Quantitation of colonic injury from argon laser, neodymium: YAG laser and monopolar electrocautery applied to flat mucosa and small sessile polyps of the canine colon

This study determined the optimum laser energy for ablation of colonic mucosal lesions and small sessile polyps in the canine colon. Neodymium (Nd):YAG laser, argon laser, and monopolar electrocautery were applied to exposed canine colonic mucosa for various application times at various power settings. At the minimum energy level necessary to ablate mucosa, the Nd:YAG laser caused greater muscularis injury than the argon laser and monopolar electrocautery. At higher energy levels, monopolar electrocautery and Nd:YAG laser caused greater muscularis injury than argon laser. Small surgically created polyps in the canine colon were ablated endoscopically with the three energy sources. Single-session complete polyp ablation occurred most frequently with Nd:YAG laser and least frequently with argon laser. The depth of tissue injury beneath polyp ablation sites was least with argon laser and greatest with Nd:YAG laser. This study suggests that the argon laser is safer than the Nd:YAG laser or monopolar electrocautery for coagulation of flat colonic mucosal lesions. Although the argon laser is safer for the coagulation of small sessile colonic polyps, it may be less effective than monopolar electrocautery or the Nd:YAG laser for the single-session fulguration of polyps greater than 5 mm in diameter.     

The tissue effect of second generation argon plasma coagulation (VIO APC) in comparison to standard APC and Nd:YAG laser in vitro

BACKGROUND: The aim of this study was to evaluate the effect of 2nd generation argon plasma coagulation (VIO APC) with respect to the tissue destruction capacity, and to compare it with standard APC and Nd:YAG laser. METHODS: 2nd generation APC (VIO APC2, Erbe, Germany), standard APC (APC 300/Erbotom ICC 200, Erbe) and Nd:YAG laser (KTP/YAG XP 800; Laserscope, San Jose, California) were applied in 35 porcine livers. Using APC, power settings (30-120 W), application time (2 and 5 sec) and gas flow (1 and 2 l/min) were varied. Using Nd:YAG laser, 30-60 W were applied (flow 21/min). Diameter and depth of tissue coagulation were evaluated. RESULTS: Using VIO APC, maximum coagulation depth was 6 mm (maximum diameter 15 mm). In comparison to standard APC, the coagulation effect was significantly higher (p < 0.001). There was no significant difference in the mean depth achieved by VIO APC and Nd:YAG laser using 30- 60 W and an application time of 2 sec (p < 0.05). Using maximum energy available for the 2 systems, maximum depth achieved by VIO APC (6 mm) was higher than the one caused by Nd:YAG laser (4 mm). CONCLUSIONS : VIO APC was more effective than standard APC. Using medium power and a limited application time, it was as effective as Nd:YAG laser. The high effectiveness of VIO APC should be a topic of clinical education.     

Argon vs. neodymium YAG laser photocoagulation of experimental canine gastric ulcers

A neodymium YAG (Nd:YAG) laser was evaluated in a dog ulcer model used in the same manner as is recommended for bleeding patients (power 55 W, divergence angle 4 degrees, with CO2 gas-jet assistance). The experiments were performed during sterile laparotomy in heparinized dogs. Bleeding gastric ulcers were photocoagulated until bleeding stopped and then examined histologically 7 days later when depth of tissue injury was maximal. In the first series of experiments, the Nd:YAG laser was compared with the 7-W argon laser in the same dogs. Both lasers stopped bleeding from all experimental ulcers. The 55-W Nd:YAG laser caused full-thickness injury to the gastric wall beneath 11 of the 14 treated ulcers, whereas the 7-W argon laser caused no full-thickness injury beneath 14 treated ulcers. In a second series of experiments, we tried to determine whether varying exposure times with the 55-W Nd:YAG laser would make it less injurious; it did not. In a third series of experiments, the 55-W Nd:YAG laser was tested with and without CO2 gas-jet assistance in order to determine if this would affect the depth of injury; it did not. In the final series of experiments, the wattage of the Nd:YAG laser was varied to see if this would reduce depth of injury; lower wattage did not stop bleeding, and intermediate and higher wattages did stop bleeding but did not reduce depth of injury. We conclude that the 55-W Nd:YAG laser as it is currently used clinically produces deeper tissue damage than the argon laser in our animal model. This damage is not reduced by changes in power, duration of exposure, or the presence of gas-jet assistance.     

Direct visualization of epicardial structures and ablation utilizing a visually guided laser balloon catheter: preliminary findings

Epicardial Laser Balloon Ablation. Background: Intrapericardial mapping and ablation can be utilized to target epicardial arrhythmic circuits. Current epicardial ablation strategies are associated with risk of damage to adjacent structures, including the coronary vasculature and phrenic nerves. Objectives: The purpose of this study was to evaluate the feasibility of an investigational, visually guided laser balloon catheter for manipulation within the pericardial space, visualization of epicardial structures, and delivery of laser ablation lesions to the ventricular myocardium. Methods: Pericardial access was obtained in 4 anesthetized swine by subxyphoid puncture. The laser balloon catheter was introduced into the pericardial space via a deflectable sheath, and was manipulated to predefined regions in all animals. Visually guided laser ablation was performed on the ventricular myocardium, with post mortem examination of lesion size and depth. Results: The laser ablation catheter could be manipulated to all targeted regions in all animals. Associated structures, including epicardial coronary arteries and veins as well as an endocardial catheter in the left atrial appendage, were easily visualized. A total of 9 laser energy applications at varying power/time settings were performed. Ablation utilizing moderate (7–8.5 W) power produced relatively uniform lesions (diameter 5–12 mm, depth 6–9 mm), while high (14 W) power produced a visible “steam pop” with a large, hemorrhagic lesion (22 × 11 × 11 mm). Conclusions: The investigational laser balloon catheter can be manipulated within the epicardial space, allowing for direct visualization of surrounding structures during ablation. Titration of laser power can be utilized to create moderate‐sized ablation lesions while avoiding steam pops . (J Cardiovasc Electrophysiol, Vol. 22, pp. 808‐812, July 2011)     

Percutaneous endocardial Nd-YAG laser energy: experimental studies of ablation of the ventricular myocardium]

The in vitro and in vivo effects of endocardial laser ablation were assessed. Energy was supplied by a Nd-YAG laser (wavelength approximately 1064 nm) and transmitted via a quartz core fiber (phi: 0.4 mm) housed within a specially designed 7 F catheter. In vitro, the effects of increasing output power (5, 10, 20, 40 watt) and impulse duration (1, 2, 4, 8 s) on lesion size were assessed in myocardial preparations of canine hearts. Preparations were superfused with saline or blood, respectively; the distance of the optical fiber to the endocardium was 5 mm. Lesion size increased in diameter (range: 0-4.0 mm) and depth (range: 0-5.2 mm) in a power- and time-dependent manner. Superfusion with blood significantly enhanced the diameter of the lesions, whereas depth of the lesions significantly decreased. In 16 anesthetized mongrel dogs, a total of 52 laser impulses (output power: 10, 20, 40 w; impulse duration: 1, 2, 4 s; energy: 10-160 J) were delivered to apical and apico-inferior sites of the left ventricle. Postmortem, 40 lesions with a diameter of 2.6-19.4 mm and a depth of 3.7-16.2 mm were found. 19 lesions revealed central vaporized craters with a depth up to 11.2 mm. Perforation of the left ventricle occurred in two cases following 80 and 160 J, respectively. In vitro and in the intact animal (in apical and apico-inferior sites of the left ventricle) endocardial laser ablation is feasible to induce distinct myocardial lesions in a power- and time-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of the thermal laser effect of laser irradiation for cardiovascular applications exemplified by the Nd:YAG laser

Techniques of percutaneous transluminal application of laser energy for vessel recanalization have been used clinically since 1983. The commonly used Nd:YAG and argon lasers achieve ablation of atherosclerotic plaques by thermal action (vaporization). In order to reduce undesirable thermal damage in the neighborhood of the target tissue and to avoid vessel perforation, optimal irradiation parameters, modified (atraumatic) fiber tips (hot tips, sapphires), and steerable catheter systems needed to be implemented. Favorable results from peripheral application have encouraged use in the coronary circulation. More recently, coagulative tissue effects of circumferential irradiation of the vessel wall during balloon dilatation have been used for stabilization of acute and late results after mechanical balloon angioplasty. Enhancement of the differential light absorption of atherosclerotic plaque by use of biological dyes may further improve selective intravascular laser application. Intraoperative ECG-guided laser coagulation of arrhythmogenic areas of myocardium is a method for treatment of malignant arrhythmias. Transluminal non-operative application of myocardial laser photocoagulation has now been tested experimentally and shown to be safe and effective. There was no arrhythmogenicity or thermal damage of coronary arteries associated with this method. Innovative techniques such as nanosecond pulsed excimer lasers (athermal action) and development of "intelligent" lasers--which are equipped with spectroscopy-guided feedback systems for plaque recognition--have opened new perspectives and will further improve safety and efficacy of clinical laser application. However, according to current experience, the thermally acting Nd:YAG laser is an effective and versatile mode of laser therapy for selected cardiovascular indications.     

Tissue ablation with excimer laser and multiple fiber catheters: effects of optical fiber density and fluence

This study was performed to assess the ablational properties of 1.4-, 1.7-, and 2.0-mm wire-guided multiple fiber catheters coupled to a XeCl excimer laser. Samples of postmortem human aorta were irradiated in blood at fluences of 40, 50, and 60 mJ/mm 2. Our results indicate that: 1) an increase in the active irradiation coverage results in an increase in the ablation efficiency; 2) the ablation efficiency is not fluence related using the 1.4- or 1.7-mm multiple fiber catheter but efficiency is fluence dependent using the 2.0-mm multiple fiber catheter; 3) the depth of tissue ablated with a multiple fiber catheter depends primarily upon the proportion of the active irradiation coverage at the catheter tip; 4) the 2.0-mm multiple fiber catheter induces craters surrounded by a larger zone of tissue damage than that observed with the 1.4- or 1.7-mm multiple fiber catheter; and 5) the 2.0-mm multiple fiber catheter should be used cautiously for laser angioplasty because of its high penetration and its risk of arterial wall damage.     

Endocardial photoablation by excimer laser

A xenon-chlorine excimer laser was used to irradiate normal endocardium of fresh sheep and pig hearts as well as unfixed human endocardial scar. Forty pulses of 370 J and 35 ns each resulted in penetration of up to 12 mm in normal tissue and only 3.5 mm in scarred endocardium. Dosimetry indicated that the volume of vaporized scarred tissue was 1/10th that of normal endocardium (0.19 to 0.40 versus 1.35 to 3.22 mm3/J). Ultrastructurally, there was a sharp demarcation of only 10 mu between the region of injury and normal myocardium, with little evidence of heat injury. The high power and short duration of these lasers coupled with the lack of a boundary zone of injury suggest that excimers may be an ideal tool for arrhythmia ablation.     

Catheter-directed laser coagulation of atrial myocardium in dogs

The feasibility of transcatheter laser coagulation of atrialmyocardium was tested in a canine model by using a combinedelectrode-laser catheter. In 17 anaesthetized beagles a totalof 264 lesions, 12–19 per dog, and 3–5 in each areawere produced in: (1) the lateral walls, (2) the posterior rightatrial walls, (3) the inter-atrial septum, and (4) the atrialappendage. The power source was a continuous wave Nd: YAG laser.Irradiance was 1 kW. cm^–2, at a wave length of 1064 nm,the irradiated spot diameter was 2.0–2.5 mm, and the pulseduration 5–60 s. Local intra-cardiac atrial potentialsrecorded from the targeted areas during laser irradiation dwindledafter onset of the laser pulse, and their amplitude was reducedpersistently by pulses of 15 s or longer. Histopathologically,the acute lesions showed intramural haemorrhage and coagulationnecrosis, but there was no tissue vaporization or crater formation.Chronic lesions showed clear-cut oval-shaped areas of transmuralfibrosis. Diameters of lesions, dependent on the amount of laserenergy applied, measured from 4.6 ± 0.5 mm (450 J) to7.8 ±1.4 mm (1800 J). Follow-up lasted 6–25 months(average 10.5). All the animals survived the procedure withoutcomplications. Transcatheter laser coagulation of atrial myocardium is safeand can be performed in a controllable manner by using the cathetersystem presented.     

A Novel Catheter Design for Laser Photocoagulation of the Myocardium to Ablate Ventricular Tachycardia

Nd:YAG laser energy has been proposed as an alternative to radiofrequency energy for ablation of ventricular tachycardia (VT) associated with coronary artery disease (CAD) in an effort to increase lesion size and success rates. However, issues of catheter design to maintain flexibility and ensure adequate tissue contact have hindered development of laser catheters.We developed and tested a prototype 8 Fr. steerable catheter with a flexible and extendible tip (designed to ensure tissue contact and efficient ventricular mapping), which projects the laser beam through a side port containing a lens-tipped optical fiber that rests against the endocardial surface. The catheter has a channel for simultaneous saline irrigation to displace the interceding blood and discharge a laser beam between two electrodes for bipolar mapping and a thermocouple for temperature monitoring. The catheter was tested on bench top using the epicardial surface of freshly slaughtered bovine hearts and in vivo using six anaesthetized closed-chest sheep. In vitro experiments demonstrated that lesion size increased linearly with applied power up to 40 watts. When compared to radio frequency, laser energy penetrated more deeply into the myocardium. In the in vivo studies, using increasing powers of up to 40 watts for application times of 60 to 120 seconds created circular or elliptical lesions with surface dimensions up to 12 mm × 12 mm and depth of 9 mm (full LV wall thickness with a mean lesion diameter of 9.9 ± 5.2 mm and depth 5.8 ± 3.2 mm). Most lesions, 16 total in both right and left ventricular walls were transmural or near transmural in thickness. Lesions demonstrated coagulation necrosis with smooth well-demarcated borders. No animal suffered cardiac perforation, hypotension, hemopericardium, damage to cardiac valves, or cavitation effect from any of the ablations. Runs of VT were seen during energy application at the highest laser outputs in two animals.In conclusion, this catheter design provides effective endocardial delivery of laser energy and is capable of creating transmural or nearly transmural lesions in vivo and in vitro, thereby potentially increasing the efficiency of VT ablation in CAD patients.     

Current Status of Lasers for Arrhythmia Ablation

Current Status of Lasers for Arrhythmia Ablation. Wavelength specific effects and mode of laser operation allow either photocoagulation or tissue removal as a means of approaching arrhythmia ablation. Successful intraoperative ablation of ventricular tachycardias has been performed with the Nd: YAG laser (photocoagulation) and argon laser (tissue vaporization). The argon laser has been used intraoperatively for transection of accessory pathways. Experimental studies indicate a strong theoretical potential for Nd:YAG laser catheter ablation of ventricular tachycardia. Laser energy has been used experimentally to evaluate the possibility of AV junctional ablation/modification and accessory pathway ablation. Adaption of laser energy to effective catheter systems for arrhythmia ablation requires solutions to problems inherent in all catheter systems and some unique to laser energy. (J Cardiovasc Electrophysiol, Vol. 3, pp. 345–353, August 1992)     

Experimental study of laser ablation on lethal arrhythmias in dogs

To study the effect of laser ablation on arrhythmogenic ventricular myocardium, we applied aconitine on 36 local epicardial sites of ventricles (22 in LV, 14 in RV) in 12 dogs. Severe monographic persistent VTs or VFs were induced by aconitine and then these foci were irradiated by Nd: YAG laser. RV refractoriness (RVR) and local epicardial pacing threshold (LEPT) were measured by programmed electrical stimulation (PES) before aconitine applying and after resuming sinus rhythm. That VT or VF could not be induced by PES and the heart had persistent sinus rhythm was considered success. Aconitine doses were 7.9 +/- 4.8 micrograms in LV, 3.3 +/- 1.9 micrograms in RV, P less than 0.01. The data of time from aconitine applying to the appearance of VT were 237 +/- 228 s in LV and 148 +/- 101 s in RV, P less than 0.05. VF incidence rate was 75% (27/36). All of VT, VF could be abolished by mapping-guided laser irradiation on VT foci. The mean laser energy was 1542 +/- 893 joules (n = 36). RVR and LEPT increased significantly (P less than 0.001) after tests. Results showed that: (1) Lethal ventricular arrhythmias could be induced by giving little aconitine on the ventricular epicardium; (2) Mapping-guided lasering on arrhythmogenic myocardium could eradicate VT and VF; (3) RVR and LEPT would increase greatly after ablation.     

应用不同射频导管电极消融犬房室环处心肌组织的损伤范围及其相邻冠状动脉损伤的研究

目的 分析应用不同射频导管电极消融房室环处心肌组织的损伤范围及其邻近冠状动脉(冠脉)的损伤,评价其临床应用的安全性.方法 取成年犬21只,随机分为3个能量组:64℃、50 W、100 s,64℃、100 W、100 s,45℃、45 W、100 s;分别应用4、8 mm电极及冷盐水灌注电极进行消融(分别简称4 mm组、8 mm组和冷盐水组).每只犬分别消融左、右房室环各1处.实验结束后以1/6π×长×宽×深计算损伤体积并对损伤的心肌及冠脉组织进行光学显微镜病理学分析.结果 观察损伤深度:4mm组为(4.54±1.38)mm,8mm组为(7.18±1.72)mm,冷盐水组为(7.99±1.77)mm.统计学分析:4 mm组与8mm组和冷盐水组的组间相比,差异均具有统计学意义(P<0.01);后两组组间的差异无统计学意义.损伤体积:4mm组为(191.34±74.52)mm3,8mm组为(356.76 ±94.44)mm3,冷盐水组为(391.69±109.54)mm3;4mm组与8 mm组和冷盐水组的组间差异具有统计学意义(P<0.01),后两组组间差异无统计学意义.42处消融灶中有5处消融灶发生透壁性损伤.8处消融灶附近的冠脉发生病理性损伤,其中3处冠脉损伤明显.结论 应用8 mm及冷盐水灌注电极消融可使心肌损伤明显扩大,可以导致透壁性损伤,可以损伤邻近的冠脉.     

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

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Parameters for and safety of contact Nd:YAG laser irradiation of early gastric cancer: an in vitro study

Early gastric cancers have been treated by endoscopic contact Nd:YAG laser irradiation. The extent of thermal damage produced by this laser system has been inadequately investigated. In an in vitro study we have shown that contact laser probes produce consistent and reproducible thermal lesions in the human stomach wall. Contact laser energies of 40 to 60 joules are optimal for the ablation of early gastric cancer. Energies greater than 90 joules are associated with a high incidence of gastric perforation. Contact laser probes may have advantages over non-contact laser techniques for the endoscopic treatment of early gastric cancer in patients who are unfit for major surgery.     

Control of radiofrequency lesion size by power regulation

The influence of power and exposure duration on lesion size in radiofrequency catheter ablation was investigated in 15 closed-chest dogs. Radiofrequency energy was delivered to the right ventricular endocardium between the tip of a standard 6F electrode catheter and a large W and durations of 5, 10, 20, 30, and 60 seconds. At necropsy 1 week later, well-demarcated homogeneous lesions were found when power had exceeded a threshold level that decreased from 1.8 W at 5 seconds to 0.7 W at 60 seconds. Lesion size ranged from 0 to 7.5 mm in depth and 0 to 9 mm in diameter. For the 5, 10, and 20 second ablations, lesion size was determined by exposure duration and power level. However, after a 20 second exposure, lesion size had reached maturity and was related to delivered power only. Therefore, a gradual, controlled growth of the lesion can be obtained by a stepwise increase of the radiofrequency power level with ample exposure duration at each level to allow for stabilization. At levels exceeding 7 W, the formation of a thin insulating layer of blood coagulum on the electrode surface caused an abrupt increase of impedance within approximately 30 seconds. Therefore, lesion size is limited to 8.5 mm in radiofrequency ablation with a standard 6F endocardial electrode catheter.     

Laser ablation and the need for intra-arterial imaging

In 48 patients with severe claudication due to a total obstruction of the femoropopliteal artery, percutaneous recanalization was attempted with a 2.2 mm diameter rounded sapphire contact probe in conjunction with a continuous wave Nd:YAG laser. In eight patients the contact probe laser catheter took a subintimal course that could not be redressed. Laser recanalization needs high-resolution diagnostic information on the complex anatomy of the obstruction. Intra-arterial ultrasound imaging may provide the necessary information to evaluate, monitor or guide novel angioplasty techniques. The design of an ultrasound catheter which combines high-resolution diagnostic imaging with steerability, flexibility and controlled ablation is now the major engineering challenge in interventional cardiology.     

A canine trial using transventricular laser channel

Revascularization of ischemic myocardium by Nd: YAG laser channels was studied in 33 dogs with myocardial infarction. The dogs were separated into epi- and endo-cardial (percutaneous and intraoperative) groups. Laser channels with a diameter of 400 microns were made by 6.7-6.8 watt lasersonics Nd: YAG unit. Then the dogs were killed and core samples of myocardium from the laser area were taken as planned. Evaluation includes pre- and post-operative echocardiography and radionuclide scanning to measure left ventricular (LV) function and regional blood flow. Improved LV function and increased uptake of radionuclides were demonstrated. There was no operative mortality. The histologic evidences of reconstructed myocardial microcirculation and communications with myocardial channels by laser were also reported.     

Neodymium:yttrium-aluminum garnet contact laser ablation of Barrett's high grade dysplasia and early adenocarcinoma

OBJECTIVES: We describe the efficacy and safety of neodymium:yttrium-aluminum garnet (Nd:YAG) contact laser ablation of Barrett's high grade dysplasia (HGD) and/or early adenocarcinoma. METHODS: Consecutive Barrett's patients in whom HGD or adenocarcinoma was detected were eligible. Radial array echoendosonography and high frequency catheter probe ultrasonography were performed. Patients were excluded if ultrasound revealed the presence of Barrett's cancer with regional lymph nodes or celiac trunk metastases or extension of the tumor into superficial submucosa (T1sm1) or greater. Nd:YAG laser used quartz contact probes, with all Barrett's epithelium targeted at each session. Complete ablation was confirmed with Lugol's iodine chromoendoscopy followed by surveillance biopsies of the neosquamous epithelium. Adverse events were ascertained by scheduled telephone contact interviews. RESULTS: A total of 36 patients with HGD/adenocarcinoma were evaluated at our center, 17 of whom met all inclusion criteria. Of the patients, 14 have remained in the study, and all have had successful elimination of HGD and cancer. In addition, 11 patients (78.6%) achieved complete endoscopic and histological ablation of all Barrett's tissue. Two patients (14.3%) achieved 95% destruction of Barrett's with residual metaplastic columnar epithelium containing goblet cells without dysplasia. The remaining patient has obtained 75% ablation of Barrett's, with residual metaplastic columnar epithelium harboring Barrett's with low grade dysplasia. Major complications included two esophageal strictures (11.8%) and one mild upper GI bleed (5.9%). CONCLUSIONS: This preliminary experience with Nd:YAG contact laser for the treatment of Barrett's HGD and early superficial cancers seems promising. The need for additional controlled trials with larger numbers of patients with longer follow-up, as well as consideration of a head-to-head trial with Photofrin photodynamic therapy, is warranted.     

Use of pulsed energy delivery to minimize tissue injury resulting from carbon dioxide laser irradiation of cardiovascular tissues

The carbon dioxide (CO2) laser has been utilized for preliminary intraoperative cardiovascular applications, including coronary endarterectomy and ventricular endocardiectomy. CO2 lasers used for these applications have been operated in the continuous wave, chopped or pulsed mode at low peak powers. To evaluate the extent of boundary tissue injury, continuous, chopped and pulsed energy delivery of CO2 laser emission was used to bore through 192 5 mm thick myocardial slices in air. Continuous, chopped and pulsed delivery at a peak power of 500 W or less failed to eliminate light microscopic or ultrastructural signs of thermal injury. Only when a high energy CO2 laser (pulse energy 80 to 300 mJ, pulse duration 1 microseconds) was used at a peak power greater than 80 kW were all signs of thermal injury eliminated; furthermore, high peak power prevented thermal injury only when the beam was focused to achieve a peak power density greater than 60 kW/mm2. Under these conditions, pathologic findings were identical to those observed using excimer wavelengths. The results of these experiments indicate that: conventional CO2 lasers fail to minimize boundary tissue injury, elimination of thermal injury during intraoperative laser ablation requires that CO2 laser energy be focused to achieve a peak power density greater than 60 kW/mm2, and elimination of thermal injury can be achieved at a variety of wavelengths, provided that an appropriate energy profile is employed.