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.     

Effects of Nd:YAG laser irradiation on ventricular myocardium in dogs using an artificial sapphire tip contact laser catheter]

To apply Nd:YAG laser irradiation through a new sapphire tip contact laser method to catheter ablation in treatment of tachy-arrhythmias, effects of laser irradiation on ventricular myocardium were investigated in 10 mongrel dogs. Nd:YAG lase (1064nm) discharges were delivered to different sites on the endomyocardium at power of 5, 10, 15, 20 or 25w with duration of 3, 5, or 10 seconds (sec.) respectively in closed beating hearts. Histopathologically, the lesion irradiated was clearly demarcated from the normal myocardium by the construction band necrosis zone. The depth of injured myocardium was less than 2mm with 3 sec. irradiations, with 5 sec. from 1 mm to 4 mm in proportion to power increase, with 10 sec. from 3mm to 8 mm in proportion to the power from 5w to 15w and could not be measured in cases of more than 20w irradiations. Although with every irradiation duration, the depth of injury increased in proportion to the power increase. With the same total energy, a longer time of irradiation produced deeper injury than a shorter time. This method makes it easier to keep the laser positioned to target than bare laser, and is suitable for use in catheter ablation.     

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.     

Only transient increase of vascular growth factors and microvascular density after percutaneous myocardial laser

OBJECTIVE: We tested the hypothesis that percutaneous myocardial laser may stimulate microvascular growth in areas surrounding the laser channels. METHODS: We conducted a study of 24 domestic pigs, which underwent percutaneous myocardial laser to left ventricular myocardium using holmium:YAG laser. The pigs were sacrificed in groups of four after one day, 3-4 days, one week, three weeks and six weeks. Frozen sections from both normal and treated myocardium were prepared for immunofluorescence microscopy and stained with antibodies against von Willebrand factor, vascular endothelial growth factor (VEGF) and Extra Domain-A cellular fibronectin (ED-AcFN). Microvascular density (MVD) and vascular area (VA) were determined in sections stained with antibodies against von Willebrand factor VIII using a digitised image analysis system. When determined in laser treated areas, channel core remnants were excluded from analysis. RESULTS: Within the laser channel remnants and in the tissue closely surrounding these, expression of VEGF and ED-AcFN increased significantly after treatment at one, 3-4, and seven days and decreased to normal at three and six weeks. Expression of ED-AcFN was detected adjacent to endothelial cells of microvessels. The original laser channels were rapidly invaded by granulation tissue. There was no sign of recanalization at any stage during the six weeks. Morphometric analysis showed no increase in MVD and VA in the myocardium surrounding the laser channels. CONCLUSION: An increase of VEGF and ED-AcFN after myocardial laser is transient and is not associated with increase of MVD or VA in myocardium not involving laser channel remnants.     

经皮激光心肌血运重建术的初步临床应用

目的初步评价采用钬YAG激光器及其导管系统对冠心病患者行经皮激光心肌血运重建治疗(PMR)的方法学和临床疗效。方法14例病人均为男性,平均年龄(63.3±7.5)岁,心绞痛史(7.3±7.0)年。病例选择标准①药物治疗无效的Ⅲ、Ⅳ级心绞痛;②冠状动脉病变不宜作经皮冠状动脉腔内成形术(PTCA)或冠状动脉旁路移植术;③左室射血分数(LVEF)≥45%;④6个月内无心肌梗死病史;⑤心电图、平板试验或ECT检查有心肌缺血证据;⑥超声检查左室壁最大舒张期厚度≥8mm。操作方法先作RAO30°和LAO60°左室造影,冻结在最大舒张期作为定位参照;将激光系统心电同步调整在T波易损期前30ms,校正实际激光能量;经大腔引导管送入激光导管,对缺血左心室壁进行激光打孔,深度控制在6mm以内;在屏幕上标示出打孔部位和序号以保护打孔均匀。随访观察心绞痛级别、心电图、心脏超声、ECT、心肌酶等。结果每例平均打孔(17.5±4.1)个,发放脉冲(68.1±9.3)个,能量(135.8±18.2)J.PMR操作中病人无不适,操作时间(87.5±24.3)min,X线透视时间(23.5±7.6)min。未发生心包填塞等并发症。随访(4.9±1.4)个月,心绞痛平均下降2.4级,药物减少2.1种,缺血心壁减少0.9个,运动耐量提高(P<0.05)。结论PMR是治疗顽固性心绞痛和改善心肌缺血的有效方法之一。其操作方法简单实用,可防止心脏穿孔和恶性心律失常发生。远期疗效尚有待进一步观察。     

AMI犬TMLR术后心肌血流量变化及意义

目的 本实验观察了激光心肌血管重建术(TMLR)后心肌血流量的变化,探讨TMLR的作用机制。方法 18只犬随机等分为三组:A组-对照组;B组-缺血组;C组-激光组。采用连续型Nd:YAG激光行心肌打孔,光纤直径0.6mm,功率20～25W,脉冲时间0.3～0.5s,孔间距离8～10mm。于LAD结扎前、结扎后30min和60min收集冠状静脉窦血计算心肌血流量。统计学处理采用随机区组设计的方差分析(α=0.05)。结果 缺血组LAD结扎后心肌血流量进行性下降(P<0.05),而激光组LAD结扎前后比较无显著性差异(P>0.05),但结扎后明显高于缺血组(P<0.05)。结论 TMLR可迅速有效地改善心肌缺血。     

Therapy with cardiac contractility modulation electrical signals improves left ventricular function and remodeling in dogs with chronic heart failure.

OBJECTIVES: This study examined the effects of long-term delivery of cardiac contractility modulation (CCM) electric signals on left ventricular (LV) function and global, cellular, and molecular remodeling in dogs with chronic heart failure (HF). BACKGROUND: Acute studies in dogs with experimentally induced HF showed that CCM signals applied to the failing myocardium during the absolute refractory period improved LV function without increasing myocardial oxygen consumption. METHODS: In one study, dogs with intracoronary microembolization-induced HF were randomized to 3 months of active CCM monotherapy or to a sham-operated control group. In another study, 19 HF dogs were randomized to 3 months chronic monotherapy with extended release metoprolol succinate (MET-ER), MET-ER with CCM, or no therapy at all (control group). RESULTS: In CCM-only treated dogs, LV ejection fraction (EF) increased (27 +/- 1% vs. 33 +/- 1%, p < 0.0001) compared with a decrease in sham-operated control animals (27 +/- 1% vs. 23 +/- 1%, p < 0.001). The increase in EF seen with CCM-treated dogs was accompanied by reduced LV volumes, improved myocardial structure, reversal of the maladaptive fetal gene program, and an improvement in sarcoplasmic reticulum calcium cycling proteins. Dogs treated with a combination of MET-ER and CCM showed a greater increase in LV EF and a greater reversal of LV global, structural, and biochemical remodeling compared with dogs treated with MET-ER alone. CONCLUSIONS: In dogs with HF, long-term CCM therapy improves LV systolic function. The improvements are additive to those seen with beta-blockers. These findings are further strengthened by the concomitant benefits of CCM therapy on LV global, cellular, and biochemical remodeling.     

Potential use of ultrasound in creating transmyocardial channels.

Although the mechanisms of the clinical benefits of transmyocardial laser revascularization (TMLR) are considered to be angiogenesis with increased perfusion, denervation and placebo effect, it is unknown whether laser energy is a prerequisite in obtaining these beneficial effects. The present study investigated whether it is possible to create transmyocardial channels and induce angiogenesis by ultrasound. Myocardium was penetrated with an ultrasonically activated surgical blade by advancing the blade tip perpendicularly to the left ventricular free wall of the beating heart of 6 mongrel dogs. The power of ultrasound was set at either the lowest or highest of the system. The animals were killed 30 min (acute; n=3) and 2 weeks (chronic; n=3) after channel creation. Holmium:YAG laser, which is currently used for clinical TMLR, was used to create myocardial channels in 4 other dogs, which were also killed 30 min (n=2) and 2 weeks (n=2) after channel creation. The areas of acute channel core, acute thermal damage and chronic fibrosis were compared between the laser and ultrasound channels by Masson's trichrome stain. Factor VIII and proliferating cell nuclear antigen (PCNA) immunostaining were carried out on the samples obtained from chronic animals. The density of vessels and that of proliferating vascular endothelial cells and vascular smooth muscle cells around the channels were measured. The area of acute core was larger in the lowest and highest outputs of ultrasound than in laser channels (0.78+/-0.09, 1.0+/-0.12 vs 0.38+/-0.04 mm2; p<0.01). The area of acute damage in both laser and the highest output of ultrasound channels was greater than in the channels produced by the lowest output of ultrasound (4.43+/-0.28, 4.63+/-0.44 vs 2.90+/-0.29 mm2; p<0.01). The ratio of acute damage area to acute core area was greater in laser channels than in either type of ultrasound channel (16.86+/-1.66 vs 6.04+/-0.67, 7.86+/-1.07; p<0.01) and the area of chronic fibrosis was greater (3.23+/-0.20 vs 1.59+/-0.18, 2.24+/-0.20 mm2; p<0.01). Factor VIII and PCNA immunostaining revealed new vessels not only inside the areas of chronic fibrosis, but also in the surrounding myocardium, in both laser and ultrasound channels. Ultrasound created transmyocardial channels histologically similar to laser channels and angiogenesis was induced in the normal myocardium surrounding ultrasound channels.     

Dynamic patch artificial myocardium; effects on the residual myocardial function

Dynamic patch artificial myocardium (D-PATCH) has been developed to replace the damaged left ventricular (LV) wall in severe cardiogenic shock patients with a massive myocardial infarction. This study was undertaken to demonstrate the effects of (1) single D-PATCH support on the global cardiac function (group 1, 12 dogs, whole heart model), (2) single D-PATCH support on the LV function and myocardial metabolism (group 2, 6 dogs, right heart bypass model), and (3) the concomitant support of D-PATCH and aortic counterpulsation (CP) on the regional myocardial function of the residual LV wall (group 3, 6 dogs, right heart bypass model with ultrasonic piezoelectric crystals). In group 1, mean aortic pressure and cardiac output were increased 20-36% (p less than 0.01) and 17-50% (p less than 0.01) respectively, and mean left atrial pressure was decreased 16% (p less than 0.01) by D-PATCH assist. In group 2, under constant preload volume, afterload pressure and heart rate, tension time index (TTI) was decreased 21-26% (p less than 0.01) and myocardial oxygen consumption was also decreased 24-29% (p less than 0.001) by D-PATCH assist. In group 3, although peak LVP was increased by single D-PATCH assist, when heart was assisted concomitantly by D-PATCH and CP peak LVP was significantly decreased (18%, p less than 0.01). Percent LV segmental shortening was not increased by CP assist, but increased 143% (p less than 0.02) by D-PATCH assist. In conclusion, D-PATCH can improve the global LV function and myocardial metabolism of the ischemic failing heart, also improve the regional myocardial function of the residual LV wall. Thus, D-PATCH is effective for the salvage of ischemic myocardium while maintaining the global cardiac function.     

Shunt between the ventricular chamber and coronary arteries preserves left ventricular function in acute myocardial infarction.

It is controversial whether newly created channels made by transmyocardial laser revascularization are functionally significant, so the present study evaluated the shunt flow from the left ventricular (LV) cavity to the ischemic myocardium in 51 patients with acute myocardial infarction (AMI) caused by complete occlusion of the proximal left anterior descending coronary artery. All patients underwent left heart catheterization within 24 h of onset and all underwent successful coronary reperfusion using primary coronary angioplasty with no angiographic restenosis on follow-up coronary angiography (CAG). The presence of the LV shunt flow was evaluated by selective left CAG after successful reperfusion. The LV global ejection fraction (EF) and regional function (centerline method) were analyzed by ventriculography in both the acute and chronic phases. The patients were divided into the 3 groups (Group A, no LV shunt without collaterals, n=20; Group B, no LV shunt with collaterals, n=24; Group C, LV shunt with collaterals, n=7). There was no difference in the grade of collateral circulation between Groups B and C. The improvements in LVEF and regional function from the acute phase to the chronic phase were significantly greater in Group C than in Groups A and B. Not only collateral circulation but also LV shunt contributes to the functional recovery of infarct myocardium in patients with AMI.     

Immediate effect of percutaneous myocardial laser revascularization on hemodynamics and left ventricular systolic function in severe angina pectoris

Experimental data suggest that myocardial revascularization with a high-energy laser may cause a significant reduction in left ventricular (LV) function immediately after creation of myocardial channels. We sought to determine if percutaneous myocardial laser revascularization (PMR) causes immediate deterioration in hemodynamic parameters or regional LV systolic function. PMR was performed in 40 patients (mean age 62.9 +/- 10.8 years) using the Eclipse Holmium laser (26 had PMR alone; 14 patients underwent PMR plus percutaneous coronary intervention). Intracardiac pressures and left ventriculograms were recorded before and after PMR. Regional wall motion was assessed using the centerline method. A mean of 18 +/- 5 channels were created per patient. There was no significant change in LV ejection fraction immediately after PMR (56 +/- 9% vs 55 +/- 10%, p = 0.25). No deterioration in regional wall motion was demonstrated in the lased region (mean chord motion for anterior wall PMR: -1.5 +/- 0.8 before vs -1.5 +/- 0.8 after the procedure, p = 0.93; inferior wall PMR: -1.5 +/- 0.9 before vs - 1.6 +/- 0.8 after the procedure, p = 0.43). Similarly, there was no change in the number of hypokinetic chords in the treated region. Systemic blood pressure, LV end-diastolic pressure, heart rate, and right-sided heart pressures were not significantly different after laser revascularization. In patients with refractory angina, PMR did not cause immediate deterioration in hemodynamic status or regional LV function.     

Percutaneous transluminal myocardial revascularization with a holmium laser system: procedural results and early clinical outcome.

Surgical transmyocardial laser revascularization has been reported to improve clinical outcome in patients with refractory angina who are not candidates for angioplasty or bypass surgery. We investigated the feasibility and safety of a nonsurgical, percutaneous technique for laser channel creation using energy from a holmium:yttrium-aluminium-garnet (YAG) laser. The laser energy was directed through a fiber enclosed in a catheter to the ventricular myocardium creating channels between the blood pool and the myocardium. Thirty-five patients with angina and coronary anatomy not amenable to revascularization with coronary angioplasty or bypass surgery underwent percutaneous transluminal myocardial revascularization. A total of 15 +/- 5 channels were formed per patient. There was no procedure-related mortality. One patient developed cardiac tamponade requiring thoracotomy and another a minor self-limiting pericardial effusion. There was no worsening of regional wall motion function in any patient. All patients were discharged alive after a postprocedure hospital stay of 2.1 +/- 1.4 days. Mean Canadian Cardiovascular Society (CCS) functional class declined from 3.68 +/- 0.4 before procedure to 0.82 +/- 0.7 at 30 days (P < 0.01). At 3 months, mean angina class was 0.94 +/- 0.65 (n = 35; P < 0.01) and at 6 months, mean angina class was 1.08 +/- 0.58 (n = 26; P < 0.01). One patient required repeat revascularization after 5 months for progression of disease in a degenerated saphenous venous graft supplying different region of myocardium. We conclude that transmyocardial revascularization using holmium:YAG laser by percutaneous technique can be carried out safely with encouraging early results and a very low complication rate. The symptomatic relief seen up to 6 months has been excellent. The long-term effects of this technique on mortality and relief of angina, however, remain to be defined. Cathet. Cardiovasc. Intervent. 47:287-291, 1999.     

Reduction of myocardial reperfusion injury by high-dose beta-blockade with esmolol

BACKGROUND: Myocardial ischemia reperfusion injury may be reduced by beta-blockade. However, how myocardial salvage is affected when beta-blockade is limited to the reperfusion period is unknown. We investigated the impact of CPB and esmolol during reperfusion on infarct size and left ventricular function in two different experimental models of acute myocardial ischemia. METHODS: In open-chest dogs, myocardial ischemia was induced by LAD occlusion in both studies. In study 1, infarct size (TTZ stain) and myocardial water content (MWC, microgravimetry) were determined, comparing reperfusion with blood and esmolol to blood without additives. Study 2 investigated the impact of esmolol on LV function (sonomicrometry, echocardiography) and MWC (microgravimetry) compared to warm blood cardioplegia in a more clinically oriented model. RESULTS: Infarct size and MWC in reperfused myocardium were significantly reduced by esmolol during reperfusion. Global LV function was better preserved in the esmolol group, whereas no difference was seen regarding regional function. CONCLUSIONS: Myocardial salvage may be significantly enhanced by CPB and esmolol, even when treatment with esmolol is initiated as late as with the onset of reperfusion.     

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.     

Myocardial laser revascularization in therapy-refractory angina pectoris

In patients with coronary artery disease and intractable angina, who are not candidates for either coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA), transmyocardial laser revascularization (TMR) has been developed as a new treatment. Several recently published, randomized trials have consistently shown improvement of clinical symptoms and increased exercise capacity after TMR compared to medical therapy. However, surgical thoracotomy is required for TMR with considerable morbidity and mortality. Therefore, catheter-based systems have been developed, which allow creation of laser channels in the myocardium from within the left ventricular cavity. These systems for "percutaneous myocardial revascularization" (PMR) use laser energy generated by Holmium: YAG lasers, which can be transmitted to the myocardium via flexible optical fibers. PMR leads to significant improvement of clinical symptoms and increased exercise capacity similar to TMR. The CCS classification is improved about 1.5 classes, independent of the PMR system used. However, evidence of improved perfusion after PMR is still lacking. The pathophysiologic mechanisms of myocardial laser revascularization are still poorly understood. Experimental studies indicate myocardial neoangiogenesis and myocardial denervation after TMR; however, clinical studies have not yet found evidence of improved myocardial perfusion after myocardial laser revascularization.     

Reduced sarcoplasmic reticulum Ca(2+)-uptake and expression of phospholamban in left ventricular myocardium of dogs with heart failure.

The purpose of this study was to examine the sarcoplasmic reticulum (SR) Ca(2+)-uptake and the expression of phospholamban (PLB) and Ca(2+)-ATPase (CAA) in left ventricular (LV) and right ventricular (RV) myocardium of 6 normal (NL) dogs and 6 dogs with chronic heart failure (HF). In addition, gene expression of PLB and CAA was also examined in LV myocardium of NL and HF dogs. HF (LV ejection fraction 23+/-2%) was produced by multiple sequential intracoronary microembolizations. Oxalate-dependent Ca(2+)-uptake was measured in isolated membrane vesicles. Using specific dog myocardial monoclonal antibody, the expression of CAA, PLB and calsequestrin (CSQ) were measured in sodium dodecyl sulfate extract prepared from LV and RV tissue. Steady-state mRNA levels were determined by Northern hybridization using specific cDNA clones of PLB, CAA, CSQ, and glyceraldehyde-3-phosphate dehydrogenase (GADPH), a house keeping gene. SR Ca(2+)-uptake of NL and HF dogs increased with increasing Ca(2+)concentrations and reached a plateau at 3 microm in both LV and RV. Total capacity (134+/-9 v 224+/-10 nmol(45)Ca/mg protein/10 min, P<0.05) and maximal velocity (15+/-2 v 2 nmol(45)Ca/mg protein/min, P<0.05) of the SR to sequester Ca(2+)was significantly lower in LV myocardium of HF dogs compared to NL, whereas the Hill coefficient and the affinity of the Ca(2+)-pump for Ca(2+)were unchanged. LV tissue levels of the PLB and CAA, normalized to noncollagen protein or to CSQ and the PLB and CAA mRNA levels, normalized to CSQ or GADPH mRNA, were also significantly lower in HF dogs compared to NL. In RV myocardial tissue, no significant differences in total capacity of SR to sequester Ca(2+), maximal velocity of SR Ca(2+)-uptake, the affinity and Hill Coefficient of the Ca(2+)-pump for Ca(2+), or tissue levels of PLB and CAA were observed between NL dogs compared to HF dogs. We conclude that SR Ca(2+)-uptake and SR PLB and CAA protein and gene expression levels are reduced in LV myocardium of dogs with chronic HF. These abnormalities can lead to Ca(2+)-overload and subsequent global LV dysfunction.     

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.     

Endoscopic gastric vagotomy: a feasibility study using laser in dogs

The aim of this study was to explore the feasibility of an endoscopic approach to gastric vagotomy using the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser in dogs. Based on gross and histologic measurements, target zones for endoscopic vagotomy were defined with reference to mucosal side landmarks. Target zones containing the unbranched segments of the major intramural vagal branches were linear and symmetrically located anterior and posterior to the midline of the lesser curvature extending from the level of the esophagogastric junction to the proximal antral border. Because of minimal variability between dogs, this zone could be accessed endoscopically and reliably injured. Unfortunately, it was necessary to produce a nearly full thickness burn to interrupt the deep intramural vagal branches. Despite efforts to control dosimetry, delayed perforations occurred in three of four dogs. We conclude that endoscopic gastric vagotomy using the Nd:YAG laser is not feasible in the dog model because of difficulty controlling the depth of thermal injury. An endoscopic approach to vagotomy remains conceptually appealing because of the predictable location of and accessibility to a target zone.     

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.     

血运重建对冠心病合并心功能不全患者心肌收缩功能和心室重构的影响

目的探讨血运重建对冠心病合并左心功能不全患者心肌收缩功能和心室重构的影响。方法86例冠心病合并心功能不全患者术前应用超声心动图进行心功能、左心室(左室)几何形态和心肌活性评定,分为有存活心肌组和无存活心肌组,两组分别行血运重建或药物治疗。随访(13±5)个月后重新评价上述指标。结果57例有存活心肌的患者中行血运重建者较药物治疗者左室射血分数(LVEF)、存活节段数、左室球状指数(LVSI)明显提高;左室舒张末容积(LVEDV)、左室收缩末容积(LVESV)、左室重量(LVM)明显降低(P值均<0.01)。29例无存活心肌的患者中上述指标两种治疗间无显著性差异(P值均>0.05)。结论血运重建能改善冠心病合并左心功能不全但有存活心肌患者的心肌收缩功能和几何形态。