Embolization and vessel wall perforation in argon laser recanalization

The primary concerns in the development of a laser catheter for intravascular use are the potential hazards of vessel wall perforation and distal embolization. We present evidence, using technetium 99-labeled thrombi in two rabbit aortas and one human cadaver coronary artery, that distal embolization does not occur after argon laser recanalization. Also, no vessel wall perforation was observed during recanalization of 15 thrombosed rabbit aortas and 1 inferior vena cava, used because of their extremely thin walls. Laser recanalization of three peripheral arteries with atherosclerotic plaque obstruction, in amputated human legs, showed no evidence of vessel wall perforation. The incidence of vessel wall perforation can be minimized by preferential use of the argon laser, strict maintainance of a coaxial relationship between the laser catheter and the vessel, and exercising care during the actual lasing process. Distal embolization does not appear to be an important consideration.     

Design and evaluation of a fiberoptic fluorescence guided laser recanalization system

Current angioplasty techniques for recanalization of totally occluded arteries are limited by the inability to cross the occlusion and by the risk of perforation. A fiberoptic fluorescence guided laser recanalization system was developed and evaluated in vitro for recanalization of 17 human femoral or tibial totally occluded arterial segments (length 1.9-6.8 cm, diameter 2.5-6.0 mm). A 400 or 600 micron silica fiber was coupled to a helium-cadmium laser (lambda = 325 nm) for fluorescence excitation and to a holmium: YAG laser (lambda = 2.1 micron) for tissue ablation. Fluorescence was recorded during recanalization after every other holmium laser pulse. During recanalization, each arterial segment was bent 30-90 degrees with respect to the fiber to simulate arterial tortuosity. Ablation continued with fiber advancement as long as the fluorescence confirmed that the target tissue was atherosclerotic. Arterial spectra were classified as normal or atherosclerotic by an on-line computerized fluorescence classification algorithm (sensitivity 93%, specificity 95%). Normal fluorescence necessitated redirection of the fiber greater than 30 times per segment to continue recanalization. Fifteen of 17 totally occluded arteries had multiple recanalization channels created following total energy delivery of 40-1,016 Joules per segment with no angiographic or histologic evidence of laser perforation. Two heavily calcified arterial occlusions were not recanalized due to inhibition of holmium: YAG laser ablation by the recording of normal fluorescence spectra. Therefore, this fluorescence guided laser recanalization system appears safe and effective for recanalization of totally occluded arteries and merits in vivo evaluation. However, the lower sensitivity of fluorescence detection of heavily calcified plaques may limit the efficacy (but not safety) of fluorescence guided recanalization of heavily calcified occlusions.     

Complete patency in thrombus-occluded arteries two weeks after laser recanalization

The potential problem of rethrombosis after laser recanalization was studied in 16 thrombus-occluded canine femoral arteries. Balloon de-endothelialization and thrombin-human blood injection produced adherent, completely occlusive thrombi 4.13 +/- 1.54 cm in length; laser exposure of the thrombi occurred at 18.35 +/- 22.1 hours. The argon laser catheter was introduced via a proximal arteriotomy and a power of 3.83 +/- 0.58 W delivered for 411.3 +/- 296.87 seconds. Follow-up period was 14 days. All arteries were patent immediately after and 14 days following lasing, as demonstrated by angiography. There was no vessel perforation. Seven of the dogs were maintained on aspirin and dipyridamole 4 days before and throughout the study, but there were no differences in thrombus length, laser power, or duration of laser exposure between these dogs and those receiving no anti-platelet therapy. Control thrombosed arteries (without laser energy application) showed no autolysis within 14 days in all dogs and up to 95 days in three dogs followed for this period of time. These data show that rethrombosis of totally occluded, thrombosed arteries is not present up to 2 weeks later after laser recanalization, with or without the aid of anti-platelet therapy.     

Fluorescence spectroscopy guidance of laser ablation of atherosclerotic plague

Laser-induced fluorescence (LIF) spectroscopy can only be used for laser angioplasty guidance if high-power laser ablation does not significantly alter the pattern of tissue fluorescence. Although the spectra of normal and atherosclerotic arteries differ, the change in fluorescence spectra following laser angioplasty has not been well studied. Therefore, the purpose of this study was to assess whether laser-induced fluorescence spectroscopy could guide selective laser ablation of atherosclerotic plaque and, if so, to develop a quantitative LIF score that could be used to control a "smart" laser angioplasty system. Baseline LIF spectroscopy of 50 normal and 50 atherosclerotic human aortic specimens was performed using an optical fiber coupled to a He-Cd laser and optical multichannel analyzer. LIF was then serially recorded during erbium:YAG laser ablation of 27 atherosclerotic specimens. Laser ablation was terminated when the arterial LIF spectrum visually appeared normal. Histologic analysis revealed a mean initial plaque thickness of 1,228 +/- 54 microns and mean residual plaque thickness of 198 +/- 27 microns. Ablation of the media occurred in only three specimens. A discriminant function was derived to discriminate atherosclerotic from normal tissue for computer guidance of laser angioplasty. The LIF score, derived from stepwise multivariate linear regression analysis of the LIF spectra, correctly classified 93% of aortic specimens. The spectra obtained from the atherosclerotic specimens subjected to fluorescence-guided laser revealed a change in score from "atherosclerotic" to "normal" following plaque ablation. Seven atherosclerotic specimens were subjected to laser angioplasty with on-line computer control using the LIF score. Mean initial plaque thickness was 1,014 +/- 86 microns, and mean residual plaque thickness was 78 +/- 29 microns. There was no evidence of ablation of the media. Therefore, LIF guidance of laser ablation resulted in minimal residual plaque without arterial perforation. These findings support the feasibility of an LIF-guided laser angioplasty system for selective atherosclerotic plaque ablation.     

Intravascular ultrasound guided holmium:YAG laser recanalization of occluded arteries.

Current angioplasty devices are limited by arterial wall dissection and perforation, and by early recurrence from inadequate debulking of lesions. This study evaluated intravascular ultrasound (IVUS) as guidance for concentric laser recanalization of arterial occlusions. Twelve, 2-4-cm-long canine iliac artery occlusions were treated at 2 weeks (organizing thrombus) to 12 weeks (firm fibrous lesions) using a Holmium:YAG laser (2,100 nm wavelength) in free running mode, FRM, (250 musec pulse, 5 Hz), n = 9; and Q-switched mode, QSM (200 ns pulse, 6 Hz), n = 3. A 200 microns (n = 2) or 600 microns (n = 10) optic fiber was centered in the artery coaxial to a 5Fr rotating A scan IVUS probe. The fiber was positioned in the center of the artery distal to the lesion and slowly advanced through the obstruction. In 8 occlusions the same fiber was used as a guidewire for passage of either a 1.6-mm-(n = 2) and/or 3.0-mm (n = 6) diameter multifiber catheter (19 x 100 and 19 x 200 microns fibers, respectively) using FRM energy to further debulk the lesion. In all cases, IVUS guidance enabled concentric initial recanalization of occlusions, although 3 vessel perforations resulted from fiber deviation off the center of the lumen at a distance of 2 to 4 cm from the IVUS imaging element. Both QSM and FRM modes ablated tissue, with FRM modes producing more tissue fragmentation and thermal effect. IVUS images accurately diagnosed the location of lesions compared to angioscopic views and pathologic analysis of the specimens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histopathology of human laser thermal angioplasty recanalization

Laserprobe thermal-assisted balloon, angioplasty (LTBA) has demonstrated promising initial clinical results in recanalizing stenotic or occluded superficial femoral and popliteal arteries. Over the past year we have obtained six specimens of laserprobe thermal (LT) and LTBA treated total occlusions (avg. length 12 cm) for histopathologic examination from patients who were treated for limb salvage. Three tissue specimens were obtained acutely, and one was obtained at 6, 8, and 13 days, respectively, after laser angioplasty at the time of revision for complications or failed procedures. Serial histologic sections of the treated LT segments demonstrated recanalization of atherosclerotic lesions to approximately 60-70% of the probe diameter. The LT channels were lined by a thin layer of carbonized or coagulated tissue and several layers of cell necrosis. The histology of the thermal injury was similar regardless of whether it was produced by the heated metal cap or by free argon laser energy. Stellate balloon angioplasty fractures were frequently filled with thrombus. Analysis of these human LT and LTBA specimens revealed that the thermal device produces a confined injury through the path of least resistance. Balloon dilatation produces fragmented cracks in the vessel wall, which appear to be more thrombogenic than the carbonized LT surface. With improved guidance methods, LTBA shows potential for continuing development.     

Recanalization of arterial occlusions with a lensed fiber and a holmium:YAG laser.

Laser recanalization of totally occluded swine iliac arteries was performed to assess the safety and efficacy of a lensed fiber laser angioplasty system with a holmium:YAG (2.1 microns) laser. Silica lenses of 1.0 mm, 1.3 mm, and 1.5 mm in diameter attached to the distal end of a 300-microns diameter silica fiber delivered fluences of 79.5 J/cm2, 31.4 J/cm2, and 25.5 J/cm2, respectively. The pulse duration of the laser was 250 microseconds and the repetition rate was 4 Hz. The mean length of the total occlusions was 5.3 +/- 2.0 cm (range 0.5 cm to 8.0 cm). Successful recanalization was obtained in 16/16 lesions without angiographic vessel perforation. Angiographically significant residual stenoses (greater than 50%) remained in every case following successful laser recanalization. Histologically there was minimal evidence of thermal or acoustic tissue injury; however, in 4 of 16 arteries there was evidence of deep arterial dissection following laser recanalization. We conclude that this lensed fiber coupled with a holmium:YAG laser is a safe and effective method for crossing total occlusions in the relatively straight iliac arteries of this animal model.     

The effect of pulsed holmium-YAG laser on in vitro and in vivo atherosclerotic plaque

Laser application for atherosclerotic ablation is still limited. The pulsed Holmium-YAG (HO-YAG) laser has physical characteristics which may improve vascular recanalization. We therefore examined the effect of this laser on cadaver human atherosclerotic aortae, human amputated legs and atherosclerotic rabbits in vivo. The pulsed HO-YAG laser successfully ablated calcific and fibrotic aortic segments. Totally occluded arteries in amputated legs including calcified atherosclerotic lesions were successfully recanalized using 165–350 pulses of 0.35–0.4 J energy per pulse transmitted through commercially available fibre optics. Percutaneous delivery of laser energy to the descending aorta of atherosclerotic rabbits was not traumatic to the arterial wall. These results demonstrate the advantages of the pulsed HO-YAG laser to ablate fibrotic and calcific atheroma and to safely recanalize occluded arteries.     

Endoscopic laser resection of atherosclerotic plaque in a live animal model. A preliminary report on some technical difficulties

This study was designed to determine whether laser energy could be used effectively to resect atherosclerotic plaque through an endoscope in a live animal model. Twelve adult Yorkshire swine with infrarenal aortic atherosclerosis had a 2.5 mm and/or 3.2 mm diameter fiberscope passed into the aorta from the femoral artery after proximal aortic balloon occlusion. Endoscopic argon laser resection of the atherosclerotic plaque was then attempted in eight pigs with an argon laser fiber (60 to 400 microns). We were able to visualize the raised atherosclerotic plaque in all 12 pigs with the larger 3.2 mm diameter fiberscope, which was easily passed into the aortoiliac system from the 4 mm diameter femoral vessel. The articulating end feature enhanced maneuverability within the lumen and allowed laser fiber direction. The 2.5 mm endoscope did not allow adequate visualization in any pig since the vessel could not be cleared of blood. The 2.5 mm endoscope was also passed from the femoral artery distally into the hind limb and still did not allow adequate visualization of the vessel wall because of persistent luminal blood. The 3.2 mm endoscope enabled vessel wall visualization distal to the femoral artery when the proximal artery was occluded. No aortas were grossly perforated by the laser energy. In all pigs undergoing endoscopic laser resection, raised plaques were removed both grossly and histologically, although the plaque edges were carbonized and frayed as well as vaporized. With the small spot size of the argon fiber, channels were drilled through plaque, frequently with incomplete recanalization of the lumen.(ABSTRACT TRUNCATED AT 250 WORDS)     

A clinical trial of laser thermal angioplasty in patients with advanced peripheral vascular disease.

A 3-year prospective trial of laser thermal-assisted balloon angioplasty in 28 patients included 27 who had advanced peripheral vascular disease (severe tissue loss, gangrene, infection, and rest pain), 7 who were failures of previous therapy (surgery and thrombolysis), and 4 who were high risk for operation (myocardial infarction within 6 weeks and/or ejection fractions of less than or equal to 20%). Laser angioplasty was performed in the operating room via a groin incision by a surgeon-radiologist team. In the 27 patients with advanced peripheral vascular disease (ankle-brachial systolic pressure index [ABI] 0.27 +/- 0.2 in 10 nondiabetic, and 0.46 +/- 0.1 in 17 diabetic patients), recanalization of the native vessel was successful in 16, and patency was restored in 2 chronically occluded polytetrafluorethylene (PTFE) grafts. In these 18 (67%) successfully recanalized patients, however, five amputations were required within 1 month, and another six were needed between 8 and 12 months. Early amputations were caused by a failure of wound healing, even through angioplasty sites were patent. Late amputations were caused by reocclusion of the treated site in five of six patients. In the remaining seven patients in whom laser angioplasty alone was successful, five had healed limbs at 6 to 24 months and two remain incompletely healed but functional. The patency for successful procedures ranged from 48 hours to 25 months (5.6 +/- 6.4 mean months, +/- SD), with cumulative patency by life-table analysis of 55.5% at 3 months, 38.8% at 6 months, and 11.1% at 12 months. There were no procedure-related deaths. Complications included seven arterial wall perforations by the laser probe. We conclude that laser angioplasty has a limited role in advanced peripheral vascular disease but may provide an interval patency, thus allowing postponement of operation for high-risk patients until their medical conditions permits surgery, or to correct local tissue necrosis or infection in the operative field before reconstruction, and to restore patency to thrombosed PTFE grafts.     

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.     

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.     

Initial experience with the "Smart" laser in the treatment of atherosclerotic occlusions

A dual laser system capable of distinguishing atherosclerotic plaque from components of normal arterial wall was used to deliver laser energy to cut a channel through occluded vessels. This system was used to facilitate balloon angioplasty of short (3-17 cm) total occlusions of the superficial femoral or popliteal arteries in 17 patients. In 10 patients the occluding lesion was traversed by the laser wire and patency was effectively restored by balloon angioplasty. Satisfactory luminal patency has persisted for 2 to 12 months (mean 6 months) in 9 cases; the lesion in the tenth patient restenosed at 3 months. The laser procedure was unsuccessful in all 3 cases with occlusions over 10 cm and in 4 others. There were no clinically important complications. This experience suggests that most patients who presently require interventional treatment can be managed by standard angioplasty methods and/or require a bypass operation. The "Smart" laser is safe and effective short-term in facilitating angioplasty in some patients in whom standard angioplasty techniques are not feasible. The implications of these findings are discussed.     

Nd-YAG laser energy distribution in an artificial obstruction: influence of lasing parameters in a model of laser angioplasty

A Nd-YAG laser (1064 nm) coupled to a silica fiber (0.6 mm core diameter) was used to create defects in a model of arterial vascular obstruction. We employed transparent agar doped with black ink as atheromatous material and studied the size and shape of defects created by various lasing parameter settings. By adding calcium sulphate to the agar its scattering properties were enhanced. The created defects correspond to a temperature boundary. The optical properties of the agar greatly influenced the size and shape of the created defects. In the agar with enhanced scattering properties, the created defects showed an unfavourable penetration width-depth ratio. Maximum width of penetration always exceeded the fiber diameter. This may contribute to an increased risk of vessel wall perforation in small vessels and, if the fiber is positioned close to the vessel wall, even when a coaxial position is maintained. With increasing cumulative energy, both maximum depth and width of penetration leveled off in both agars. The results suggest that agar can be used to obtain empirically the lasing parameters that will minimize the risk of vessel wall perforation by an axially positioned fiber. The agar model needs further study to determine its limitations, but agar seems to be a useful substitute for atheroma in the study of laser catheter angioplasty.     

True ablation of atheromatous plaques with laser energy. A phase I safety study.

A laser system coupling pulsed dye laser to a 2-mm fiberoptic catheter with incorporated angioscope has been developed for recanalization of occluded arteries. Nine patients with superficial femoral artery occlusions of 4.5 to 49 cm in length were operated on and the recanalized artery harvested for pathologic examination. There were two arterial perforations. The ease of recanalization was determined by plaque composition. Heavily calcified and yellow fibro-fatty lesions were rapidly removed. Smooth white fibrous lesions resisted laser ablation. Direct angioscopy often disclosed discontinuous areas of occlusion that were more susceptible to recanalization. These were not seen on preoperative arteriograms. Microscopic examination of the specimens showed a central core of ablation. There was no evidence of acute damage to the vessel wall, with intact internal elastic lamina demonstrated in the recanalized segments. It appears that fibrous lesions will require a different laser for ablation; however, the delivery/angioscope systems function satisfactorily.     

Absence of distal emboli during in vivo laser recanalization

We used an argon laser to recanalize occluded arteries in vivo and to determine the extent of any particulate matter resulting from the procedure that might cause embolization. Thrombosis was achieved by balloon de-endothelialization and thrombin injection in 12 canine femoral or carotid arteries in six dogs. The resulting totally occlusive thrombi (2.5-8.5 cm in length) were laser treated in situ 2-29 days after formation, using laser tip power outputs of 0.8-3.4 W. The treated arterial segment was perfused before, during, and after the recanalization procedure with 1,000 ml of heparinized saline. All saline passing through the artery was collected and studied by filtration through 20-micron pore filter paper; 50-ml unfiltered aliquots were studied by automated, calibrated cell counting and microscopically after centrifugation and staining. All vessels except one were completely recanalized. Filtration yielded a thin reddish, dust-like residue. No large fragments were found in 11 of 12 effluents. The residue after centrifugation was almost entirely composed of erythrocytes plus one to four 20-30-micron strands of amorphous cellular material per high-power field. Cell counting showed that 99.1% of the material in the effluents was smaller than 9.37 micron. These results demonstrate the presence of some filterable debris following laser recanalization of intraarterial thrombi, but it probably lacks any physiologic significance. Further study of this effect of laser recanalization is needed.     

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.     

Laser radiation in the treatment of prosthetic graft stenosis. A preliminary study of prosthesis damage by laser energy

Transluminal laser recanalization is potentially an important new treatment of anastomotic intimal hyperplasia. However, currently used grafts or sutures may be damaged by laser radiation at power and energy levels required for plaque removal. To investigate this problem, two commonly used grafts (Dacron and polytetrafluoroethylene [PTFE]) and two types of vascular suture (polypropylene and PTFE) were exposed to argon laser radiation in vitro. Dacron and PTFE grafts recovered from amputations were also studied to determine whether graft "healing" affected graft resistance to laser damage. Power and energy levels required to perforate atherosclerotic superficial femoral arteries were determined for comparison. PTFE grafts were significantly (1.5 to 7 times) more resistant to perforation by laser energy than atherosclerotic arteries under all conditions. In contrast, Dacron grafts perforated at power and energy levels one half to one third of that required for vaporization of atherosclerotic plaque. PTFE sutures remained intact at power and energy levels above the levels that perforated atherosclerotic arteries, whereas polypropylene sutures were destroyed by very low levels of power and energy (0.5 joules at 0.5 watts). Because of the variable levels of power and energy that damage different types of prosthetic grafts and sutures, laser angioplasty should only be investigated clinically as a therapy for anastomotic intimal hyperplasia when PTFE grafts and sutures are present.     

Laser angioplasty with a pulsed NdYAG laser: early clinical experience

Since December 1986, 40 laser angioplasty procedures have been performed using the energy from a pulsed NdYAG laser, delivering near infrared light (1064 nm) in 100-microseconds pulses of approximately 300 mJ per pulse, directly through a transparent sapphire tipped device. All patients had total occlusion of the superficial femoral artery and symptoms severe enough to warrant surgery, with ulceration or gangrene in eight, rest pain in 14 and severe claudication interfering with life-style in the others. The device was introduced through an antegrade puncture of the superficial or common femoral artery and laser recanalization was followed by attempted balloon angioplasty in all cases. Occlusions were a median length of 15 cm (range 2-35 cm); ten patients had previously undergone failed attempts at conventional balloon angioplasty and four had occluded femoropopliteal grafts. Thirty-seven legs of 34 patients were treated with an average of 60 J (range 10-235 J) with successful recanalization in 27 and immediate reocclusion in seven. The 20 successful recanalizations have been followed up for up to 24 months (median 7 months) with only one late occlusion at 5 months. Failed recanalization was due to poor transmission by the delivery device in the early part of the series (five cases), repeated passage of the device down a collateral branch (four cases), dissection at the site of previous surgery (two cases) or no apparent reason (two cases). Immediate reocclusion was due to very poor run off in patients with severely ischaemic limbs (three cases) or technical difficulties with balloon dilatation (two cases). Complete symptomatic relief was obtained in all the cases of radiologically successful laser angioplasty. Early surgery was required in one case following reocclusion of the artery when an angioplasty balloon failed to deflate, and one patient suffered a skin reaction thought to be due to inadequate removal of the sterilizing solution. A different sterilizing procedure is now followed. Laser angioplasty can reduce the number of patients requiring bypass surgery and improvements in the device and access methods may reduce the number of untreatable cases.     

The effect of plaque composition on laser recanalization

Laser recanalization using metal-capped laser fibers and continuous-wave laser energy occurs by thermal ablation of atherosclerotic plaque. Different types of plaque respond differently to laser energy and plaque composition may be an important determinant of the success of laser recanalization. To investigate this hypothesis, 16 patients with symptomatic arterial occlusions in the mid and distal superficial femoral artery underwent B-mode ultrasound arterial imaging prior to attempted argon laser recanalization. The composition of the occlusions was classified as soft (echogenicity less than the adjacent arterial wall), dense (echogenicity equal to the adjacent arterial wall), or calcified (echoreflective). Recanalization was successful in 100% (8/8) of patients with soft occlusions versus 38% (3/8) with dense or calcified occlusions (P = 0.01). Thus, plaque composition as assessed by B-mode ultrasound imaging appears to be an important predictor of the success or failure of arterial recanalization using a thermal laser probe.