Responses of atherosclerotic aorta to argon laser

Lasers have been advocated to resect atherosclerotic plaques in the cardiovascular system, yet little information is available regarding the effects of laser on the range of occlusive lesions seen in the peripheral arterial tree. This study was conducted to assess the risk of perforation in human cadaveric aorta involved with variable degrees of atherosclerosis. Ten fresh segments of atherosclerotic human aorta were graded for extent of atherosclerosis, then subjected to argon laser energy within 48 hours. Using air as the conduction medium and with the fiber tip 2 or 5 mm from the vessel wall, the argon laser was applied to matched calcified and non-calcified arteries at 3.0-7.0 W and 10.0–13.5 W with energy density identical for matched pairs. Results were compared among segments which were normal in appearance or had only fatty streaks grossly with those with gross regional wall calcification. The mean penetration time (T) for calcified and non-calcified lesions at low and high power outputs was compared. Mean time to perforation and range of time necessary to produce perforation were greater in calcified than non-calcified segments at all power levels employed. These data suggest that atherosclerotic lesions vary in their response to argon laser. The presence of calcium may preclude resection of some plaques and protect against wall perforation.     

Acute effects of argon laser on human atherosclerotic plaque

Although the laser has been demonstrated to vaporize coronary artery plaque, there is little information about its ability to resect or vaporize the range of plaques present in peripheral vessels. This study attempts to determine the ability of the argon laser to resect all grades of atherosclerotic plaque, the risk of perforation during plaque resection, the effects on surrounding arteries, and the effect of different transmission media (air, saline solution, and blood) on the delivery of laser energy to the vessel. Seventy-five adult human cadaveric aortic specimens with a range of atherosclerosis from grossly normal artery to extensive calcification with ulceration were exposed to variable energy densities (200 to greater than 20,000 J/cm2) within 48 hours of harvesting. Specimens were examined grossly for the visual effects of laser and microscopically after preparation with hematoxylin-eosin, trichrome, and/or Verhoeff's elastin stains. Our results indicate that normal arteries and noncalcified plaques absorb laser energy and are vaporized. As the atherosclerosis becomes more complex with calcification, calcified regions are not vaporized and cannot be resected. In normal arteries and noncalcified plaque, perforation times were less than 5 seconds. Where palpable calcification was present in atherosclerotic lesions, average perforation time was doubled. In some vessels areas of calcification prevented wall perforation, but areas of subintimal hemorrhage perforated rapidly because of the selective absorption of laser energy by the red color of hemorrhagic tissue. These results remain the same when saline solution is used as a transmission media, although the amount of energy required to achieve the effects is increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

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

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

Factors influencing the ablation of atherosclerotic plaque with the argon laser

This paper describes the ablative effect of argon laser light, delivered fibre optically in vitro, on 234 segments of atherosclerotic human aorta. Variables such as energy density, type of atheroma and immersion media were taken into account. All irradiated specimens were subsequently submitted to histological examination and crater volumes in mm³ were derived from micrometer measurements made at light microscopy. Results showed: (1) a linear relationship between energy dose and crater volume in fibrous atheroma; (2) significantly greater surrounding tissue damage in the higher energy dose groups; (3) a lower dose response in calcified tissue than in fatty streaks or fibrous atheroma; (4) immersion of tissue in blood during ablation resulted in a significantly greater dose response than immersion in plasma or saline, and the corresponding surrounding tissue damage was greatest under blood. Thus, argon laser light is both effective and predictable in response when ablating atheromatous tissue, and the efficiency of the process depends on the immersion medium. The degree of surrounding tissue damage depends on the energy dose.     

XeCl laser ablation of atherosclerotic aorta: optical properties and energy pathways.

The energetics of 308-nm excimer laser irradiation of human aorta were studied. The heat generation that occurred during laser irradiation of atherosclerotic aorta equaled the absorbed laser energy minus the fraction of energy for escaping fluorescence (0.8-1.6%) and photochemical decomposition (2%). The absorbed laser energy is equal to the total delivered light energy minus the energy lost as specular reflectance (2.4%, air/tissue) and diffuse reflectance (11.5-15.5%). Overall, about 79-83.5% of the delivered light energy was converted to heat. We conclude that the mechanism of XeCl laser ablation of soft tissue involves thermal overheating of the irradiated volume with subsequent explosive vaporization. The optical properties of normal wall of human aorta and fibrous plaque, both native and denatured were determined. The light scattering was significant and sufficient to cause a subsurface fluence (J/cm2) in native aorta that equaled 1.8 times the broad-beam radiant exposure, phi o (2.7 phi o for denatured aorta). An optical fiber must have a diameter of at least 800 microns to achieve a maximum light penetration (approximately 200 microns for phi o/e) in the aorta along the central axis of the beam.     

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.     

Penetrating atherosclerotic ulcers of the aorta

Purpose: This study investigates the natural history and optimal imaging modality of penetrating atherosclerotic ulcers of the aorta.Methods: We reviewed our experience with 29 penetrating ulcers in 18 patients. Computed tomography (17 patients), magnetic resonance imaging (nine patients), and aortography (five patients) were used for diagnosis and follow-up. Patients were typically elderly (average age 74 years) and had hypertension and coronary artery disease. Ulcers were most common in the distal descending thoracic aorta (31%) and were characterized by a discrete ulcer crater (100%) and thickened aortic wall (89%). Modes of presentation included chest or back pain in four patients, distal embolization in two patients, and abnormal chest radiography results in one; the remaining were incidental findings.Results: Follow-up was available in ten patients with 17 ulcers from 1 to 7 years. Recurrent pain occurred in two patients, recurrent embolization occurred in one patient, and seven patients remained symptom free. Progression to saccular pseudoaneurysm occurred in five ulcers, and fusiform aneurysm occurred in two ulcers. Two ulcers were associated with an increase in aortic diameter, and nine ulcers did not change. There were no cases of aortic dissection or rupture in the follow-up period. There were no deaths and only one patient underwent resection.Conclusion: The natural history of penetrating atherosclerotic ulcers is one of progressive aortic enlargement, with saccular and fusiform aneurysms the result if follow-up is sufficient. Aortic dissection, aortic rupture, and embolization can also occur but are less common. Contrast-enhanced computed tomography is the primary imaging modality. (J VASC SURG 1994;19:90-9.)     

Penetrating atherosclerotic ulcers of the aorta

BACKGROUND: Penetrating aortic ulcers burrow into the aortic wall and can have fatal consequences. Although they were first described as long ago as 1934 they have only recently been recognized as a distinct pathological entity. METHOD: A review of the current literature was undertaken, based primarily on an English language Medline search with secondary references obtained from key articles. RESULTS: Penetrating aortic ulcer is principally a disease of elderly hypertensive men. It may run a benign course or may produce complications such as aortic rupture, embolization and aneurysm formation. Presentation may be identical to that of classical aortic dissection, but the distinction is important because an ulcer may be more likely to cause rupture. CONCLUSION: Open surgical repair has been the 'gold standard' of treatment but endovascular stenting is an attractive option in this group of frail patients.     

Application of the argon laser to dentistry.

A review was conducted to determine specific areas of application of the argon laser to dentistry. When appropriate, comparisons between the argon laser and other treatment methods were made. It was concluded that the argon laser has applicability in composite resin placement, in enamel and dentin bonding procedures, in preventive dental therapies, and in endodontic procedures.     

Hybrid one-stage approach to extensive atherosclerotic aneurysm of thoracoabdominal aorta

We report a 62-year-old man with an atherosclerotic Crawford type II aneurysm involving both common iliac arteries who underwent surgical revascularization of the visceral vessels and renal arteries from the ascending aorta and subsequent endovascular aneurysmal exclusion. Computed tomography imaging at 2 years showed complete exclusion of the aneurysm throughout the thoracoabdominal aorta, confirming the successful antegrade revascularization of visceral vessels and renal arteries. A hybrid approach to thoracoabdominal aneurysms using antegrade visceral and renal revascularization from the ascending aorta before endovascular repair is technically feasible and might constitute an attractive alternative to conventional surgical treatment.     

Using the argon laser to cut corneoscleral sutures

The Coherent 900 argon blue-green laser can be used to cut pigmented corneoscleral sutures without damage to the overlying tissue. This is useful in tight corneoscleral sutures causing undue corneal astigmatism.     

Pigmentation-dependent side effects to copper vapor laser and argon laser treatment

Background and Objective: Melanin is a limiting factor for obtaining beneficial results in dermatological treatment of vascular malformations. The aim of our study was to establish a relation between pretreatment skin pigmentation and the occurrence of side effects. Study Design/Materials and Methods: Thirteen human volunters selected to have a varying degree of skin pigmentation were laser-treated on the inside of the brachium with an argon laser (AL, 488 nm and 514.5 nm) and a copper vapor laser (CVL, 578 nm), both connected to a Hexascan. Total exposure areas were 1.26 cm² and beam diameters were 1 mm. Three intensities were used, 0.7, 1.0, and 1.3 W. Pulse duration was 200 ms, resulting in fluences of 17.8, 25.5, and 33.1 J/cm². Pretreatment skin pigmentation was objectified by skin reflectance measurements. Results: At 1, 2, and 6 months after laser treatment, significant correlations were demonstrated between pretreatment skin pigmentation and laser-induced pigmentary changes and scar formation. At the 6-month assessment, the AL induced significantly higher scores of clinically evaluated scar formation as compared with the CVL (1.0 and 1.3 W/spot) and tended to induce higher clinical scores of pigmentary changes (not significant, ns). Conclusions: We recommend skin pigmentation to be taken into consideration in dermatological laser treatment of vascular malformations. © 1995 Wiley-Liss, Inc.     

Penetrating atherosclerotic ulcers of the thoracic aorta

Penetrating ulcer of the thoracic aorta is defined as an atherosclerotic lesion of the descending thoracic aorta with ulceration that penetrates the internal elastic lamina, allowing hematoma formation in the media. There is controversy whether this lesion differs from classic acute type III aortic dissection, based on its location, radiographic findings, natural history, and recommended therapeutic approach. Of 47 patients with a diagnosis of aortic dissection seen at our hospital during a 2-year period, five patients had clinical and radiographic findings of penetrating ulcer. Each of the five patients had characteristic computerized tomographic (CT) findings and two patients had angiographic confirmation. In all patients CT showed subintimal hemorrhage, aortic wall enhancement, absence of a double lumen, and contrast extravasation through the ulceration. In both patients who underwent angiography, ulceration, subintimal hematoma, and absence of a false lumen were demonstrated. The clinical presentation in four patients simulated acute aortic dissection or expanding thoracic aneurysm. The other patient, who was normotensive, did not have symptoms referable to the thoracic aorta but was studied because of an abnormal chest x-ray film. None of these five patients required surgical intervention. All five patients were alive and free of symptoms at 6 months, 8 months, 14 months (two patients), and 30 months after the original diagnosis. Follow-up CT scans in four patients showed resolution of subintimal hematoma and some dilatation of the lumen but no progression to rupture or aneurysm. Other authors stress the importance of differentiating symptomatic penetrating atherosclerotic ulcers from acute type III aortic dissection because of the higher incidence of rupture of penetrating ulcers and therefore recommend early surgical intervention.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute penetrating atherosclerotic ulcer of the ascending aorta

A 67‐year‐old man presented with chest pain. Clinical examination revealed hypertension (160/90 mm Hg). Electrocardiogram indicated no acute coronary syndrome and cardiac enzymes were normal. Catheterization was performed owing to the patient’s continuing chest pain and ascending aortogram revealed irregular aortic wall. A computed tomography image showed the shape of penetrating ulcer. The patient was taken to the operating room and intraoperative examination confirmed the diagnosis of penetrating atherosclerotic ulcer (PAU). Coronary artery bypass graft and bovine pericardial patch repair of PAU was performed. A bovine pericardial patch was done as aortic root was heavily calcified and was easy to handle and more hemostatic.     

Rhinophyma treated by argon laser

Results are reported of rhinophyma treated by argon laser. The therapy is assumed to be based on two features: first, selective coagulation of the blood capillaries which cause redness of the nose and which feed the hypertrophic regions; second, direct coagulation shrinkage of the hypertrophic connective tissue. The therapy is simple, causes no noticeable discomfort, requires no (local) anaesthesia or admission, and can be performed more than once. Thirteen patients were treated, eleven men and two women. Systemic treatment could be stopped in all but one case (seven patients). Two out of ten patients still use resorcinol but at a reduced frequency. The general result is a smooth and more natural appearance of the nose without redness. Pustulosis has become an exception.     

Clinical aspects of ophthalmic argon laser

This paper reviews the historical events leading to the development of the ophthalmic laser. The formation of the argon laser beam and its biological effects on ocular tissues are outlined, with the major emphasis on the retinal and choroidal tissues. The clinical indications, contraindications, and complications of ophthalmic argon laser photocoagulation for the anterior segment as well as the posterior segment structures of the eye are also thoroughly discussed.     

Experimental studies on argon laser angioplasty

To evaluate the safety and efficacy of recanalization of the occlusive arterial diseases by Argon laser, we investigated the effects of the laser irradiation using bare-ended probe (BEP) and metal-tip probe (MTP) on human cadaveric aorta and canine femoral arteries with thrombotic occlusion. In case of the BEP, the incidence of perforation of the arterial wall was high as compared with the MTP. However, laser angioplasty with angioscopic guidance could reduce the perforation rate, and made it possible to observe the new channel recanalized by laser. In case of the MTP, it was confirmed that the smaller MTP showed higher tip temperature and was more effective on plaques under the same laser energy. Optimal laser energy for single ablation was from 15J to 25J in case of 2.0mm tip and from 30J to 40J in case of 2.5mm tip. Application of the MTP equipped with thermal feedback control system could avoid the excessive thermal damage in comparison with the conventional MTP. It was considered that optimal temperature of the MTP equipped with thermal feedback control system ranged between 200 degrees C and 300 degrees C. It was concluded that laser angioplasty would be a useful treatment for the occlusive diseases of the peripheral arteries.