laser balloon angioplasty over conventional balloon angioplasty. © 1994 Wiley-Liss, Inc.     

Large port-wine stains: Continuous argon laser treatment with neuroleptanalgesia

An original technique is presented for the treatment of large port-wine stains (PWSs) extending over several skin areas using the argon laser on continuous modelwith the patient under neuroleptanalgesia. Sufficient experience of this technique, used since August 1983, has now been gained to affirm that it is totally innocuous and has definite advantages. Small port-wine stains are still treated using a classic ambulatory method (1,3), while PWSs with a surface area greater than 35 cm² are treated by our technique. The technique and results are detailed and the advantages and disadvantages are discussed, based on a study carried out in Lille on the effects on tissue of continuous irradiation with a power output of 3 to 5 W.     

Arterial response to laser operation for removal of atherosclerotic plaques

The cellular response of normal and atherosclerotic aortic intima after exposure in vivo to a 0.9 mm diameter carbon dioxide laser was examined in hypercholesterolemic swine with light and electron microscopy to evaluate tissue damage, thrombosis, and healing. At energy levels of greater than 5 joules, laser burns appeared as craters less than 1 mm in depth and 2 mm in diameter. Two days after the operation, craters were filled with platelet-fibrin thrombi that did not protrude above the level of adjacent endothelium. The internal elastic lamina was exposed 1 to 2 mm around the crater. This area was surrounded by a ring of densely packed leukocytes at the edge of the normal endothelium. Two weeks after the operation, the depressed crater surface was mostly reendothelialized with small, closely packed endothelial cells. The subjacent thrombus contained numerous phagocytic cells with inclusion of fibrin, erythrocytes, and membranous debris. Proliferative invaginations containing medial smooth muscle cells, mitotic figures, and collagen extended into the pit from the lateral aspects. Eight weeks after the operation, the burned area was still depressed and therefore less occlusive than adjacent lesion areas, and a fibrous cap had formed over the remaining necrotic area. The results suggest that a focused, low-energy carbon dioxide laser can be used to remove focal atherosclerotic plaques from arteries without inducing excessive thrombogenicity. Rapid healing, including reendothelialization and intimal fibrous scarring, with minimal damage to surrounding tissue, was observed.     

Three years experience with thermal and excimer lasers in the treatment of peripheral artery disease

Laser angioplasty is an effective tool to revascularize peripheral artery disease, but the major limitation is a high restenosis rate. Our experience with the hot tip laser system has shown a high primary success, 59–73% of the arteries were patent at 18 months, although 21% resulted in severe restenosis. The excimer laser seems to have a better long-term patency. Histology of restenosis specimens removed by atherectomy, shows the key role of the smooth muscle cells in this process.     

Arborizing telangiectasia of the lower limb responds well to treatment with the argon laser; superficial venular dilatation does not

The response of vascular dilatation of the lower limb to treatment with the argon laser was found to correlate with clinical diagnosis. Nine patients with superficial venular dilatation of the lower limb associated with varicose veins were treated with the argon laser and the results were uniformly poor. However, two patients with the clinically distinct condition of arborizing telangiectasia (or essential progressive telangiectasia) of the legs responded well to treatment. No other satisfactory treatment is available for this cosmetically distressing condition, so that argon laser therapy appears to be the treatment of choice.     

Next generation catheters for excimer laser coronary angioplasty

. In response to the need for maximising debulking in complex lesions, three new excimer laser coronary angioplasty catheter designs have been introduced. The eccentric laser catheter features a fibreoptic bundle disposed opposite the guide-wire lumen at the catheter tip and a torque mechanism that allows the user to rotate the fibre bundle toward the lesion mass. Residual lumens 50% larger than the catheter tip diameter have been obtained when multiple passes were made, with each pass performed using a different tip rotation. A recent case series utilising this catheter in restenosed stents resulted in larger lumens and lower 6-month restenosis rates. The optimal spaced (OS) laser catheter features a fibre bundle placed concentrically around the guide-wire lumen. The 61 μm diameter core fibres are spaced at a nominal centre-to-centre distance of 90 μm, resulting in a 40% increase in ablative area as compared to previous concentric catheter designs. In vitro testing and clinical evaluation demonstrated OS catheters routinely achieve an ablated area ≥90% of the catheter tip size. The 0.9 mm catheter features a high-density fibre pack composed of 65 fibres. Peripheral dead space has been minimised to maximise penetration of calcified plaque. When combined with laser parameters of up to 80 mJ/mm², and 80 Hz pulse repetition rate, the catheter demonstrated improved hard tissue and calcified tissue penetration in vitro. Clinical evaluation in Canada revealed a 94% lesion recanalisation rate in high-grade stenoses with angiographic evidence of calcification, chronic total occlusions, and lesions which have failed balloon angioplasty.     

Percutaneous peripheral revascularisation with excimer laser: equipment, technique and results

. Laser angioplasty has been evaluated for coronary applications since the early 1980s. Early complications of dissection, perforation and thermal injury led to a loss of enthusiasm for this technique. Recent advances in catheter development, including optimally spaced laser fibres, athermic 308 nm wavelength catheters, and saline infusion techniques have produced larger laser channels, minimised thermal injury and significantly reduced vessel dissection. This improvement in equipment and technique has led to the growing use of lasers in the field of percutaneous treatment of peripheral vascular interventions. Convincing data supporting laser use in thrombus may lead to widespread use of laser in diffuse, thrombotic, long occlusions in the SFA (superficial femoral artery) and for infrapopliteal disease treatment in patients with non-healing ulcers. Little literature exists on the specific results of 308 nm Excimer laser catheter use for peripheral angioplasty. Significant research is still needed to prove the role of debulking in peripheral applications, but upcoming clinical trial data from the PELA (peripheral angioplasty vs. laser study in long SFA occlusions) and LACI (laser angioplasty in chronic ishaemia) may help to solve these questions in the near future. This article attempts to outline the technical issues of laser catheter use in percutaneous peripheral interventions, including access, sheath selection and wire techniques to cross even the most challenging obstructions in the peripheral circulation.