Laser recanalization of occluded atherosclerotic arteries in vivo and in vitro

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)

Retention of haematoporphyrin in the aorta of hypertensive rats: in-vivo and in-vitro studies

Porphyrins are known to be accumulated and retained by tumours and atherosclerotic plaques. This property has been used for a new therapeutic approach called photodynamic therapy. In this study we assessed whether the presence of arterial hypertension could modify porphyrin turnover in the vascular wall. At various times after intravenous injection, haematoporphyrin concentration was assessed by a spectrophotofluorimetric method in the aortas of normotensive and hypertensive rats. Moreover, we studied the binding of haematoporphyrin to cultured smooth muscle cells obtained from normotensive and hypertensive rats. Larger amounts of haematoporphyrin were accumulated by the aorta of hypertensive rats and cleared at a slower rate, compared with normotensive rats. As for in-vitro experiments, cultured smooth muscle cells from hypertensive rats bound larger amounts of haematoporphyrin than cells from normotensive rats.

Dynamic angioplasty--a milling catheter for transcutaneous and intraoperative treatment of vascular occlusive disease

Balloon angioplasty and bypass graft surgery are common procedures for treating vascular occlusive disease. The purpose of this preliminary investigation was to evaluate the effectiveness and the safety of a new catheter system, first introduced by KR Kensey. The system involves a flexible catheter with a high speed rotating tip, driven by an electrical motor. The tip is cooled by a continuous flow of sterile saline containing dextran 40, heparin and urokinase. Radiopaque contrast medium may be infused through the catheter to allow the device to be guided and to detect lesions and to evaluate the efficacy of treatment. The system was applied in three patients with occlusive vascular disease (Stage IIb) and segmental or total occlusion of the superficial femoral artery (SFA). The milling catheter was introduced percutaneously into the common femoral artery and guided to the area of occlusion under DSA control. In two patients total recanalisation was achieved after passage of the milling catheter. In one patient the totally occluded SFA could not be cannulated and a femoro-popliteal bypass was performed one week later. Complications such as perforation of the vessel or peripheral embolisation were not observed. Pedal pulses were improved significantly in one patient. Further investigations will be necessary to demonstrate whether the milling catheter can be safely used to revascularise patients with limb threatening peripheral vascular disease.

The use of carbon dioxide fiberoptic laser catheter for atrial septostomy

The development of optical fibers capable of transmitting laser energy has encouraged the experimental use of laser irradiation for the treatment of acquired cardiovascular disorders. One of the key questions is which combination of laser source, energy parameters, and transmitting fiberoptic would be best suited for intravascular use. In most experiments argon, neodymium-YAG, and excimer lasers, coupled to suitable optical fibers, have been used. We now describe the use of a carbon dioxide fiberoptic laser catheter for the creation of an atrial septal defect. Silver halide infrared transmitting fibers were inserted into standard 6 French cardiovascular catheters. This laser catheter system, capable of transmitting several watts of pulsed CO2 laser energy, was initially used to create atrial septal defects in isolated dog hearts to determine the best energy parameters. Atrial septostomy was later performed successfully in four of five anesthetized dogs. The thermal damage extended 50 to 60 micron beyond the "holes" created by the laser irradiation in the interatrial septum. Thus, pulsed CO2 laser irradiation, delivered through optical fibers, can create an atrial septal defect.

Additional improvement of stenosis geometry in human coronary arteries by stenting after balloon dilatation

The purpose of this study was to assess the early changes in stenosis geometry after insertion of intravascular stents in human coronary arteries. Morphologic changes were evaluated by quantitative coronary angiography (using automated edge detection) and by calculation of the theoretical pressure decrease across the dilated and stented stenosis from the Poiseuille and turbulent resistances assuming a coronary blood flow of either 1 or 3 ml/s. Twenty-six patients were studied before and after angioplasty, as well as immediately after stent implantation. The stented coronary artery was the left anterior descending artery in 19 cases, the circumflex artery in 2 cases, the right coronary artery in 2 cases and a coronary artery bypass vein graft in 3 cases. After stent implantation, an additional increase in minimal luminal cross-sectional area of the dilated vessel was observed, suggesting that the self-expanding stainless steel endoprosthesis used in this study has a dilating function in addition to its stenting role.

Perforation thresholds and safety factors in in vivo coronary laser angioplasty

Laser angioplasty can cause early (acute perforation) or late (stenosis or aneurysm) complications. To find how much intravascular laser energy can be delivered via a 100 microns core optical fibre passed down a balloon angioplasty catheter without causing angiographic abnormalities up to 10 days later, argon laser energy was delivered percutaneously under radiographic screening to the coronary circulation of 12 normal closed chest dogs. With the balloon inflated, sequential laser pulses were delivered to the same site. Angiograms were recorded before, immediately, and again at one week, after laser delivery. There were two laser-induced perforations (both fatal). Mechanical perforation with the 100 microns fibre occurred four times, but there were no haemodynamic sequelae. To find the acute perforation threshold of similar sized arteries to energy delivered via the bare 100 microns core fibre, the tip of which was held in contact with the luminal surface, 32 argon laser pulses were delivered transluminally in vivo to separate sites in normal rabbit iliac and canine coronary arteries. The acute perforation threshold with energy delivered via the angioplasty catheter lay between 6 and 10 J and that without the balloon angioplasty catheter lay between 3 and 4 J. After delivery of up to 6 J via a balloon angioplasty catheter, there were no angiographic abnormalities at one week. Fibre optic transluminal delivery of laser energy may improve the primary success rate of, and perhaps widen the indications for, coronary angioplasty.

Early and late assessment of stenosis geometry after coronary arterial stenting

Early and late modifications of stenosis geometry after stenting of coronary arteries were assessed. Morphologic changes were evaluated by quantitative coronary angiography (automated edge-detection) and theoretical pressure drop across the dilated and stented stenosis was calculated from the Poiseuille formula, with turbulent resistances assuming a coronary blood flow of 1 or 3 ml/s. Eleven patients (ages 41 to 69 years, mean 55) were studied before and after angioplasty, and immediately after stent implantation. The stented coronary artery was the left anterior descending artery in 9 patients and the left circumflex in 2. Following stent implantation, an additional increase in minimal luminal cross-sectional area of the dilated vessel was observed, suggesting that the self-expanding stainless-steel endoprosthesis used had a dilating function in addition to its stenting role. Repeat angiography in 6 patients 3 months after stent implantation showed a decrease in the minimal luminal cross-sectional area without a significant change in theoretic pressure decrease. This slight reduction in vessel caliber had no hemodynamically significant repercussions. Thus, stenting of coronary arteries following dilatation is a potentially valuable technique for preventing both abrupt closure and late reduction in lumen diameter.

Laser recanalisation of coronary arteries by metal-capped optical fibres: early clinical experience in patients with stable angina pectoris

The delivery of laser energy to the coronary circulation by bare optical fibres may cause perforation of the vessel. Experimental studies have shown that this complication can be avoided if the optical fibre is fitted with a metal cap to prevent the potentially dangerous forward projection of the laser beam. This study was performed to assess the feasibility and short term effects of percutaneous coronary laser recanalisation with these modified fibres. Recanalisation of a severe stenosis of the left anterior descending artery was attempted in six patients who were referred for coronary artery bypass grafting. Although the percutaneous technique was used, the laser procedure was performed during coronary bypass surgery before the start of cardiopulmonary bypass to minimise the effects of potential complications. A 1.5 mm diameter metal-capped fibre coupled to an argon laser was advanced percutaneously over a guide wire positioned across the stenosis. In the first patient the delivery of 152 J resulted in the gradual passage of the fibre through a 3 cm long stenosis. Repeat angiography showed a reduction in the severity of the stenosis. In the second patient the delivery of 112 J failed to allow fibre advancement; a further 80 J pulse caused perforation which was repaired. In the remaining four patients the delivery of laser energy in the attempt to traverse the stenosis was limited to less than 90 J. In two of the four patients the severity of stenosis was reduced. No further complications were seen. Percutaneous coronary laser recanalisation with metal-capped optical fibres is feasible but improvements of currently available technology are needed to increase the primary success rate.

In vitro effects of Nd:YAG laser radiation on blood: a quantitative and morphologic analysis

Use of the Neodymium: yttrium -aluminum -garnet (Nd:YAG) laser to recanalize stenosed arteries may require delivery of the beam through blood. To assess the degree of hemolysis and debris formation, 54 samples of citrated whole blood were exposed to Nd:YAG laser radiation of varying powers (10, 20 and 30 watts) and duration (1, 2.5 and 5 seconds). Compared to control samples which were not subjected to laser light, there was no significant decrease in hematocrit (41 to 40.5 +/- 5%), hemoglobin concentration (13.8 to 13.8 +/- .06 g/1OO ml), or increase in "free" hemoglobin concentration. Debris weight (from .45 +/- .002 to .45 +/- .002 mg), as well as the white blood cell count, was also not significantly changed (from 5,400 to 5,200 +/- 240 WBC/cm). Light microscopy examination of debris from samples of whole blood, washed erythrocytes, and platelet-rich plasma subjected to the laser at 30 watts for five seconds failed to demonstrate the presence of membrane denaturation of blood elements, as compared with the morphologic changes observed in whole blood samples exposed to a "hot tip" rather than Nd:YAG laser radiation. Nd:YAG laser can be used intravascularly without fear of hemolysis or debris "micro-embolization" up to a power of 30 watts for five seconds.

Rotational atherectomy in atherosclerotic rabbit iliac arteries

PTCA is not technically possible in many patients with symptoms of coronary artery disease. In addition, atheroma is not physically removed by PTCA, and restenosis of the treated vessel is common. We have tested a new, rotating, abrasive-tipped angioplasty device in vivo in 13 atherosclerotic rabbit iliac vessels. Atherosclerosis was generated in rabbit iliac vessels by a 2% cholesterol diet combined with balloon endothelial injury for 10 weeks. The diseased vessels were then treated with the rotational atherectomy device. Before treatment, contrast angiograms demonstrated that initial percent diameter stenosis was 81% +/- 9%. After atherectomy, there was significant improvement, with residual 38% +/- 22% narrowing (p less than 0.001). One perforation resulted from distal guidewire manipulation, and one vessel was occluded by the device. Histologic examination demonstrated loss of portions of the diseased intima in all cases. Particles were produced for analysis in vitro by operating the atherectomy device in atherosclerotic rabbit aortas perfused with saline solution. Ninety-eight percent of the particles produced by the device were less than 10 micron in diameter. We conclude that this new rotational device can remove atheromatous material from diseased arteries in rabbits. Such a device may complement other angioplasty techniques and lead to wider application of catheter-based therapeutic interventions.

Carbon dioxide laser effect on platelet function and surface ultrastructure in vitro

Platelet aggregation may be an important factor in the feasibility of transcatheter laser angioplasty. The in vitro effects of increasing doses of CO2 laser irradiation on platelet number, function, and surface ultrastructure were examined. Results indicated a progressive dose-response reduction of both platelet number and function following laser irradiation. By scanning electron microscopy the irradiated platelets showed dose-related changes in pseudopods as well as progressive damage of the cell membrane.

Laser angioplasty: an atherosclerotic swine model

Rapid production of occlusive, atherosclerotic iliac artery lesions was achieved in 25 of 27 (93%) Yucatan miniature swine, using a combination of high cholesterol diet and mechanical endothelial denudation. Animals were fed a diet with 2% of their calories as raw cholesterol 2 weeks prior to balloon denudation of iliac arteries, which resulted in atherosclerotic lesions within 8 weeks. Early after denudation we have demonstrated total occlusion of arteries by fibrin thrombi, which in time organize and ultimately result in fibrotic occlusive disease. The arterial walls and intima show varying degrees of foam cell infiltration with destruction of the internal elastic lamina and calcification. Totally occluded lesions show fibrointimal proliferation, fibrosis, and multiluminal channels, which are probably secondary to organized thrombus. Our model of occlusive iliac artery disease involving vessels of 1 to 3 mm in diameter allows the development of catheter systems suitable for use in human peripheral and coronary arteries. This model is useful for the study of angioplasty, whether mechanical, balloon, or laser-mediated.

Effects of varying argon ion laser intensity and exposure time on the ablation of atherosclerotic plaque

Using continuous wave (CW) argon ion laser light, a total of 253 laser exposures of varying power (1.5, 3, 5, 8 or 10 W) and duration (20-1,333 ms) were delivered to four segments of human atheromatous aorta obtained at autopsy. Exposure conditions were controlled by using an optically shielded laser catheter that provided a 500 micron spot of light of known power. Two thresholds for consistently reproducible ablation could be defined-an intensity threshold at 25.5 W/mm2 and a fluence threshold at 3.2 J/mm2. Above threshold, a fluence of 5.1 J/mm2 was found to produce the most efficient ablation, ie, removed the greatest volume (mm3) per energy delivered (J) compared to other fluence levels employed (p less than 0.0001). Between aortic segments, however, considerable variability in efficiency (mm3/J) was observed, possibly owing to different optical properties and/or plaque composition. Low-intensity laser radiation produced inconsistent ablation and extensive coagulation effects to surrounding tissue. When a fluence of 5.1 J/mm2 was constructed with a high-intensity laser beam and a short exposure time, consistent and efficient tissue removal resulted without histologic evidence of coagulation necrosis.

Mechanical thrombectomy: a comparison of two rotational devices and balloon angioplasty in subacute canine femoral thrombosis

In this study, two prototype rotational devices were compared to balloon angioplasty in a canine model of subacute arterial thrombosis. Radiographic 2- to 8-day-old total thrombotic occlusions were produced in 30 canine femoral arteries. A high-speed rotating device with a cutting tip was used in 18 arteries. Successful opening occurred in every case, with a residual percent diameter stenosis at 45 +/- 25%. Vessel perforation was seen in 6 of the 18 arteries. A noncutting rotational thrombectomy catheter was used in six arteries. Radiographic patency was established in two of six (residual stenosis 86 +/- 28%), with one perforation with the use of the noncutting thrombectomy catheter. Balloon angioplasty reestablished radiographic patency in three of six arteries (residual stenosis 77 +/- 2%). No perforations were seen with balloon dilation, but radiographic distal emboli were always observed. No radiographic emboli were observed with either of the rotational devices. We conclude that subacute arterial thromboses are easily opened with an abrasive-tipped rotating angioplasty device. Although perforations are relatively common with this prototype equipment, design changes may produce a clinically useful angioplasty device.

Efficiency and safety of optically modified fiber tips for laser angioplasty

To evaluate the safety and efficiency of optically modified fiber tips, craters were created in human cadaver atherosclerotic arterial walls using sapphire contact probes and lensed fibers connected to a continuous wave neodymium yttrium aluminum garnet (Nd-YAG) laser. Laser energy was emitted at a constant level of 50 J. The sapphire contact probe catheter consisted of a round 2.2 mm diameter synthetic sapphire attached to an 8F catheter into which a 0.2 mm diameter optical fiber was inserted with the distal tip maintained at 3 mm from the sapphire. The lensed fiber catheter consisted of a 0.2 mm optical fiber at the end of which a 1 mm diameter lens was made. The fiber was inserted into a 5F low profile balloon catheter with the lens maintained 3 mm beyond the catheter tip. During laser emissions the catheter tips were maintained in a stationary position in contact with tissue targets immersed in blood at an angle of 90 degrees. The diameter of holes at the entry and exit of craters, the depth of craters and thermal injury to adjacent tissue (rim of carbonization and vacuolization) were measured with microscopy. The volume of tissue removed was derived from these values. Controlled effect index was determined as the ratio of diameter of holes and the extent of thermal injury. Efficiency was determined as the ratio of volume of tissue removed and the energy required to vaporize tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Argon laser angioplasty with a laser probe

A preliminary basic study of argon laser angioplasty with the use of a specially designed probe is presented. Arterial specimens were harvested from 10 amputated lower extremities. The studies included the evaluation of coaxial laser angioplasty in 10 partially or totally occluded arteries; the observation of the effect of perpendicularly applied laser energy on 35 thrombi, 54 soft and 10 hard atherosclerotic, and 51 normal arterial walls; the comparison of laser energy requirements for coaxial vessel lumen enlargement or recanalization vs. perpendicular penetration in 10 occluded, hard atherosclerotic arteries; and the spectrographic analysis of calcium density gradient in two specimens. The results showed that the power required for vessel lumen enlargement was 10 +/- 6 J/mm of atherosclerotic vessel (mean +/- standard deviation). The probe followed the original arterial lumen, did not perforate the vessel wall, and created a smooth, enlarged path. The power required to penetrate perpendicularly to a similar depth for thrombi, soft and hard atherosclerotic plaques, and normal arterial walls was 15 +/- 4, 30 +/- 15, 65 +/- 32, and 246 +/- 123 J/mm, respectively. In the hard calcified specimens, laser energy required for coaxial lumen enlargement or recanalization was significantly less than that for perpendicular penetration (p less than 0.05), which correlated with the calcium density map indicating an increase from inside to outside.

Arterial healing in the dog after intraluminal delivery of pulsed Nd-YAG laser energy

The application of laser energy to percutaneous recanalization of diseased blood vessels is of interest to vascular surgeons and radiologists. We have examined the effect of pulsed infrared light from a 100 microseconds pulsed Nd-YAG laser on the dog aorta in order to determine the dose response, perforation thresholds and healing properties in vascular tissue. We used 100 microseconds pulses of 0.5 J energy at 10 Hz repetition rate via a 400 micron optical fibre to make 205 craters in 10 dogs at total energies of 5-25 J. The perforation threshold was 15 J in six animals and 20 J in four. The dose response was linear at 10 micron tissue vaporized per Joule delivered. Animals were killed immediately and at intervals of 24 h, 4, 7 and 10 days, 2, 3 and 6 weeks, and 3 and 6 months. Material was retrieved for histology and examined by light and scanning electron microscopy. The tissue exhibited features of laser damage that were less marked than those seen with continuous wave lasers; there was less heat damage surrounding the craters which healed well, even after perforation. This laser is likely to be suitable for human laser angioplasty provided the energy is given in increments of 15 J or less.

Intravascular stents to prevent occlusion and restenosis after transluminal angioplasty

Occlusion and restenosis are the most common reasons that transluminal balloon angioplasty may fail to provide long-term benefit. An intravascular mechanical support was therefore developed with the aim of preventing restenosis and sudden closure of diseased arteries after angioplasty. The endoprosthesis consists of a self-expandable stainless-steel mesh that can be implanted nonsurgically in the coronary or peripheral arteries. Experiments in animals showed complete intimal coverage within weeks and no late thrombosis during a follow-up period of up to one year. We performed 10 implantations in 6 patients for iliac or femoral arterial disease; 24 coronary-artery stents were implanted in 19 patients who presented with coronary-artery restenoses (n = 17) or abrupt closure (n = 4) after transluminal angioplasty or deterioration of coronary-bypass grafts (n = 3). We observed three complications in the group with coronary disease. One thrombotic occlusion of a stent resulted in asymptomatic closure, a second acute thrombosis was managed successfully with thrombolysis, and one patient died after bypass surgery for a suspected but unfound occlusion. Follow-up in the patients has continued for nine months without evidence of any further restenoses within the stented segments. Our preliminary experience suggests that this vascular endoprosthesis may offer a useful way to prevent occlusion and restenosis after transluminal angioplasty. Long-term follow-up will be required to validate the early success of this procedure.

Photosensitization of experimental atheromas by porphyrins

Arteriosclerotic arteries have been shown to fluoresce when treated with hematoporphyrin derivative. This study investigates the incorporation and distribution of a partially purified form of hematoporphyrin derivative (Photofrin II) in normal and arteriosclerotic rabbit aortas. A thoracoabdominal exploration was performed in 15 rabbits. Group I comprised normal rabbits, Group II normal rabbits given 5 mg/kg Photofrin II 48 hours before surgery, Group III arteriosclerotic rabbits and Group IV arteriosclerotic rabbits given 5 mg/kg Photofrin II 48 hours before surgery. Multiple aortic biopsy specimens for frozen section were taken from all rabbits. In addition, open laser endarterectomy (with an argon ion laser) was performed on Group III and Group IV rabbits. Frozen sections were studied by digital video fluorescence microscopy to determine the distribution of Photofrin II within the layers of the aortic wall. The fluorescence of the intima of Group IV rabbits was found to be significantly greater than that of the intima, internal elastic lamina, media or adventitia of the other groups (p less than 0.01) and significantly greater than that of the internal elastic lamina, media or adventitia of Group IV rabbits (p less than 0.01). When open laser endarterectomy was performed, Group III rabbits required 103 +/- 14 J/cm2 and Group IV required 33 +/- 3 J/cm2 (p less than 0.01). It is concluded that porphyrins are selectively localized within the intima of arteriosclerotic arteries. This localization sensitizes atheromas to argon ion laser light and facilitates laser endarterectomy.

The thrombogenic potential of argon ion laser endarterectomy

The surface thrombogenicity of atheromas, conventional endarterectomy (CE), laser endarterectomy (LE), and laser angioplasty (LA) were compared in the rabbit arteriosclerosis model. Normal (N = 6) and arteriosclerotic (N = 15) rabbits underwent thoracoabdominal exploration. Multiple CEs and LEs were performed in 12 arteriosclerotic rabbits leaving a segment of intact atheroma between each endarterectomy. Multiple LAs were performed in three arteriosclerotic rabbits. Argon ion laser radiation was used for all laser procedures. Blood (0.05 ml) from normal rabbits was placed on the CE surface, LE surface, LA surface, atheroma, and normal intima and clotting times were determined. Surface thrombogenicity was calculated as the ratio of the clotting time of the CE, LE, LA, or atheroma to normal intima. Surface thrombogenicity was 1.0 +/- 0.03 for normal intima (control), 0.58 +/- 0.06 for atheromas (P less than 0.001), 0.46 +/- 0.08 for CE (P less than 0.001 from atheromas), 0.46 +/- 0.08 for LE (P = NS from CE), and 0.27 +/- 0.09 for LA (P less than 0.001 from CE and LE). The thrombogenicity of LE is the same as the thrombogenicity of CE. Both forms of endarterectomy are less thrombogenic than LA in the rabbit model.

Laser irradiation and balloon dilatation in experimental transluminal angioplasty

Percutaneous transluminal balloon angioplasty (PTA) is being currently used in patients with coronary artery disease. Laser irradiation (LI) has been effective in vaporizing atherosclerotic plaques. The purpose of this work was twofold: to compare PTA and LI techniques in the recanalization of experimental obstructive arterial lesions, and to evaluate the possibility of reducing the failures and local complications and increasing the success rate of PTA by the combined use of LI. Atherosclerotic iliac stenoses were induced in 27 rabbits; lesions were evaluated angiographically before and after intervention and were studied histologically and by electron microscopy. Argon-ion LI delivered through microlens-tip optic fibers reduced the stenotic area from 64.2 +/- 21.8% to 40.3 +/- 10.7% (n = 10, P less than .01) and PTA from 60.7 +/- 15.9% to 30.4 +/- 7.7% (n = 9, P less than .01). However, percentage reduction was higher in PTA-treated stenoses (48.4 +/- 10.1% vs 34.5 +/- 13.5%, P less than .0125). In eight more rabbits, low power LI (4.55 +/- 1.25 J) was delivered after PTA in dilated segments. Post-PTA LI further decreased stenoses (from 31.2 +/- 7.8% to 29.1 +/- 8.1%, P less than .0125); laser-irradiated segments showed diffuse carbonization of the disrupted intimal layer. The normalized transtenotic pressure gradient decreased significantly in all groups: LI reduced the gradient from .40 +/- .25 to .17 +/- .07 (P = .005); PTA from .37 +/- .14 to .11 +/- .04 (P = .001); LI after PTA from .40 +/- .16 to .12 +/- .06 (P = .001). Thus, LI is effective (less than PTA) in relieving experimental atherosclerotic stenoses and seems useful when combined with PTA.

Development and experimental application of contact probe catheter for laser angioplasty

A sapphire contact probe laser catheter was developed to increase the dimensions of tunnels created by laser angioplasty. The device consisted of a round sapphire probe (2.2 mm diameter) attached to an 8F catheter into which a 0.2 mm optical fiber was inserted with a tip maintained at 3 mm from the sapphire. The fiber was connected to a continuous wave neodymium yttrium aluminum garnet (Nd-YAG) laser. A saline perfusate was circulated through the catheter during laser emissions to prevent excessive heating of the fiber tip. The system was used in vitro on 16 sections of atherosclerotic calcified human cadaver aortic walls, using diluted blood as a medium, at powers ranging from 10 to 40 W and exposure times from 1 to 4 seconds. Six craters were created at each energy level. The system was also used on six human cadaver, agar-embedded, obstructed iliac and femoral arteries, using 40 W and 2 second laser emissions. Dimensions of probe-created craters were compared with those obtained using bare fibers. The shape of the probe craters was that of a truncated cone with the entry hole wider than the exit, as opposed to the cylindrical shape created with unmodified bare fibers. At 120 J (seconds X watts), areas of entry and exit probe-formed holes were greater than those created with the bare fibers (6.7 +/- 0.5 and 3.4 +/- 0.6 versus 0.2 +/- 0.01 mm2, respectively, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Coaxial laser energy delivery using a steerable catheter in canine coronary arteries

Intracoronary delivery of argon laser energy was studied in eight anesthetized mongrel dogs. A No. 4.5 French single lumen catheter, with steerable guidewire and an optical fiber, was introduced through a Judkins-type femoral-coronary guiding catheter into three left anterior descending and eight left circumflex coronary arteries. A total of 65 laser energy exposures were made coaxially at 24 sites in the 11 arteries. At five sites, angiographically evident arterial perforation occurred with the first laser exposure, while at seven sites multiple laser exposures were made without angiographically evident perforation. All eight dogs remained hemodynamically stable, and were electively killed 5 +/- 1 hours following the procedure. Sections of myocardium from territories supplied by treated arteries demonstrated minimal or no pathology in 10 cases, while one territory had a small zone of early myocardial necrosis. This study suggests that standard coronary artery catheterization techniques can be used to introduce and position a steerable guidewire and an optical fiber in canine coronary arteries. Laser energy can repeatedly be delivered coaxially. Short-term deleterious effects may be reduced or eliminated, and exposure of blood elements to argon laser energy does not appear to create debris.

Percutaneous coronary laser thermal angioplasty

Percutaneous coronary laser thermal angioplasty was successfully performed before conventional balloon angioplasty in a 55 year old white man with a 90% left anterior descending artery stenotic lesion and angina at rest (Canadian Heart Association class IV). The lesion was reduced to 50% residual stenosis using a 1.7 mm laser-heated metallic capped fiber and two pulses of 8 W of argon laser energy, each delivered for 5 seconds. With subsequent balloon angioplasty, the lesion was further decreased to 10% residual stenosis. The entire procedure was well tolerated without chest pain or burning, vessel perforation or spasm, thrombus formation or embolization of debris. The patient was free of pain at 1 month follow-up. This case demonstrates the feasibility of safely performing percutaneous coronary laser thermal angioplasty. Additional studies are indicated to determine the clinical role and potential benefits of coronary laser thermal angioplasty in relation to the established procedures of bypass surgery and conventional balloon angioplasty.

Uptake of hematoporphyrin derivative by atheromatous plaques: studies in human in vitro and rabbit in vivo

Hematoporphyrin derivative, a photosensitive material used to identify and treat neoplastic tissue in humans, has been found to localize in atheromatous plaques in animals and has recently been found in postmortem human atherosclerotic plaques. It is not known whether human plaques take up hematoporphyrin derivative in vivo. In five patients undergoing surgical vascular procedures, specimens containing atheromatous plaques were removed and immediately incubated in autologous oxygenated blood at 37 degrees C with hematoporphyrin derivative at a clinically relevant concentration for 2 hours. On exposure to ultraviolet light, porphyrin fluorescence was noted throughout each plaque, whereas adjacent plaque-free tissue showed no fluorescence. To compare in vitro with in vivo hematoporphyrin derivative uptake by plaques, the fluorescence of three types of arterial lesions (induced by a high cholesterol diet, catheters or balloon injury) was studied in 16 New Zealand White rabbits. Each lesion fluoresced selectively with the same intensity whether hematoporphyrin derivative exposure was performed in vitro or in vivo. Fluorescence microscopy did not show a difference in the pattern of hematoporphyrin derivative fluorescence between in vitro and in vivo specimens. The results suggest that human atheromatous plaques should take up hematoporphyrin derivative in vivo and are, therefore, potentially suitable for photochemical treatment as a new therapeutic approach to atherosclerosis.

Histopathology after Nd-YAG laser percutaneous transluminal angioplasty of peripheral arteries

Laser recanalization of occluded femoral or popliteal arteries was performed in 12 patients using a continuous wave neodymium yttrium aluminum garnet (Nd-YAG) laser. The histologic findings of the laser-irradiated arterial segments in two of these patients are reported. The specimens were obtained 2 and 4 weeks after the laser procedure. The laser-irradiated vessel in Patient 1 had been partially recanalized with reduction of the atherosclerotic occlusion from 3 to 1 cm. The lased arterial lumen manifested thermal injury to the inner quarter of the arterial wall with vacuolization and a rim of carbonization occupying 10% of the width of the arterial wall, but without thrombus formation. Histologic examination in Patient 2 revealed no fibrin deposits, atherosclerotic debris or thrombi at the intimal arterial edge. At the crater site, thermal injury was apparent with vacuolization of the intimal fibrous tissue. The histologic sections obtained 4 weeks after the procedure revealed new fibrous intimal tissue without endothelialization in some of the heavily calcified tissue sections. Where the plaques were noncalcified, reendothelialization was noted with only minimal damage to the surrounding tissue. No medial or elastic fiber disruption was seen, and no aneurysmal dilation had occurred. Intimal splitting with a cleft between the tunica media and the intima was noted at the site of previous balloon angioplasty. In conclusion, the follow-up histologic findings 2 and 4 weeks after laser angioplasty in two patients using a specially designed catheter delivery system and cooling blood perfusate revealed thermal injury to the inner quarter of the arterial vessel wall and no evidence of thrombus formation.

Laser-assisted percutaneous angioplasty: initial clinical experience in peripheral arteries

Experimental and animal studies have shown that laser energy can vaporize intra-vascular thrombus and atheroma, suggesting that it may have a role in percutaneous angioplasty. Argon laser energy transmitted via a flexible fibre introduced through a percutaneous catheter was used in 15 patients undergoing balloon angioplasty of femoral or popliteal arteries. Of four stenoses, laser alone produced improvement of the lumen in two. Of 11 occlusions some degree of clearance of the lumen was achieved by laser in eight prior to balloon dilatation. Extravasation of contrast medium indicating wall perforation occurred in two patients, without clinical sequelae. No other complications, such as embolism, arterial spasm or toxic effects were observed. There was one acute re-occlusion, almost certainly not related to the use of laser. There have been no late complications. The ability of laser to influence favourably vascular occlusion is confirmed, but technical advances are necessary to avoid vessel wall perforation consistently and to improve the production of an adequate lumen before its potential can be fully realized.

Thermal effects of laser and electrical discharge on cardiovascular tissue: implications for coronary artery recanalization and endocardial ablation

To determine the thermal responses of cardiovascular tissues to laser and electrical ablation, and to characterize the effects of different superfusing media and temperatures on target tissue temperatures and resulting extent of tissue injury, 184 laser and 15 electrical discharges were delivered to segments of human and canine aorta and canine ventricular endocardium. Tissue temperatures were measured 2 mm from the point of contact of laser fiber tip and tissue. When superfusing media consisted of whole blood or plasma at room temperature, a standard 40 J laser discharge caused peak arterial temperatures to rise 29.2 +/- 1.6 degrees C and 30 +/- 1.4 degrees C, respectively; however, tissue cooling was significantly slower in blood than in plasma. When saline solution was superfused, tissue temperatures rose by 11.4 +/- 2.2 degrees C, and tissue cooling occurred significantly faster than with either plasma or blood. The dimensions of the resulting aortic lesions were larger when blood (1.69 +/- 0.26 mm) was superfused than when plasma (1.39 +/- 0.04 mm) or saline (0.77 +/- 0.13 mm) was superfused (p less than 0.0001). Similar findings were observed with ventricular endocardium using blood or saline as the superfusing medium. In arterial tissue, superfusion with cold blood or saline solution resulted in lower peak temperature elevations (22 +/- 3.8 degrees C and 13.5 +/- 1.3 degrees C, respectively) and faster tissue cooling after laser discharge. Corresponding aortic lesion sizes were significantly smaller (1.4 +/- 0.03 and 0.5 +/- 0.02 mm, respectively) than when blood or saline medium was superfused at room temperature (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Preferential light absorption in atheromas in vitro. Implications for laser angioplasty

Laser angioplasty, the in situ ablation of arterial obstructions with laser radiation, has been demonstrated in animal models and early clinical trials. A problem with this technique, however, is the possibility of thermal damage to adjacent or underlying normal tissues that also absorb the radiation. Using a spectrophotometer with an integrating sphere and a specially constructed tunable-dye laser-based spectrophotometer, we evaluated the transmittance and remittance of human cadaveric atheromas and adjacent normal aorta from 250 to 1,300 nm to identify wavebands where there is preferential light absorption by atheromas. Data were analyzed by both the Kubelka-Munk formalism and a Beer's law model. Both methods indicate that atheromas absorb more than normal aorta between 420 and 530 nm. At 470 nm the average Kubelka-Munk absorption coefficient of atheromas from 10 cadavers was 54 +/- 9 cm-1 compared with 26 +/- 6 cm-1 for normal aortic specimens from seven cadavers. Yellow chromophores responsible for the atheroma absorbance were extractable with xylenes. Thin-layer chromatography and absorption spectra identified the extracted chromophores as predominantly consisting of a mix of carotenoids, which are known constituents of atheromatous lesions. Preferential absorption of blue light by carotenoids in atheromas may permit selective ablation of atheromatous obstructions with appropriate pulses of laser radiation.

Laser angioplasty with angioscopic guidance in humans

An experimental study was conducted in 11 patients to evaluate the immediate effects of laser recanalization during peripheral arterial bypass surgery. Angioscopy allowed precise localization and identification of the occlusion. A 1 or 2 mm optical fiber probe was used. Laser energy was regulated using the least amount of energy necessary for recanalization. New vascular channels were made in 10 of the 11 patients. After recanalization the arterial segment was excised for histologic evaluation. Smaller channel diameters were made with the 1 mm probe (1.5 +/- 0.6 mm) than with the 2 mm probe (3 +/- 0.3 mm) (p less than 0.05). Flow through channels (mean pressure 80 mm Hg) made with the 2 mm probe was greater than that through channels made with the 1 mm probe (150 +/- 102 versus 19.7 +/- 10 cc/min) (p less than 0.05). The amount of debris formed was small with both probes. Vascular perforations were less frequent with the 2 mm probe (two of nine arteries) compared with the 1 mm probe (four of four arteries). Successful recanalization with flow rates expected to maintain vascular patency was achieved only with the 2 mm probe. Histologic studies at nonperforated sites demonstrated that the elastica of the artery appeared to be preserved whereas the overlying plaque and underlying media were thermally disrupted. This suggests that the elastic tissue acts as an optical window allowing the argon beam to go through it without causing morphologic damage. Except for fresh thrombus, atheromas including calcific plaque and old organized thrombus were readily vaporized. These results are encouraging for the use of the laser for vascular recanalization in humans.

Percutaneous laser thermal angioplasty: initial clinical results with a laser probe in total peripheral artery occlusions

A metal-tipped laser fibre was used during percutaneous angioplasty of femoral/popliteal or iliac artery occlusions in 56 patients. Primary success was achieved in 50 (89%) of these total occlusions, providing a channel for subsequent balloon dilatation. Before the procedure, 18 lesions had been judged untreatable by conventional angioplasty and four of the six failures were in these. Complications directly attributable to the laser probe were one case of vessel perforation and two cases of entry into vessel walls; these had no sequelae. Other acute complications were a distal thrombosis in a non-heparinised patient, requiring local streptokinase treatment, and two reocclusions and one transient peripheral embolic episode in the first 24 hours. The laser probe technique has potential for increasing the proportion of patients suitable for angioplasty.

Steerable fiberoptic catheter delivery of laser energy in atherosclerotic rabbits

Imprecision in guiding and positioning is a recurring problem with fiberoptic delivery of laser energy (E) in small arteries. Manipulation can produce mechanical perforation of the vessel, and noncoaxial alignment can result in thermal perforation at relatively low laser energy levels. A No. 4.5 French single-lumen catheter was designed to accommodate both a steerable guidewire and an optical fiber. It was passed, under fluoroscopic control, into the abdominal aorta in 18 atherosclerotic rabbits. Argon laser energy was delivered coaxially at three sites in each of 14 rabbits (total = 42 sites); four rabbits were controls. Laser power levels (1 to 6 W) and exposure times (20 to 60 seconds) were varied. Energy level in joules (J) was calculated for each exposure. Saline flush at 25 ml/min was delivered through the catheter during laser exposures. Angiographic or microscopic evidence of vessel perforation was observed at 10 sites (E = 174 +/- 108 J). Another six sites exhibited microscopic laser effect only, without evidence of vessel perforation (E = 155 +/- 91 J). The remaining 26 sites exhibited no effects of laser energy (E = 117 +/- 92 J). No angiographically visible perforation occurred with E less than 120 J. This study suggests that a fiberoptic catheter with steerable guidewire allows safer intravascular manipulation of optical fibers, improves coaxial alignment in the arterial lumen, and may permit substantial laser energy delivery into atherosclerotic arteries.

Use of pulsed energy delivery to minimize tissue injury resulting from carbon dioxide laser irradiation of cardiovascular tissues

The carbon dioxide (CO2) laser has been utilized for preliminary intraoperative cardiovascular applications, including coronary endarterectomy and ventricular endocardiectomy. CO2 lasers used for these applications have been operated in the continuous wave, chopped or pulsed mode at low peak powers. To evaluate the extent of boundary tissue injury, continuous, chopped and pulsed energy delivery of CO2 laser emission was used to bore through 192 5 mm thick myocardial slices in air. Continuous, chopped and pulsed delivery at a peak power of 500 W or less failed to eliminate light microscopic or ultrastructural signs of thermal injury. Only when a high energy CO2 laser (pulse energy 80 to 300 mJ, pulse duration 1 microseconds) was used at a peak power greater than 80 kW were all signs of thermal injury eliminated; furthermore, high peak power prevented thermal injury only when the beam was focused to achieve a peak power density greater than 60 kW/mm2. Under these conditions, pathologic findings were identical to those observed using excimer wavelengths. The results of these experiments indicate that: conventional CO2 lasers fail to minimize boundary tissue injury, elimination of thermal injury during intraoperative laser ablation requires that CO2 laser energy be focused to achieve a peak power density greater than 60 kW/mm2, and elimination of thermal injury can be achieved at a variety of wavelengths, provided that an appropriate energy profile is employed.