Ablation Of Atheroma Research Articles

Forward viewing ultrasonic imaging catheter

A simple forward viewing ultrasound catheter includes one or more transducers (10) and an ultrasound mirror (14) supported by a bearing (12) in a sealed end of a catheter (16) with a drive cable (18) imparting relative motion to the transducer (10) and mirror (14) . The mirror directs ultrasound waves forward of the catheter. An optical fiber can be provided to direct a laser beam for ablation of atheroma while under guidance of simultaneous intravascular ultrasound.

Determining Light Dose for Photodynamic Therapy of Atherosclerotic Lesions in the Yucatan Miniswine

Purpose: To determine the light dose required for photodynamic therapy of atherosclerotic lesions in the miniswine. Methods: Aortic atherosclerosis was created in seven Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard for 7 weeks. Six animals received the photosensitizer PhotofrinR 2.5 mg/kg, while an additional swine received no drug. After 24 hours, the abdominal aorta was exposed and the aorta opened longitudinally in each animal. Three 1-cm spots were illuminated with energy densities of 60, 120, and 240 J/cm2 from an argon-pumped dye laser tuned to 630 nm with a laser output of 1 W. Four weeks later, the animals were killed, abdominal aortae removed, and intimal thickness determined by morphometry. Results: The percentage intimal thickness (mean ± SD) was 36.7 ± 27.1, 9.1 ± 5.0, and 6.4 ± 8.1 for the three energy densities, respectively. Although both 120 and 240 J/cm2 energy densities produced significant (p < 0.05) reduction in atheroma, considerable damage to the underlying media was also observed in the 240 J/cm2 group. Conclusions: A Photofrin dose of 2.5 mg/kg and 120 J/cm2 light are necessary for adequate ablation of atheroma while avoiding extensive medial damage.

Determining light dose for photodynamic therapy of atherosclerotic lesions in the Yucatan miniswine.

To determine the light dose required for photodynamic therapy of atherosclerotic lesions in the miniswine. Aortic atherosclerosis was created in seven Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard for 7 weeks. Six animals received the photosensitizer Photofrin 2.5 mg/kg, while an additional swine received no drug. After 24 hours, the abdominal aorta was exposed and the aorta opened longitudinally in each animal. Three 1-cm spots were illuminated with energy densities of 60, 120, and 240 J/cm2 from an argon-pumped dye laser tuned to 630 nm with a laser output of 1 W. Four weeks later, the animals were killed, abdominal aortae removed, and intimal thickness determined by morphometry. The percentage intimal thickness (mean +/- SD) was 36.7 +/- 27.1, 9.1 +/- 5.0, and 6.4 +/- 8.1 for the three energy densities, respectively. Although both 120 and 240 J/cm2 energy densities produced significant (p < 0.05) reduction in atheroma, considerable damage to the underlying media was also observed in the 240 J/cm2 group. A Photofrin dose of 2.5 mg/kg and 120 J/cm2 light are necessary for adequate ablation of atheroma while avoiding extensive medial damage.

Rotational coronary atherectomy after unsuccessful coronary balloon angioplasty

The clinical and angiographic outcome of patients undergoing rotational coronary atherectomy after unsuccessful balloon angioplasty was evaluated using quantitative angiographic methods to provide insight into this procedure's mechanism of benefit. During the study period, 41 patients (50 lesions) were referred for rotational atherectomy after standard balloon angioplasty was unsuccessful. After rotational atherectomy, percent diameter stenosis was reduced from 72 ± 14% to 41 ± 16% (p < 0.001); adjunct balloon angioplasty was performed in 44 lesions (88%), resulting in a 25 ± 17% final diameter stenosis (p < 0.001). The acute gain in minimal lumen diameter was 1.20 ± 0.59 mm. In lesions needing adjunct balloon dilatation, lesion stretch was 73 ± 27%, and elastic recoil was 22 ± 18%, with no variation by etiology of the initial balloon failure. Overall angiographic success (<50% residual diameter stenosis) was obtained in 49 lesions (98%). Procedural success, defined as <50% residual diameter stenosis and the absence of major in-hospital complications (death, Q-wave myocardial infarction or emergency bypass surgery), was obtained in 37 of 41 procedures (90%); complications developed in 3 patients (7%), including 2 who needed emergency bypass surgery after development of delayed abrupt closure. It is concluded that rotational coronary atherectomy may be used in selected patients when standard balloon angioplasty is unsuccessful. Its mechanism of benefit appears related, at least in part, to changes in plaque compliance resulting from partial atheroma ablation.

Experimental and clinical results with a pulsed dye laser for angioplasty

We investigated a pulsed 504 nm dye laser at a pulse duration of 1.44 μ and a pulse rate of 10 Hz for its angioplasty capabilities. Laser energy was delivered via 9 F multi-fiber ring catheters. Our experimental data showed effective ablation of atheroma and disruption of calcified plaques at an energy fluence of 9.5 J/cm2 under saline and blood. Histologically, there was only minimal thermal injury to adjacent tissues. Irregular tissue borders after radiant energy exposure of 12.7 J/cm2, under blood, provide strong evidence for ablation by a shock-or pressure-wave mechanism.

Enhancement of pulsed-dye laser arlation of arterial tissues with blood medium: Effects of laser-induced shock waves

The influence of blood medium on tissue ablation by a pulsed dye laser and its selectivity for atheroma were investigated. The role of shock waves on tissue ablation was also evaluated. Normal and atherosclerotic human aortas were irradiated by a 480 nm pulsed dye laser activated at 5 Hz. The laser was coupled with a single 0.2 mm fiber (Uni-gulde) (40 mjoules/pulse) or a multifiber catheter (14× 150 μm) (100 mjoules/pulse). Shock waves were measured using a fluid-filled catheter connected to a strain gauge manometer. With the Uni-guide, pulse-dye lasing resulted in greater ablation of atheroma in blood (11.6 × 10 −3 mm 3/joule, p <0.001 versus atheroma measured in saline and normal tissue in blood) followed by normal tissue in blood (2.5 × 10 −3mm 3/joule), atheroma in saline (1.71 × 10 −3mm 3/joule, p < 0.05 versus normal tissue in saline), and normal tissue in saline (0.54 × 10 −3 mm 3/joule). With the multifiber catheter, laser ablation was the greatest in atheroma in blood (0.55 ± 0.26 mm 3/joule p < 0.001 versus atheroma in saline and normal tissue in blood), followed by normal tissue in blood (0.27 ± 0.12 mm 3/joule), atheroma in saline (0.14 ± 0.15 mm 3/joule, p < 0.001 versus normal tissue in saline), and normal tissue in saline (0 mm 3/joule). The ablation efficlency of the muitifiber catheter was greater than that of the Uni-gulde ( p < 0.0001) At 100 mjoules/pulse, shock waves were the greatest for atheroma in blood (1.47 mm Hg, p < .005 versus normal tissue in blood, p < 0.001 versus atheroma in saline), followed by 0.28 mm Hg in normal tissue in blood, 0.09 mm Hg for atheroma in saline, and 0 mm Hg for normal tissue in saline. The magnitude of shock waves was correlated with ablation officiency ( r = 0.64). In the same specimens ( n = 5), shock waves were 0 at 25 mjoules/pulse, 0.56 mm Hg/pulse at 50 mjoules/pulse, and 1.45 mm Hg at 100 mjoules/pulse ( p < 0.05 versus 50 mjoules/pulse). Heavily calcifled plaques were also ablated with the laser. The craters created in blood occasionally showed irregular edges; however, no extensive thermal injury was observed. In conclusion, we determined: (1) pulsed dye laser at 480 nm selectively ablates atheromatous tissue; (2) blood medium enhances the ablation efficiency of pulsed-dye laser; (3) ablation efficiency is correlated with the magnitude of shock waves; (4) calcified plaques can be ablated by a pulsed-dye laser; and (5) a multifiber catheter is more sultable for laser angloplasty than the Uni-guide.

Acute effects of a copper vapour laser on atheroma

The acute histological effects of a commercially available copper vapour laser (CVL) on normal and atherosclerotic arterial wall were studied. The multi-cyclic CVL produces a quasi continuous wave output at 511 nm (green) and 578 nm (yellow) [green/yellow ratio 2∶1]. Tissue craters were produced in segments of normal and atherosclerotic human femoral artery using a maximum of 8 J of laser energy delivered with a bare 1 mm quartz fibre in contact and perpendicular to the tissue. Crater dimensions and ablation volumes were determined histologically using an optical graticule. Ablation of atheroma was almost three times more efficient than ablation of normal arterial wall (p<0.001). A narrow zone of vacuolization and coagulative thermal damage lined the crater margins suggesting a predominantly photothermal ablative mechanism. In conclusion, selective ablation of atheroma using low power copper vapour laser light is possible. The CVL is an attractive alternative to the argon ion laser because of its low running costs and applicability to other medical disciplines. Therefore, its potential application in laser angioplasty merits further study, preferably using a modified optical fibretip delivery system.

Book reviews

This book is an introduction to the clinical use of lasers in cardiovascular disease. It is, however, devoted almost entirely to one type of laser device, the metal-tipped laser probe, although a brief last chapter describes alternative devices for delivering laser energy to atherosclerotic plaques. The use of lasers for ablation of atheroma is still experimental, but it is a rapidly developing field.

Selective ablation of atheroma by pulsed Holmium YAG laser

Selective ablation of atheroma by pulsed Holmium YAG laser

Laser‐Tissue Interactions With the Pulsed Dye Laser

The laser‐tissue interaction of the pulsed dye laser was assessed. The histological appearance of the craters showed precise margins with no evidence of collateral thermal tissue damage. The ablation of soft yellow atheroma was consistently about two‐ to threefold that of normal wall, but fibrous white atheroma was resistant to laser energy, and was ablated less than normal wall. The maximum probe tip temperature in air was 197°C, but there was relatively little heating of the coronary artery wall during lasing, and this was minimized by saline perfusion at low flow rates. Lasing produces up to 1012 irregularly shaped debris particles per liter. Debris from thrombus and normal aorta caused significant platelet aggregation in vitro, but atheromatous debris did not. In conclusion, the characteristics of the pulsed dye laser are suitable for intravascular lasing, but selective ablation of atheroma was not achieved.

Fluorescence-guided laser-assisted balloon angioplasty in patients with femoropopliteal occlusions.

In 12 patients (aged 64 +/- 10 years) with femoropopliteal occlusions (1-27 cm; average, 8.4 cm length) that could not be recanalized by standard guidewire-balloon angioplasty techniques, percutaneous laser-assisted balloon angioplasty was performed by use of a new fluorescence-guided dual-laser system. Plaque detection by 325-nm laser-excited fluorescence spectroscopy provided real-time feedback control to a 480-nm pulsed dye laser (2-microseconds pulses) for atheroma ablation. By means of a common 200-microns optical fiber, after diagnostic fluorescence sensing, computer algorithms directed a fire or no-fire signal (5 Hz) to the treatment laser for selective plaque removal. Laser recanalization (15-50 mJ/pulse) was successful in 10 of 12 patients; this procedure was followed by definitive balloon angioplasty in seven of 12 patients with increased ankle/arm indexes (from 0.60 +/- 0.12 at baseline to 0.84 +/- 0.11 after treatment, p = 0.0043). In laser and balloon angioplasty failures, all femoropopliteal occlusions were heavily calcified, and there were two mechanical guidewire perforations without clinical sequelae. Ablation of calcified lesions required higher pulse energies and greater total energy per centimeter of recanalized tissue (1,837 +/- 1,251 mJ/cm vs. 90 +/- 39 mJ/cm, p = 0.0036). Fluorescence spectroscopy (n = 219 sites) was helpful in flush occlusions and correctly identified plaque, underlying media, and thrombus by changes in fluorescence intensity, shape, and peak position. Thus, when fluorescence-guided laser angioplasty was used in a subgroup of patients refractory to standard angioplasty techniques, primary recanalization and subsequent balloon angioplasty of femoropopliteal occlusions was successful in 83% and 58% of the patients, respectively. Importantly, treatment of heavily calcified lesions accounted for all of the failures and will require modified delivery systems to create larger primary channels and to increase catheter-tip control, which should improve clinical results in the future.

Laser thermal angioplasty probe (“hot tip”) temperature: Effects of flow

The temperature developed by the laser thermal ("hot tip") probe during arterial recanalisation is primarily dependent on the rate of energy delivery and the rate of dissipation to the surrounding medium. While higher probe tip temperatures enhance the efficacy of atheroma ablation, so too is the incidence of adverse effects increased. We studied the temperature developed in the probe tip in an artificial circulation using both saline and blood. In saline the peak probe temperatures were limited to 100 degrees C (boiling point), falling with each increment in flow. Small discrepancies in probes at different times and may be due to malalignment of the optical fibre-metal cap coupling, temperature measurement inaccuracy, tip insulation, or generator output instability. In blood, charring and clot formation insulated the tip raising the temperature (up to 700 degrees C within 5 seconds at 10 W) but also retarded dissipation of heat to the surroundings. The degree of clot and char formation was critical in determining subsequent thermal responses in any particular probe. The unknown rate and quantity of char buildup and changing blood flow during in vivo angioplasty are likely to be important obstacles to developing a reliable thermal feedback control system.

Human arterial surface fluorescence: Atherosclerotic plaque identification and effects of laser atheroma ablation

In vivo plaque recognition may be important for safe and precise intra-arterial atheroma ablation during laser coronary angioplasty. This study examined the feasibility and sensitivity of utilizing quantitative fluorescence spectroscopy and video-enhanced fluorescence imaging for plaque identification in atherosclerotic human necropsy arterial wall before and after laser atheroma ablation. With wide band (450 to 490 nm) blue light excitation, the 540 nm fluorescence intensity ratio of normal to diseased sites (n = 13) was 2.09 ± 0.82 (p < 0.001) and video fluorescence imaging provided enhanced delineation of atheroma surface characteristics.Continuous argon and pulsed excimer (308 nm) laser ablation of atheroma decreased fluorescence intensity ratios by 42 and 20% (p < 0.001), respectively (that is, from abnormal to nearly normal). Low power 325 nm laserexcited fluorescence spectroscopy from normal (n = 115) and abnormal (n = 146) necropsy sites revealed an average 45% decrease in atheroma fluorescence intensity (p < 0.0001) and changes in fluorescence spectra appearance that corresponded to plaque morphologic subtypes. Studies using a dual laser system combining 325 nm laser-excited fluorescence plaque recognition and a 480 nm pulsed dye laser for tissue ablation with common optical fibers demonstrated normalization of both fluorescence intensity and spectra appearance after laser atheroma ablation.Thus, in vitro analysis of surface arterial fluorescence by quantitative spectroscopy and video fluorescence imaging reliably differentiate plaque from normal tissue and may provide the feedback signal needed to activate a laser source for selective plaque removal.

Autofluorescence maps of atherosclerotic human arteries--A new technique in medical imaging

A new medical imaging technique for arterial walls based on laser-induced autoflnorescence spectroscopy is reported. The internal surface of isolated arteries with or without atherosclerosis is irradiated with an argon ion laser (458 nm) and the peak intensity of the excited autofluorescence spectrum is related to the composition of the arterial wall. The higher autofluorescence intensity in the range between approximately 480 and 630 nm for grossly calcified tissue compared to normal or noncalcified atherosclerotic tissue is used to produce maps of the arterial wall. These images delineate the calcified areas of the sample with good spatial resolution. If this technique can be adapted to the endoscopic visualization of arteries in vivo (angios, Copy), it could become an important tool for the diagnosis of atherosclerosis and for the monitoring of atheroma ablation during laser angioplasty.

Pulsed ultraviolet lasers and the potential for safe laser angioplasty

Endoscopic laser ablation of atheroma using continuous wave lasers is limited by imprecise control of thermal ablation, resulting in a crater that expands in width and depth, with thermal damage to adjacent normal tissue. We compared the gross and histologic effects of pulsed 308 mm excimer irradiation to continuous-wave Nd:YAG and Argon Ion laser irradiation, and pulsed 1,060 nm, 532 nm, 355 nm, and 266 nm laser irradiation in 205 atherosclerotic aortic segments. In contrast to the continuous-wave Nd: YAG, Argon Ion, and pulsed 1,060 nm, 532 nm, and 355 nm laser irradiation, which produced gross and histologic evidence of uncontrolled ablation, the 308 nm and 266 nm pulsed lasers induced incisions that conformed precisely to the beam configuration without gross evidence of thermal injury. The incision edges from these two lasers were histologically smooth and comparable to a scalpel incision. Our histologic findings suggest that rapid, precise endoscopic ablation of vascular and nonvascular tissue can be performed at these shorter pulsed wavelengths with very high precision with relatively little damage or risk to adjacent tissue.