Open-irrigated laser catheter ablation: influence of catheter irrigation and of contact and noncontact mode of laser application on lesion formation in bovine myocardium

Lesions achieved by radiofrequency application increase with catheter irrigation and with catheter pressure on the endocardial surface. Purpose of this study was to test the influence of catheter irrigation and of contact vs. noncontact mode of laser application on lesion formation in bovine myocardium. By applying continuous wave 1,064 nm laser light via an open-irrigated catheter lesions were produced at 15 W (9.5 W/mm²)/30 s (285 J/mm²), in stagnant blood (activated clotting time?>?350 s) at 18 °C, on bovine myocardium. During flow rates of 15, 30, and 50 ml/min radiation was applied with the catheter end hole in contact (n?=?10, each) or 2 mm away from the endocardial surface (n?=?5, each). Lesions were evaluated morphometrically, and groups of lesions were compared by using the unpaired t test. By augmentation of irrigation flow from 15 to 30 ml/min, contact lesions increased significantly (p?=?0.0001). A further increase of flow from 30 to 50 ml/min increased lesions significantly in depth (p?=?0.0011) but not in width (p?=?0.639) and volume (p?=?0.218). Noncontact lesions were significantly smaller than contact lesions (p?>?0.05). Lesions of homogenous coagulation necrosis were clear-cut and sharply demarcated from the surrounding normal myocardium. There was no occurrence of steam-pop with intramural cavitation or with tissue vaporization with crater or thrombus formation. It is suggested that by using an open-irrigated laser catheter as described in this study, catheter irrigation at flow rates of 30 to 40 ml/min are optimal for myocardial coagulation, and catheter pressure on the endocardial surface is not needed for lesion formation. Laser lesions can be achieved also without intimate endocardial catheter contact.     

Cooled-tip diode laser catheter for improved catheter ablation of ventricular tachycardia.

Catheter ablation for the treatment of arrhythmias has evolved dramatically over the past two decades. Researchers have investigated alternative energy sources and catheter constructs to improve the efficacy and safety of catheter ablation. This study tested the hypothesis that a new prototype cooled-tip laser catheter used with a low-power diode laser would improve catheter ablation of ventricular tachycardias. Four mongrel dogs underwent a median sternotomy. The cooled-tip laser catheter was advanced into the left ventricle via the left carotid artery and positioned adjacent to the endocardium. Laser powers of 3 and 4 W were delivered at four exposure times to select areas of the endocardium. During application of laser energy, room-temperature saline was circulated through the catheter. At necropsy the hearts were examined and fixed in formalin for histologic examination. Gross examination of the endocardial surfaces showed no indication of crater or thrombus formation. Cross-section of the lesions revealed sharply demarcated, circular-shaped areas of coagulative necrosis extending into the mid-myocardium. Areas of coagulative necrosis were identified within the myocardium extending into the mid-myocardium and occasionally the subepicardium. A sharp line of demarcation was observed between the lesions and the surrounding normal myocardium. The results of this study showed that we could use surface cooling during slow laser heating to create large subsurface lesions with characteristics appropriate for treatment of ventricular tachycardia and little to no surface damage. We believe our catheter system addresses many of the previous issues with laser-based approaches.     

Influence of water-layer thickness on Er:YAG laser ablation of enamel of bovine anterior teeth

Different ideas have been presented to describe the mechanism of augmented laser ablation of dental enamel with different shapes by adding water to the working environment. In this study, the influence of water–laser interaction on the surface of enamel during ablation was investigated at a wavelength of 2.94 μm with different distances between the laser tip and the enamel surface. A motion-control system was used to produce linear incisions uniformly on flat enamel surfaces of bovine anterior teeth, with free-running Er:YAG laser very short pulses (pulse length = 90–120 μs, repetition rate = 10 pulses per second). Four different output energies (100, 200, 300 and 400 mJ) were radiated on samples under distilled water from different distances (0.5, 0.75, 1, 1.25, 1.75 and 2.00 mm). The tooth slices were prepared with a cutting machine, and the surfaces of the ablated areas were measured with software under a light microscope. The average and standard deviation of all cut areas in different groups were reported. There was no significant difference when using a different pulse ablation speed (cm³/J) and a water-layer thickness between the tip and enamel surface of 0.5–1.25 mm with energy densities of 30–60 J/cm² (200–400 mJ). However, using an output energy of 15 J/cm² (100 mJ) and a thicker water layer than 1 mm, a linear ablation did not take place. This information led to a clearer view of the efficiency of Er:YAG laser in the conditions of this study. There are several hypotheses which describe a hydrokinetic effect of Er,Cr:YSGG. These basic studies could guide us to have a correct attitude regarding hydro-mechanical effects of water, although the wavelength of 2.78 μm has a better absorption in hydroxyl branch of water molecules. Therefore, our results do not directly interrupt with the series of investigations done with Er,Cr:YSGG. Water propagation and channel formation under water are investigated during the ablation of tooth enamel with the Er:YAG laser from different distances. Comparing the results of this study with the same research done with water/air spray concludes that the bubble formation and channel propagation in water with this wavelength leads to a more symmetric (linear) ablation process with cavity-preparation-recommended parameters.     

Tumour ablation by laser in dermatology

The role of CO₂ laser in plastic surgery and dermatology is nowadays well established. It has proved to be efficient within different contexts (haemorrhagic-infectious-necrotic ...) or on different tissues as skin, muscles and mucosae. But the role of lasers in oncologic cutaneous surgery is not as precise.The CO₂ laser is to be used in a focused mode, to realize the excision of tumour, whatever its size. The advantages lie in minimized blood loss, and in permitting all types of reconstruction (suture, graft or flap). Some clinical cases of photodynamic therapy are reported, but do not appear to be conclusive. Anyhow, PDT is still under investigation and does not seem to be ready yet for routine clinical use. The principle of tissue photo-ablation with excimer of Er-YAG lasers shows some possible interest in the case of tumour treatment. But, here again, this technique has not yet proved to be for any real advantage, as far as technology is concerned. Whatever the type of laser to be used, one basic principle is to completely excise the tumour to meet the classical requirements of oncologic surgery, i.e. to be far enough from the lesion, and to get a microscopic identification of the whole specimen.     

Influence of external cooling on the femtosecond laser ablation of dentin

In the present work, the influence of external cooling on the temperature rise in the tooth pulpal chamber during femtosecond laser ablation was investigated. The influence of the cooling method on the morphology and constitution of the laser-treated surfaces was studied as well. The ablation experiments were performed on dentin specimens using an Yb:KYW chirped-pulse-regenerative amplification laser system (560 fs, 1030 nm). Cavities were created by scanning the specimens at a velocity of 5 mm/s while pulsing the stationary laser beam at 1 kHz and with fluences in the range of 2–14 J/cm². The experiments were performed in air and with surface cooling by a lateral air jet and by a combination of an air jet and water irrigation. The temperature in the pulpal chamber of the tooth was measured during the laser experiments. The ablation surfaces were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The temperature rise reached 17.5 °C for the treatments performed with 14 J/cm² and without cooling, which was reduced to 10.8 ± 1.0 and 6.6 ± 2.3 °C with forced air cooling and water cooling, respectively, without significant reduction of the ablation rate. The ablation surfaces were covered by ablation debris and resolidified droplets containing mainly amorphous calcium phosphate, but the amount of redeposited debris was much lower for the water-cooled specimens. The redeposited debris could be removed by ultrasonication, revealing that the structure and constitution of the tissue remained essentially unaltered. The present results show that water cooling is mandatory for the femtosecond laser treatment of dentin, in particular, when high fluences and high pulse repetition rates are used to achieve high material removal rates.     

Acute and chronic effects of transmyocardial laser revascularization in the nonischemic pig myocardium by using three laser systems

BACKGROUND AND OBJECTIVE: Transmyocardial laser revascularization (TMLR) improves symptoms in patients with coronary heart disease. It is based on the hypothesis of direct perfusion of ischemic myocardium by means of laser-created channels. Three different lasers were used to study alternative effects on myocardium. STUDY DESIGN/MATERIALS AND METHODS: The present study was conducted to evaluate comprehensively and compare the short and long-term tissue effects and the basic interaction mechanisms of CO2, Ho:YAG, and Er:YAG laser radiation with myocardium. The dynamics of laser-induced impacts in gel used as tissue phantom was visualized by time-resolved flash photography. Pressure measurements performed during perforation of myocardium in vitro revealed the explosive character of the ablation process. Channels made into the left ventricle of normal pig hearts were examined immediately and 6 weeks after creation. RESULTS: Regardless of laser source, all channels became occluded within 6 weeks by scar. Minimal acute thermal damage by Er:YAG laser corresponded to smaller scars. Pulsed Ho:YAG caused stronger tissue tearing than continuous wave CO2 irradiation. An increased volume density of intramyocardial vessels was found about the scars 6 weeks after treatment with all lasers. CONCLUSION: The laser sources permitted to study outcome of pressure effects and thermal damage in vivo. There were only minor differences between the three laser systems used. Rapid channel occlusion suggests that rather than revascularization, subsidiary physiologic tissue effects elicited by the thermal, oxidative, or mechanical action of the laser impact may contribute to the beneficial clinical effects of TMLR.     

Holmium-YAG and carbon dioxide laser ablation of normal and infarcted myocardium in the canine model

Surgical and transcatheter ablative treatment of ventricular tachycardias is based on endocardial mapping and removal of myocardial areas involved in sustaining the arrhythmia. Recently, argon and neodymium-YAG laser energy have been employed for the ablative treatment of ventricular tachycardia. In the present study the effects of holmium-YAG laser irradiation on normal and infarcted myocardium in the canine model were compared with those of the CO₂ laser. Myocardial infarction was created in 11 dogs by a two-stage left anterior descending coronary artery ligation. Laser irradiation of normal and infarcted myocardium was performed at about 1, 4 and 12 weeks following ligation, with energies of 5, 10, 20 and 30 J. A total of 218 irradiation induced craters were sectioned through the central axis and the evaporized, vacuole and denatured crater areas were morphometrically calculated. Total crater areas following holmium-YAG laser irradiation were significantly larger, with shallower penetration but larger lateral extension of evaporized, vacuole and denaturation areas. Perforations occurred only with CO₂ laser irradiation. Effects on normal and infarcted myocardium were similar and independent of infarct age. It is concluded that the holmium-YAG laser is probably more effective and safer than the CO₂ laser for myocardial ablation.     

Mechanism of laser ablation in an absorbing fluid field

Selection of a laser source for intravascular applications has frequently been predicated upon assumptions involving transmissibility in blood of the wavelength of light emitted by a given laser. Standard absorption curves for ultraviolet radiation in blood and infrared radiation in water would suggest that transmission of ultraviolet radiation through a blood field and infrared radiation through any aqueous fluid field would be insufficient for tissue ablation. The present series of experiments was undertaken to determine whether these theoretical predictions would in fact obviate the use of these wavelengths in a blood field. Specimens of normal human myocardium and/or polyvinylchloride were submerged under blood and water and irradiated with ultraviolet radiation (351 nm) delivered as a focused beam and via an optical fiber and infrared radiation (10,600 nm) delivered as a focused beam. Ablation of myocardium was successfully accomplished with a focused beam of both ultraviolet and infrared radiation under as much as 5 mm of blood and with ultraviolet radiation via an optical fiber with the fiber tip up to 3 mm distant from the tissue specimen. High-speed cine recordings of ablation carried out using a focused beam of laser radiation demonstrated that formation of a dynamic optical cavity is the basis for successful pulsed ultraviolet and infrared laser transanguineous tissue ablation. These results thus demonstrate that prediction of wavelength transmission through fluid media based on optical properties of a static fluid does not predict ability to accomplish ablation under dynamic circumstances of laser irradiation.     

Tumour ablation by laser in general surgery

More surgeons are becoming interested in laser surgery, but, in laser tumour ablation the real improvement in open surgery can only be provided by:

Influence of the bridging effect by sequential laser application on tissue ablation in an ex vivo model, taking organ perfusion into account

OBJECTIVE: To improve the efficacy of interstitial laser coagulation of tissue by causing a 'bridging' effect, using a sequential multiple-probe procedure on an ex vivo kidney model, as only a limited area of tissue is destroyed with a single probe and the coagulation takes longer when multiple punctures are used. MATERIALS AND METHODS: A laser beam was generated using a Nd:YAG laser and applied to kidney tissue by a diffuser tip (quartz glass cap 2 x 19 mm). For sequential laser application (SLA), three probes were placed through punctures into kidney tissue, at 5 or 10 mm apart. The laser energy was applied in different time-energy combinations through the three probes. The effect of SLA was compared with that from one probe delivering the optimal PowerMode 180 protocol (Dornier, Germering, Germany), which represents the standard energy protocol for the clinical treatment of parenchymal organs using this laser device. An isolated porcine kidney was chosen for laser coagulation under different conditions of perfusion. The ablative efficacy was defined as the volume of necrosis per minute. RESULTS: Applying various time-energy combinations to isolated unperfused porcine kidney caused extensive tissue ablation (5.6 mL). In trials with saline and blood perfusion for improved cooling, the necrotic volume was 2.5 and 3.9 mL, respectively (with no carbonization, 3.2 mL). Compared with a single-probe procedure, the ablation efficacy was 10 times better with SLA coagulation. This improvement was initiated by the bridging effect: coagulation in neighbouring areas affects perfusion and convection to an extent that induces the formation of bridges of necrosis between the probes. CONCLUSION: Tissue ablation is markedly improved by interstitial laser coagulation using a sequential multiple-probe technique.     

Gallbladder ablation with a laser in an animal model

IntroductionAttempts to remove the gallbladder by non-surgical means began in the 1980's, by applying chemicals, heat or laser to remove its mucosa and reduce it to an innocuous scar. The aim of this work is to determine whether complete ablation of this organ is possible using total ablation by applying a diode laser.Material and methodsThirty rabbits were divided into 3 groups of 10 animals. The gallbladder was surgically accessed and a 980 nm diode laser was applied endoluminally using fibre optics until it shrunk. Ethanol was used as a sclerosing agent plus a fibrin tail to seal the gallbladder lumen in one of the control groups, and a physiological solution was used in the rest. The animals were slaughtered at 65 days and the results of the procedure were observed macroscopically and histologically, evaluating the remains of the gallbladder lumen, fibrosis, and areas of re-epithelialisation. Statistical analysis was made using the Fisher test.ResultsEight of the gallbladders treated by laser disappeared leaving a small sub-hepatic scar. There were no complications during or after surgery. The results were successful in only case in the ethanol group, and there was no ablation with physiological solution. The comparison of the results showed a significant positive difference in the group treated with laser compared to those with ethanol plus fibrin tail (P<.0055) and the physiological solution (P<.0007).ConclusionsAblation of the gallbladder using a diode laser was possible in this experimental model.     

Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel

. The present study examines the dependence of the ablation threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 μm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm², while the duration of the pulses applied was changed in four steps from 100 μs to 700 μs. The irradiated tooth surfaces were examined for visible signs of ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which ablation sets in is reduced by up to approx. 3 J/cm². This expands the ablation threshold range of Er:YAG laser radiation to between 6 and 10 J/cm². In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the ablation threshold (logistic regression, p<0.0001). Although the ablation threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight. Paper received 11 March 2001; accepted after revision 22 May 2002. Correspondence to: Dr Christian Apel, Department of Conservative Dentistry, Periodontology and Preventive Dentistry, University of Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany. Tel.: +49 241 8089088; Fax: +49 241 8082468; e-mail: capel@ukaachen.de     

Evaluation of different laser wavelengths on ablation lesion and residual thermal injury in intervertebral discs of the lumbar spine

Laser discectomy or nucleotomy is an increasingly important method for less invasive procedures of column, but the ideal kind of laser is still not established. As the wavelength is an important parameter for water absorption, this study was performed to investigate the action of the laser emission in the near infrared (808 to 1908 nm) region in the context of surgical procedures for percutaneous intervertebral disc decompression (nucleotomy). Forty intervertebral discs from pigs lumbar spines were irradiated with laser (λ?=?808, 980, 1470 and 1908 nm), 1-s on/off time cycles, for 120 cycles and 10 W of power (808, 980, and 1470 nm) or 240 cycles and 5 W of power (1908 nm), with total power of 1200 J, and subjected to microscopic evaluation through hematoxylin-eosin (HE) staining in order to measure the ablation lesions and the residual thermal injury. Ten other discs were not irradiated and worked as controls. The ablation lesions were measured (in mm) at 1.08?±?1.25, 1.70?±?0.63, 2.23?±?1.02, 1.37?±?0.39, and 0.94?±?0.41 (median?±?SD) for the control, 808, 980, 1470, and 1908 nm groups, respectively. The difference between 1908 nm and all the other groups was statistically significant (p?<?0.05). The residual thermal injury was less evident in 1908 nm laser and sharper in 980 nm laser wavelengths. The laser at a wavelength of 1908 nm was considered the most efficient for the vaporization of the nucleus pulposus, followed by the laser wavelengths of 1470, 808, and 980 nm, and proved to be useful for laser nucleotomy procedure.     

Selective ablation of orthodontic composite by using sub-microsecond IR laser pulses with optical feedback

BACKGROUND AND OBJECTIVE: Conventional methods of residual composite removal after debonding orthodontic brackets involve the use of abrasives that damage the underlying enamel. The objective of this study was to determine whether infrared pulsed lasers are suitable for the removal of composite through selective laser ablation. STUDY DESIGN/MATERIALS AND METHODS: Pulsed CO(2) and Er:YAG lasers were evaluated for their ability to selectively ablate orthodontic composites. Optical emission spectra of the luminous plasma produced during composite and enamel ablation were acquired to differentiate between enamel and composite ablation to minimize accidental removal of enamel. RESULTS: TEA CO(2) laser pulses at a wavelength of 10.6 microm were best suited for the selective ablation of composite. Spectral analysis of plume emission identified several calcium emission lines that can potentially be used to distinguish between enamel and composite ablation. CONCLUSION: TEA CO(2) lasers operating at 10.6 microm used in conjunction with optical feedback have the potential to selectively ablate residual dental composite and minimize inadvertent removal of enamel.     

Production of narrow but deep lesions suitable for ablation of atrial fibrillation using a saline-cooled narrow beam Nd:YAG laser catheter

BACKGROUND AND OBJECTIVE: Lines of radiofrequency ablation for cure of atrial fibrillation are broad, and the consequent loss of atrial mass may impair atrial function and contribute to the risk of stroke. We studied whether Nd:YAG laser could produce deep but narrower lesions. STUDY DESIGN/MATERIALS AND METHODS: Laser lesions were made in ventricular myocardium of nonperfused ovine hearts and at thoracotomy in dogs. RESULTS: Lesions were well demarcated, deep, and narrow. Saline irrigation prevented crater formation for energy levels below 200 J. Lesion depth increased with increasing duration of ablation (maximum 5.3 +/- 0.8mm, P < 0.01). The depth to width ratio was >1 in all cases (maximum 2.5 +/- 1.6). The narrowest lesions were made by using high power, short duration of exposure, and intermittent delivery. CONCLUSIONS: Irrigated Nd:YAG laser can be used to make deep narrow myocardial lesions without crater formation. Laser ablation may be more suitable than radiofrequency ablation for intraoperative or catheter-based cure of atrial fibrillation.     

Successful repair of an atrioesophageal fistula after catheter ablation for atrial fibrillation

Catheter ablation of arrhythmias can result in the rare but devastating complication of an atrioesophageal fistula. This complication can be associated with significant neurologic morbidity and high mortality and requires a high index of suspicion to facilitate life-saving surgical intervention. Herein, we report the successful repair of an atrioesophageal fistula after catheter ablation for atrial fibrillation.     

Gas volume quantitation during argon ion laser ablation of atheromatous aorta in blood and 0.9% saline media with an optically shielded catheter

Using an optically shielded fiber optic laser catheter, the amount of gas produced when firing an argon ion laser into 0.9% saline solution or blood alone and into atheromatous aorta in either a blood or 0.9% saline medium was quantitated. Energies from 0.25 to 4 joules (J) were used at powers of 2, 5, and 8 W. We found that total volume of gas produced is small not only at equilibrium (0.3 +/- 0.1 microliter/J when firing in blood alone and also when ablating aorta in blood or saline media) but also at peak (2.5 +/- 0.2 microliters/J firing in blood alone and 1.0 +/- 0.1 microliter/J or 0.9 +/- 0.1 microliter/J when ablating aorta in saline or blood, respectively). Because these volumes are small, a clinically significant event from a gas embolus is unlikely during intravascular laser ablation of atheromatous plaque in the energy and power range studied. No gas was quantitated when firing the argon ion laser into 0.9% saline solution alone. The peak gas volume when firing in blood alone was significantly greater than that produced in the other chamber environments. This is thought to be due to increased absorption of argon laser light by hemoglobin. The gas volumes produced by lasing aorta in 0.9% saline or blood were not statistically different.