Sapphire and metal tip recanalisation: Implications for safety

The characteristics of two modified fiber tips, the metal laser probe and the rounded sapphire contact probe, were examined in vitro and in vivo with respect to some of the risks of laser angioplasty.Both probes have an atraumatic, blunt shape. The laser beam profile of the sapphire contact probe looses its focussing properties in water. In vitro, we found a large temperature gradient from the front to the rim of the probe. Ablative temperatures were reached at the tip whereas the temperature of the metal connector near the rim of the sapphire crystal rose only 30 °C in blood when 15 W Nd-YAG was applied for 1 s. In contrast, the metal laser probe reached temperatures over 500 °C in an in vitro tissue/blood environment when 10 W was applied for 5 s. The metal probe ablated both in the forward and the radial direction. In a rabbit model there was a large variation in temperature of the metal in vivo (70 – 320 °C). The highest temperatures were associated with acute complications. However, in spite of transmural coagulation necrosis the artery wall remained functionally intact during a follow up period of up to 56 days.     

Laser thermal angioplasty for early repair of anastomotic stenosis after lower extremity arterial reconstruction: initial experience

Laser thermal angioplasty with a sapphire hot-tip Nd-YAG laser system was effectively used for five grafts with anastomotic stenotic lesions which occurred after femoro-popliteal arterial reconstructions. Stenotic lesions were detected by a combination of Doppler flow waveform analysis and ankle/brachial index measurement in 32 femoro-popliteal and five femoro-tibial arterial bypass grafts in the postoperative period. The laser probe used was 3 to 4 mm in diameter. There were no perforations of the arterial wall caused by thermal ablation, even with repeated pulses of 40 watts of laser energy for 3 s. Contact Nd-YAG laser thermal angioplasty using this rounded, 3-4 mm hot-tip facilitated effective widening of the lumen of the anastomotic stenotic lesion. All patients remain well at follow-up from 9 to 20 months after laser thermal angioplasty.     

Temperature along the surface of modified fiber tips for Nd:YAG laser angioplasty

For laser angioplasty probes, the thermal properties of the probes will primarily determine their mechanism of action. We examined the absorption, temperature increase, and probe degradation of transparent contact probes (hemispherical contact probe and ball-shaped fibers) and metal laser probes coupled to a continuous-wave Nd-YAG laser. Temperature was recorded by means of thermocouples and the measurements were corrected for direct light absorption by the thermocouple. During 15 W, 1 s exposure, the peak temperature rise of the hemispherical contact probe in contact with tissue dropped from approximately 1,000 degrees C at the front end to below 45 degrees C (95% drop) at the lateral side. In contrast, during continuous exposure the peak temperature rise of metal laser probes in contact with tissue dropped from 560 degrees C at the front end to near 400 degrees C (30% drop) at the 5.5 mm proximal rear end. During exposure in blood or tissue, the transparent contact probes became contaminated. Their absorption increased from 5 to 33% and the probe deteriorated. Repeated use of metal laser probes in blood resulted in a higher temperature at the rear than at the front end due to backburing of the fiber. Owing to the large temperature drop along the surface of transparent contact probes, the area of thermal destruction is limited to the tissue in front of the probe, whereas along the entire surface of metal laser probes the tissue will be affected. The large difference between these temperature distributions should be respected during clinical application of the transparent contact probe and the metal laser probe.     

Carbon dioxide gas as a perfusion medium for the sapphire probe in laser ablation of human atheromatous plaques: comparison study with saline

The effectiveness of CO2 gas as a perfusion medium was compared to that of saline in laser ablation of human atheromatous plaque. In an experimental circulation-occlusion model using flowing whole blood, human cadaveric arterial samples were irradiated by a sapphire probe with the Nd-YAG laser. The following experiments were performed: 1) lasing without perfusion, 2) lasing with saline perfusion of the probe, and 3) lasing with CO2 perfusion. Different perfusion flow rates of saline and CO2 were used. Results showed that the mean ablation area was 1.6-fold larger with CO2 than with saline perfusion (P less than 0.05, Student's t test). The mean lateral injury at the site adjacent to the ablation crater and at the area directly facing the probe was not significantly different with either perfusion medium. The larger ablation area with CO2 was probably due to the fact that CO2 is a good insulator for maintaining a higher probe temperature and keeps the probe free of blood debris. In conclusion, our results show that CO2 perfusion facilitates more effective laser ablation of atheromatous plaque than saline perfusion by the sapphire probe with the continuous wave Nd-YAG laser.     

Splenic resection with the Contact Nd:YAG laser system

Splenic resection in the dog was proven to have decreased blood loss (52%), decreased operating time (44%), and decreased surgical manipulation using the SLT Contact Nd:YAG Laser System with the synthetic sapphire probe, as compared with the noncontact CO2 laser. Tissue damage and hematologic changes were minimal and equivalent in both laser systems. The overall ease of use and operating technique was subjectively better with the contact Nd:YAG laser, and the danger of scattered and reflective beam damage was eliminated. The contact Nd:YAG laser with the synthetic sapphire probes offers a significant advantage over the noncontact CO2 laser in the resection of splenic tissue. Future applications in pediatric surgery now need to be evaluated.     

Interstitial laser thermotherapy: Comparison between bare fibre and sapphire probe

A sapphire probe and a bare fibre were compared with respect to temperature control and distribution and light fluence in interstitial laser thermotherapy. Experiments were performed in processed liver using an Nd-YAG laser and output power levels of 1–4 W. The temperature was controlled at a distance of 10 mm using a feedback circuit with an automatic thermometry system and thermistor probes. With the sapphire probe, carbonization was rare at power levels of 1–2 W but was observed in half of the experiments at 3 W and in all experiments at 4 W. Using the bare fibre, carbonization was seen in almost all experiments. Absence of carbonization was associated with a moderate decrease in the penetration of light and excellent control of the temperature, whereas carbonization led to rapid impairment of light penetration and temperature control. In addition, the temperature gradient was smaller with the sapphire probe than with the bare fibre or when carbonization was absent. It is concluded that a diffuser tip, such as the sapphire probe, may be preferable to the bare fibre for interstitial laser thermotherapy because it gives a smaller temperature gradient and helps to avoid carbonization which results in preserved light penetration and improved temperature control.     

Comparison of contact and free beam laser endarterectomy

Free beam laser endarterectomy (LE) and contact laser endarterectomy (CLE) were compared in 15 arteriosclerotic New Zealand white rabbits. The rabbits underwent balloon catheter trauma to the thoracoabdominal aorta and were fed a 2% cholesterol diet for 18 weeks. Thoracoabdominal exploration was performed under general anesthesia and multiple endarterectomies were performed in each rabbit. Atheromas were dissected from arteries with laser radiation and end points were welded in place with laser radiation. LEs (N = 8) were performed with argon ion radiation delivered through a 400 microns fiberoptic. Power was kept constant at 1 W and the average fluence was 97.5 +/- 6.6 J/cm2. CLEs were performed with conical sapphire probes powered by either argon ion radiation (N = 12) or Nd-YAG radiation (N = 10). Power used was 1 W to 4 W for each laser. Average argon ion fluence was 117.8 +/- 3.1 J/cm2 and average Nd-YAG fluence was 611.1 +/- 34.4 J/cm2. Following the operations, aortas were removed, fixed, serially sectioned, and stained. Microscopic study revealed welded end points with LE but not with CLE. There were no perforations with LE. There were 11/12 perforations with argon ion CLE and 8/10 perforations with Nd-YAG CLE. Free beam laser endarterectomy is superior to contact laser endarterectomy for experimental atheromas.     

The histological measurement of laser-induced thermal damage in vascular tissue using the stain picrosirius red F3BA

A histological technique for the measurement of laser-induced thermal tissue damage is described using the stain picrosirius red F3BA. This stain enhances the birefringence of normal collagen when viewed in polarized light. Areas of (thermally) denatured collagen, however, have no optical activity and can be measured directly by optical micrometry. The technique has been applied to experimental studies on both laser angioplasty and laser vascular anastomosis.The tissue ablation characteristics of various 2.2 mm diameter rounded sapphire laser angioplasty probes were compared by lasing (at 1064 nm) segments of porcine aorta under blood in vitro. A marked difference was observed between probes from different manufacturers, the Surgical Laser Technologies probe producing significantly greater forward tissue ablation with less associated lateral thermal damage.The relative degree of thermal damage caused by argon (488/514 nm) and Nd-YAG lasers during in vitro arteriotomy repair was also investigated. No difference was seen between the two wavelengths. However, the use of absorption-enhancing chromophore dyes as an aid to laser welding significantly reduced damage, particularly for the argon laser.In conclusion, we suggest that this histological technique is of considerable value in the investigation of the thermal effects of continuous-wave lasers.     

A new transluminal angioplasty for the treatment of arteriosclerosis obliterans

A Peripheral Simpson Atherectomy Catheter (PSAC), which permits transluminal excision and removal of diseased intima, has been tested experimentally and clinically. The device consists of a tubular housing and a cutting mechanism to excise the intima protruding into the housing. Experimentally, vascular clay model was used to estimate its efficacy. Multiple passages improved lumen size and inner smoothness, and there was some difficulty to treat curved models. Clinically, 9 lesions in 7 patients of iliofemoral atheromatous disease were treated with PSAC. Recanalization was achieved successfully except for two lesions, one a soft atheroma and the other a curved vessel. No angiographic dissections or acute arterial occlusions occurred. Despite the procedure was complicated, it seemed safe and effective. In order to improve this method, an angioplastic catheter which had a laser probe in its housing was newly designed. Nd-YAG laser was irradiated with this catheter to the atherosclerotic lesions which were induced by a high cholesterol diet in rabbit. It left smoother surface and less thermal injury than usual irradiation with contact laser probe, but it needed more energy. These results showed that PSAC can be an alternative transluminal angioplasty and the new designed laser catheter is useful, but more experiments are required to establish these procedures.     

Laser thermal angioplasty probe ("hot tip") temperature: effects of flow

The temperature developed by the laser thermal ("hot tip") probe during arterial recanalisation is primarily dependent on the rate of energy delivery and the rate of dissipation to the surrounding medium. While higher probe tip temperatures enhance the efficacy of atheroma ablation, so too is the incidence of adverse effects increased. We studied the temperature developed in the probe tip in an artificial circulation using both saline and blood. In saline the peak probe temperatures were limited to 100 degrees C (boiling point), falling with each increment in flow. Small discrepancies in probes at different times and may be due to malalignment of the optical fibre-metal cap coupling, temperature measurement inaccuracy, tip insulation, or generator output instability. In blood, charring and clot formation insulated the tip raising the temperature (up to 700 degrees C within 5 seconds at 10 W) but also retarded dissipation of heat to the surroundings. The degree of clot and char formation was critical in determining subsequent thermal responses in any particular probe. The unknown rate and quantity of char buildup and changing blood flow during in vivo angioplasty are likely to be important obstacles to developing a reliable thermal feedback control system.     

Early and late arterial healing response to catheter-induced laser, thermal, and mechanical wall damage in the rabbit

Pulsed lasers are being promoted for laser angioplasty because of their capacity to ablate obstructions without producing adjacent thermal tissue injury. The implicit assumption that thermal injury to the artery is to be avoided was tested. Thermal lesions were produced in the iliac arteries and aorta of normal rabbits by a) electrical spark erosion, b) the metal laser probe, and c) continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser energy through the sapphire contact probe. High-energy doses were used to induce substantial damage without perforating the vessel wall. Thermal lesions (n = 77) were compared with mechanical lesions (n = 22) induced by oversized balloon dilation. Medial necrosis was induced by all four injury methods. Provided no extravascular contrast was observed after the injury, all damaged segments were patent after 1 to 56 days. The progression of healing with myointimal proliferation was remarkably similar for all injuries. At 56 days, the neointima measured up to 370 microns. In conclusion, provided no perforation with contrast extravasation occurred, the normal rabbit artery recovered well from transmural thermal injury. The wall healing response is largely nonspecific.     

Evaluation of the effect on normal liver of interstitial laser hyperthermia using artificial sapphire probes

There has recently been renewed interest in the use of hyperthermia (42.5–44°C) for the management of malignant disease. One method of producing these temperatures is to deliver Nd-YAG laser light via an artificial sapphire probe. This technique has been evaluated on normal rat liver using powers of 1–3W and exposure times of 100–1200s. Discrete areas of hepatic necrosis were produced which healed by the development of an inflammatory response to form fibrotic scars. Thermometry showed that 3W produced a temperature of 42.5°C at 5 mm from the probe and this technique should therefore be capable of heating tumours.     

Percutaneous recanalization of arteries: Status and prospects of laser angioplasty with modified fibre tips

Percutaneous balloon dilatation of arterial stenoses is a firmly established non-surgical treatment of ischaemic disease. The number of percutaneous transluminal coronary angioplasties performed per year in the USA approaches the number of coronary artery bypass graft operations. A great number of novel percutaneous recanalization schemes address the major problems of balloon angioplasty: failure to cross the stenosis (occlusion), failure to dilate effectively (15–20%), acute complications (5%) and re-stenosis within six months (30–40%). Laser energy can effectively evaporate atheromatous plaque, but delivery by an unmodified bare fibre creates only a small channel and carries a high risk of vessel-wall perforation in the coronary arteries. It appears impossible to maintain an axial position in small, tortuous and moving arteries with multiple side-branches. Coronary lesions are anatomically and structurally heterogeneous. Reduction of the perforation risk is being approached by four strategies: (a) optimization of the power source; (b) enhancement of laser-light absorption by plaque relative to artery wall; (c) improvement of plaque recognition; and (d) modification of the delivery system, which is discussed in detail. Recanalization of occluded femoropopliteal arteries with the 2.0-mm metal laser probe has proved to be safe and effective in more than 100 patients. The 2.2-mm rounded sapphire contact probe has been used with success in the peripheral arteries of over 30 patients. The recanalization mechanism of both probes is not yet fully understood. Closed-chest attempts at recanalization of coronary arteries by the 1.7-mm metal laser probe have been reported in 13 patients, with success in the majority. There were no complications requiring emergency surgery. The possible occurrence of embolism or spasm in three cases warrants a cautious approach to application of the metal laser probe in the coronary catheterization room. The primary benefit of laser recanalization with modified fibre tips is the possible transformation of a candidate for surgery into a candidate for balloon angioplasty. It remains to be established whether prior laser debulking of the atheroma will reduce the incidence of acute complications of balloon dilatation and will reduce restenosis in the subsequent year. In the past two years an avalanche of laser and non-laser recanalization schemes have been developed. In peripheral arteries, early results of most methods have shown an acceptably low incidence of acute perforations or other complications. The human arterial wall can take a heavy beating, both mechanically and thermally. In the next decade, catheter intervention techniques will progressively contribute to the treatment of peripheral and coronary artery disease.     

Thermal effects of stationary "hot tip" laser coronary probes: an in vitro assessment

Percutaneous laser thermal probe angioplasty requires sufficient laser probe flexibility to access the coronary tree. This may entail a loss of axial strength and the resultant slow advancement may lead to unwanted heating of the normal coronary artery proximal to the lesion. To assess the lateral thermal effects of stationary coronary laser probes, laser thermal energy (50-150 J) was delivered to 25 coronary artery segments (diameter 1.9-4.0 mm) in a perfused cadaver heart preparation using a 1.7 mm tip probe. Adherence to the vessel wall occurred in 19 segments, endothelial charring in 8 segments, and perforation in 3 segments. Endothelial charring was seen in 8 of 13 nonperfused segments but in 0 of 12 segments perfused at 60 ml/minute (P less than 0.01). In all three perforations the vessel to probe diameter ratio was less than 1.6:1, perfusion was absent, and traction to dislodge the adherent probe was necessary. Lateral wall damage is a complication of stationary laser probes: smaller-tipped probes which are advanced rapidly at the time of energy delivery may enhance the safety margins of coronary laser thermal probe angioplasty.     

The contact neodymium-yttrium aluminum garnet laser. A new approach to arthroscopic laser surgery

Arthroscopic treatment of meniscal lesions has been modified as technological advances have occurred. However, alternatives to conventional arthroscopic cutting tools, including electrocautery and CO2 lasers, have thus far met with limited success. The recent development of a sapphire tip has enabled the use of the neodymium-yttrium aluminum garnet (Nd-YAG) laser in a contact mode in a saline medium. This study compares the biology of the Nd-YAG laser to that of electrocautery and scalpel techniques with respect to its effects on articular cartilage and the meniscus. The contact Nd-YAG laser has advantages over both scalpel and electrocautery with regard to its effects on articular cartilage. It also has significant biologic advantages over electrocautery for meniscal lesions. Although in its infancy in the clinical setting, the contact Nd-YAG laser represents the possible beginning of a new era for application of laser energy in arthroscopy.     

Transvenous ablation of the atrioventricular conduction system by laser irradiation under endoscopic control

We report ten successful experiments of transvenous destruction of the His bundle by laser radiation. An endoscope coupled with a special laser catheter was introduced through the jugular vein into the right atrium of dogs. The tip of the laser catheter was positioned in front of A-V conduction system under visual control using anatomic landmarks. Injection of saline solution coaxial with the laser power-transmitting fiber was performed before and during laser coagulation. Twenty watts constant wave Nd-YAG laser operating at 1.06 micron was enough to produce complete A-V block in approximately 15 sec. The safety of the proposed technique is especially discussed.     

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.     

What is the safest endotracheal tube for Nd-YAG laser surgery? A comparative study

To determine whether a safe endotracheal tube for Nd-YAG surgery could be found, an Nd-YAG laser operating at 50 W was directed at six different endotracheal tubes that had 5 L/min of oxygen flowing through them. A plain Rusch red rubber endotracheal tube, a Bivona Fome-cuff laser endotracheal tube, a stainless steel Mallinckrodt Laser-Flex endotracheal tube, and a Xomed Laser-shield endotracheal tube were all ignited and perforated by the laser within 12 s. The combustion of the Mallinckrodt endotracheal tube can be explained by the high energy density of the laser that, in rapidly heating the metal, was able to cause its combustion in 100% oxygen. Red rubber endotracheal tubes wrapped with 3M No. 425 or Venture copper foil tape were unaffected by 1 min of exposure to the laser beam. They are recommended for clinical use.     

Nd-YAG laser photocoagulation of canine myocardium with the transparent contact probe

Laser photocoagulation of myocardium is an alternative to surgical resection in the treatment of drug resistant ventricular tachycardia. In certain areas, of the heart, however, bare fibre delivery of laser energy involves a risk of unintentional damage to nearby structures. The purpose of the study was to determine whether Nd-YAG laser irradiation, delivered with the transparent contact probe, would produce adequate laser photocoagulation of the canine myocardium in comparison to bare fibre delivery of the laser energy. In nine mongrel dogs, continuous wave Nd-YAG laser irradiation with and without a transparent contact probe was directed at the epicardium. Pulse power was 10, 15 and 20 W, pulse duration 5, 7 and 10 s, and spot size was 1 mm. A total of 178 lesions were analyzed microscopically. After a 200 J pulse energy delivered by the contact probe, the lesion depth was 4.9±0.5 mm (mean±s.d.), which is usually adequate to ablate arrhythmia sites. Bare fibre delivery of laser energy did not produce deeper lesions. There was no difference between the bare fibre and the transparent probe in the occurrence of major arrhythmias (4/86 bare fibre, 3/92 transparent probe). We conclude that the transparent contact probe allows safe and effective laser irradiation of sites of origin of ventricular arrhythmias.     

Technique of laser lesser-curve seromyotomy

A new technique for performing a lesser-curve superficial myotomy of the stomach for the treatment of chronic duodenal ulceration has been proposed, using Nd-YAG laser energy delivered to the target via sapphire tips. A total of 12 patients have been operated on with only one haemorrhagic complication.