Excimer laser angioplasty: Quantitative comparison in vitro of three ultraviolet wavelengths on tissue ablation and haemolysis

The effects of three ultraviolet excimer laser wavelengths on normal and atheromatous human cadaver aortic wall are presented. Ultraviolet radiation successfully ablates vessel wall; the dose response is greatest at 249 nm followed by 193 nm and 351 nm, where the effect is negligible for the equivalent energy dose. Wavelengths 249 and 193 nm have a selective effect on fibrous atheroma; ablation proceeds at a higher rate in this tissue. Non-linear effects observed at 249 nm may be due to thermal as well as photoablative mechanisms. In addition, blood samples were exposed to all three wavelengths and potassium concentrations were measured; the dose of energy required to produce tissue ablation may also produce significant haemolysis and hyperkalaemia at 249 and 193 nm but not with 351 nm. This finding may be important for coronary angioplasty but less so for peripheral work. The wavelength that produces the strongest dose response is 249 nm; this is the wavelength for which a fibre-optic delivery system should be developed.     

Excimer laser (308 nm) recanalisation of in-stent restenosis: thermal considerations

. Excimer laser recanalisation of in-stent restenosis may be a viable modality for improving coronary patency. However, the presence of arterial stents modifies the thermal properties of the irradiated area and may alter temperature patterns generated during ablation. The goal of this study was to evaluate, in vitro, temperature changes during excimer laser ablation of stented vessels and compare them with those obtained from unstented (control) vessels. Six different stent types (AVE Microstent-II, AVE-GFX, ACS Multi-link, JJ Palmaz-Schatz, JJ Crown, and NIR) were deployed in freshly excised porcine coronary vessels. Three control unstented samples were also measured. Blood or saline was infused through the vessels, while the tissue environment was kept at ∼37°C. A 308 nm excimer laser (Spectranetics, CVX300) with an eccentric 2.0 mm laser catheter (Spectranetics, EII) delivered two trains of 200 pulses each, 10 s apart, at 60 mJ/mm², and 40 Hz, simulating maximum clinical exposure. The catheter was positioned midway in the stent, first coaxially parallel to the vessel wall, and then at an angle against the stent and vessel wall. Temperature measurements (n=168 for blood, n=96 for saline) were performed with a ∼210 μm diameter, fast-response thermocouple with 0.1°C resolution. The probe was positioned to within ∼250 μm from the inner surface of the vessels. Tissue temperature was measured at the catheter tip and at the distal and proximal edges of the stents. Maximum recorded temperatures for coaxial and angular alignment, did not exceed 42.2°C (∼6°C above baseline) and 54.2°C (∼18.1°C above baseline) respectively, for all stents types tested, controls, and all probe locations. Both stented and unstented vessels exhibited comparable temperature gradients. The observed maximum temperatures, obtained under extreme lasing conditions, indicated that 308 nm ablation, in the presence of stents under blood or saline infusion, produces clinically acceptable temperatures.     

Acute effects of a copper vapour laser on atheroma

The acute histological effects of a commercially available copper vapour laser (CVL) on normal and atherosclerotic arterial wall were studied. The multi-cyclic CVL produces a quasi continuous wave output at 511 nm (green) and 578 nm (yellow) [green/yellow ratio 21]. Tissue craters were produced in segments of normal and atherosclerotic human femoral artery using a maximum of 8 J of laser energy delivered with a bare 1 mm quartz fibre in contact and perpendicular to the tissue. Crater dimensions and ablation volumes were determined histologically using an optical graticule. Ablation of atheroma was almost three times more efficient than ablation of normal arterial wall (p<0.001). A narrow zone of vacuolization and coagulative thermal damage lined the crater margins suggesting a predominantly photothermal ablative mechanism. In conclusion, selective ablation of atheroma using low power copper vapour laser light is possible. The CVL is an attractive alternative to the argon ion laser because of its low running costs and applicability to other medical disciplines. Therefore, its potential application in laser angioplasty merits further study, preferably using a modified optical fibretip delivery system.     

Excimer laser (248 nm) drilling of tooth tissue: Preliminary investigation

Removal of bulk dental hard tissue is carried out conventionally using burrs and turbine handpieces. This paper reports on the use of excimer laser radiation in the production of tunnel preparations to access deep caries. Using energy densities which were calculated to produce a clinically acceptable rate of tissue removal, extracted human teeth were irradiated. Both enamel and dentine were subjected to numbers of pulses ranging from 500 to 2500 with an energy per pulse of 15 J cm⁻². The cross-section and depth of the lesions produced were measured using the Reflex microscope. The results showed that the ablation for dentine appears to be relatively constant while there is a gradual reduction in ablation rate in enamel as the depth increases. This may be attributable to the interaction between the plume of debris and the laser beam.     

308 nm Excimer laser ablation of cartilage

This article reports the investigation of the XeCl excimer laser as a cutting-ablating tool for human fibrocartilage and hyaline cartilage. Quantitative measurements were made of tissue ablation rates as a function of fluence in meniscal fibrocartilage and articular hyaline cartilage. A force of 1.47 Newtons was applied to an 800-μm fiber with the laser delivering a range of fluences (40-190 mJ/mm²) firing at a frequency of 5 Hz. To assess the effect of repetition rate on depth per pulse, a set of measurements was made at a constant fluence of 60 mJ/mm², with the repetition rate varying from 10 to 40 Hz. Histologic and morphometric analysis of preserved specimens was performed using light microscopy. The results of these studies revealed that the ablation rate was directly proportional to fluence over the range tested. Fibrocartilage was ablated at a rate 2.56 times faster than hyaline cartilage. Repetition rate had no effect on the penetration per pulse. Adjacent tissue damage was noted to be minimal (10–70 μm). The excimer laser achieved ablation rates adequate for arthroscopic applications. © 1994 Wiley-Liss, Inc.     

Excimer laser for revascularisation of saphenous vein grafts

Coronary artery bypass grafting has been a major advance in cardiovascular medicine over the past 30 years. Saphenous venous bypass grafts, however, are prone to develop atherosclerotic disease within several years of the procedure. Unfortunately, percutaneous interventional techniques in saphenous venous bypass grafts are associated with significant risks of distal embolisation and resultant non-Q wave myocardial infarction. Preliminary results suggest excimer laser angioplasty may significantly reduce this complication. This article summarises the results of percutaneous interventions in spahenous venous bypass grafts, emphasising the potential role of excimer laser angioplasty in this group of patients.     

Excimer laser coronary angioplasty (ELCA) for diffuse in-stent restenosis: beneficial long-term results after sufficient debulking with a lesion-specific approach using various laser catheters

Although brachytherapy became frequently used technique for treating in-stent restenosis (ISR) in 2000 (stenosis recurrence: 14–25%), removing the tissue (i.e., debulking) is still under evaluation. Regarding XeCl Excimer laser no randomised trials have been completed so far. The entirely attainable and published data originate from five one-centre and one multicentre registries which showed a high procedural success- (98%) and a very low complication rate (<2%), but heterogeneous results based on (I) manifold laser- and lasing technology due to evolving catheter and lasing technology during the studies and (II) inhomogeneous patient-populations, which had been documented only occasionally, although we now know that ISR-recurrence rates are significantly higher in patients with (1) high grade stenosis (>70%), (2) long lesions (>15mm in length), (3) recurrent ISR, (4) ISR in saphenous vein grafts, (5) early-ISR (<3 months after stent implantation), (6) multi-vessel disease and (7) low ejection fraction. Because all athero-ablative procedures are typically finalised by adjunctive balloon PCI, diameter stenosis before adjunctive PTCA was between 23% and 64%, reflecting the different lasing (and therefor debulking) intensity between the studies. The mean lesion-length, vessel diameter, stent-type and coronary differed significantly between the studies (i.e. mean lesion length between 14 and 32 mm) and although of major influence, the speed of lasing (=ablation) was not recorded in the various studies. Concerning eccentric ELCA the invention of the area-ablation technique provide a significant greater ablation effect and the new OS-technology provide 60% more ablating area. In summary, the feasibility, effectiveness, procedural success and presumably long-term outcome of the Excimer laser for treating ISR depend on multiple outcome-influencing aspects. The lack of recording variables make analysis of various laser-for-ISR trials difficult or even impossible. ELCA seems to have advantageous procedural and long term results in lesions, where aggressive debulking effect using eccentric ELCA catheters can be achieved. The OS-catheter can provide a maximum debulking in distal lesions and tortuous vessels, where the debulking abilities of the eccentric catheter are limited. If laser debulking is inadequate (DS 30%), the incidence of recurrent restenosis appear to be higher and brachytherapy is probably more suitable. Sufficient laser debulking can only be achieved through use of precise technique respecting the laser-specific abilities of plaque dissolution, appropriate energy levels and quantities, and possibly recovery time.     

Excimer laser coronary angioplasty: Initial experience at St. Thomas' Hospital

Photochemical ablation of coronary artery atheroma using pulsed xenon-chloride excimer laser has, over the past 18 months produced promising results. Worldwide experience amounts to some 2000 cases.In the first 6 months following installation of the Dymer 200+ laser (Advanced Interventional Systems, Irvine, California, USA) at St. Thomas' Hospital, 53 procedures have been performed in 49 patients. Of these, 52.8% were high risk (triple vessel disease, unstable angina, LV ejection fraction <35%, need to treat sole remaining coronary conduit).Complications were two in hospital deaths (18 and 48 h post-procedure-3.8%); one ELCA related myocardial infarct (1.9%); two haemorrhage requiring transfusion (3.8%); no emergency bypass graft surgery (0%).Current indications for the use of laser include: (1) long-segment diffuse disease; (2) proximal or ostial stenoses in coronary artery or graft; (3) restenosis after balloon angioplasty; (4) total occlusions crossed by a guidewire; (5) severe stenoses crossed by guidewire but not balloon; and (6) bifurcation lesions or stenoses compromising an important side-branch.Potential complications include: arterial perforation; aneurysm formation; peripheral embolization by plaque material; abrupt thrombotic closure; dissection; late sudden occlusion; spasm; and restenosis.Minor problems at the start of the programme involved: modifications to the machine to meet local laser safety requirements; special gases required for the machine; supply and design of fibre optic catheters; guiding catheters; heparin dose; dissection of the coronary artery (major and minor); and selection of patients.     

Excimer laser coronary angioplasty: Initial experience in Amsterdam

This paper reports on the initial clinical experience with 308 nm XeCl-excimer laser coronary angioplasty (ELCA) in the Academic Medical Center in Amsterdam and on calculations of light fluence rate distributions resulting from laser beams incident on tissue.Monte Carlo numerical computations were used to compute the light fluence rate distributions of a finite 308 nm excimer laser beam with various diameters incident on a liquid-tissue interface. It was found that light scattering is an important component in the resulting light distribution in aortic tissue. The calculations predict that there will be hardly any broadening of the beam outside the laser beam area. Therefore, the distributions from different fibres in multifibre catheters will not overlap unless the fibres are closely packed together. As a consequence of scattering the fluence rate at the surface of the tissue was larger than the incident power density and showed a considerable decrease from the centre to the edge of the beam. However, the physics of tissue ablation by fibres in contact with tissue are different and at present not well understood.The clinical results of the first 18 patients treated with the Dymer 200+ excimer laser (Advanced Interventional Systems, Irvine, CA, USA) are given. Six patients had abrupt closure solved by balloon angioplasty, but complicated by a small myocardial infarction. One patient had emergency by-pass surgery for abrupt closure after laser followed by balloon angioplasty (probably a dissection and thrombus). In one patient we perforated in a bend of a RCA with a 2.0 catheter following a second pass. We had two in hospital deaths (4 and 14 days after treatment). At 6 months follow-up, eight patients had restenosis or occlusion at the lased segment.However, the results of the first 1000 patients enrolled in the American ELCA-Registry are more promising. In the light of these results it can be concluded that a randomized trial balloon angioplasty versus excimer laser angioplasty appears to be indicated.     

Arterial response to excimer and argon laser irradiation in the atherosclerotic swine

Injury associated with laser-induced tissue ablation may be reduced by using pulsed energy delivery at low repetition rates, as opposed to using continuous wave energy delivery. This study was designed to examine the similarities and differences between these two systems as regards the healing process, and to examine whether one is superior to the other. In order to test this postulate, the healing response of normal and atherosclerotic aorta were examined after exposure in vivo to argon and excimer (XeCl 308 nm) laser radiation in hypercholesterolemic swine. Swine were fed hyperlipidemic diets for eight months following balloon denudation of the descending aorta. Following general anaesthetic, the descending aorta was isolated and laser burns were made on both normal and atherosclerotic intima using a continuous wave argon laser delivered through a 50 diameter quartz fibre, and a XeCl excimer laser carried through a 1 mm diameter fibre. Energy levels of 3 to 5 J were applied with the argon laser. The pulse duration for the excimer laser was 30 ns and craters were produced using 10 to 60 pulses at a repetition rate of 20 Hz and an energy density of 2 J cm^–2.Forty-eight hours after laser application, craters created by both lasers were filled with thrombus material. Argon burns were surrounded by thermal and acoustic injury which was not seen with excimer burns. Three weeks after laser application all crater surfaces were reconstituted. Unlike the excimer burns, argon craters demonstrated necrosis well beyond the crater margins and were characterized by multinucleate giant-cell reaction surrounding char debris. By nine weeks both excimer and argon laser burns were covered by fibrous tissue but could be distinguished by the fact that char debris and subjacent tissue injury arose with the argon burns.The results suggest that both lasers can be used to remove focal atherosclerotic plaque from arteries without inducing excessive thrombogenicity. Rapid healing is observed with both; however, damage to surrounding tissue is significantly greater with a continuous energy delivery laser as opposed to pulsed energy delivery.Work supported in part by: Heart and Stroke Foundation of Ontario, Grant-in-Aid No. 5-17     

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.     

Coronary laser angioplasty

Percutaneous coronary angioplasty has become an accepted method of non-surgical myocardial revascularization. The constant problem of restenosis has stimulated the research of new techniques able to completely eliminate the atherosclerotic plaque. Excimer laser energy has demonstrated in vitro and in vivo capability of plaque dissolution with minimal damage to surrounding tissue.In seven patients with critical coronary stenoses, before surgical anastomoses, a mono- or multifibre catheter (0.6–1.6 mm) was introduced via the coronary arteriotomy coupled with a specifically designed Xe-Cl pulsed laser (308 nm) at the time of cardio-pulmonary by-pass. Eleven stenoses were treated: three successfully and five with perforation. Technical progress is needed to eliminate this serious complication.     

Characteristics of 308 nm excimer laser activated arterial tissue photoemission under ablative and non-ablative conditions

The present study was designed to assess the characteristics of tissue photoemission obtained from normal and atherosclerotic segments of human postmortem femoral arteries by 308 nm excimer laser irradiation of 60 ns pulsewidth. Three ablative (20, 30, and 40 mJ/pulse) and three non-ablative (2.5, 5, and 10 mJ/pulse) energy fluences were employed. Both the activating laser pulses and the induced photoemission were guided simultaneously over one and the same 1,000 micron core optical fiber that was positioned in direct tissue contact perpendicular to the vascular surface. The spectral lineshape of normal arterial and noncalcified atherosclerotic structures was characterized by a broad-continuum, double-peak emission of relevant intensity between wavelengths of 360 and 500 nm, with the most prominent emission in the range of 400-415 (407 nm peak) and 430-445 nm (437 nm peak). Fibrous and lipid atherosclerotic lesions, however, exhibited a significantly reduced intensity at 437 nm compared to normal artery layers (P less than 0.001), expressed as a 407/437 nm ratio of 1.321 +/- 0.075 for fibrous and 1.392 +/- 0.104 for lipid lesions. Normal artery components presented with approximately equal intensity at both emission peaks (407/437 nm ratio: intima, 1.054 +/- 0.033; media, 1.024 +/- 0.019; adventitia, 0.976 +/- 0.021). Comparison of spectral lineshape obtained under various energy fluences within a group of noncalcified tissues disclosed no substantial difference using the 407/437 nm ratio (P greater than 0.05). In contrast, calcified lesions revealed high-intensity multiple-line (397, 442, 461, and 528 nm) emission spectra under ablative energy fluences, whereas a low-intensity broad-continuum, single-peak spectrum resulted from irradiation beyond the ablation threshold. Thus, these findings suggest fluorescence phenomena for broad-continuum spectra, and plasma emission for multiple-line spectra as an underlying photodynamic process. Regardless of the activating energy fluence, spectral analysis of 308 nm activated photoemission provides accurate information about the laser target under standardized in vitro conditions. It is demonstrated that direct contact ablation and simultaneous spectral imaging of the target tissue via the same optical fiber is feasible.(ABSTRACT TRUNCATED AT 400 WORDS)     

Excimer laser revascularisation: current indications, applications and techniques

. The ultraviolet pulsed excimer laser (308 nm wavelength) is currently the only laser approved by the FDA for percutaneous intervention in patients with ischemic coronary artery disease. The clinical presentation of the treated patients varies from stable and unstable angina to acute myocardial infarction. Potential advantages of excimer laser revascularisation in acute coronary syndromes and in ischaemic obstructive peripheral vascular disease include concomitant plaque debulking and thrombus removal; absence of systemic lytic state; shortened thrombus clearing time and facilitation of adjunct balloon angioplasty and stenting. Improved understanding of laser–tissue interactions and positive clinical outcomes through the use of safe lasing techniques have led to expansion of indications/applications for laser angioplasty. These include stent restenosis, complex lesions and thrombotic stenoses, bifurcation lesions, balloon failure, total occlusions, focal saphenous vein graft lesions and peripheral arterial obstructions. The excimer laser can be effectively utilised in patients with depressed left ventricular ejection fraction and does not require implantation of a temporary pacemaker as no-reflow phenomenon and severe arrhythmias are rarely encountered. Careful case selection, proper utilisation of equipment and incorporation of efficient lasing techniques play a crucial role in effective and safe cardiovascular laser applications.     

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.     

Percutaneous peripheral laser angioplasty with a pulsed Nd-YAG laser and sapphire tips

Percutaneous transluminal laser angioplasty with a pulsed Nd-YAG laser (1064 nm wavelength, 100s pulse duration, up to 0.4 J per pulse, 10 Hz repetition rate) coupled to optical fibres with sapphire tips of 1.8 and 2.2 mm diameter was performed under experimental conditions and then in 30 chronic occlusions of femoral and popliteal arteries in 22 patients.The experimental study in 11 human cadaverous arteries revealed that this laser system was effective in the recanalization of seven femoropopliteal occlusions, but the relative rigidity of the sapphire-tipped contact probe prevented its access to two infrapopliteal vessels. Two perforations occurred after the recanalization of 18 and 15 cm, respectively.Clinically the procedure was successful in 17 out of 25 sessions (68%). The probe formed a primary channel of at least 2.0 mm width which was further dilated by conventional balloon catheter. Ankle/brachial systolic pressure index (ABPI) increased from 0.43±0.13 to 0.79±0.21 after the procedure. In eight cases complications occurred. Two reocclusions were treated by Streptokinase infusion, two procedures were repeated 2 months later, one patient was referred to elective bypass surgery, and three patients were treated conservatively. Six patients were followed-up for more than 6 months. In one patient claudication of 400 m reappeared. ABPI showed a moderate decrease from 0.84±0.20 to 0.69±0.19.These first results are encouraging and it is likely that this method could become an important adjunct to balloon angioplasty.     

Enhancement of tissue lesion depth by dual wavelength irradiation with the Nd-YAG/KTP laser: Perspectives for laser prostatectomy

The Nd-YAG/KTP laser coagulates and vaporizes prostate tissue. The objective of this study was to investigate the combined effects of both wavelengths and to determine the irradiation parameters allowing the largest lesion volume. Chicken breast tissue was irradiated ex vivo. Consecutive 1064 and 532 nm Nd-YAG/KTP laser irradiations were performed for different combinations (30 W/10 W, 20 W/20 W, 10 W/30 W) with variable total fluence (1200 J, 2400 J, 3600 J) and compared to isofluent single wavelengths at 40 W irradiation. The depths, diameters and volumes of the total lesion as well as the vaporization effects of the 532 nm wavelength on normal and on priorly coagulated tissue were analysed. Maximum total lesion depths (p< 0.001) were found under combined Nd-YAG/KTP (20 W/20 W) irradiation conditions. Ablation efficacy of the 532 nm wavelength was reduced after prior 1064 nm irradiation, but crater depths were increased. Dual wavelength irradiation with the Nd-YAG/KTP laser induces a specific denaturation process. This may represent a new approach to increase the depth of coagulation necrosis, and thus the treated volume, thereby improving long-term results.