Limitations, risks and complications of laser recanalization: a cautious approach warranted

Highly Nd3+-doped Y3Al5O12 crystal fiber tip for laser thermotherapy

Based on phonon relaxation, a 12-at. % neodymium-doped YAG (Y3AlrO12) crystal fiber tip has been developed for photothermal conversion. The near-cylindrical tip, with an average diameter of 0.68 mm and a length of 1.8 mm, is fabricated on a 0.65-mm-thick 220-mm-long pure YAG single-crystal fiber by laser-heated growth. Pumped by an 810-nm wavelength diode laser with a pump power of less than 2 W, the temperatures of the tip reach 725 degrees C in air, 78 degrees C in egg white, and 79 degrees C in porcine liver, with acceptable reproducibilities and thermal response times. The photothermal conversion efficiency of the doped tip is approximately 89%, and the high stability of the tip is also proved. Experimental results show that the doped fiber tip is promising for laser thermotherapy applications.

Experimental study on the early efficacy of excimer laser with adjunctive balloon angioplasty in dog's femoral artery

The effect of domestically-manufactured excimer laser with adjunctive balloon angioplasty in achieving revascularization and reduction of residual stenosis was assessed. 20 femoral arteries with thrombosis and occlusion from 12 dogs were subject to angiography. At first excimer laser angioplasty was done followed by balloon angioplasty. The diameter and residual stenosis of revascularized vessel were measured. The result showed that 17 out of 20 vessels (85%) were revascularized. The diameter of revascularized vessel by excimer laser were 1.22 +/- 0.14 mm, while residual stenoses were 54% +/- 5%. After adjunctive balloon angioplasty the diameter and residual stenoses were 2.04 +/- 0.16 mm and 20% +/- 7% respectively (P < 0.05 and P < 0.01). Complication in form of vasoperforation occurred in 3/20 vessels (15%). It is concluded that China- manufactured excimer laser angioplasty is effective when used for revascularization. While the reduction of narrowing and residual stenoses was enhanced after adjunction of balloon angioplasty. This method can be employed in treating peripheral occlusive disease effectively and safely.

Analysis of particle size generated during plaque ablation with a flashlamp pumped pulsed dye laser

PURPOSE

To examine debris size generated during in vitro plaque ablation by laser energy and estimate the risk of peripheral embolization following laser angioplasty.

METHODS

A flashlamp pumped pulsed dye laser of 480-nm wavelength was used to ablate calcified arteriosclerotic plaque, fibrous fatty plaque, and normal aortic wall on samples of human cadaver aortas. Each tissue sample was immersed in saline solution and treated with the same amounts of laser energy transmitted by a 320 microns-diameter glass fiber in direct tissue contact. The debris generated during plaque ablation was then separated from the supernatant and the particles were counted and analyzed for size.

RESULTS

Depending on the underlying type of tissue and the setting of laser energy, a wide range of particles with sizes between 5.3 mm2 and 64 microns 2 was found in samples. The largest particles were found after ablation of calcified atherosclerotic plaque, whereas fibrous, fatty plaque and normal aortic wall showed smaller particles and a lesser amount of debris.

CONCLUSION

Our study demonstrates that a considerable amount of debris is generated during laser angioplasty at 480 nm and that particle size is sufficient to cause potentially symptomatic embolic occlusions of mid- and small-sized peripheral arteries.

Comparison of the thermal tissue effects produced by aged sapphire and silica hemispherical tips

This study evaluated the performance of sapphire and fused silica hemispherical tips under the same exposure conditions. Lesions produced in the chicken breast and a blood field were sectioned for light and transmission polarizing microscopy. Lesion size and thermal damage area were recorded as a function of the tips accumulated exposure. The tips transmission was measured after every 1,000 J of exposure. Fused silica tips lasted for approximately 5,000 J and experienced significant surface and transmission deterioration. The sapphire hemispherical tips lasted for > 12,000 J with no surface and transmission deterioration. Lesions produced with the fused silica tips generally increased in depth with use, and depths of 6 mm were common. Lesions produced by the sapphire tips were subsurface spherical areas of coagulation with the tissue surface relatively intact. This difference in resulting lesions may be attributed to the higher thermal conductivity of sapphire.

The Bard Rotary Atherectomy System (BRAS): initial experience in patients with peripheral vascular disease

Sixteen patients with a mean age of 65.4 +/- 9.8 years and suffering from peripheral vascular disease underwent peripheral atherectomy using a new mechanical device--the BARD Rotary Atherectomy System (BRAS). The BRAS is an "over the wire" system that consists of a spiral guidewire and a handheld motor drive unit, which rotates at 1,500 rpm. Prior to the procedure angiography demonstrated the presence of 18 obstructions (1 tibial, 2 popliteal, 15 superficial femoral arteries) with a mean stenosis of 95.7 +/- 8%. Successful atherectomy was achieved in 16 of 18 lesions and resulted in an 89% immediate success rate and a significant (P less than 0.01) reduction of stenosis to 37.8 +/- 12.5%. There were no significant complications. The excised and removed material embedded over the spiral guidewire demonstrated the presence of fibrotic tissue, fatty lesions, and calcium deposits. Medial or adventitial layers were not present in the removed atherosclerotic material. Mean ABI was significantly (P less than 0.01) increased from 0.38 +/- 0.17 to 0.55 +/- 0.21 following atherectomy. Angiographic follow-up obtained in ten patients 8.8 +/- 5.2 months following the procedure demonstrated restenosis in six of those ten patients. The ABI at this time remained unchanged. These results demonstrated that the new BRAS mechanical atherectomy system is feasible and safe for recanalization of severely stenosed arteries in patients with peripheral vascular disease.

Assessing Photofrin uptake in atherosclerosis with a fluorescent probe: comparison with photography and tissue measurements

The purpose of this study was to assess Photofrin porfimer sodium (P*) concentration in atherosclerotic plaque (ASP) using a fluorescence detector (Fluoroprobe) compared with fluorescent photography and chemical extraction of P*. ASP was created in the aortoiliac segments of Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard diet for 7 weeks. At that time, swine were given P* I.V. in one of the following single dosages: Group I, 2.5; Group II, 1.0; or Group III, 0.5 mg/kg. Swine were sacrificed 24 hours later and aortoiliac and control carotid artery segments removed. Fluorescence was determined from these segments using photographic techniques, the Fluoroprobe, and a spectrofluorometer after chemical extraction. ASP were identified in all swine using photography and the Fluoroprobe. The intensity of fluorescence measured with the Fluoroprobe for Groups I to III was 1,098 +/- 524, 471 +/- 337, and 295 +/- 173 units, respectively (P < 0.01). The tissue concentration of P* in ASP from each group was 130.4 +/- 82.7, 10.0 +/- 1.2, and 9.1 +/- 0.6 ng/g, respectively (P < 0.01). There was a linear correlation between the fluorescence intensity measured with the Fluoroprobe and the extracted tissue concentration (r = 0.88, P < 0.0001). This study showed that a fluorescent detector such as the Fluoroprobe accurately detects the uptake of P* into atherosclerotic plaque.

Case report: formation of vessel aneurysm after stand alone coronary excimer laser angioplasty

Formation of aneurysms in coronary arteries can be observed following percutaneous transluminal balloon angioplasty but has not been reported previously after coronary excimer laser angioplasty in humans. Stand alone coronary excimer laser angioplasty was performed in a 49-year-old man with a 75% left anterior descending artery stenotic lesion and exertional angina, documenting a good angiographic result postintervention. Control angiography 6 months after the procedure revealed an aneurysm distal to a 90% restenosis in the area of ablation.

Electrical impedance of layered atherosclerotic plaques on human aortas

Electrical impedance measurements were performed on 13 atherosclerotic human aortic segments at 67 measuring spots in order to determine whether or not on the basis of these data a distinction can be made between atherosclerotic lesions and normal tissue. Stenosis localization and guidance of interventional techniques could be among the applications of an impedance measuring technique implemented on a catheter system. The experimental results, obtained with a two-electrode measuring technique, show that the apparent resistivity of an atherosclerotic spot does not necessarily deviate much from the resistivity of normal tissue. This is clarified by histology which shows that the majority of lesions has a surface layer of connective, fibrous tissue having almost similar conducting properties as the normal arterial wall. For gaining a deeper understanding of the way in which the measured data come about, a physical model of an atherosclerotic lesion is presented and confronted with the data. Both experimental data and theoretical considerations lead to the conclusion that only when the superficial fibrous layer is absent or very thin in relation to the size of the measuring electrode, the measured resistivity at a lesion is much higher than at normal spots. This occurs as a consequence of the high ohmic properties of the calcified or lipid deposits in the atherosclerotic lesion.

Laser-assisted versus mechanical recanalization of femoral arterial occlusions

A randomized clinical trial was performed to test the hypothesis that a laser-heated probe is superior to standard techniques to reopen occluded femoral arteries. Twenty patients were treated with a standard guidewire and balloon dilation method. In a second group of 20 patients, the laser probe was initially used as a nonheated mechanical device. If the probe was unsuccessful in mechanically reopening the artery, an Argon laser was activated to heat the probe. The mean length of occlusion was 15.9 +/- 10.3 cm. The success rate for the laser probe was 15 of 20 (75%), which was not significantly different from the standard method, 19 of 20 (95%). Most of the success in the laser-probe group was due to the probe's mechanical properties. The laser probe was successful as a cold, mechanical device in 13 of 15 (87%) arteries. It was necessary to heat the probe in 5 patients. When heated, the laser probe assisted recanalization in 2 but perforated the artery in 3 cases. The results of this randomized trial do not support the hypotheses behind the use of the thermal laser probe. The laser probe functions primarily as a mechanical device. The thermal activation does not significantly improve the success rate without increasing the risk of perforation. This small additional benefit does not justify the large cost of current thermal laser devices. This controlled study also demonstrates a higher success rate in long occlusions than previous reports of mechanical balloon recanalization. This is due to a combination approach of retrograde and anterograde probing of the occluded segment.

Isotope limb blood flow measurement in patients undergoing peripheral laser angioplasty

A technique of isotope limb blood flow (ILBF) measurement employing Technetium-labelled human albumin and a gamma camera, was used to assess limb perfusion in 19 patients undergoing percutaneous laser angioplasty, both before and one month after treatment. Twenty-three limbs with femoro-popliteal occlusions ranging in length from 3-35 cm (median 8 cm) were recanalized using an Nd-YAG laser and sapphire tipped optical fibre. Primary angiographic success was achieved in 19 lesions of which 6 re-occluded within the first month, and 13 remained patent with relief of symptoms. Clinically successful procedures were associated with a large increase in ILBF. However, normal blood flow was restored in only 54% of limbs. There was a slight decrease in limb perfusion after failed laser angioplasty but this was not statistically significant in this small series. Furthermore, there was no clinically apparent circulatory compromise, or need for urgent surgical bypass in failed cases. We conclude that ILBF is a useful means of assessing patients undergoing laser angioplasty, particularly for detecting small flow changes in patients who are unable to complete a standard exercise test. Its use can be recommended for assessing blood flow changes following other forms of limb revascularization.

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.

Peripheral laser angioplasty with sapphire tip

To improve the result of peripheral laser recanalization (less perforation with wider tunnels of vaporization), we used the technique of sapphire laser angioplasty. A Nd:YAG laser with continuous emission was connected to a catheter with a 600 mum fiber and a sapphire probe to its extremity (1.8-3 mm in diameter). Treatment was performed on 127 patients with severe stenosis or occlusion of peripheral arteries (iliac, femoral, or popliteal arteries). Recanalization was obtained in 102 cases (80%) and was further embellished by balloon dilatation. The rate of success decreased proportionally with the length of occlusions (93% for 3 cm, 33% for 15 cm and more). Most failures were due to wall perforation or wall entry of the probe; passage of the sapphire tip was rarely blocked by the occlusion. At follow-up, 26.4% of arteries were reoccluded after 2 months.

IN CONCLUSION

laser angioplasty with a sapphire tip can totally recanalize occluded arteries with low rate of failure and complications.

Experimental analysis of sapphire contact probes for Nd-YAG laser angioplasty

Laser angioplasty may offer percutaneous recanalization of occluded vessels where conventional guidewire and balloon techniques fail. Metal laser thermal angioplasty probes may, however, cause excessive thermal damage due to high tip temperatures (greater than 400.C). Therefore, contact probes made from artificial sapphire crystal designed for general laser surgery are currently being evaluated for use in laser angioplasty with continuous wave Nd-YAG energy. The sapphire modifies the laser energy in various ways, and this paper examines the physical characteristics of five types of rounded sapphire probe (SMTR, MTR, MTRL, OS, LT) and how these properties are affected by clinical usage. The laser beam profile emitted by these probes demonstrates a focal spot 1-2 mm in front of the tip. However, the forward transmission of Nd-YAG energy through the sapphires varied (SMTR, 85%; MTR, 83%; MTRL, 75%; OS, 54%; LT, 69%). Probe heating occurs owing to energy absorption within the sapphire. The surface temperature of the sapphires was measured in air by infrared thermography and the hottest region within the probes localized by an isothermographic technique. At energy settings used clinically (20 J, 10 watts for 2 s) the SMTR, MTR, and MTRL probes exhibited higher temperature rises (94-112.C) than the OS and LT probes (30.C), and heating was localized to the front surface of the former probes. Peak sapphire temperatures remained lower than those of metal probes even at higher energies. After clinical use, the MTR probe demonstrated reduced transmission, beam defocusing, and increased heating, due to surface pitting. Thus, recanalization with sapphire probes occurs by a combination of photothermal and contact thermal effects that are localized to the probe tip and may reduce the degree of thermal injury associated with metal probes. Understanding these basic properties is important to the application and development of contact probes for laser recanalization.

Percutaneous arterial recanalization

The current status of new techniques for percutaneous arterial recanalization, including laser, thermal and mechanical angioplasty techniques, is described. The reported results, potential advantages and possible future developments are discussed.

Experimental ultrasonic angioplasty: disruption of atherosclerotic plaques and thrombi in vitro and arterial recanalization in vivo

To investigate the use of high energy ultrasound as an alternative energy for angioplasty, an experimental ultrasonic angioplasty device was developed. The device was studied in two bioassay systems: an in vitro system for the disruption of atherosclerotic plaques and thrombi and an in vivo system for the recanalization of occluded canine femoral arteries. In vitro, sonication efficiently reduced the size of the plaques. Atheromatous plaques (n = 11) disrupted at a rate of 21 +/- 8 s/cm2; complicated plaques (n = 14) disrupted at a rate of 132 +/- 45 s/cm2 (p less than 0.001). Histologic examination revealed that the disruption of the plaques took place without concurrent damage to the media or adventitia. Ninety percent of the disrupted plaque debris had a diameter of less than 20 microns and was composed primarily of cholesterol monohydrate crystals. Solid thrombus (n = 5) weight was reduced from 1.6 +/- 0.2 to 0.4 +/- 0.1 g (p less than 0.0001) after 20 s of sonication. In vivo, sonication resulted in recanalization in all seven arteries tested in seven dogs. The obstruction was reduced from 93 +/- 11% to 18 +/- 7% (p less than 0.001). On histologic examination, the arterial wall injury index was found to be 1.56 +/- 0.42 in the test arteries compared with 1.37 +/- 0.47 in the control arteries (p = NS). The disruption of atherosclerotic plaques and thrombi, together with the efficient recanalization of the occluded arteries, demonstrates the potential of ultrasound angioplasty as a catheter-based technique for angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of lasers in the management of peripheral vascular disease

Although it has been almost twenty-five years since the first studies of McGuff et al, who employed the laser for atheroablation, problems still require resolution. The various laser wavelengths from ultraviolet through visible to infrared have been employed for atheroablation. The laser's greatest appeal and the most spectacular results have been in reopening channels in totally occluded vessels. The laser's greatest problem has been damage of the arterial wall and even perforation. The purpose of this presentation is to clarify the present status of available lasers for the treatment of peripheral vascular disease of the lower extremities. To this end, the initial experience with angioscopically guided laser-assisted angioplasty with a new hybrid laser probe is reported.

Choice of lasers for laser angioplasty

Thrombi in test-tube, intraarterial thrombi and pig aorta wall were in vitro irradiated with continuous CO2 laser, short pulsal and ultrashort pulsal YAG laser (with pulse-width of 10 ns and 40 ps, respectively) and their double frequency laser and excimer laser with a wave-length of 308 nm and pulse-width of 20 ns. Their effect of vaporizing and ablating (photodecomposing) thrombi and their thermal injuring effect on adjacent tissues were compared and assessed in order to select optimal laser with little thermal injuring and more rapid vaporizing or ablating thrombi effect for laser angioplasty. The experimental results showed that excimer laser, ultrashort pulsal YAG laser and its double frequency laser, and double frequency laser of short pulsal YAG laser, with laser beam and blood vessel kept in a coaxial position, can effectively vaporize or ablate thrombi without thermal injury to vessel wall. So they may be used for laser angioplasty. Of them, especially, excimer laser and double frequency laser of ultrashort pulsal YAG laser have short wave-length and high peak power, and more effectively ablate thrombi than others, so they proved to be optimal lasers for laser angioplasty.

Peripheral percutaneous transluminal laser angioplasty in humans: in vitro investigations and clinical results with a novel laser catheter system

Percutaneous transluminal laser angioplasty has become an accepted method of treatment of peripheral arterial occlusive disease. To minimize the risk of arterial wall perforation during laser angioplasty, a novel laser catheter system was developed. In 113 obliterated postmortem human arteries the perforation rate was 0.9%. The mean degree of stenosis was reduced from 89 +/- 9% before, to 53 +/- 11% after laser irradiation. Clinical Nd:YAG laser angioplasty was performed in 19 patients suffering from peripheral arterial occlusive disease. The Fontaine stage improved in 16 patients; in no case did it deteriorate. The mean degree of stenosis was reduced by laser angioplasty from 91 +/- 12% to 31 +/- 19%. A further reduction down to 13 +/- 18% was achieved by subsequent percutaneous transluminal balloon angioplasty. The systolic Doppler ankle-arm pressure gradient was improved from 0.58 +/- 0.26 to 0.89 +/- 0.25. In 7 patients microembolisms were detectable on the final angiogram. There was no acute reocclusion and no perforation. Within a follow-up period of 12 months, four restenoses were diagnosed by digital subtraction angiography. On average, the Doppler index was 0.75 +/- 0.32.

Laser-induced autofluorescence of human arteries

A new technique for imaging the intimal surface of arteries through optic fibers has been devised. With the aid of an optical multichannel analyzer, we recorded in real time fluorescence spectra during excitation of the arterial surface with an argon ion laser. Spectral parameters were used to detect atherosclerotic plaques and to discriminate normal tissue from lipid rich and calcified atheromas. By digitizing relative intensity values and the ratios of the peak at 550 nm to that at 520 nm into a gray scale, we generated pseudocolor maps of the arterial wall of 10 human aortas. Specific color distributions were congruent with the distribution of calcified tissue visualized by soft x-ray radiography and the distribution of lipid delineated by staining with Sudan IV. Thus, bidimensional maps obtained by laser spectroscopy can be used to identify the presence and composition of atherosclerotic lesions. Fluorescence imaging may prove to be an important application of laser techniques for the diagnosis and treatment of atherosclerosis.

Electromagnetic field focusing (EFF) probe for intravascular endarterectomy. Preliminary feasibility study

Vaporization of atheromas in 10 human aorta segments immersed under flowing blood in vitro were done using the EFF probe. No increase in packed cells of the flowing blood following atheroma vaporization were noted suggesting absence of post vaporization debris. No damage to the aorta underlying the vaporized atheroma was noted on light microscopy suggesting well localized vaporization process. This study suggests that EFF probe might be a safe tool for intravascular endarterectomy.

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.

Coronary angioscopy during cardiac catheterization and cardiac surgery

Coronary angioscopy (CA) was performed in 30 patients (pts) during cardiac catheterization (Group 1) and in 11 pts during coronary bypass surgery (Group 2) using ultrathin fiberoptic angioscopes (phi 1.2-1.8 mm). For percutaneous CA (Group 1) the angioscope was introduced through a 9F guiding catheter from the femoral artery. The viewing field was cleared by flushing Ringer's solution and short-time occlusion of the coronary ostium by the guiding catheter. In Group 2 CA was performed retrogradely from the distal arteriotomy and through the bypass vein during flushing with cardioplegic solution. In Group 1 in 17/30 pts the coronary artery could be successfully examined by CA. In 13 pts the obstruction was eccentric and irregular shaped. In 2/5 pts, in whom CA was performed successfully pre and post balloon dilatation, CA after PTCA revealed an intimal rupture without clinical or angiographical signs of the intimal dissection. In Group 2 in 9/11 pts good visualization of stenoses could be achieved. At the obstruction site CA revealed thrombi in 3 pts and ulcer in 1 pts. In contrast to angiography, which estimates the lumen diameter of a segmental lesion, CA gives information about the luminal shape and the underlying substance of the obstruction (e.g. atheroma, thrombus, ulceration). The main problems in percutaneous CA are the insufficient intraluminal guidance, the insufficient depth of view of the angioscopes, and the limited examination time.

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.

Effects of simultaneous viewing and vaporization of plaques using the steerable, laser-heated metal cap in the atherosclerotic monkey model

A steerable, fiberoptic catheter coupled to a laser light guide tipped with a metal cap was used. Four monkeys fed an atherogenic diet for 7-8 years were angiographed and were found to have extensive mural plaque in the iliac arteries. Plaque sites in these monkeys were vaporized using the laser-heated metal cap. Energies of 1.5-9 Joules were employed. Application of the energy was tangential of perpendicular to the plaque. Lased sites were examined histologically at 24 hr or at 3 months after treatment. No effect was seen at 1.5 Joules. Three to six Joules tangentially produced a superficial lesion that extended into the tunica intima. Six Joules perpendicularly produced a burn into the tunica adventitia, with damage to the vasavasorum. Nine Joules tangentially produced a burn into the tunica media. Three months after treatment, this lased site showed no stenosis or aneurysm formation.

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.

Selective ablation of atheromas using a flashlamp-excited dye laser at 465 nm

Ablation of human atheromas with laser pulses that had only a small effect on normal artery tissue was shown in vitro in air and under saline using 1-mu sec pulses at 465 nm from a flashlamp-excited dye laser. At this wavelength, there is preferential absorption in atheromas due to carotenoids. The threshold fluence for ablation was 6.8 +/- 2.0 J/cm2 for atheromas and 15.9 +/- 2.2 J/cm2 for normal aorta tissue. At a fluence of 18 J/cm2 per pulse, the ablated mass per unit of energy ranged from 161 to 370 micrograms/J for atheromas and from 50 to 74 micrograms/J for normal aorta tissue. Ablation products consisted of cholesterol crystals, shredded collagen fibers, and small bits of calcific material. Most debris was less than 100 micron in diameter, but a few pieces were as large as 300 micron. High-speed photography of ablation in air suggested explosive ejection of debris, caused by vapor formation, at speeds on the scale of 300 m/sec. Histological analysis showed minimal thermal damage to residual tissue. These data indicate that selective laser ablation of atheromas is possible in vitro.

A new model to study quantitative effects of laser angioplasty on human atherosclerotic plaque

A new model for analyzing the major effects of the use of any laser angioplasty system is described. Changes in any of the six major determinants of effect (energy, duration, wavelength, medium, absorption, geometry) can be evaluated. In this report a neodymium: yttrium aluminum garnet (Nd:YAG) laser was used to make 408 laser exposures in vitro on segments of human cadaveric atherosclerotic aorta. Energy, medium (air, human blood, perfluorochemical and saline), geometry and duration were varied. The depth and width of the resultant plaque craters were measured. A large amount of exposure to exposure variability was found in all groups of experiments, even when conditions were held as constant as possible in this rigidly controlled laboratory setting. This variability is attributable to differences in energy absorption by the plaque. Changes in media and fiber optic tip to plaque distance also markedly altered exposure outcome. For example, the average depth of the hole created by a 15 W, 2 second blast with the fiber tip adjacent to the plaque in blood was 1.7 +/- 0.1 mm (n = 27), but the range was between 0.5 and 2.7 mm. Under the same conditions, except with the fiber tip 1 mm away from the plaque, the average hole depth was 0.4 +/- 0.1 mm (n = 12) and the range was 0.0 to 1.7 mm. The use of this model to analyze the major determinants of lasing effects in different laser angioplasty systems should help to select the best conditions for lasing and allow assessment of the variability of outcome.

Applicability of laser to assist coronary balloon angioplasty

Severe atherosclerotic obstructed coronary artery disease (CAD) may preclude passage of a balloon catheter for transluminal coronary angioplasty (TCA). Since lasers have been shown to effectively vaporize CAD plaque, the initial application of laser to effect a lumen large enough to accommodate the angioplasty catheter for further dilatation was explored. Eleven postmortem human CAD segments which did not permit passage of a 1.33 mm shaft diameter angioplasty catheter were studied. Argon laser radiation (14 to 90 J) transmitted via 400 micron core diameter quartz fiber onto the stenotic channel of 0.58 mm created a vaporized lumen of 1.77 mm (mean increase of 1.31 +/- 0.25 mm, p less than 0.001). The laser procedure allowed the balloon angioplasty catheter to be pushed into the stenosis. TCA was then performed (7 atm, 45 seconds) and expanded the channel to 2.12 mm (additional mean increase of 0.38 +/- 0.07 mm, p less than 0.001). In terms of percent luminal narrowing, laser radiation reduced obstruction from 80% to 45% (mean difference of -38.7 +/- 4.6%, p less than 0.001), and TCA caused a further decrease to 37% (mean difference of -9.3 +/- 1.9%, p less than 0.001). Thus, in tight atherosclerotic lesions, the laser may be useful in creating an initial opening enabling the placement of the balloon angioplasty catheter which, in turn, can further dilate the lased stenotic coronary lumen.