Simulation of heat generation for transcatheter Nd-YAG laser photocoagulation of myocardium

Nd-YAG laser photocoagulation is a successful technique for the intraoperative treatment of arrhythmia. Experimental endocardial transcatheter laser application, however, occasionally causes tissue vaporization and perforation. Intramural heat generation was simulated in a Monte Carlo model as a function of laser beam profile and divergence versus individually varying tissue properties. Heat generation at the tissue surface was dominated both by the beam profile and the individual tissue properties. High beam divergence may help to reduce heat accumulation in subsurface regions. Heat distribution in depth as well as backscattering are not substantially influenced by beam parameters but are mainly determined by the optical tissue properties. Surface colling can help to avoid overheating. A catheter, concept for safe endocardial photocoagulation is presented including a highly divergent beam of maximized, spot size, an effective catheter flushing, and shielding of blood.     

Nd-YAG laser photocoagulation in gastroenterology: Its role in palliation of colorectal cancer

The merits of the Nd-YAG laser were evaluated in palliation of obstruction, or bleeding, or both, in 84 patients with colorectal malignancy. Luminal patency was restored in 20 of the 24 patients with obstructing colonic cancers. Haemostasis was achieved in 37 of the 40 patients with bleeding. Combined bleeding and obstruction responded favourably in 19 of the 20 patients treated. Only a few laser photocoagulation sessions, over a short period of time, were needed, and further laser treatment could be continued on an outpatient basis.Major complications such as perforation (6), stenosis necessitating a colostomy (3), and delayed post-treatment bleeding (2) were seen in 13% of patients, with a laser-related mortality in three patients. Minor complications, such as transient stenosis (22) and laser-induced bleeding (11), responded well to further laser application. Pain and warmth (20) resolved spontaneously. Treatment failures and complications were mainly due to inadequate accessibility or were related to tissue characteristics. Laser photocoagulation appears to constitute a valuable alternative treatment, not only to resection and colostomy, in the case of obstruction, but also for haemorrhage that cannot be controlled in other ways. Palliation, in its broad sense, is guaranteed because of the rapid results, reduced time in hospital, the avoidance of hospital admission, and the good tolerance of treatment.     

Laser angioplasty with a metal laser probe (‘hot tip’): Probe temperature in blood

In vitro experiments to determine the physical characteristics of a metal laser probe for laser angioplasty are described. The probe was filmed in stationary saline and plasma. The temperature of the probe was measured with thermocouples in air, stationary saline, whole blood, diluted packed cells (40%) and plasma. In the latter three media an envelope of denatured blood elements was found on the probe. This envelope entrapped a vapour layer which acts as an effective insulator, allowing the probe temperature to reach 600°C within 3 s of application of 10 W from an neodymium-YAG laser. Our observations suggest that the transfer of heat from the metal to the tissue will depend both on the formation and destruction of this thermally insulating envelope, which may well protect the arterial wall from heat injury during laser angioplasty.     

X-Ray- and catheter-guided intracardial laser photocoagulation of arrhythmogenic substrates

Cardiac arrhythmias resistant to drug treatment and correlated to an arrhythmogenic anatomic structure can be treated in several cases by surgical intervention. A further method of treatment is the percutaneous, ECG mapping-guided catheter ablation with either direct current (DC) or radio frequency (RF) ablation of localized arrhythmogenic foci. These methods overcome some complications inherent to open surgery to the heart; DC ablation, however, often induces further arrhythmias or ventricular or auricular fibrillation, while RF ablation shows only little success. In the method presented here disturbing electric effects are avoided by laser photocoagulation via a transcatheter quartz fibre. An electrode/laser catheter recently developed simultaneously allows for a mapping-guided localization of arrhythmogenic substrates and their percutaneous transluminal and intracardial deactivation. An anchoring mechanism at the catheter's tip keeps it in place during the treatment. This mechanism also prevents contact of the quartz fibre to the endomyocardium in order to avoid destruction of the fibre tip due to local overheating of the myocardium. A Nd-YAG laser (wavelength 1.064m) delivers pulses of 5–10 s and a power of 10–15 W at the tip of a quartz fibre with a core diameter of 400m. The corresponding parameter or irradiation of the myocardium are power densities of 700–1500 W cm^–2 and energy densities of 8–15 kJ cm^–2. In dog hearts lesions 2–10 mm in diameter and up to 11 mm in depth were obtained. Simultaneously registered electrocardiograms show that primarily induced arrhythmias lasted only for about 3 min but could not again be observed during the 2–3 months follow-up. Crater formation or perforation of the myocardium always could be avoided by an ECG-controlled laser irradiation. This indicates the safety and efficacy of the laser method for intracardial intervention in arrhythmogenic substrates. Clinical tests have been started recently.     

Non-excision treatment of multiple cutaneous neurofibromas by laser photocoagulation

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disorder characterized by skin tumours derived from peripheral nerves. It is a clinically diagnosed disorder of a mainly cosmetic concern. There are different excision modalities for treatment of cutaneous neurofibromas; however, none is considered to be universally accepted treatment. This study was conducted to evaluate a non-excision treatment of multiple cutaneous neurofibromas, using surface and interstitial approaches of neodymium:yttrium aluminum garnet (Nd:YAG) laser (1,064 nm) photocoagulation, depending upon the size and location of the lesions. Twelve patients with multiple cutaneous neurofibromas were included. Surface laser photocoagulation by long-pulsed Nd:YAG laser has been used for treatment of flat lesions, while interstitial laser photocoagulation by continuous wave (CW) Nd:YAG laser has been used for treatment of bulkier lesions. After 14 months of follow up, both approaches of laser photocoagulation have shown different success rates, as denoted by the regression of the lesions, an overall acceptable cosmetic outcome, and, generally, patients' satisfaction. Within the limitations of the present study, laser photocoagulation has proven to be a promising technique that may be an alternative or additive modality for treatment of multiple cutaneous neurofibromas. It is a minimally invasive, office-based technique that could be used safely and effectively, with a limited rate of complications. Surface laser photocoagulation has proven to be an effective tool for treatment of flat lesions, especially those located in exposed areas, with a favourable cosmetic result, while interstitial laser photocoagulation could be reserved for bulkier lesions, especially those located in non-exposed areas. However, further studies are necessary to refine the procedure, and to confirm the present encouraging findings, especially over a longer period of follow up, as well as to evaluate laser parameters for optimization of the technique.     

Local control of rectal cancer with the Nd-YAG laser

Summary Three patients with locally recurrent rectal cancer were treated using the Neodymium YAG laser to palliate the symptoms of tenesmus, discharge and bleeding. All were considered unfit for further surgical excision. The local tumour was completely removed following repeated laser therapy over a period of 4, 6 and 11 months, respectively. These patients remain well without evidence of local or systemic disease 26, 33 and 42 months after laser treatment. Laser therapy for palliation of local disease may be rewarded by prolonged local control and possible cure.     

Denudation of the entire mucosa of the canine urinary bladder using the neodymium:YAG laser with the MTR 1.5 contact probe

Although the procedure of mucosal stripping or denudation of the urinary bladder was developed over 25 years ago to treat the potentially neoplastic mucosa in patients with low-grade superficial transitional cell carcinoma of the bladder, the procedure was abandoned because of serious complications, including short-term bladder hemorrhage and urinary extravasation and long-term severe bladder contracture, ureteral reflux, and hydronephrosis. In this study, we used the neodymium:YAG laser with the MTR 1.5 contact probe to denude the entire mucosa of the canine urinary bladder. Evaluation of our results showed that mucosal denudation by this technique can be performed simply and safely without complications. Specifically, we encountered no significant bladder hemorrhage, urinary extravasation, bladder contracture, ureteral reflux, or hydronephrosis. We believe that the denudation procedure may be useful as a surgical means of treating the entire bladder mucosa in patients with proliferative epithelial lesions of the bladder including multifocal carcinoma in situ.     

Use of the Nd-YAG laser in neurosurgery

Summary After many years of experience, in general we prefere the Nd-YAG laser, although the CO₂ laser is an advantage in a few specific cases (lipomas, cranial synostosis). While the focused CO₂ laser may be used as a cutting instrument in less vascular tissue with little trauma to the surroundings, the Nd-YAG laser produces a homogeneous coagulation with an energy dependent depth effect. Thus, with the Nd-YAG laser residual tumour tissue can be selectively and with a predictable depth effect thermally destroyed. Because of its excellent coagulation property, the use of the Nd-YAG laser is particularly indicated in highly vascular meningeal tumours. The shrinkage of a tumour and its demarcation which is due to the varying absorption properties facilitates the dissection and allows in addition the preservation of normal tissue.     

Histological studies of myocardium zones irradiated with Nd-YAG laser

Histological investigation of the dog's myocardium performed 7 and 25 days after irradiation with different doses of Nd-YAG laser show that the damage zone has the shape of a hollow sphere with minor changes in cardiomyocytes in the central part of the sphere. The small blood vessels in the irradiated zone remained undamaged as well. A tentative explanation of the physical process that leads to this type of coagulation zone is given.     

Hysteroscopic treatment of uterine bleeding with the Nd-YAG laser

This preliminary study involves 45 patients, referred to us for hysterectomy, who complained of uterine bleeding that was resistant to conventional treatment. Prior to surgery, these patients had a diagnostic hysteroscopy which showed that the bleeding was due to submucosal fibroids, to intrauterine or cervical polyps, either alone or in association with adenomyosis, or to adenomyosis alone. These patients were treated as outpatients with the Nd-YAG laser, by using paracervical anaesthesia. In 80%, the menstrual cycle has returned to normal after a short follow-up (four cycles). Three patients required hysterectomy because hysteroscopy was impossible owing to multiple fibroids. Two patients have been lost to follow-up observations. In addition, there was a beneficial result on secondary dysmenorrhoea. Wherever necessary, uterine septa and synechiae were divided. Between six and 10 weeks after treatment, a follow-up hysteroscopy was performed. This confirmed that there was no recurrence of the underlying lesion, that the treated areas were scarred and that the endometrium in these areas was functional. Longer follow-up is necessary to assess the precise proportion of hysterectomies that can be avoided by using this technique.     

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty

Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires compared with the SLT probes [P less than 0.001, one-way ANOVA]. The SLT system is, therefore, potentially safer in this respect. These results suggest that some degree of surface heating of contact probes due to energy absorption within the sapphire does occur, but is localised to the front of the probe. This effect may contribute to the process of arterial recanalisation with this device. However, variation in the thermal and optical properties of sapphires from different sources has been demonstrated. The influence of these properties on plaque ablation, and ultimately the clinical performance of different contact probe systems, requires further investigation.     

激光心肌打孔后远期心肌血供的实验研究：带蒂大网膜覆盖心表面

为进一步了解激光心肌打孔的远期疗效，作者用２６条犬，制成心肌梗塞模型，并分为三组：（１）对照组；（２）Ｎｄ：ＹＡＧ激光心肌打孔组；（３）Ｎｄ：ＹＡＧ激光心肌打孔加带蒂大网膜覆盖心表面。观察近期（１周、２周）、远期（１～１８个月）的结果。监测指标：死亡率、心电图、心输出量、放射性同位素８６Ｒｂ摄取量和组织学检查。结果显示：Ｎｄ：ＹＡＧ激光心肌打孔后，可立即改善缺血心肌血供，重建心肌血循，增强心功能。但２周后打孔孔道开始逐渐闭塞。带蒂移植的大网膜在短期（３～５天）内即开始与心肌建立侧支循环，５～１２天时大大增强，向缺血心肌提供血液，弥补了远期激光孔道闭塞后血流减少的不足。此法远期效果明显优于单纯激光心肌打孔术。     

PHACES syndrome: Diode laser photocoagulation of intraoral hemangiomas in six young patients

IntroductionThe acronym PHACES describes the association of posterior fossa malformations, facial hemangiomas, arterial anomalies (cardiovascular or cerebrovascular), coarctation of the aorta and cardiac defects, eye abnormalities, and sternal or ventral defects. In this study we report on 6 patients affected by the PHACES syndrome and showing 34 intraoral hemangiomas (IH), treated by diode laser photocoagulation (DLP).Case presentationIH appeared as red-bluish soft masses, smooth or lobulated, from a few millimetre to several centimetres in size, covered by intact mucosa and blanching on pressure. IHs were treated by DLP with 320 μm fibres at a wavelength of 800 ± 10 nm. The diode laser techniques applied were: Transmucosal DLP (DLTP), a no-contact technique in which laser energy is delivered by a flexible optic quartz fiber, which is kept 2–3 mm apart from the lesion, and Intralesional DLP (DLIP), in which the fibre is introduced into the lesion through a transmucosal access. DLTP was used for 20 flat, superficial IHs and, after a variable number of laser sessions (average = 3) depending on the size of the lesion, 65% completely regressed, while in the remaining 35% shrinkage of the lesion was achieved with minor and few complications.The remaining 14 deep/multi-lobulated IHs were treated by DLIP, resulting in complete regression of 79% of them.ConclusionsDLP techniques are an effective and minimally invasive procedure for IH in patients with PHACES, in consideration of the multiple lesions to treat, of the necessity of multiple interventions and the higher compliance of the patients.     

Arthroscopic shoulder surgeyr with three different laser systems: An evaluation of laser applications

Twelve cadaveric shoulder arthroscopies were performed to evaluate the use of lasers as an adjunctive tool in arthroscopic shoulder surgery. The three most common lasers historically used in orthopedic surgery were examined: Holmium:YAG, Neodymium:YAG, and the CO₂. The following parameters were evaluated for each laser system: (1) each of use of the laser system and handpiece; (2) ability to excise and trim bursae, synovium, ligament, tendon, bone, and articular cartilage; and (3) ability to contract ligaments and capsule by heat transfer. None of these lasers efficiently cut bone, whereas all three systems readily debrided the soft tissues around the shoulder. The free-beam Ho:YAG and CO₂ systems heat contracted soft tissues with more control than the contact Nd:YAG. The fiberoptic delivery system of the Neodymium:YAG and Holmium:YAG laser performed well in the saline arthroscopy, and the CO₂ delivery system was cumbersome. Overall, the CO₂ system removed tissue better than the others, but its difficult use favored the Holmium laser as the best overall current laser system for shoulder arthroscopy.     

Electroresection followed by neodymium-YAG laser photocoagulation of the dog prostate for establishment of safety parameters

Electroresection of the prostate followed by Nd-YAG laser coagulation of residual prostate was carried out in eight dogs. All dogs voided spontaneously without significant bleeding in the immediate postoperative period. At the time of sacrifice in 6 to 8 weeks, no damage to adjacent tissue was seen on microscopic examination. Re-epithelization had occurred. This study suggests that the addition of neodymium-YAG coagulation to residual tissue after TURP in humans can be done safely.     

Effects of super-pulsed Nd-YAG laser on arterial tissue: comparison with continuous wave

The effects of a super-pulsed Nd-YAG laser at 1.32 μm wavelength on normal or atherosclerotic human arterial tissue were evaluated and compared with those obtained with continuous wave. One joule per pulse was delivered through a 0.2 mm optical fibre with a pulse width of 10 ms at 10 Hz (super-pulse), or 10 W (10 J) were delivered at continuous wave in saline or blood. Ten joules were delivered with super-pulse or continuous wave for each tissue specimen. The aortic specimens were lased either by continuous wave or super-pulse. At super-pulse mode, ablation efficiency (mm³ J⁻¹) was 0.0149±0.0044 for normal tissue in saline, 0.0148±0.0043 for atheroma in saline, 0.0138±0.0062 for normal tissue in blood, and 0.0146±0.0049 for atheroma in blood. There was no significant difference between the groups. At continuous wave mode, ablation efficiency was 0.0507±0.0299 for atheroma in blood (p<0.001 vs super-pulse). However, extensive charring was observed with continuous wave lasing (41% with continuous against 14% with pulsed mode,p<0.001). Heavily calcified plaques were also ablated at 1.5 J per pulse and 15 W (continuous wave), resulting in extensive charring with continuous wave (77% vs 18% with super-pulse,p<0.01). In conclusion, at super-pulse mode, 1.32 μm Nd-YAG laser has neither the selectivity for atheroma nor influence of blood, thermal injury induced by super-pulse is less than that induced by continuous wave (cw), calcified plaques can be ablated by super-pulse, and super-pulsed Nd-YAG laser angioplasty is safer to use than continuous wave.     

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.     

Sapphire probe laser ablation of human arteries with CO2 gas and saline perfusion: The effect of flow rate,lasing power and lasing time

To evaluate flow rate dependence of CO₂ gas and saline perfusion for sapphire probe ablation, all together 204 human arterial specimens of atheroma and normal vessel were irradiated with Nd-YAG laser, in an experimental circulation-occlusion model within 37°C flowing whole blood. During lasing procedures, various flow rates of CO₂ gas (0.2–2.01 min⁻¹) and saline (2.0–20.0 ml min⁻¹), and various lasing powers (7, 12 and 17 W) and lasing time (1–20 s) were used. Histological changes of all specimens irradiated were microscopically examined. The results showed that the laser ablation area enlarged with increasing CO₂ flow rates and decreasing saline flow rates. Relative ablation efficiency on atheromatous plaque, in comparison to those on normal vessel wall and surrounding tissue site, increased slightly with increasing lasing power and lasing time. In this experimental setting, the mode of action of the sapphire probe ablation on human arterial atheroma seems to be more satisfactory with CO₂ gas perfusion than with saline perfusion.     

The use of the Nd-YAG and the CO2 laser in neurosurgery

Summary Over the last 3 years 120 patients have been operated on using laser techniques. This technique was chosen where technical difficulties were anticipated due to the size, the vascular supply or the localization of the process. Although the use of laser technique requires experimental work, before it can be applied clinically some distinct advantages could be demonstrated when compared with the use of the bipolar cautery.Due to its shrinking effect the laser beam is target oriented and makes the surgical procedure safe without the use of additional instruments. The Nd-YAG laser was preferred in tumors with a rich vascular supply. Thus there was a definitely decreased need for blood transfusions in patients operated on with the laser. Even those parts of the tumors that can not easily be reached, using conventional techniques can now be eliminated by laser irradiation.The variable distance between the handpiece of the laser instrument and the target organ allows a pin point as well as a more diffuse irradiation. Since it is not necessary to touch the tissue, laser techniques are particularly useful in critical areas, e. g. close to the brainstem or the spinal cord, because they make it unnecessary to touch the tissue.The question as to whether the use of laser technique will reduce the rate of recurrent tumor growth needs further studies based on longer follow-up periods. Further technical improvements are needed to make the laser device a true microinstrument. Finally a combination of both laser types — that is the Nd-YAG laser for coagulation and the CO₂ laser for cutting -might be a definite advantage.Dedicated to Prof. Dr. Dr. h. c. K. J. Zülch on occasion of his 70th birthday.     

The role of pulse length in limiting distant damage to vascular tissue caused by the Nd-YAG laser

The total damage caused by equivalent doses of energy given to human cadaver vascular tissue over the same time scale from three Nd-YAG lasers of different pulse lengths is quantified. The continuous wave (c.w.) laser produces vacuolation and coagulation around a vaporized crater; the 100 μs pulsed laser produces less surrounding damage and the 10 ns pulsed laser none at all. The areas of damage in five craters made with 10 J energy were measured from histology slides using a digitising platten, and it was found that in each case the total amount of damage was the same, even though the depth of the craters made varied. The dose response for vaporization of the 10 ns pulsed laser was the greatest at 35 μm/J and that of the c.w. laser was least at 8 μm/J. A pulse length of 100 μs may not be the optimum for limiting surrounding tissue damage during laser angioplasty but it produces much less damage than a c.w. laser and unlike the 10 ns pulses is easily transmissible down an optical fibre.