Conditions for effective Nd-YAG laser angioplasty

To establish the optimal conditions for recanalisation of obstructed arteries without damage to vessel walls, a Nd-YAG laser coupled to a 0.2 mm diameter optic fibre was used on obstructed human cadaver coronary and peripheral arteries and on popliteal arteries in amputated limbs. Vaporization of atheromatous plaques was consistently obtained with an energy of 360-600 J and a diluted blood perfusate (3 g/100 ml haemoglobin) at a rate of 20 ml/min. The arterial wall was protected from thermal injury by inserting the optic fibre into an inflated balloon catheter and by cooling the system with the perfusate. Since recanalisation of occluded arteries was consistently obtained without damage to the arterial wall or debris and thin and flexible optic fibres were easy to guide in the arteries, percutaneous transluminal Nd-YAG laser angioplasty was used in obstructed femoral and popliteal arteries in three patients. The first European trials in man showed the method to be feasible, effective, and harmless, although further studies are required to improve penetration of the obstruction and increase the diameter of tunnel.     

Conditions for effective Nd-YAG laser angioplasty.

To establish the optimal conditions for recanalisation of obstructed arteries without damage to vessel walls, a Nd-YAG laser coupled to a 0.2 mm diameter optic fibre was used on obstructed human cadaver coronary and peripheral arteries and on popliteal arteries in amputated limbs. Vaporization of atheromatous plaques was consistently obtained with an energy of 360-600 J and a diluted blood perfusate (3 g/100 ml haemoglobin) at a rate of 20 ml/min. The arterial wall was protected from thermal injury by inserting the optic fibre into an inflated balloon catheter and by cooling the system with the perfusate. Since recanalisation of occluded arteries was consistently obtained without damage to the arterial wall or debris and thin and flexible optic fibres were easy to guide in the arteries, percutaneous transluminal Nd-YAG laser angioplasty was used in obstructed femoral and popliteal arteries in three patients. The first European trials in man showed the method to be feasible, effective, and harmless, although further studies are required to improve penetration of the obstruction and increase the diameter of tunnel.     

Effects of different types of continuous emission laser on human atheromatous plaques in vitro

The laser beam is a punctual source of thermal energy which can be used to vaporize human atheroma. The physical characteristics of optimal utilisation (total energy, wave length, continuous or pulsed emission) have not been clearly defined. We carried out in vitro irradiations of human atheromatous material and healthy arterial wall with different combinations of power-emission time and three different wave lengths, using four continuous emission laser beams (Nd-Yag, two CO2 with different lenses, Argon). The beam emitted by the Nd-Yag was absorbed less than the CO2 and Argon lasers, which had comparable effects above a threshold of 2 to 14 joules. The weight of vaporized fibro-atheromatous material was 0.11 mg per joule of optical energy dissipated (CO2). No radical difference was observed in the nature of the effects of the three types of laser studied. The problems of using this technique on the beating heart remain unsolved (ballistics of the emerging ray). Other modes of emission (pulsed) and different wave lengths should be studied.     

Pulsed emission in laser coronary angioplasty. Theoretical bases and experimental application

The aim of this study was to evaluate the thermal diffusion of a pulsed laser beam in atheroma and to obtain in vitro vaporisation of the plaque without causing arterial wall lesions. A computerised mathematical model integrated 4 parameters: reflectivity, thermal conduction, the absorption factor and coefficient of diffusion. The thermal diffusion was shown to be dependent on the time constant and the temperature of vaporisation may be best attained with a short burst (200 ns) with a high peak power (6000 w). The experimentation was performed on fresh debris and segments of epicardial coronary arteries which were exposed to a pulsed laser beam with a frequency of 1000 Hz in bursts of 200 ns at wave lengths of 1060 and 532 nm. The results were evaluated by microscopic examination of transverse sections perpendicular to the lumen of the artery. Effective vaporisation of atheroma was observed with weak mean dissipating powers (0.4 w) about 10 times weaker than with continuous node emission; examination of the underlying arterial wall showed no thermal or mechanical damage.     

Myocardial infarction with normal coronary angiogram. Possible mechanism of smoking risk in coronary artery disease.

The coronary angiograms of 120 consecutive patients under 40 years of age were examined. Ten new cases of myocardial infarction with normal coronary arteriogram were identified (group 1) and compared with 30 cases of myocardial infarction and obstructive coronary disease (group 2). Heavy cigarette smoking was the sole major risk factor in group 1. Patients in group 2 smoked as well but most also had hypercholesterolaemia or hypertension. Pre- and postinfarction angina was rare among the patients with myocardial infarction and normal coronary arteriogram, and recanalisation after smoking-induced thrombotic occlusion is thought to be the most likely mechanism. Smoking-induced thrombosis is only likely to be recognised in special circumstances, when it develops in apparently normal coronary arteries, is followed by recanalisation, and is complicated by infarction as a permanent marker of previous obstruction to regional myocardial blood flow. Thrombotic occlusion of a "normal" coronary artery without recanalisation will only be recognised when infarction is fatal. If smoking can predispose to thrombosis in "normal" coronary arteries, it may be even more likely to accelerate thrombosis in atheromatous coronary arteries. The importance of recognising group 1 may well be in relation to the much commoner group 2.     

Arterial disobliteration by the laser

In order to determine the optimal conditions for disobliteration of occluded arteries without damaging the arterial wall, the effects of a Nd-YAG laser connected to a 0.2 mm diameter fibre optic system were studied on post-mortem coronary arteries and popliteal and tibial arteries of amputated limbs. Vaporisation of atheromatous plaques was consistently obtained with energies of 300 to 600 joules associated with perfusion of the vessel with dilated blood (3 g/100 ml of haemoglobin) at a flow rate of 20 ml/min. Protection of the arterial wall was ensured by introducing the fibre aortic system through a balloon catheter and by cooling with the perfusion liquid. The reproducibity of these results in the absence of major arterial wall damage, and the facility of manipulation of the fibre optic system due to its flexibility and narrow diameter, encouraged us to use this method clinically. The first three applications on peripheral arteries (femoral and popliteal arteries) confirmed that this method of arterial disobliteration can be used with a certain degree of efficacy with only a slight risk of arterial perforation. Further studies are essential to improve the degree of laser penetration of the arterial obstruction and to increase the diameter of the tunnel of recanalisation.     

Intracoronary thrombolysis in evolving myocardial infarction. Sequential angiographic analysis of left ventricular performance

Since November 1979 left ventricular angiography and coronary arteriography have been performed in 80 patients with evolving acute myocardial infarction in order to attempt coronary recanalisation by local streptokinase infusion. The average delay between the onset of symptoms and streptokinase infusion was 3.6 hours. Thrombolysis was successful in 64% of cases. No serious complications related to the procedure were noted. Of the 12 patients in cardiogenic shock, recanalisation was achieved in only four, of whom two survived. To evaluate the left ventricular salvage resulting from early recanalisation the last 58 patients had a second left ventricular angiogram and further coronary arteriograms 21 +/- 10 days later and 16 patients had a third study three months later. From the left ventricular angiogram in the right anterior oblique projection the ejection fraction and two graphic variables of regional wall motion were computed quantifying the hypokinetic zone. Patients were divided into two groups, according to the patency of the infarct related artery at the second control: group 1 consisted of 28 patients with successful recanalisation confirmed, and group 2 of 30 patients in whom no recanalisation was achieved or secondary reocclusion had occurred. At the second study the ejection fraction was unchanged in group 1 but had significantly decreased in group 2. Regional wall motion improved in group 1 and worsened in group 2, more so in patients without recanalisation than in those in whom secondary reocclusion had occurred. The third study showed a further decrease in ejection fraction in group 2. A progressive decrease in percentage residual stenosis was observed in group 1. This sequential angiographic study confirms the partial myocardial salvage resulting from early coronary recanalisation during acute myocardial infarction.     

Intracoronary thrombolysis in evolving myocardial infarction. Sequential angiographic analysis of left ventricular performance.

Since November 1979 left ventricular angiography and coronary arteriography have been performed in 80 patients with evolving acute myocardial infarction in order to attempt coronary recanalisation by local streptokinase infusion. The average delay between the onset of symptoms and streptokinase infusion was 3.6 hours. Thrombolysis was successful in 64% of cases. No serious complications related to the procedure were noted. Of the 12 patients in cardiogenic shock, recanalisation was achieved in only four, of whom two survived. To evaluate the left ventricular salvage resulting from early recanalisation the last 58 patients had a second left ventricular angiogram and further coronary arteriograms 21 +/- 10 days later and 16 patients had a third study three months later. From the left ventricular angiogram in the right anterior oblique projection the ejection fraction and two graphic variables of regional wall motion were computed quantifying the hypokinetic zone. Patients were divided into two groups, according to the patency of the infarct related artery at the second control: group 1 consisted of 28 patients with successful recanalisation confirmed, and group 2 of 30 patients in whom no recanalisation was achieved or secondary reocclusion had occurred. At the second study the ejection fraction was unchanged in group 1 but had significantly decreased in group 2. Regional wall motion improved in group 1 and worsened in group 2, more so in patients without recanalisation than in those in whom secondary reocclusion had occurred. The third study showed a further decrease in ejection fraction in group 2. A progressive decrease in percentage residual stenosis was observed in group 1. This sequential angiographic study confirms the partial myocardial salvage resulting from early coronary recanalisation during acute myocardial infarction.     

Anatomic-ultrasound correlations for intraoperative open chest imaging of coronary artery atherosclerotic lesions in human beings

This study was performed to further validate a method for intraoperative ultrasound imaging of coronary arteries. Ultrasound images of coronary atherosclerotic lesions were compared with anatomic specimens of the coronary arteries obtained from open chest human subjects. The anatomic specimens were derived from four cardiac transplant recipients, accepted as candidates for transplantation because they had severe diffuse atherosclerotic disease, and one patient who died in the early postoperative period after a coronary artery bypass procedure. Twenty-six ultrasonically imaged atherosclerotic areas of the coronary arteries in these patients were compared with formalin-fixed and decalcified anatomic specimens. Specific ultrasound appearances for atherosclerotic lesions were observed, including 1) discrete (focal) stenosing fibrous/atheromatous plaques; 2) diffuse nonobstructive fibrous/atheromatous disease (detectable even in anatomically small vessels); 3) complete occlusion by fibrous/atheromatous lesions or organizing thrombus; and 4) "shadowing," an ultrasound pattern characteristic of significant calcification within atherosclerotic plaques. As part of this study, a new 12 MHz water path probe was evaluated for coronary artery scanning. The new probe allowed improved access to coronary arteries and increased detail of anatomic visualization. Both the performance of the new high resolution probe and the knowledge gained by the anatomic correlations obtained in this study should aid the development of intraoperative coronary artery scanning for surgical localization of atherosclerotic disease during coronary bypass surgery.     

Laser angioplasty

Laser energy is capable of breaking up plaques of atheroma to clear obstructed arteries. Laser rays are transmitted by optic fibers, fine and flexible, or bundles of fibers. In order to avoid perforation of the arterial wall, major difficulty and pitfall of this technique, a centering balloon is used or an absorption gradient between plaque and normal tissue, or improved guiding devices such as angioscopy, ultrasounds or detection of the atheroma by spectroscopy. The laser energy may also be transformed into heat, procedure carried out by thermoplasty. In order to avoid the drawbacks of the cutting end of the bare optic fibers, it may be covered with sapphire optics which conducts well laser energy. Arterial and coronary disobstructions were performed by so called continuous lasers, such as Argon, YAG of pulsed laser such as Excimer or color lasers. These are selectively absorbed by the atheroma and operate according to a computerized system after detection of atheromatous plaques by spectroscopy. Excellent results have recently been obtained with such a system on short and long term complete peripheral arterial obstructions.     

Percutaneous coronary mid-infra-red laser angioplasty.

A pilot study was performed to determine the safety and efficacy of coronary pulsed mid-infra-red laser angioplasty. The laser was coupled with a novel 2.0 mm multifiber catheter consisting of 37 optical fibers of 150 microns each arranged concentrically around a 0.018-inch central lumen and a soft leading tapered distal tip to maintain coaxial alignment and position plaque in front of fibers. The laser was operated at 500 millijoules/pulse, 3.5 Hz, and 250 microseconds/pulse. Twenty-three patients with stenosis or occlusion of the left anterior descending or right coronary artery were selected for laser treatment. In three patients the catheter could not be positioned against the obstruction. In the 20 remaining patients laser angioplasty increased the diameter of the lumen from 0.3 +/- 0.3 mm to 1.4 +/- 0.3 mm and reduced the stenosis from 91 +/- 8% to 57 +/- 10%. In three patients "stand-alone" laser treatment was sufficient. In 17 patients balloon dilatation further reduced the stenosis to 20 +/- 18%. In two patients who had previously undergone unsuccessful balloon angioplasty with high inflation pressure, laser angioplasty allowed subsequent successful dilatation with low inflation pressure. There were no deaths, perforations, dissections, or arrhythmias. One patient had abrupt reclosure 24 hours after the procedure. Spasm occurred in four patients, and six patients had chest sensations during laser emission. Thus mid-infra-red pulsed coronary laser angioplasty is safe and effective for recanalization of stenosed and totally occluded arteries. The efficacy may be sufficient for "stand-alone" laser treatment. The technique may improve the efficacy of balloon angioplasty in cases of unsuccessful primary dilatation.     

Experimental intracoronary Excimer laser angioplasty

To determine the feasibility of intracoronary application of pulsed ultraviolet laser light 38 coronary arteries of 18 in situ hearts were treated with the bare fiber technique and a specially constructed catheter device. Eight hearts had no coronary artery disease, in 10 hearts coronary artery disease of one or more vessels could be documented angiographically. Total time of laser irradiation varied from 30-490 seconds. Radiation was performed until vessel wall perforation was documented. In all cases a reduction of the stenotic area was realized using the bare fiber technique. Due to a lack in the flexibility of the bare fiber only proximal lesions could be treated and the time of perforation could not be precisely predicted. Dissections were observed in six coronary arteries. The handling of the catheter device was comparable to the conventionally used balloon technique. Ablative treatment of distal vessel lesions was possible. Perforations did not occur. The histologic specimens documented smooth lumen margins not revealing thermal damage. It can be expected that the innovative catheter device will enhance the intracoronary use of pulsed laser light.     

Results of pulsed laser angioplasty of peripheral arteries guided by spectroscopy]

Seventy-six patients with complete occlusion of the iliac, femoropopliteal or distal arteries underwent laser angioplasty after failure of attempted mechanical recanalization by conventional angioplasty. The energy source was a dye pulsed laser emitting at 480 nm, 2 microseconds, 35 to 50 mJ/pulse and 5 Hz. The laser was coupled with an optical fiber of 200 microns diameter covered by a metallic spring. In order to center the laser in the arterial lumen, the fibre optic was introduced with a balloon catheter or a modified Van Andel catheter with a tapered and curved distal end with controlled torsion to direct the laser towards the lesion to be treated. The therapeutic laser was connected to a diagnostic Helium-Cadmium laser emitting at 325 nm, 50 ms and 5 mW, for the induction of tissue fluorescence analysed by a multichannel detector, itself connected to a computer programmed to differentiate atheromatous from normal tissues. The therapeutic laser was only activated when atheromatous tissue was in contact with the distal tip of the fiber optic. After vaporizing a narrow pilot channel conventional balloon angioplasty was performed. The immediate success rate was 83%; it was higher in iliac than in femoral arteries. This was less dependent on the length of occlusion than on the presence of calcification which was a common cause of failure. The complications were immediate reocclusion, perforation due to the sharp tip of the fibre and dissections without major clinical consequences. After 18 months, 64% of the arteries remained patent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Value of the combined Lastac laser-angioplasty technic in symptomatic superficial femoral occlusion

The results of peripheral transluminal angioplasty are satisfactory in stenotic arteries but those observed in the recanalisation of occluded peripheral arteries are not so good. There would therefore seem to be a good therapeutic opportunity for laser between angioplasty and surgery for patients with symptomatic arterial occlusion. The authors report their experience with the Lastac laser in 12 patients with symptomatic superficial femoral arterial occlusion. This is a no-contact laser. All patients had surgical indications in case of failure to recanalise by laser, despite collateral circulation by the profunda artery which was inadequate on effort leading to claudication and a limited walking perimeter. After 1 initial failure, 11 successful procedures were performed. There were no perforations due to the Argon laser beam but 2 were observed with the guide wire which was rapidly sealed by the balloon catheter. A surgical haematoma at the percutaneous puncture point resulted in 1 reocclusion during the patient's hospital period so that the 11 technical successes became 10 clinical successes. At medium-term follow-up, one asymptomatic occlusion had occurred and one restenosis was successfully redilated. The advantages of a continuous Argon "Lastac" laser compared with a contact laser are its capacity for auto-control, its coaxial fibre placement and the absence of direct contact with the lesion. The coaxial fibre arrangement plays an important role in preventing vascular perforation. These factors enable it to be used with more safety in patients with arterial occlusion.     

Cineangiographic and pathological features of the infarct related vessel in successful and unsuccessful thrombolysis

The postmortem histology and the results of cineangiography after selective intracoronary thrombolysis in vessels that were recanalized and in those that were not were compared in 21 patients who died within seven days (mean 2 days) of selective intracoronary thrombolysis. There was a persistent intraluminal thrombus in the infarct related coronary artery in five of six segments in which recanalisation was unsuccessful and in one of 15 segments in which recanalisation was successful. Rupture and haemorrhage of the atheromatous plaque were seen in most of the infarct related segments, both in those in which recanalisation was achieved and in those in which it was not. Irregular narrowing and filling defects on the coronary cineangiograms were associated with rupture and haemorrhage of the atheromatous plaque. These results suggest that failure of coronary thrombolysis to recanalize the infarct related artery does not indicate that the occlusion was not caused by thrombus.     

Cineangiographic and pathological features of the infarct related vessel in successful and unsuccessful thrombolysis.

The postmortem histology and the results of cineangiography after selective intracoronary thrombolysis in vessels that were recanalized and in those that were not were compared in 21 patients who died within seven days (mean 2 days) of selective intracoronary thrombolysis. There was a persistent intraluminal thrombus in the infarct related coronary artery in five of six segments in which recanalisation was unsuccessful and in one of 15 segments in which recanalisation was successful. Rupture and haemorrhage of the atheromatous plaque were seen in most of the infarct related segments, both in those in which recanalisation was achieved and in those in which it was not. Irregular narrowing and filling defects on the coronary cineangiograms were associated with rupture and haemorrhage of the atheromatous plaque. These results suggest that failure of coronary thrombolysis to recanalize the infarct related artery does not indicate that the occlusion was not caused by thrombus.     

Diagnostic contribution of ultrasonic diagnosis coupled with pulsed Doppler combined with continuous Doppler to the exploration of the vertebral arteries of atherosclerotic patients. Preliminary report

Velocimetric exploration by continuous emission Doppler is still essential for non-invasive evaluation of vertebral circulation but it does not provide morphologic data. Results were compared of exploration with combined continuous emission Doppler and a Duplex examination (sectorial scanning ultrasound imaging coupled with pulsed emission Doppler) and data from arteriography of 186 vertebral arteries in patients, mean age 57 years, admitted for exploration of a cerebral ischemic accident or a cervical murmur. The Duplex examination allowed identification of proximal segment (VI) in 98% of permeable vertebral arteries. The ostium of the vertebral artery was more difficult to visualize because of possible tortuosities, of sometimes a too posterior or intrathoracic localization or of a short neck. Nevertheless the vertebral ostium was identified in 78% of cases on the right and 48% on the left. The Duplex examination demonstrated sensitivity of 72% and specificity of 98% for detection of proximal stenosis of vertebral artery, and its sensitivity was therefore twice as sensitive as continuous emission Doppler for detection of stenoses of less than 50%. The Duplex examination should complete data from continuous emission Doppler by providing an evaluation of vertebral artery diameter and information on presence and characters of an elongation or stenosis. In this way, 9 atheromatous plaques not identified on arteriography were detected by ultrasound imaging. Similarly, the Duplex examination is particularly useful for identification of a hypoplastic vertebral artery, to distinguish the specific lesions of the subclavian artery from those extending onto vertebral ostium, and to characterize ostial lesions when these are accessible to examination.(ABSTRACT TRUNCATED AT 250 WORDS)     

The mechanism of transluminal angioplasty

Normal coronary arteries in dogs, atherosclerotic human coronary arteries at autopsy, and rabbit iliac arteries with experimental atherosclerosis were subjected to angioplasty and studied histologically or by electron microscopy. The studies showed desquamation of endothelium, deposition of platelets in the area of angioplasty, and splitting of atheromatous plaques frequently down to the internal elastic membrane. Human coronary arteries studied at post-mortem after successful angioplasty also have demonstrated splitting of the atheromatous plaque at its weakest point. Compression of atheromatous material from the plaque has not been demonstrated experimentally. The mechanism of angioplasty is complex. As the angioplasty balloon expands, splitting of the atheromatous plaque occurs at its weakest, thinnest point. The media and adventitia of the artery are then stretched, producing an enlarged lumen and increased blood flow. Splitting of the atherosclerotic plaque explains the angiographic appearance frequently seen after angioplasty--a separate column of angiographic dye or a small radiolucent filling defect in the area of successful angioplasty.     

Arterial recanalization using the laser. A technic for the future?

On the basis of two years' experience, a technique for the use of percutaneous endoluminal continuous emission Nd-YAG laser has been developed for arterial recanalisation. The effectiveness of this type of laser has been demonstrated in a large number of clots and atheromatous plaques, including calcified plaques. A balloon catheter gives a coaxial position of the fiber in center of the artery. Infusion of a blood solution containing 3 g of haemoglobin/100 ml at a rate of 20 ml/minute limits the thermal parietal lesions, improves the conditions of laser treatment and eliminates any risk of arterial perforation. No embolic debris is collected down-stream. Recanalisation of long arterial segments in amputated legs was performed prior to the human application. Ten patients have been treated with no mortality and virtually no morbidity. The narrowness of the reformed arterial lumina resulted in early re-thrombosis in the first 5 cases, requiring balloon modelling to ensure patency with a follow-up of 1 to 3 months in the 5 following patients.     

Characterization of human coronary artery atherosclerotic plaque fluorescence emission

Preliminary trials using fluorescence guidance of laser ablation in femoral arteries have been successful. There have, however, been few studies of the characteristics of fluorescence emissions from coronary arteries. A large series of fluorescence emission spectra from human coronary artery specimens was examined. Analysis included: fluorescence emission during excitation with ultraviolet and visible light; histologic correlations between plaque content and thickness, averaged spectra and fluorescence intensity ratios; and differences in specific plaque morphology with excitation of the same coronary specimens at 325 or 458 nm. Ratios of fluorescence emission intensity at selected wavelengths were calculated for both 325 and 458 nm excitation (13 wavelengths, 78 ratios for 325 nm; 11 wavelengths, 55 ratios for 458 nm). The following were found: atherosclerotic lesions in human coronary arteries were characterized by an increase in normalized fluorescence intensity at longer wavelengths when excited with either ultraviolet or visible light; calcific plaque content greater than 10% in lesions more than 1 mm thick was identified by increased normalized fluorescence intensity at 443 nm during excitation at 325 nm; and fatty plaque content correlated with fluorescence intensity ratios during 325 nm excitation, whereas fibrous and calcific content correlated well with fluorescence ratios during 458 nm excitation. It is concluded that characteristic fluorescence emission has the potential to correctly identify and characterize plaque morphology in human coronary arteries.