Coronary stents--implantation of foreign bodies into stenotic human coronary arteries: dream or nightmare?
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Angioplasty, Balloon, Coronary↗
Biomedical subjects
K K Haase
Publications and source records attributed to K K Haase.
Occurrence and magnitude of pressure waves during Er:YAG laser ablation of atherosclerotic tissue: comparison to XeCl excimer laser ablation.
BACKGROUND AND OBJECTIVE: Since excimer laser ablation has not shown advantages in comparison to conventional balloon angioplasty, the search for other laser light sources came up with the Er:YAG laser, operating at a wavelength of 2.94 microns. STUDY DESIGN/MATERIALS AND METHODS: Normal and atherosclerotic human vessel segments were irradiated in vitro, using pulsed Er:YAG laser systems. The laser beam was either focused onto the tissue in air or delivered via a fibre system onto the tissue being immersed in saline. Needle-type hydrophones were used for pressure pulse detection. RESULTS: Er:YAG laser irradiation results in effective tissue ablation of normal and calcified atherosclerotic vessel segments. In comparison to excimer lasers, ablation rates can be increased by a factor of 5 to 10 at least. Er:YAG laser ablation is also associated with a generation of pressure waves. On calcified plaque, the acoustic signals differ significantly from those on normal tissue. Histological tissue analysis reveals small zones of discoloration and tissue fissures that are found 100-200 microns lateral to the crater edge, depending on the energy density used. CONCLUSION: Er:YAG lasers generate pressure waves that are comparable to excimer laser ablation. Er:YAG lasers, however, show a markedly improved ablation efficiency, which may favour these systems as effectively cutting, less traumatic tools for removal of atherosclerotic plaque.
Aortic Diseases↗
Ablation characteristics of arterial vessel walls irradiated with the pulsed dye laser--an analysis of variance.
BACKGROUND AND OBJECTIVE: Since most clinical laser angioplasties require the use of over-the-wire delivery systems, we studied the effects of pulsed dye laser energy (504 nm, 1.4 microseconds on arterial vessel walls in combination with a multifiber catheter system. MATERIAL AND METHODS: Postmortem arterial segments (n = 368) were exposed under blood or saline. Laser pulses (n = 100-800) were transmitted via 9F-multifiber-catheters, at energy densities of 3-16 J/cm2. Ablation characteristics revealed by histologic examination and morphometry were analyzed by multiple analysis of variance. RESULTS: Ablation occurred more frequently in saline compared to blood. Below an energy density of 10 J/cm2 ablation occurred in saline only. Specimens irradiated under blood showed only thermal changes at 10 J/cm2. In saline, 92% of normal, 88% of fibro-fatty and 60% of calcified tissue showed ablation at 13 J/cm2. The average ablation threshold in saline was about 3-4 J/cm2 per pulse for normal tissue, 5 J/cm2 for fatty plaques, and 8-9 J/cm2 for calcified plaques. In blood, the average ablation thresholds did not differ significantly between the different stages of arteriosclerosis (12 J/cm2 for normal tissue, 11 J/cm2 for fatty plaque, and 10 J/cm2 for calcified tissue). Carbonization and vacuolization were seen regularly at energy levels > or = 13.4 J/cm2. CONCLUSIONS: Selective ablation of arteriosclerotic tissue with the pulsed dye laser could not be found. Further investigation is needed before an effective ablation of arteriosclerotic arterial tissue can be expected.
Arteries↗
[Coronary laser angioplasty: clinical value and experimental progress].
From 1988 to 1995, approximately 10,000 patients with coronary artery disease have been treated using excimer laser angioplasty. All data underline the feasibility and safety of this technique. However, coronary excimer laser angioplasty has been performed as a stand-alone procedure in a minority of patients, only, either due to an insufficient angiographic result, or due to complications such as abrupt vessel closure, severe dissection or perforation. Clinical and angiographic follow-up studies have also documented that excimer laser angioplasty does not reduce the incidence of restenosis following the coronary intervention. Experimental results underline the importance of pressure waves and bubble formations, which can cause additional vessel wall trauma despite thermal injury. Promising new laser devices should offer high ablation rates with only minimal thermal and acoustic tissue injury. It is expected that such laser devices will emit in the mid-infrared spectrum of light.
Angioplasty, Laser↗
Double-blind comparison of the acute effects of two relevant doses of oral nicorandil on central hemodynamics, left ventricular function, and myocardial contractility.
Nicorandil is a nicotinamide derivative with potent vasodilator properties. Oral and sublingual administration of this compound in patients with coronary artery disease resulted in a predominant reduction of afterload and a small decrease in left ventricular preload. The effects of nicorandil in different doses on contractile left ventricular (LV) function, however, are not well defined. The aim of the present study was to assess the effects of nicorandil on hemodynamics, left ventricular volume and function, as well as the LV contractility index dP/dt measured by Millar-tip manometers. A total of 16 patients with coronary artery disease were included in this study. After diagnostic coronary angiography and ventriculography, the patients randomly received either 10 or 20 mg of oral nicorandil. The hemodynamic parameters, cardiac output, and LV end-diastolic and systolic pressures were determined after 15, 30, and 60 minutes, and a second angiogram was performed 60 minutes after administration. The predominant effect was a decrease in the mean aortic pressure with a concomitant decrease in the peripheral arterial resistance. Clinically relevant changes in aortic pressure, systemic vascular resistance, and rate-pressure product, however, were documented only after oral administration of 20 mg nicorandil, as opposed to minimal changes in the 10 mg group. LV volume and cardiac output were not changed significantly. LV contractility remained unchanged during the observation period. The hemodynamic profile of this compound is dose-dependent afterload reduction without a change in contractility. Because there was no concomitant increase in heart rate, calculated oxygen consumption was reduced, especially in the higher dose group.
Adult↗
Intracoronary ultrasound following excimer-laser angioplasty. An in-vitro study in human coronary arteries.
UNLABELLED: To study the ablation effects induced by excimer laser coronary angioplasty (ELCA), we examined 41 segments of nine isolated coronary arteries. An electronic intracoronary ultrasound device (ICUS: 20 MHz, 3.5F, Endosonics) was positioned coaxially within the vessel. Angioplasty was performed using a 1.7 mm ELCA catheter (Spectranetics) which was placed in the lumen and directed vertically onto the intimal surface of the vessel (fluence: 10-50 mJ.mm-2). The laser catheter was removed after each lasing cycle to allow the stepwise evaluation of the morphological effects of ELCA and to avoid reaching the adventitia. Ultrasound images were compared with the corresponding histological specimens. In all cases, the ablation site could be correctly identified by ICUS. No penetration of the adventitia was seen at histology. Ablation depth was 0.31 +/- 0.18 mm as determined by histology and 0.34 +/- 0.18 mm as determined by ultrasound; the diameter of the crater was 0.63 +/- 0.21 mm, and 0.75 +/- 0.16 mm, respectively, and wall thickness was 0.68 +/- 0.18 mm, and 0.83 +/- 0.20 mm, respectively. A statistical relationship between ultrasonic and histology measurements was only found, however, for assessment of wall thickness (r = 0.71). CONCLUSIONS: The identification of small ablation effects by ICUS was possible with great accuracy and ELCA could be performed without penetration of the adventitial layers. However, exact quantification of the crater dimensions was not possible due to limitations of the axial and lateral resolution. Thus, for the guidance of ELCA by ICUS a further improvement in the resolution capabilities of ICUS devices is mandatory.
Angioplasty, Laser↗
Prolonged proliferative response of smooth muscle cells after experimental intravascular stenting.
The purpose of this experimental in vivo study was to determine the time course of smooth muscle cell proliferation early and late after intravascular stenting compared to conventional balloon angioplasty in normal vessels. A balloon expandable 2.0 mm tantalum Strecker stent was placed in the right carotid artery of 33 male New Zealand White rabbits after they had been fed a 0.5% cholesterol diet for 28 days. In addition, balloon angioplasty was performed in 27 of the animals; 19 contralateral vessels served as controls without treatment. The vessels were excised at 7, 14, 28, 42 or 90 days after treatment. During the final 18 h before the rabbits were killed, bromodeoxyuridine (BrdU) was applied and proliferating cells were detected by using a monoclonal antibody against BrdU. In histological cross sections the proportion of cells undergoing DNA synthesis was determined. Analysis was performed separately in the intimal and medial layers. Additionally, the area adjacent to the stent wire was compared with the intermediate area. Smooth muscle cells were identified by alpha-actin staining. Intimal wall thickness increased from 23 +/- 28 microns (control group without intervention) to 323 +/- 84 microns within 42 days after stenting (P < 0.01), and to 81 +/- 82 microns at day 42 after balloon angioplasty (P < 0.05). However, between 42 and 90 days following stent implantation a significant (P < 0.05) decrease in neointimal thickness was observed (90 days: 215 +/- 15 microns).(ABSTRACT TRUNCATED AT 250 WORDS)
Angioplasty, Balloon↗
Formation of pressure waves during in vitro excimer laser irradiation in whole blood and the effect of dilution with contrast media and saline.
Pressure waves during excimer laser ablation of vascular tissue may be responsible for complications of coronary excimer laser angioplasty. In this experimental study, pressure waves were measured during excimer laser irradiation in blood and contrast media using a polyvinilidenefluoride hydrophone. At a distance of 4 mm lateral to the tip of a 1.7 mm multifiber laser catheter, excimer laser irradiation in blood resulted in a linear increase of peak pressures from 1,365 +/- 165 kPa at 30 mJ/mm2 to 2,866 +/- 404 kPa at 60 mJ/mm2. In contrast media, peak pressure increased from 3,172 +/- 573 kPa (30 mJ/mm2) to 5,763 +/- 467 kPa (60 mJ/mm2). Contrast media and saline were added to blood. At a concentration of 60% contrast in blood, a 3.4 fold increase of peak pressures was documented as compared to pure blood. Further increase of the concentration did not result in higher pressure waves. Concentrations of saline in blood of 90% and 96% reduced the peak pressures by 16% and > 50%, respectively, as compared to pure blood.
Angioplasty, Laser↗
Accumulation of macrophages in the arterial vessel wall following experimental balloon angioplasty.
Smooth muscle cell (SMC) proliferation is a key event in the development of restenosis after balloon angioplasty, and it is thought that macrophages play an important role in the complex process of activation of SMCs after vascular injury induced by balloon angioplasty. The study was designed to determine the time course of the accumulation of macrophages in the intimal layer following experimental balloon angioplasty. To determine the extent and time course of the accumulation of macrophages after experimental balloon angioplasty, an intimal atheroma was produced by repeated weak electrical stimulation of the right carotid artery of 45 male New Zealand White rabbits. Additionally, the animals received an 0.5% cholesterol diet during the 28 days of plaque development. Transluminal balloon angioplasty was subsequently performed. At 3, 7, 14, 21, 28 and 42 days after balloon treatment the vessels from at least five animals from each group were excised and analysed for the presence of macrophages using immunocytochemical techniques. In one group of five animals plaque development occurred without subsequent balloon angioplasty; the animals were killed after 21 days (sham group). SMCs were identified by immunohistological staining of alpha-actin. Intimal thickening increased after dilatation from 137 +/- 62 microns (control group without balloon treatment) to 244 +/- 47 microns in the 42 days after angioplasty (P < 0.05). The percentage of macrophages in the intimal layer displayed a significant increase (P < 0.01) at 14 days after angioplasty (9.1 +/- 4.3% vs 2.0 +/- 1.7% in the control group).(ABSTRACT TRUNCATED AT 250 WORDS)
Angioplasty, Balloon↗
Occurrence, extent, and implications of pressure waves during excimer laser ablation of normal arterial wall and atherosclerotic plaque.
Ablation of atherosclerotic plaque and normal arterial wall was performed using a Xenon-Chloride Excimer laser with a wave-length of 308 nm and a pulse duration of 115 ns. The light was transmitted via a 600 microns bare fibre and adjusted to an energy density of 3.5J/cm2. The acoustic signals generated by the laser pulse were measured with two types of hydrophones consisting of polyvinylidenefluoride with active diameters of 0.3 mm and 0.5 mm and recorded on a dual channel digital storage oscilloscope using either a 0.5 m coaxial cable or a broadband fibre-optic transmission system. Tissue was retrieved from nine cadaver human aortas and macroscopically classified as either normal or calcified atherosclerotic plaque. Histological analysis (Haematoxylin eosin, elastica van Gieson, and immunohistochemical staining) was carried out after the experiments to verify the macroscopic diagnosis and to correlate the acoustic responses with the tissue characteristics. For normal arterial wall, maximum peak pressure was 1.28 MPa +/- 0.85 MPa, rise time 163 ns +/- 43 ns, and pressure increase 8.2k Pa +/- 5.4k Pa/ns. For calcified, atheromatous segments, a maximum peak pressure of 2.02 MPa +/- 1.16 MPa, a rise time of 69.9 ns +/- 25.8 ns, and a pressure increase of 32.3 kPa +/- 21.3 kPa/ns was found. Statistical analysis showed a significant shorter rise time (P < 0.0001) and a higher pressure increase (P < 0.0001) for calcified tissue in comparison to normal arterial wall, whereas maximum pressures alone did not allow a differentiation of tissue characteristics. Several hundred kPa are generated during Excimer laser ablation.(ABSTRACT TRUNCATED AT 250 WORDS)
Acoustics↗
In vitro evaluation of ablation parameters of normal and fibrous aorta using smooth excimer laser coronary angioplasty.
A modified excimer laser energy delivery system was used to irradiate 100 segments of normal and fibrous aorta in vitro. The laser beam was scanned into 8 fiber bundles consisting of 50 fibers each resulting in a reduction of the applied pulse energy. The total repetition rate was increased to 150 Hz in order to keep the repetition rate per fiber bundle close to 20 Hz and to minimize thermal injury. The results demonstrate that effective ablation (etch rate per 8 pulses > 2.0 microns) occurred at an energy fluency of 50 mJ/mm2 in both normal and fibrous aorta. Tissue damage (carbonization, tissue separation, fissures, cracks, and vacuolization) was in a range of 100 +/- 28 to 152 +/- 30 microns for normal aorta and in a range of 57 +/- 35 to 110 +/- 39 microns for fibrous aorta. We conclude that effective ablation of normal and fibrous human aorta can be achieved by the application of smooth excimer laser coronary angioplasty. This improvement of excimer laser technology may result in a reduction of shock wave- and cavitation-induced damage leading to a reduction of tissue injury. However, this awaits further in vitro and in vivo confirmation.
Angioplasty, Laser↗
Effect of exercise on valvular resistance in patients with mitral stenosis.
OBJECTIVES: This exercise study assessed the relation between valvular resistance and flow in patients with mitral stenosis. BACKGROUND: Valvular resistance has been proposed as an alternative measure of stenotic valvular lesions, which is speculated to remain stable under changing hemodynamic conditions. METHODS: In 35 of 40 patients with pure or predominant mitral stenosis, continuous wave Doppler measurements of the mitral stenotic jet were possible at rest and during supine bicycle ergometry. Simultaneously, transvalvular flow was assessed by thermodilution technique. For calculation of valvular resistance, the mean mitral valve pressure gradient was determined according to the simplified Bernoulli equation and divided by transvalvular flow. Additionally, effective mitral valve area was calculated according to the continuity equation method, dividing flow by the mean diastolic flow velocity. RESULTS: Valvular resistance was 65 +/- 32 dynes.s.cm-5 at rest and increased to 82 +/- 43 dynes.s.cm-5 at 25 W (p < 0.001). The most prominent increase in valvular resistance (rest to 25 W 63 +/- 28 to 95 +/- 48 dynes.s.cm-5, p < 0.001) was found in those patients who had no or only a moderate (< 20%) change in effective mitral valve area. In contrast, valvular resistance remained constant (67 +/- 36 vs. 70 +/- 32 dynes.s.cm-5) in patients with a significant (> or = 20%) increase in mitral valve area with exercise. CONCLUSIONS: In patients with mitral stenosis, the exercise-induced changes in valvular resistance are heterogeneous. This is the result of the variable response of mitral valve area to an increase in flow. In the individual patient, mitral valve area can significantly increase, a factor that has to be taken into account when interpreting the hemodynamic relevance of the obstruction. Calculated valvular resistance is flow dependent and has no advantage over valve area calculations for quantifying mitral stenosis.
Adult↗
[In vitro studies of shock wave effects during ablation of normal and atherosclerotic vascular wall by excimer laser].
Ablation of atherosclerotic plaque and normal arterial wall was performed using a xenon-chloride-excimer laser with a wavelength of 308 nm and a pulse duration of 115 ns. The light was transmitted via a 600 micron fiber and adjusted to an energy density of 3.5 J/cm2. The acoustic signals generated by the laser pulse were measured with hydrophones consisting of polyvinylidenefluoride with active diameters of 0.3 mm and recorded on a dual-channel digital storage oscilloscope using either a 0.5 m coaxial cable or a broadband transmission system. From 19 cadavers human aortic tissue segments were excised and macroscopically classified as either normal or calcified atherosclerotic plaque. Approximately 500 measurements were performed in saline and blood each. Histological analysis was carried out after the experiments to verify the macroscopic diagnosis and to correlate the acoustic responses with the tissue characteristics. For "normal" arterial segments, maximum peak pressure was 1.25 MPa +/- 0.85 MPa, rise time 163 ns +/- 43 ns, and pressure increase 8.2 kPa +/- 5.4 kPa/ns in saline. For calcified, atheromatous segments a significantly higher maximum pressure (2.20 MPa +/- 1.16 MPa), a significantly shorter rise time (69.9 ns +/- 25.8 ns), and a significantly higher pressure increase (32.3 kPa +/- 21.3 kPa/ns) was found in saline (p < or = 0.0001). In blood, maximum peak pressure was 1.29 MPa +/- 0.43 MPa, rise time 93.3 ns +/- 27.7 ns, and pressure increase 14.6 kPa +/- 5.2 kPa/ns for "normal" arterial segments. Maximum peak pressure (2.28 MPa +/- 0.63 MPa) and pressure increase (32.8 kPa +/- Pa/ns) were significantly higher for calcified tissue segments.(ABSTRACT TRUNCATED AT 250 WORDS)
Angioplasty, Balloon, Laser-Assisted↗
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.
Angioplasty, Laser↗
Ultrafast imaging of tissue ablation by a XeCl excimer laser in saline.
To determine the temporal evolution of laser induced tissue ablation, arterial wall specimens with either hard calcified or fatty plaques and normal tissue were irradiated in a 0.9% saline solution using a XeCl excimer laser (wavelength 308 nm, energy fluence 7 J/cm2, pulse width 30 ns) through a 600 microns fused silica fiber pointing perpendicular either at a 0.5 mm distance or in direct contact to the vascular surface. Radiation of a pulsed dye laser (wavelength 580 nm) was used to illuminate the tissue surface. The ablation process and the arising bubble above the tissue surface were recorded with a CCD camera attached to a computer based image-processing system. Spherical cavitation bubbles and small tissue particles emerging from the irradiated area have been recorded. The volume of this bubble increased faster for calcified plaques than for normal tissue.
Angioplasty, Laser↗
In vitro and clinical feasibility study with an over-the-wire delivery system for pulsed dye laser angioplasty.
The suitability of a pulsed dye laser (504 nm) in experimental and clinical angioplasty was investigated. In an experimental study, the ablation thresholds were 3 J/cm2 +/- 8 (mean +/- standard deviation) for fibrofatty plaque and 25 J/cm2 for calcified tissues under saline. At a radiant exposure of 10 J/cm2 the etch rates were 1.7 microns per pulse +/- 0.3 for media, 2.8 microns/pulse +/- 0.4 for normal intima, and 3.9 microns/pulse +/- 1.1 for fibrofatty plaque (P less than .05). Pressure wave effects with a separation of tissue layers were predominantly localized at the internal elastic lamina. Thermal injury with vacuolations extended 15 microns +/- 6 into adjacent tissue. For clinical study, laser-assisted balloon angioplasty was performed in 10 patients (64 years +/- 14) with occlusions of peripheral arteries using a 9-F multifiber ring catheter. Lesion length ranged from 2 to 12 cm (mean, 7 cm). Laser angioplasty with an 80 mJ/pulse decreased the mean stenosis from 100% to 58% +/- 12% (P less than .005). The ankle-brachial index rose from a median of 0.48 to 0.88 (P less than .001). In 33% of patients, there were subintimal dissections after laser angioplasty. After a mean follow-up of 10.2 months, the overall clinical success was 70% with a primary patency of 78%. The over-the-wire approach with a pulsed dye laser may constitute a safe and feasible tool in laser angioplasty.
Angioplasty, Laser↗
Success rate and incidence of restenosis following coronary excimer laser angioplasty: results of a single center experience.
The initial single center experience of percutaneous coronary excimer laser angioplasty is described for the first three series of 147 patients. Sixty patients were treated with a prototype 1.4-mm laser catheter, 40 patients with improved transmission devices, and the third series of 47 patients with an increased pulse width of the laser system allowing improved energy transmission. In 17 patients (12%) laser angioplasty could not be initiated due to inability to cross the lesion with the guidewire or to place the catheter coaxially within the vessel. In 32 patients (58%) of series 1, 11 patients (31%) of series 2, and 17 patients (43%) of series 3, additional balloon dilatation following laser treatment was necessary due to vessel closure (24%) or due to an insufficient angiographic result (35%). There was one death in series 1 (2%) and 2 (3%) each, one perforation in series 2 (3%), two transmural myocardial infarctions in series 1 (4%), and one myocardial infarction in series 2 (3%). During the 6-month follow-up period one patient in series 2 (2%), and one patient in series 3 (3%) died. Angiographic restenosis was found in 22, 12, and 11 patients of series 1 (40%), 2 (34%), and 3 (27%), respectively. No patient developed a transmural myocardial infarction. Thus, percutaneous coronary excimer laser angioplasty can be performed as a safe and feasible procedure in patients with coronary artery disease.(ABSTRACT TRUNCATED AT 250 WORDS)
Aged↗
Vascular injury and time course of smooth muscle cell proliferation after experimental holmium laser angioplasty.
BACKGROUND: In vitro experiments have shown that holmium laser energy can effectively ablate even calcified plaque in human arterial vessels. Because high-energy densities from holmium lasers can easily be transmitted through quartz fibers, this solid-state laser has been suggested as an alternative intraluminal treatment of atherosclerotic plaque. METHODS AND RESULTS: To develop an intimal plaque, 35 New Zealand White rabbits underwent electrical stimulation of their right carotid artery for 28 days. Subsequently, in 25 rabbits, holmium laser angioplasty (wavelength, 2.12 microns; pulse duration, 150 microseconds; energy density, 350 mJ/mm2) was performed. To study the morphological results, the vessels were excised after 7, 14, 28, and 42 days. Cross sections were analyzed in regard to laser-specific injury. Staining of alpha-actin was used to identify smooth muscle cells (SMCs). After bromodeoxyuridine labeling, the extent of proliferation (number of cells undergoing DNA synthesis) was determined by using a monoclonal antibody. Holmium laser ablation resulted in an initial decrease of the numbers of intimal cell layers in the early group (7 days after treatment: 5 +/- 1 cell layers with 76 +/- 39 microns; control: 13 +/- 3 cell layers with 144 +/- 44 microns). Quantification of SMCs undergoing DNA synthesis in the intima (control: 51 +/- 19 cells/mm2) showed a significant increase of labeled cells after 7 (216 +/- 74 cells/mm2, p = 0.003) and 14 days (281 +/- 139 cells/mm2, p = 0.011). Integrity of the internal elastic lamina was disrupted in all animals after intervention. Seven and 14 days after treatment, a considerable reduction of medial cell nuclei was found in 10 of 12 animals. SMC proliferation in the medial layer was increased within the first 2 weeks after laser ablation (168 +/- 113 cells/mm2; control: 8 +/- 4 cells/mm2; p = 0.023). Six weeks after holmium laser angioplasty, SMC proliferation had returned to control levels in the intima and remained increased in the medial layer. This proliferative response resulted in a significant increase of intimal thickening within 6 weeks after laser ablation (30 +/- 6 cell layers, 375 +/- 97 microns resp.; p = 0.001 each). CONCLUSIONS: Holmium laser treatment leads to considerable vessel wall injury and results in SMC proliferation in the intimal and medial layer with a maximum of proliferative activity within the first 2 weeks. Subsequently, this results in considerable intimal and medial hyperplasia within 6 weeks after treatment.
Angioplasty, Laser↗