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.     

Pulsed ultraviolet lasers and the potential for safe laser angioplasty

Endoscopic laser ablation of atheroma using continuous wave lasers is limited by imprecise control of thermal ablation, resulting in a crater that expands in width and depth, with thermal damage to adjacent normal tissue. We compared the gross and histologic effects of pulsed 308 mm excimer irradiation to continuous-wave Nd:YAG and Argon Ion laser irradiation, and pulsed 1,060 nm, 532 nm, 355 nm, and 266 nm laser irradiation in 205 atherosclerotic aortic segments. In contrast to the continuous-wave Nd: YAG, Argon Ion, and pulsed 1,060 nm, 532 nm, and 355 nm laser irradiation, which produced gross and histologic evidence of uncontrolled ablation, the 308 nm and 266 nm pulsed lasers induced incisions that conformed precisely to the beam configuration without gross evidence of thermal injury. The incision edges from these two lasers were histologically smooth and comparable to a scalpel incision. Our histologic findings suggest that rapid, precise endoscopic ablation of vascular and nonvascular tissue can be performed at these shorter pulsed wavelengths with very high precision with relatively little damage or risk to adjacent tissue.     

Early and late healing responses of normal canine artery to excimer laser irradiation

Acute in vitro histologic studies have shown that the pulsed xenon chloride excimer laser causes precise microablation without the surrounding thermal tissue injury associated with frequently used continuous-wave lasers such as the argon, carbon dioxide, and neodymium:yttrium aluminum garnet lasers. However, the in vivo healing response of artery wall to excimer laser injury is not known. Accordingly, a xenon chloride excimer laser (308 nm, 40 nsec pulse width, 39 mJ/mm2/pulse) was transmitted via a 600 micron fused silica fiber to create 420 craters of varying depths (30 to 270 micron) in 21 normal canine femoral and carotid arteries. At 2 hours, 2 days, 10 days, and 42 days after excimer laser ablation, the artery segments were perfusion fixed in situ and analyzed by light, scanning, and transmission electron microscopy. At 2 hours, craters were covered by a carpet of platelets and entrapped red blood cells. Fibrin and exposed collagen fibers were seen at the crater base. There was a sharp demarcation of the crater-artery wall interface without lateral laser tissue injury. At 2 days, adherent platelets persisted with thrombus covering the base of the craters. Early healing responses were present, consisting of polymorphonucleated leukocytes and new endothelial cells, which extended over the crater rims. At 10 days, no thrombi were seen, and healing continued with almost complete reendothelialization. Macrophages, fibroblasts, fibrin, and entrapped red blood cells were present below the reendothelialized surface. At 42 days, healing was complete with obliteration of the craters by fibrointimal ingrowth. The surface was completely covered by a smooth monolayer of axially aligned endothelial cells. There were no aneurysms or surface hyperplastic responses. These favorable healing responses in normal canine arteries suggest that pulsed lasers with high tissue absorption coefficients, such as the xenon chloride excimer laser, may be suitable energy sources for clinical laser angioplasty procedures. However, further studies in atherosclerotic animals are required before human clinical responses can be accurately predicted.     

In vitro Alexandrite laser angioplasty: A study on fibre conduction and tissue effects

Pulsed ultra-violet excimer laser radiation is capable of tissue ablation with only minimal thermal injury of adjacent tissue structures. Since difficult fibre optic coupling of energy was observed, alternative Q-switched laser sources capable of ablation of atherosclerotic plaque are under current investigation. To evaluate tissue effects of Alexandrite laser radiation, 160 arterial segments with macroscopic evidence of atherosclerotic disease were treated. The laser light was transmitted via silica based quartz fibres with different diameters. Using the Q-switched Alexandrite laser at the fundamental wavelength (748 nm) with a pulse duration of 300 ns the energy density threshold for tissue ablation was found to be in the range of 63 to 126 J cm^–2 using a 300m fibre. On macroscopic examination only limited thermal and acoustic injury was found in crater adjacent tissue structures. Crater edges were even and did not reveal signs of crater charring or debris in the crater lumen. However, the histological cross-sections revealed thermal injury extending from 100 up to 200m lateral into adjacent tissue. The crater margins revealed fissuring as a result of shock wave injury. Thermal damage was most evident if irradiation of atherosclerotic tissue was performed in blood.     

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.     

An experimental study of excimer laser angioplasty]

An excimer laser, which is a pulsed ultraviolet laser and ablates tissue precisely with no thermal injury, is expected to coronary laser angioplasty. We transmitted XeCl excimer laser (308 nm) via a 400 microns fused silica fiber. In the first experiment, we studied about excimer laser ablative effects to normal canine arteries and atherosclerotic rabbit aortas, and about healing responses following excimer laser irradiation in both models. Surfaces after excimer laser ablation were slightly rough but no thermal injury was found in the media. And for healing process of normal canine arteries, endothelial cells appeared at 3 weeks and completely covered surfaces with fibrointimal ingrowth at 3 months. In the rabbit aortas, at 3 weeks there was reconstruction of the surface. At 2 months no accelerated atherosclerotic or aneurysmal changes were observed. In the second, with this excimer laser (short pulse) and 400 microns fused silica fibers (distal fiber-end power: 3-6 mJ/pulse), we performed transluminal laser angioplasty to recanalize totally occluded canine femoral arteries under an angioscopic guidance. We cold recanalize 8 of 9 totally occluded arteries with no thermal injury of adjacent tissue, though perforations were observed in 7 of 9 arteries. In the third, we used a newly-developed long pulse excimer laser, with which distal fiber-end energy was about 3 to 4 times as much as the short pulse one, to recanalize totally occluded canine arteries. In result, recanalization was performed in 6 of 8 arteries rapidly with little thermal injury. However, we observed perforations in 6 of 8 arteries like the short pulse one. Multifiber catheter ("over the wire system") coupled with this long-pulse excimer laser was used to reconstruct stenotic iliac arteries of atherosclerotic rabbit models. The procedure was successful in all the 5 rabbits. In conclusion, our preliminary results suggested that further developments of a more powerful and longer pulse-duration excimer laser, optic delivery system and guidance system would make excimer laser angioplasty safer and more effective method in the near future.     

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     

Far-ultraviolet laser ablation of atherosclerotic lesions

Far-ultraviolet (far-UV) (193 nm) laser radiation ablates arterial wall tissue, including noncalcified atherosclerotic lesions, with no apparent thermal damage to remaining tissue. This effect contrasts sharply with the thermal damage produced by visible-wavelength laser irradiation. The mechanism by which far-UV radiation interacts with tissue is predominantly photochemical rather than photothermal. Potential clinical applications include thsoe in which geometrically precise removal of tissue, without thermal damage to the reamaining substrate, is desired. Ultraviolet laser catheterization appears practical with respect to the availability of fiberoptic materials and high-pulse-rate excimer lasers.     

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)     

Ablation of bone and polymethylmethacrylate by an XeCl (308 nm) excimer laser

One of the main problems in orthopaedics is the surgical removal of hard substances, such as bone and polymethylmethacrylate (PMMA). Such materials are often very difficult to remove without mechanical trauma to the remaining tissue. This study investigated the feasibility of the ultraviolet 308 nm excimer laser in the ablation of these materials. The beam was delivered through a 1 mm-diameter fiber optic at 40 Hz with energy densities at the target surface of 20-80 J/cm2 per pulse. The goal of the study was to establish the ideal dosimetry for removing bone and PMMA with minimum trauma to the adjacent tissue. Histology revealed that the 308 nm laser effectively removed bone leaving a thermal damage zone of only 2-3 microns in the remaining tissue. Increasing the energy per pulse gave correspondingly larger and deeper cuts with increasing zones of thermal damage. The excimer laser was also effective in the ablation of PMMA, creating craters in the substrate with a thermal damage zone of 10-40 microns. The debris from both substrates was evaluated.     

Percutaneous, in vivo excimer laser angioplasty: results in two experimental animal models

Pulsed ultraviolet light from an excimer laser was successfully transmitted via conventional fused silica optical fibers and used to accomplish recanalization of stenotic or totally occluded arteries in an intact, flowing blood field of two atherosclerotic animal models. The fibers, 300-600 micron in diameter, were delivered percutaneously in wire-guided multilumen catheters and then used to transmit wavelengths of 308 or 351 nm from excimer lasers with pulse durations of 12 nsec or less. Lesions from 70-100% diameter narrowing, and 0.6 to 5.5 cm in length were successfully recanalized (less than 50% residual diameter narrowing) in eight animals, using 3-4 J/cm2/pulse, 10-50 Hz, and 48-370-sec cumulative exposure. Necropsy examination in six of the eight animals disclosed no signs of thermal injury. Perforations were observed in four of eight animals. Thus, while use of an excimer laser power source did not obviate vascular perforation as a complication of laser angioplasty, these preliminary results indicate that energies of pulsed ultraviolet light sufficient to ablate atherosclerotic plaque can be both transmitted via conventional fused silica optical fibers and used successfully within an intact, flowing blood field. It may therefore be possible to use pulsed ultraviolet light from an excimer laser to accomplish percutaneous ablation of atherosclerotic arterial obstructions in humans.     

Holmium and thulium lasers: Comparison of solid state systems with potential applications for laser angioplasty

Three different Mid-infra-red laser systems with potential applications in peripheral and coronary angioplasty have been investigated: Free running Ho-Tm-Cr-YAG, Q-switched Ho-Tm-Cr-YAG and free running Tm-Cr-YAG. In vitro ablation experiments were performed with atherosclerotic plaque, using both single quartz fibres and multifibre ring catheters. Despite high ablation rates, the free running Ho-Tm-Cr-YAG laser caused thermal and acoustic damage to the tissue with carbonization effects, charring of the crater edges and severe vacuole formation. Using Q-switched Ho-Tm-Cr-YAG irradiation, thermal and acoustic side-effects were reduced, but the energy available from the system was too low to reach the ablation threshold with ring catheters. A free running Tm-Cr-YAG laser also showed limited tissue damage but its output energy was in excess of 1 J, allowing, therefore, effective catheter ablation.     

The paradox of thermal ablation without thermal injury

Previous investigations have demonstrated in vitro that the excimer laser may be used to accomplish cardiovascular tissue ablation without causing thermal injury to boundary sites. Initial investigations suggested that results achieved with the excimer laser were related to photochemical breaking of molecular bonds, rather than thermal degradation. More recent investigations, however, have suggested that the mechanism of excimer tissue ablation may not be unique. Results indistiguishable from those accomplished with the excimer laser have been reproduced using both visible and infrared wavelengths. Experiments utilizing gas chromatography have indicated that the vapour-phase photoproducts liberated during excimer laser tissue ablation are indistinguishable from those observed following continuous wave laser irradiation or flame torching of cardiovascular tissue. While photoemission spectroscopic analysis has identified free radicals released in gas phase during excimer laser ablation, electron paramagnetic resonance spectroscopy has similarly identified free radicals released in solution during continuous wave laser ablation; while these two techniques may detect different types of radicals with different kinetic behaviour, these results indicate, that the finding of free radical photoproducts per se during laser ablation does not necessarily exclude a non-thermal mechanism. Finally, plasma-mediated photodisruption represents a third alternative to explain pulsed laser ablation; experiments are required, however, to define whether plasma generated during pulsed laser irradiation is central to the ablation process, or represents an epiphenomenon. However it is done, it is certain that a beam of heat is the essence of the matter. H.G. WellsThe War of the Worlds (1)     

The histological measurement of laser-induced thermal damage in vascular tissue using the stain picrosirius red F3BA

A histological technique for the measurement of laser-induced thermal tissue damage is described using the stain picrosirius red F3BA. This stain enhances the birefringence of normal collagen when viewed in polarized light. Areas of (thermally) denatured collagen, however, have no optical activity and can be measured directly by optical micrometry. The technique has been applied to experimental studies on both laser angioplasty and laser vascular anastomosis.The tissue ablation characteristics of various 2.2 mm diameter rounded sapphire laser angioplasty probes were compared by lasing (at 1064 nm) segments of porcine aorta under blood in vitro. A marked difference was observed between probes from different manufacturers, the Surgical Laser Technologies probe producing significantly greater forward tissue ablation with less associated lateral thermal damage.The relative degree of thermal damage caused by argon (488/514 nm) and Nd-YAG lasers during in vitro arteriotomy repair was also investigated. No difference was seen between the two wavelengths. However, the use of absorption-enhancing chromophore dyes as an aid to laser welding significantly reduced damage, particularly for the argon laser.In conclusion, we suggest that this histological technique is of considerable value in the investigation of the thermal effects of continuous-wave lasers.     

Experimental study of application of excimer laser to laser angioplasty

The possible application of excimer laser to laser angioplasty was studied. In the first experiment, the ablative effects of excimer laser at wavelengths of 248 nm and 308 nm on the pig myocardium were examined in vitro at an air-tissue interface. Crater depth increased with total delivered energy and energy per pulse. Very clear cuts could be observed by histological examination. There was no evidence of thermal damage at a wavelength of 248 nm, at 10 pps. Above 10 pps, a thin bordering zone of suspicious thermal damage was noted with the wavelengths of 248 nm and 308 nm. Thermal damage increased with pulse repetition rate. In the second experiment, the effects of excimer laser irradiation on blood were examined. Five vials, each of which contained 3 ml of blood, were exposed to 37.5 mJ laser beam at 10 pps in repetition rate for 10, 20, 30, 40, 50 seconds. One vial was left untreated as a control. No change in hematocrit value was observed after excimer laser irradiation. In contrast, the level of plasma free hemoglobin rose progressively with each increased duration of exposure. This result indicates that the lysis of erythrocytes does not occur in the laser-exposed cells. However, the damage to erythrocyte membrane took place as it was evidenced by progressive hemoglobin leakage into plasma. In the third experiment, the excimer laser was coupled to a 400 microns quartz optical fiber and the laser energy transmitted through the fiber was measured. At a wavelength of 308 nm, pulse energies up to 9 mJ were noted at the tip of the fiber. At a wavelength of 248 nm, the fiber tip was destroyed. In the fourth experiment, acute and chronic healing responses of normal canine arteries to excimer laser irradiation were studied in 4 mongrel dogs. The artery healed completely at the 18th day after the excimer laser irradiation. There was no evidence of thrombus formation and intimal hyperplasia in these arteries. The results suggest the applicability of excimer laser to laser angioplasty.     

Far-ultraviolet laser ablation of the cornea: photoacoustic studies

Wide bandwidth piezoelectric transducers made of thin (9 microns) polyvinylidene fluoride film have been used to make time-resolved measurements of the stress-wave generated by far-ultraviolet (193 nm) laser ablation in corneal tissue in vitro. At high fluence (approximately 250 mJ/cm2), ablation commences within 10 ns (+/- 5 ns) of the laser pulse and generates short acoustic impulses (approximately 30 ns). The time profile of the ablation, when coupled to the energy requirements for ablation from earlier work, allows the estimation of a temperature and a half-life for the thermal decomposition of the collagen in cornea. These values do not support a photothermal mechanism for the ablation under the experimental conditions.     

Autofluorescence spectroscopy using a XeCl excimer laser system for simultaneous plaque ablation and fluorescence excitation

Laser–induced fluorescence may be used to guide laser ablation of atherosclerotic lesions. This study was performed to evaluate arterial autofluorescence spectroscopy in vitro using a single XeCl excimer laser (308 nm) for simultaneous tissue ablation and fluorescence excitation. The laser beam was coupled to a 600-μm silica fiber transmitting 40–50 mJ/mm² per pulse. The fluorescence radiation emanating retrogradely from the fiber was collected by a concave mirror for spectroscopic analysis over a range of 321–657 nm. The arterial media (n = 26), lipid plaques (n = 26), and calcified lesions (n = 27) of aortic specimens from ten human cadavers were investigated in air, saline, and blood. Whereas the spectrum of calcified lesions changed with the surrounding optical medium, the other spectra remained constant. In air and blood, the spectra of arterial media, lipid plaques, and calcified lesions could be differentiated qualitatively and quantitatively (P < 0.0001). In saline, there was no clearcut spectroscopic difference between lipid plaques and calcified lesions. However, normal arterial media and atherosclerotic lesions (lipid plaques plus calcified lesions) could still be discriminated. Thus spectroscopy and plaque ablation can be combined using a single XeCl excimer laser. These encouraging results should stimulate further studies to determine the potential use of this approach to guide laser angioplasty in humans. © 1994 Wiley-Liss, Inc.     

Tissue interactions and measurement of ablation rates with ultraviolet and visible lasers in canine and human arteries

Ablation rates measured as the depth of tissue excavation per unit time were determined in human and canine aortas subjected to radiation with ultraviolet (UV) excimer (ArF 193 nm, KrF 248 nm, XeF 351 nm) and visible lasers [continuous wave (cw) and 50-ms chopped argon ion, 478 nm-514 nm; pulsed double-frequency Nd:YAG, 532 nm]. For UV and pulsed double-frequency Nd:YAG lasers ablation rates were constant in time and depended linearly on average laser power, but for cw and chopped argon lasers ablation rates varied with irradiation time and were nonlinearly dependent on laser power. In human aortas, atherosclerosis without gross calcification had no influence on ablation rates. Charring and tissue disruption were observed with cw and chopped argon ion, whereas excimer and pulsed Nd:YAG lasers produced only minimal injury to surrounding tissue. We conclude that the determination of ablation rates is useful for the selection of laser wavelengths and power densities applicable to angioplasty and that UV and pulsed visible laser permit a better control of ablation compared to continuous wave lasers.     

Xenon light therapy

The xenon light, generated by high-intensity electrical stimulation of xenon gas, is used to sterilize wounds, aid tissue repair, and relieve pain as a low-level light therapy. The light produced consists of non-coherent beams of multiple wavelengths in the ultraviolet to infrared spectrum. This broad-band light can be emitted in a continuous wave or pulsed mode, with the wave band chosen and the energy distribution controlled for the purpose. Specifically, wavelengths in the 500-700 nm range are suitable for treating superficial tissue, and wavelengths between 800 and 1,000 nm are suitable for deeper-seated tissues, due to longer optical penetration distances through tissue. One of the most common benefits in the xenon light therapy is considered to be the wide and deep irradiation of optimal rays to living tissue. Research into the use of xenon light for tissue repair and pain reduction is restricted within open-label studies and case reports. The present review expounded the effects of xenon light therapy on the basis of the available evidence in vitro and in vivo studies using a laser beam of single wavelength.     

Endoscopic thoracic sympathectomy: evaluation of pulsatile laser, non-pulsatile laser, and radiofrequency-generated thermocoagulation

We describe a modified technique for percutaneous denervation of the thoracic sympathetic chain by laser to treat selected cases of sympathetic causalgia of the upper extremities. The technique involves transpleural ablation with laser under thoracoscopic guidance through the second or third intercostal space-anterior axillary line. We also compare four different modalities of endoscopic denervation: A xenon chloride excimer laser (308 nm, 35 mJ/pulse, 20 pulses/sec, 2.2 mm catheter tip), CO2 laser (14 W, CW, 2 mm spot size), Nd:YAG laser (88 W, CW, 3 mm spot size), and radiofrequency-generated thermocoagulation (3 W, CW, 2.1 mm catheter tip) by performing bilateral thoracic sympathectomy on 12 mongrel dogs (three dogs each). Criteria analyzed included duration of exposure, power density, total energy output, laser penetration and spread, gross morphology, and scanning electron microscopy (SEM) of the destroyed neural tissue. Total ablation of the inferior segment of the stellate ganglion and the T1-T2 nerve roots by excimer laser required 83 +/1 1 Joules over an exposure period of 118 seconds. Ablation by CO2 and Nd:YAG laser required 153 +/- 13 Joules and 554 +/- 47 Joules delivered over 11 and 6 seconds respectively. In contrast, ablation of the same volume of nerve tissue by RF required 810 +/- 50 Joules over 270 seconds. SEM evaluation revealed that excimer and CO2 laser lesions were narrower in configuration compared to RF and Nd:YAG lesions which showed more lateral spread. The actual depth of penetration per 1 second exposure was similar for Excimer and CO2 (1.5 mm) and RF (1.3 mm), but deeper for Nd:YAG (3 mm).(ABSTRACT TRUNCATED AT 250 WORDS)