Ablation Of Atherosclerotic Plaque Research Articles

A New Conformal Penetrating Heating Strategy for Atherosclerotic Plaque

(1) Background: A combination of radiofrequency (RF) volumetric heating and convection cooling has been proposed to realize plaque ablation while protecting the endothelial layer. However, the depth of the plaque and the thickness of the endothelial layer vary in different atherosclerotic lesions. Current techniques cannot be used to achieve penetrating heating for atherosclerosis with two targets (the specified protection depth and the ablation depth). (2) Methods: A tissue-mimicking phantom heating experiment simulating atherosclerotic plaque ablation was conducted to investigate the effects of the control parameters, the target temperature (Ttarget), the cooling water temperature (Tf), and the cooling water velocity (Vf). To further quantitatively analyze and evaluate the ablation depth and the protection depth of the control parameters, a three-dimensional model was established. In addition, a conformal penetrating heating strategy was proposed based on the numerical results. (3) Results: It was found that Ttarget and Tf were factors that regulated the ablation results, and the temperatures of the plaques varied linearly with Ttarget or Tf. The simulation results showed that the ablation depth increased with the Ttarget while the protection depth decreased correspondently. This relationship reversed with the Tf. When the two parameters Ttarget and Tfwere controlled together, the ablation depth was 0.47 mm-1.43 mm and the protection depth was 0 mm-0.26 mm within 2 min of heating. (4) Conclusions: With the proposed control algorithm, the requirements of both the ablation depth and the endothelium protection depth can be met for most plaques through the simultaneous control of Ttarget and Tf.

Numerical evaluation of high-intensity focused ultrasound- induced thermal lesions in atherosclerotic plaques.

The aim of this study is to estimate the effects of some acoustic parameters on thermal lesions of atherosclerotic plaques in high-intensity focused ultrasound (HIFU) fields. A fluid-solid thermal coupling model is presented for describing the temperature elevation and thermal ablation of atherosclerotic plaque. A finite element approach is used to solve the coupling equations in cylindrical coordinates. The model considers the effect of the wall thickness of large arteries. The extent of the tissue lesion is determined by the accumulated thermal lesion with Arrhenius integral equation at each location. The results show the lesion size of atherosclerotic plaque is positively correlated to the excited frequency and acoustic output power with heating time. The computational model indicates HIFU may present a novel option for thermal ablation of atherosclerotic plaques with a completely non-invasive treatment paradigm.

Abstract 12082: Radiofrequency Ablation of the Atherosclerotic Plaque: A Safety and Feasibility Study in an Atherosclerotic Rabbit Model

Introduction: Angiogenesis from the vasa vasorum plays a key role in atheroprogression and plaque vulnerability. Immature neovessels are prone to leakage, hence facilitating additional lipid and inflammatory cell accumulation and increasing intraplaque hemorrhage risk. Hypothesis: Heat-generating radiofrequency ablation (RFA) safely reduces vasa vasorum, decreases inflammatory cell influx and stabilizes the plaque. Methods: Thirteen New-Zealand White rabbits on a 0.5% cholesterol-enriched diet were subjected to balloon denudation of the infrarenal aorta. After 13 weeks, either the proximal or distal half of the infrarenal aorta was exposed to transluminal RFA, the untreated half served as an intra-individual control. Optical coherence tomography (OCT) was performed directly after RFA. Results: Within 24 hours after RFA, no plaque ruptures or adverse events were observed by OCT or histology. Treated regions showed widespread decellularization of intimal, medial and (to a lesser extent) adventitial layers, which were recellularized after 7 and 28 days. Vasa vasorum density was not different between both regions at short-term (24 hours; RFA 19.8±5.1 vs. control 29.2±8.3/mm 2 ; p=0.15) or long-term follow-up (7 days; 39.1±11.5 vs. 41.7±8.6/mm 2 ; p=0.81 and 28 days; 46.4±13.4 vs. 38.5±6.6/mm 2 ; p=0.06). After 7 days, treated regions were comparable to control areas with respect to plaque size (5.6±1.7 vs. 5.5±1.5mm 2 ; p=0.62), intimal collagen (34.6±11.9 vs. 32.7±13.0%; p=0.22) and macrophage content (14.3±2.8 vs. 18.5±5.8%; p=0.32). RFA-treated regions did show a major decrease in intimal smooth muscle cell (αSMA) content (1.8±0.4 vs. 18.0±5.9%; p=0.038), which remained decreased after 28 days (6.8±3.8 vs. 12.6±1.6%; p=0.020). Again, after 28 days no differences were observed in plaque area (4.6±0.9 vs. 4.4±1.1 mm 2 ; p=0.46), intimal collagen (39.2±9.1 vs. 40.3±12.4%; p=0.85) or macrophage content (13.2±2.5 vs. 12.6±2.0%; p=0.73). Conclusion: Radiofrequency ablation of the rabbit atherosclerotic plaque is safe and leads to a major reduction in αSMA content, but does not affect other aspects of plaque stability over time. It may thus serve as a therapeutic option for major (re)stenosis in peripheral arterial disease.

Subsurface ablation of atherosclerotic plaque using ultrafast laser pulses.

We perform subsurface ablation of atherosclerotic plaque using ultrafast pulses. Excised mouse aortas containing atherosclerotic plaque were ablated with ultrafast near-infrared (NIR) laser pulses. Optical coherence tomography (OCT) was used to observe the ablation result, while the physical damage was inspected in histological sections. We characterize the effects of incident pulse energy on surface damage, ablation hole size, and filament propagation. We find that it is possible to ablate plaque just below the surface without causing surface damage, which motivates further investigation of ultrafast ablation for subsurface atherosclerotic plaque removal.

History of Lasers in Medicine

While the history of laser begins in 1951, the first medical application is reported by Goldman in 1962. In cardiovascular surgery McGuff first used a Ruby-Laser in 1963 for the experimental ablation of atherosclerotic plaques. After a long time of investigations and new developments in laser technology first clinical applications were performed by Choy and Ginsburg in 1983. Since that time the effectiveness of laser angioplasty in coronary and peripheral vessel is investigated in several clinical trials and first results are encouraging, so that laser is about to find its place in the treatment of cardiovascular diseases too.

Thermal Ablation of Atherosclerotic Plaque by a Quantum Cascade Laser in the 5.7 µm Wavelength Range for Less-Invasive Laser Angioplasty

Thermal Ablation of Atherosclerotic Plaque by a Quantum Cascade Laser in the 5.7 µm Wavelength Range for Less-Invasive Laser Angioplasty

Image-guided Tumor Ablation: Standardization of Terminology and Reporting Criteria

The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency (RF), laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes. The intent of this standardization of terminology is to provide an appropriate vehicle for reporting the various aspects of image-guided ablation therapy.

Image-guided Tumor Ablation: Standardization of Terminology and Reporting Criteria

The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency (RF), laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes. The intent of this standardization of terminology is to provide an appropriate vehicle for reporting the various aspects of image-guided ablation therapy.

Laser coronary angioplasty: history, present and future.

The efficacy of percutaneous transluminal coronary angioplasty (PTCA) is limited by remaining plaque tissue and the development of restenosis. It has been demonstrated that the restenosis rate is low if a large lumen diameter is achieved after coronary intervention. Debulking of coronary stenoses is a concept to increase the luminal diameter after intervention. Laser angioplasty debulks coronary stenoses by ablation of atherosclerotic plaque. Since the first intravascular laser intervention, the technique has been significantly improved by the use of optimized wavelength, the development of flexible optimally spaced multifiber catheters and an additional saline flush technique. These technical advancements allowed a reduction in the incidence of adverse events, such as the number of dissections and perforations, associated with the use of the laser technique. Coronary laser angioplasty is commonly combined with adjunctive balloon angioplasty to optimize the outcome. Laser coronary angioplasty was not followed by a lower restenosis rate compared with plain balloon angioplasty in lesions without stents, however, a randomized comparison of the techniques including the use of the saline flush technique is not available yet. The value of excimer (acronym for excited dimer) laser coronary angioplasty for treatment of in-stent restenosis is still under investigation. So far, nonrandomized single center studies have not suggested a relevant benefit for this technique used for in-stent restenosis. In nonstented lesions there remain niche indications for laser angioplasty such as the treatment of ostial lesions, diffuse lesions or lesions traversable with a guidewire but not with an angioplasty balloon. Laser coronary angioplasty may also be useful after a failed balloon angioplasty and in patients with chronic total occlusions. The potential advantages of combining laser coronary angioplasty with vaporization of thrombus in patients with acute coronary syndromes are currently under evaluation.

Effectiveness and safety of ultrasonic atherosclerotic plaque ablation: in vitro investigation.

Ultrasound energy was applied to 137 segments of human cadaver atherosclerotic arteries, 90 with calcified and 47 with noncalcified atheromatous plaque, and to 100 segments of healthy swine aorta. The average depth of penetration was dependent on the forward force of the ultrasonic probe, the duration of treatment, and the degree of atherosclerosis. There was one perforation of a fibrous plaque using a forward force of 2 Newton and 45 sec of application time. Injury of healthy intima was minimal. It is concluded that catheter-delivered ultrasound is effective and safe for the disintegration of atherosclerotic plaques. Presently, the main limitations of the system are the lack of flexibility and steerability.

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)

Application of a new real-time temperature control pulsed laser for ablation of atherosclerotic plaque

Application of a new real-time temperature control pulsed laser for ablation of atherosclerotic plaque

Holmium: Yag Laser Angioplasty

This experimental study was designed to define the potential value of a mid-infrared holmium laser in the free running mode for angioplasty. Immediately after removal, fresh normal and diseased human cadaveric arteries were irradiated under saline with a Ho:YAG laser (wavelength 2.13 μm). The laser was pulsed at 3 Hz, 250 μs pulse width and fluences of 10 to 40 J/cm2. The laser beam was coupled to ring catheters with multiple low-OH quartz fibers. The tip of the delivery device was held in direct contact with the vessel surface with the laser beam oriented perpendicularly. Ablation of atherosclerotic plaque was accomplished at an ablation threshold of 10 J/cm2. The ablation rate was 2.1 to 8.3 μm/pulse. Removal of calcified plaque was only partially effective. There were marked thermal effects with vacuolizations extending up to 1505 ± 178 μm into the adjacent tissue. Laser light at the mid-infrared wavelength of 2.13 μm is supposed to be attractive as it is readily absorbed in water and can easily be transmitted through optical fibers. However, Q-switching seems to be essential to minimize thermal side effects and to make effective ablation of calcium possible.

Holmium: Yag Laser Angioplasty

This experimental study was designed to define the potential value of a mid-infrared holmium laser in the free running mode for angioplasty. Immediately after removal, fresh normal and diseased human cadaveric arteries were irradiated under saline with a Ho:YAG laser (wavelength 2.13 μm). The laser was pulsed at 3 Hz, 250 μs pulse width and fluences of 10 to 40 J/cm2. The laser beam was coupled to ring catheters with multiple low-OH quartz fibers. The tip of the delivery device was held in direct contact with the vessel surface with the laser beam oriented perpendicularly. Ablation of atherosclerotic plaque was accomplished at an ablation threshold of 10 J/cm2. The ablation rate was 2.1 to 8.3 μm/pulse. Removal of calcified plaque was only partially effective. There were marked thermal effects with vacuolizations extending up to 1505 ± 178 μm into the adjacent tissue. Laser light at the mid-infrared wavelength of 2.13 μm is supposed to be attractive as it is readily absorbed in water and can easily be tra...

Histological and angiographic effects of a pulsed holmium:YAG laser in normal and atherosclerotic human coronary arteries and aorta.

The aims were (1) To determine the histological and angiographic effects of holmium:YAG laser energy delivered through clinical multifibre laser catheters on fresh cadaveric coronary arteries; and (2) to relate the placement of optical fibres in the catheter to patterns of tissue ablation in cadaveric aorta. Eight fresh cadaveric hearts and segments of aorta were used. Hearts were mounted on a new pressure perfusion device. The laser catheter was delivered over a guidewire in the lumen until it met an area of resistance. The coronary artery lumen was perfused at approximately 100 mm Hg mean pressure. These arterial areas were identified on angiography, marked, and then exposed to laser energy in the range 600-3000 mJ.mm-2. Normal and atherosclerotic areas of fresh cadaveric aortic strips were exposed to increasing laser energies using either constant or increasing fluence. Coronary arteries were pressure perfused with formalin for 18-24 h at 100 mm Hg mean pressure, and aortic strips were immersed in 5% formalin. Light and scanning electron microscopy studies were carried out. There were no perforations or dissections by angiography in the fresh coronary arteries. One of 15 normal coronary artery segments and 10 of 16 of the pressure perfused, fixed, atherosclerotic coronary artery segments showed thermal changes associated with atherosclerotic plaque ablation. In aortic tissue, thermal effects extended 0 to 0.6 mm lateral to the ablated crater. Acoustic effects were seen only in the aortic strips after ablation at fluences > 1000 mJ.mm-2. The "dead spaces" around the optical fibres in the catheter resulted in significant amounts of coagulated tissue fragments remaining in the crater. Holmium:YAG laser energy delivered through multifibre catheters ablated atherosclerotic tissue in coronary arteries with minimal damage to the normal walls. The cadaveric coronary artery perfusion apparatus is useful for assessing catheter delivery and mobility and the effects of laser energy on the coaxially orientated normal and atherosclerotic coronary arterial wall.

Laser Angioplasty

Laser energy has the potential for selective ablation of atherosclerotic plaque through minimally invasive means. As currently practiced, laser angioplasty requires the adjunct of balloon angioplasty in most cases and has limited application compared with more conventional methods of revascularization. However, new advances in guidance systems, delivery devices, and laser sources may allow realization of the full benefit of this technology at some point in the future.

Pulsed laser and thermal ablation of atherosclerotic plaque: Morphometrically defined surface thrombogenicity in studies using an annular perfusion chamber

Although clinical trials using laser and thermal angioplasty devices have been underway, the effects of pulsed laser and thermal ablation of atherosclerotic plaque on surface thrombogenicity are poorly understood. This study examined the changes in platelet adherence and thrombus formation on freshly harvested atherosclerotic aorta segments from Watanabe-heritable hyperlipidemic rabbits after ablation by two pulsed laser sources (308-nm xenon chloride excimer and 2,940-nm erbium:yttrium-aluminum-garnet [YAG] lasers) and a prototype catalytic hot-tip catheter. Specimens were placed in a modified Baumgartner annular chamber and perfused with citrated whole human blood, followed by quantitative morphometric analysis to determine the percent surface coverage by adherent platelets and thrombi in the treated and contiguous control areas.Pulsed excimer laser ablation of plaque did not change platelet adherence or thrombus formation in the treated versus control zones. However, photothermal plaque ablation with a pulsed erbium: YAG laser resulted in a 67% reduction in platelet adherence, compared with levels in control areas (from 16.7 ± 2.2% to 5.5 ± 1.8%; p < 0.005). Similarly, after plaque ablation using a catalytic thermal angioplasty device, there was a 74% reduction in platelet adherence (from 29.2 ± 5.1% to 7.7 ± 1.6%; p < 0.005) and a virtual absence of platelet thrombi (from 8.6 ± 2.3% to 0.03 ± 0.03%; p < 0.095).This reduced surface thrombogenicity after plaque ablation with either an erbium: YAG laser or a catalytic hot-tip catheter suggests that thermal modifications in the arterial surface ultrastructure or thermal denaturation of surface proteins, or both, may be responsible for reduced platelet adherence. These in vitro findings indicate that controlled thermal plaqae ablation by catheter-based techniques may elicit endovascular responses that can reduce early thrombus formation during angioplasty procedures.

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.

Holmium: Yag Laser Angioplasty

This experimental study was designed to define the potential value of a mid-infrared holmium laser in the free running mode for angioplasty. Immediately after removal, fresh normal and diseased human cadaveric arteries were irradiated under saline with a Ho:YAG laser (wavelength 2.13 microns). The laser was pulsed at 3 Hz, 250 microseconds pulse width and fluences of 10 to 40 J/cm2. The laser beam was coupled to ring catheters with multiple low-OH quartz fibers. The tip of the delivery device was held in direct contact with the vessel surface with the laser beam oriented perpendicularly. Ablation of atherosclerotic plaque was accomplished at an ablation threshold of 10 J/cm2. The ablation rate was 2.1 to 8.3 microns/pulse. Removal of calcified plaque was only partially effective. There were marked thermal effects with vacuolizations extending up to 1505 +/- 178 microns into the adjacent tissue. Laser light at the mid-infrared wavelength of 2.13 microns is supposed to be attractive as it is readily absorbed in water and can easily be transmitted through optical fibers. However, Q-switching seems to be essential to minimize thermal side effects and to make effective ablation of calcium possible.

Laser angioplasty versus balloon angioplasty: The need for imaging

The current state of clinical laser angioplasty is reviewed. Compared to balloon dilation at the beginning of the past decade, both peripheral and coronary laser angioplasty devices produce better results. Compared to current balloon angioplasty techniques, however, laser angioplasty does not seem to offer improved initial or long term results. Intravascular ultrasound imaging may help to improve laser ablation of atherosclerotic plaque. It remains to be established, however, whether precise debulking of the obstruction will result in a reduced restenosis rate compared to balloon angioplasty.