Laser recanalization of occluded atherosclerotic arteries in vivo and in vitro

Laser vaporization of atherothrombotic burden before drug-coated balloon application in ST-segment elevation myocardial infarction: Two-year outcomes of the laser-DCB trial

OBJECTIVES

This study aimed to examine whether the combination of excimer laser coronary atherectomy (ELCA) and drug-coated balloon (DCB) angioplasty can provide feasible clinical outcome in patients with ST-segment elevation myocardial infarction (STEMI) with 8-month and 2-year scheduled follow-up angiography.

BACKGROUND

Intracoronary thrombus elevates the risk of interventional treatment in patients with STEMI and hampers drug absorption into the vasculature released from DCB.

METHODS

Sixty-two patients with STEMI within 24 h after the onset of symptoms were enrolled in this prospective, single-center, single-arm study.

RESULTS

The laser catheter was successfully crossed distal to the culprit lesion in all cases. No ELCA-related adverse events occurred. Bail-out stenting was required in two patients (3.2%) after adjunctive ballooning; thus, the remaining 60 patients were completed with DCB angioplasty without stenting. Scheduled angiography at 8 months and 2 years was completed in 100% and 85.2%, respectively, and minimal lumen diameters were 3.4 ± 0.5, 3.4 ± 0.6, and 3.4 ± 0.5 mm after the procedure, at 8 months and at 2 years, respectively. Binary restenosis was observed in five patients (8.1%) in whom target lesion revascularization was performed. The duration of dual antiplatelet therapy was 2.3 ± 2.2 months, and neither abrupt vessel closure, reinfarction, cardiac death nor major bleeding was observed.

CONCLUSION

A combination of DCB angioplasty with ELCA is a feasible therapeutic option for STEMI.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Plaque Rupture and Thrombosis: the Value of the Atherosclerotic Rabbit Model in Defining the Mechanism

Persistent inflammation and mechanical injury associated with cholesterol crystal accretion within atherosclerotic plaques typically precedes plaque disruption (rupture and/or erosion) and thrombosis--often the terminal events of atherosclerotic cardiovascular disease. To elucidate the mechanisms of these events, the atherosclerotic rabbit model provides a unique and powerful tool that facilitates studies of atherogenesis starting with plaque buildup to eventual disruption. Examination of human coronary arteries obtained from patients who died with myocardial infarction demonstrates evidence of cholesterol crystals perforating the plaque cap and intimal surface of the arterial wall that can lead to rupture. These observations were made possible by omitting ethanol, an avid lipid solvent, from the tissue processing steps. Importantly, the atherosclerotic rabbit model exhibits a similar pathology of cholesterol crystals perforating the intimal surface as seen in ruptured human plaques. Local and systemic inflammatory responses in the model are also similar to those observed in humans. The strong parallel between the rabbit and human pathology validates the atherosclerotic rabbit model as a predictor of human pathophysiology of atherosclerosis. Thus, the atherosclerotic rabbit model can be used with confidence to evaluate diagnostic imaging and efficacy of novel anti-atherosclerotic therapy.

The Popliteal Approach: A New Approach to Percutaneous Laser-Assisted Angioplasty

"Hot-tip" laser angioplasty has been proven safe and effective in treating periperal vascular disease. There is, however, a group of patients with lesions or occlusions at the origin of the superficial femoral artery (SFA) that are difficult to approach from a standard antegrade femoral approach. The authors have developed a new retrograde popliteal approach that allows laser angioplasty to be performed percutaneously in these patients; 51 consecutive cases have been treated and followed up for more than one year. There were 40 cases with lesions greater than 9 cm long (Group A), while 11 cases had lesions less than 9 cm long (Group B). The mean lesion length was 15 cm. The initial success rate was 32 of 51 cases (63%): 24 of 40 cases (60%) in Group A and 8 of 11 cases (73%) in Group B proved successful. A three-month follow-up showed that clinical patency was 100% in initially successful cases (32 of 32 cases overall, 24 of 24 cases in Group A, and 8 of 8 cases in Group B). A twelve-month follow-up showed clinical patency in 20 of 32 initally successful cases (63%); 14 of 24 cases (58%) in Group A and 6 of 8 cases in Group B (75%) remained patent at twelve months.

The authors conclude that the popliteal approach to laser-assisted angioplasty is a safe and effective method of treating lesions at the origin of the SFA that could not be treated with any other percutaneous approach. One-year follow-up results in these patients are encouraging.

Argon Laser-Assisted Peripheral Angioplasty

Pioneered several years ago by cardiologists and interventional radiologists, laser-assisted angioplasty for the ablation of occlusive atherosclerotic lesions in the peripheral and coronary circulations is now entering the domain of the vas cular surgeon, who has the ability to progress beyond the limitations of the percutaneous approach.

In the initial 38 patients undergoing 51 lower extremity laser angioplasty/ balloon dilatation procedures for peripheral vascular occlusive disease, pedal pulses were restored in 32 (63%) limbs. The tandem procedure failed in 16 (31%); however, when improvement was assessed objectively by postoperative ankle/arm index evaluation, a positive outcome was achieved in 72 % of the patients. Three (6%) patients required femoral-popliteal bypass after balloon- related arterial dissection was identified.

Although laser angioplasty can successfully open occluded arteries, new in traoperative angiographic equipment compatible with laser angioplasty and a variety of incrementally sized laser probes will facilitate refinement of the tech nology and enhance its application.

Excimer laser angioplasty in acute myocardial infarction (the CARMEL multicenter trial)

Patients with acute myocardial infarction (AMI) with thrombus-laden lesions constitute a revascularization challenge. Thrombus and atherosclerotic plaque absorb laser energy; thus, we studied the safety and efficacy of excimer laser in AMI. In a multicenter trial, 151 patients with AMI underwent excimer laser angioplasty. Baseline left ventricular ejection fraction was 44 +/- 13%, and 13% of patients were in cardiogenic shock. A saphenous vein graft was the target vessel in 21%. Quantitative coronary angiography and statistical analysis were performed by independent core laboratories. A 95% device success, 97% angiographic success, and 91% overall procedural success rate were recorded. Maximal laser gain was achieved in lesions with extensive thrombus burden (p <0.03 vs small burden). Thrombolysis In Myocardial Infarction (TIMI) trial flow increased significantly by laser: 1.2 +/- 1.1 to 2.8 +/- 0.5 (p <0.001), reaching a final 3.0 +/- 0.2 (p <0.001 vs baseline). Minimal luminal diameter increased by laser from 0.5 +/- 0.5 to 1.6 +/- 0.5 mm (mean +/- SD, p <0.001), followed by 2.7 +/- 0.6 mm after stenting (p <0.001 vs baseline and vs after laser). Laser decreased target stenosis from 83 +/- 17% to 52 +/- 15% (mean +/- SD, p <0.001 vs baseline), followed by 20 +/- 16% after stenting (p <0.001 vs baseline and vs after laser). Six patients (4%) died, each presented with cardiogenic shock. Complications included perforation (0.6%), dissection (5% major, 3% minor), acute closure (0.6%), distal embolization (2%), and bleeding (3%). In a multivariant regression model, absence of cardiogenic shock was a significant factor affecting procedural success. Thus, in the setting of AMI, gaining maximal thrombus dissolution in lesions with extensive thrombus burden, combined with a considerable increase in minimal luminal diameter and restoration of anterograde TIMI flow, support successful debulking by excimer laser. The presence of thrombus does not adversely affect procedural success; however, cardiogenic shock remains a predictor of major adverse events during hospitalization.

Comparison of effectiveness of excimer laser angioplasty in patients with acute coronary syndromes in those with versus those without normal left ventricular function

Depressed left ventricular (LV) ejection fraction (EF) adversely affects procedural outcome during percutaneous coronary revascularization. This study examined the acute results, effectiveness, and safety of excimer laser coronary angioplasty (ELCA) in patients with acute coronary ischemic syndromes whose LVEF was depressed (<40%) versus those with preserved LVEF. One hundred patients with acute coronary syndromes (51 with unstable angina and 49 with acute myocardial infarction) underwent ELCA. Twenty-five patients (group 1) (29 lesions; 72% thrombotic) had decreased LVEF (mean 28 +/- 6%) and 75 patients (group 2) (81 lesions; 60% thrombotic) had preserved LVEF (mean 53 +/- 8%). Group 1 had a higher incidence of 3-vessel disease, Q-wave acute myocardial infarction, cardiogenic shock, diabetes, and hypertension. High laser success (87% group 1 vs 93% group 2, p = NS) and procedural success (93% group 1 vs 98% group 2, p = NS) were achieved in both groups. Minimal luminal diameter in group 1 increased from 0.7 +/- 0.5 to 1.4 +/- 0.5 mm after the laser procedure and finally to 3.0 +/- 0.4 mm; in group 2, minimal luminal diameter increased from 0.7 +/- 0.4 to 1.3 +/- 0.5 mm after the procedure to a final of 3.0 +/- 0.5 mm. The laser energy vaporized 75% of thrombus burden from the target lesion in group 1 versus 79% in group 2 (p = NS). Thrombolysis In Myocardial Infarction flow in group 1 increased from 1.4 +/- 1.2 to 2.7 +/- 0.7 by laser and finally to 2.9 +/- 0.3, and in group 2 from 2.0 +/- 1.0 to 2.8 +/- 0.6 after the laser procedure to a final of 2.9 +/- 0.4. There were no deaths, emergency bypass surgeries, strokes, or acute vessel closures in either group. Thus, ELCA is a safe and feasible revascularization modality for patients with acute coronary syndromes whose LVEF is depressed. The laser energy vaporizes a large thrombus burden from the treated plaque. Angiographic intracoronary thrombus does not adversely affect device and procedural success in these select patients.

Application of excimer laser angioplasty in acute myocardial infarction

BACKGROUND AND OBJECTIVE

Patients presenting with acute myocardial infarction who fail to respond to standard therapy with thrombolytics or have contraindications for their use oftentimes need revascularization with a mechanical device for removal of an occlusive coronary thrombus and its underlying atherosclerotic plaque. As both thrombi and plaques absorb laser energy in the ultraviolet wavelength (308 nm), we studied the feasibility and safety of excimer laser angioplasty in selective patients with complicated acute myocardial infarction.

STUDY DESIGN/MATERIALS AND METHODS

Fifty patients with acute myocardial infarction complicated by continuous chest pain and/or ischemia who had a total of 54 obstructive lesions were treated with percutaneous excimer coronary laser angioplasty (ELCA). A Q-wave myocardial infarction was documented in 56% and a non-Q-wave myocardial infarction in 44%. The baseline left ventricular ejection fraction was reduced at 43 +/- 13% and six patients (12%) presented to the cardiac catheterization laboratory in cardiogenic shock. Twenty-nine patients failed to respond to thrombolytic therapy and 16 had contraindications for thrombolytics and IIb/IIIa receptor antagonists. Following laser debulking, all patients received adjunct balloon dilation and then stents were deployed in 83% of the target lesions. Quantitative coronary arteriography (QCA) was performed at an independent core laboratory.

RESULTS

Ninety-eight percent laser success and 100% procedural success were achieved. By QCA the minimal luminal diameter increased from baseline of 0.7 +/- 0.5 to 1.3 +/- 0.5 mm post-lasing and then to 2.0 +/- 0.6 with balloon dilation to a final of 3.0 +/- 0.5 mm. Pre-laser percent stenosis diameter of 77 +/- 17% was reduced to 51 +/- 22% post-laser to 3.0 +/- 17% post-balloon and to a final of 15 +/- 25%. An 83% laser-induced reduction of thrombus burden area was achieved as well as an increase in TIMI flow from baseline of 1.7 +/- 1.1 to 2.8 +/- 0.4 by laser to a 2.9 +/- 0.4 final. There were no deaths, emergency bypass surgery, cerebral vascular accident, neurologic injury, or major perforation. In one case, a laser-induced major dissection was successfully treated by stenting. All 50 patients survived the procedure, improved clinically, and were discharged.

CONCLUSION

Application of excimer laser coronary angioplasty is feasible and safe in selected patients with acute myocardial infarction who either fail to respond to thrombolytics or have contraindications to these agents. Intracoronary thrombus at the target lesion can be successfully dissolved with this wavelength laser energy without adverse effect on the procedure results.

Effectiveness of excimer laser coronary angioplasty in acute myocardial infarction or in unstable angina pectoris

This study was conducted to evaluate the feasibility, safety, and acute results of percutaneous excimer laser coronary angioplasty (ELCA) in acute coronary syndromes. Fifty-nine patients were treated with ELCA (308 nm), including 33 patients with unstable angina pectoris (UAP) (35 vessels with 39 lesions) and 26 patients with acute myocardial infarction (AMI) (26 vessels with 29 lesions). In each patient the target lesion had a complex morphology. Overall, 71% of the patients had contraindications for pharmacologic thrombolytic agents or glycoprotein IIb/IIIa receptor antagonists. All patients received adjunct balloon dilation followed by stent implantation in 88% of patients with AMI versus 76% of patients with UAP (p = NS). Quantitative angiography was performed at an independent core laboratory; 86% laser success and 100% procedural success was achieved in the AMI group versus 87% laser success and 97% procedural success in the UAP group (p = NS). In the AMI group, the minimal luminal diameter increased from 0.77 +/- 0.56 to 1.44 +/- 0.47 mm after lasing to a final 2.65 +/- 0.47 mm versus 0.77 +/- 0.38 to 1.35 +/- 0.4 mm after lasing to 2.66 +/- 0.5 mm final in the UAP group. A prelaser percent stenosis of 76 +/- 17% for the AMI group versus 70 +/- 16% for the UAP group (p = NS) was decreased after lasing to 52 +/- 16% for the AMI group versus 51 +/- 14% for the UAP group (p = NS) and to a final stenosis of 15 +/- 17% for the AMI group versus 12 +/- 15% for the UAP group (p = NS). A 96% laser-induced reduction of thrombus burden area was achieved in the AMI group versus 97% in the UAP group (p = NS). Preprocedure Thrombolysis In Myocardial Infarction flow of 1.3 +/- 0.9 in the AMI group versus 2.3 +/- 1.2 for the UAP group (p = 0.01) increased to a final flow of 3.0 +/- 0 for the AMI group versus 3.0 +/- 0 for the UAP group (p = NS). There were no deaths, cerebrovascular accident, emergency bypass surgery, acute closure, major perforation or major dissection, distal embolization, or bleeding complications in either group. One patient with AMI had localized perforation (caused by guidewire) without sequelae and 1 patient with UAP had an abnormal increase in creatine kinase levels. All 59 patients survived the laser procedure, improved clinically, and were discharged. Thus, early experience in patients with acute coronary syndromes suggest that percutaneous ELCA is feasible and safe.

Peripheral artery recanalization in humans using balloon and laser angioplasty

The treatment of patients with complex peripheral arterial disease and those who have had previous unsuccessful attempted revascularization procedures can be clinically challenging. Initial treatment was begun using therapy by percutaneous balloon and laser angioplasty, then proceeding to bypass surgery if severe ischemia persisted. Both percutaneous and cut-down approaches were used to access totally occluded arteries. An attempt was made to cross the occlusion mechanically with either a guide wire or an activated laser probe. If laser recanalization was not successful, the patient underwent bypass surgery or was managed with medication unless an amputation was necessary. Following initial screening of 381 patients, 115 procedures were performed on 103 patients. In 31 procedures (28 patients), only balloon angioplasty was performed. In 84 procedures (75 patients), laser recanalization was attempted: 55 percutaneously and 29 by cut-down. Overall technical success (crossing the obstruction without perforation) was 86/115 (75%). Technically successful procedures were characterized by shorter arterial occlusions than were technical failures (8.4 +/- 1 cm vs. 14.3 +/- 1.9 cm; p < 0.004). Clinical success (residual stenosis < 50%, symptom relief, improved ankle brachial index > or = 0.15, and no complications) was achieved in 22/31 (71%) of balloon angioplasty procedures alone. The stenoses decreased from 98 +/- 4% to 31 +/- 24%, p < 0.00001. Combined percutaneous laser and balloon angioplasty had a technical success of 36/55 (65%). Stenoses were reduced from 99 +/- 2% to 56 +/- 14% after laser angioplasty, to 30 +/- 15% after balloon angioplasty, p < 0.0001. Laser angioplasty performed via a cut-down had a clinical success of 9/29 (31%). However, major complications were rare. Device staging for treatment of peripheral vascular disease provides additional options for patients who are at high surgical risk and/or in whom standard therapy has failed.

Vasoreactivity and structure of human coronary arteries irradiated by excimer laser

In this study the effects of excimer laser (308 nm) angioplasty on arteries have been studied. We report histology and vasoreactivity properties of human atherosclerotic and normal coronary arteries and bovine coronary arteries after exposure to pulsed excimer laser irradiation. Segments of isolated and pharmacologically active human coronary arteries were obtained within 5-8 hr postmortem. Segments of bovine arteries were obtained from fresh hearts. Side branches were ligated and vessels perfused with Krebs-Ringer's-bicarbonate solution in a perfusion apparatus to maintain their viability. Excimer laser irradiation was performed using a fused silica fiber advanced through the artery within a polyethylene cannula to assist with steerability and to protect against perforation. The fiber delivered a total of 40-60 J at its tip at 100 mJ/pulse at 15 pulses/sec. A total of 5 human atherosclerotic, 2 human normal, and 8 bovine arteries were used. Ablation of plaque was accomplished with remarkable ease and little resistance. Histologic studies showed clear-cut wedges inscribed by the catheter along the arterial wall without charring or thermal effects of coagulation necrosis. Vasoreactivity was assessed by measuring flow changes during perfusion before and after excimer angioplasty using a transient challenge with the vasoconstrictor serotonin. All excimer-irradiated arteries showed no increase in vasoreactivity during the challenge and showed preservation of relaxation properties following the challenge. In conclusion, coronary artery angioplasty by excimer laser appears to allow for effective plaque ablation with simultaneous preservation of structure and pharmacological properties of arteries.

Comparison of the thermal tissue effects produced by aged sapphire and silica hemispherical tips

This study evaluated the performance of sapphire and fused silica hemispherical tips under the same exposure conditions. Lesions produced in the chicken breast and a blood field were sectioned for light and transmission polarizing microscopy. Lesion size and thermal damage area were recorded as a function of the tips accumulated exposure. The tips transmission was measured after every 1,000 J of exposure. Fused silica tips lasted for approximately 5,000 J and experienced significant surface and transmission deterioration. The sapphire hemispherical tips lasted for > 12,000 J with no surface and transmission deterioration. Lesions produced with the fused silica tips generally increased in depth with use, and depths of 6 mm were common. Lesions produced by the sapphire tips were subsurface spherical areas of coagulation with the tissue surface relatively intact. This difference in resulting lesions may be attributed to the higher thermal conductivity of sapphire.

Laser-induced stimulation of thromboxane B2 synthesis in human blood platelets: role of superoxide radicals

Exposure of platelet-rich plasma to laser radiation at 3.5 W for 30 seconds reduced the threshold concentrations of adenosine diphosphate and L-epinephrine needed from complete platelet aggregation by 20% to 60% and by 30% to 50%, respectively. The irradiation of platelet-rich plasma with laser also increased the basal level of thromboxane A2 from < 0.5 pmol/10(8) platelets for each second of exposure. In contrast, the exposure of gel-filtered platelets to laser produced no effect on the prostanoid formation. However, the addition of laser-exposed platelet-free plasma to gel-filtered platelets stimulated the synthesis of thromboxane A2 in these cells. The effect of laser was completely blocked by adding superoxide dismutase or catalase to the platelet-rich plasma, indicating that the radiation-induced stimulation of thromboxane A2 production was mediated through the generation of superoxide radicals. Electron microscopic studies indicated that the laser-induced stimulation of thromboxane A2 production in platelet can occur without any noticeable damage in the cellular structure.

A new expandable intracoronary tantalum (Strecker) stent: early experimental results and follow-up to twelve months

A new radiopaque balloon expandable tantalum stent was tested in the coronary arteries of sheep. A total of 28 stents with a diameter of 2.0 to 3.8 mm were successfully deployed. The stent to coronary artery diameter ratio was 1.1-1.2:1. The animals were heparinized with 100 U/kg of heparin but did not receive antiplatelet drugs. Coronary angiography that was performed 10 minutes after stent implantation showed 100% patency with no side-branch occlusion. Four sheep died within 2 hours of stent implantation, and pathologic studies showed thrombosis of the smaller sized stents: 2 mm (n = 2), 2.8 mm (n = 1), and 3.2 mm (n = 1); three fourths of the sheep had two stents implanted. An oversized stent caused coronary rupture and cardiac tamponade in one other sheep. Follow-up study protocol included coronary angiography before animal sacrifice and pathologic studies within 48 hours (n = 11), 2 weeks (n = 1), 3 months (n = 2), 5 months (n = 1), 10 months (n = 7), and 12 months (n = 1). At 3 to 12 months of follow-up the coronary stent was completely covered with a layer of neointima, and there was no angiographic evidence of coronary stenosis and patent side branches. According to histologic examination, the neointima had nonuniform thickness (20 to 330 microns) and consisted of smooth muscle cells and some collagen. At 7 months of follow-up one of seven stents had angiographic (20%) and pathologic evidence of stenosis, which was secondary to thrombus. The tantalum device is easily deployed technically and notable for its excellent fluoroscopic visibility and flexibility. Thrombosis with a tantalum stent remains a problem, and therefore the larger diameter stents > or = 3.2 mm, antiplatelet drugs, and anticoagulation therapy are indicated for human studies. Implantation of multiple coronary stents increases the risk of stent thrombosis. The long-term, mild neointimal thickness and the patency of the stent and side branches are encouraging.

Thermal laser-assisted angioplasty of renal artery stenosis for renovascular hypertension

Percutaneous transluminal laser-assisted angioplasty of a renal artery stenosis was performed in a 16-year-old woman with renovascular hypertension. The stenotic portion of the renal artery was predilated by delivering Nd-YAG laser energy to the terminal tip of a laser catheter. Although the luminal diameter did not increase sufficiently with laser angioplasty alone, it allowed passage of the balloon catheter and subsequent successful balloon angioplasty. Immediately after dilatation, the patient's blood pressure fell to normal, and plasma renin activity decreased. There were no serious complications. Thermal laser angioplasty seems to be an effective adjunct technique for the treatment of severe renal artery stenosis which does not allow initial passage of a balloon catheter.

Beta-carotene enhances plaque detection by fluorescence attenuation in an atherosclerotic rabbit model

Improved detection of plaque during cardiovascular procedures could enhance the outcome of diagnosis and therapy. We evaluated a new method to stain plaque using a special intravenous preparation of beta-carotene (beta-C) in an in vivo model. beta-C was used to enhance the absorption coefficient of plaque and decrease the laser-induced fluorescence emission. Using this approach the difference in fluorescence emission was accentuated between normal artery and atherosclerotic plaque. Twenty-nine NZW rabbits were divided into five groups, each receiving a different intervention. This included the administration of beta-C to rabbits on a normal or a high cholesterol diet, with or without endothelial debridement. Aortae were examined grossly, by histology, and relative total fluorescence was detected at 886 sites using 488 nm or 514 nm laser excitation. At 488 nm excitation, unstained plaque attenuated total fluorescence twice as much as normal controls (7.55 +/- 1.46 vs. 15.06 +/- 3.12; P < 0.0001); beta-C stained plaque attenuated total fluorescence 17 times more than normal controls (0.89 +/- 0.29 vs. 15.06 +/- 3.12; P < 0.0001). Total fluorescence from unstained plaque was eight times greater than plaque stained with beta-C (7.55 +/- 1.46 vs. 0.89 +/- 0.29; P < 0.0001). Results obtained using 514 nm excitation were similar. The attenuation effect persisted up to 8 weeks following beta-C administration. Thus, beta-C stained plaque displayed fluorescence attenuation, which suggests that pretreatment with beta-C may greatly enhance plaque detection. This may be useful as a guide during plaque removal procedures.

Biology of restenosis and therapeutic approach

Numerous attempts have been made to prevent restenosis after successful transluminal dilation of an atherosclerotic vessel using a variety of pharmacologic and mechanical approaches. This article reviews the pathobiology of the restenosis process, offers a hypothesis as to its cause, reviews attempts to modify the process, and outlines therapeutic approaches to future treatment.

Laser recanalization of thrombosed arteries using thermal and/or modified optical probes; angiographic and angioscopic study

The degree of residual stenosis by fresh thrombus after laser recanalization was compared by use of angiography and angioscopy. Fifteen NZW rabbits were used. Occlusive fresh thrombus in rabbit aorta was produced by mechanical deendothelialization and external constrictions simulating clinical situations. Argon laser angioplasty using microlens-tipped optical fiber and/or 2 mm hot-tip probe was done to recanalize thrombosed aorta in 10 animals. Two-mm hybrid probe was used in 5. Percent area stenosis (% AST) was derived by use of the mean radius method obtained by angiography of stenotic segments in two orthogonal views and/or from angioscopy. All 15 totally occluded vessels with fresh thrombus were recanalized. Four minor perforations occurred. Following argon laser angioplasty with the microlens optical fiber, percent stenosis was reduced to 53% in diameter by angiography and 66 in % AST by angioscopy, and to 48% and 55 respectively following hot-tip probe. After laser angioplasty with the hybrid probe, residual stenosis by fresh thrombus was 37% in diameter on angiography and 63 in % AST on angioscopy. Mean percent AST was 62% with angiography and 52% with angioscopy, and there was no correlation between them (r = -0.028). Angioscopy provided cross-sectional topographic views of thrombosed lumen and showed charring and shrinkage of thrombus following laser angioplasty. This study suggests that (1) continuous-wave laser angioplasty using modified optical fibers can recanalize thrombotic vascular occlusion, (2) laser angioplasty by hot-tip probe could evacuate fresh thrombus more than microlens fiber on angioscopy, and (3) angiographic % AST did not correlate with angioscopic % AST.

Initial results of laser angioplasty under angioscopic guidance for salvage of an ischemic lower limb: preliminary report

From March to July 1989, nine patients at risk for peripheral artery disease underwent intraoperative Nd:YAG laser angioplasty using angioscopy at the Veterans General Hospital (Taipei, Taiwan, Republic of China). Following the laser angioplasty, balloon dilatation was performed in all cases. Eight men and one woman at an average age of 68 were included in the study (range: 58 to 78 years old). Ischemic symptoms included five patients with disabling claudication, four with pain at rest and one with gangrene on the toes. Eight of the nine patients had complete occlusions ranging from 2 to 19 cm in length. Two patients had high degree multiple segmental stenosis of the superficial femoral artery from 1 to 2 cm in length. Initial clinical success (indicated by relief of symptoms and increase in Doppler ankle pressure and index) and improvement in the angiographic luminal diameter was noted in 9 of 10 occluded vessels (90%) that underwent Nd:YAG laser treatment which was delivered at 10 to 12 watts through laser probes. Prelaser intraluminal diameter increased from 0.05 +/- 0.07 to 0.53 +/- 0.07 mm, Doppler ankle pressure index rose from 0.51 +/- 0.12 to 0.81 +/- 0.12, Doppler ankle pressure increased from 62.44 +/- 16.10 to 104 +/- 21.21 mmHg and the amplitude of pulse volume recorder at ankle level rose from 5.77 +/- 2.80 to 12.11 +/- 2.77 mm as compared with prelaser therapy (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo human atherosclerotic plaque recognition by laser-excited fluorescence spectroscopy

Arterial wall perforation and chronic restenosis represent important factors limiting the clinical application of laser angioplasty. Discrimination of normal and atherosclerotic vessels by laser-excited fluorescence spectroscopy may offer a means of targeting plaque ablation, thereby reducing the frequency of restenosis and transmural perforation. In this study, with use of a 325 nm low power helium-cadmium laser, in vivo endogenous surface fluorescence was excited through a flexible 200 microns optical fiber within a 0.018 in. (0.046 cm) guide wire in contact with the intima of 268 vascular interrogation sites from 48 patients either during open heart surgery or during percutaneous catheterization procedures. Fluorescence spectra could be recorded in all patients in bloodless and blood-filled arteries. Endogenous surface fluorescence was analyzed measuring peak intensity, peak position and shape index of the spectra. Compared with normal wall, noncalcified and calcified coronary atheroma showed a 42% (p less than 0.001) and a 58% (p less than 0.001) decrease of peak intensity, and higher shape index (p less than 0.001 and p less than 0.01, respectively). In addition, peak position was shifted to longer wavelengths for noncalcified coronary atheroma (p less than 0.001). Compared with normal aorta sites, aortic plaques demonstrated a 46% decrease of peak intensity, longer peak position wavelengths (p less than 0.05) and a higher shape index (p less than 0.001). Using an atheroma detection algorithm, prospective analysis of aorta and coronary spectra showed a specificity of 100% for identifying normal sites and a sensitivity of 73% for recognizing atherosclerotic sites.(ABSTRACT TRUNCATED AT 250 WORDS)

New technologies for the treatment of obstructive arterial disease

The well-known limitations of balloon angioplasty include unpredictable abrupt closure, chronic total occlusion, diffuse disease, and restenosis, among other factors. These limitations have prompted the development of new technologic approaches to angioplasty including laser applications for plaque ablation, mechanical device applications for plaque removal/debridement, and stent devices for structural maintenance of vascular lumen patency. Devices which directly apply laser energy for ablation of plaque material include a balloon-centered laser angioplasty system, excimer laser ablation catheter systems, and a fluorescence-guided spectral feedback laser system. Experience with these devices indicates that plaque can be successfully ablated by using laser energy. Vessel perforation and dissection are complications reported with these devices and the effects of laser angioplasty on restenosis remain unclear. Indirect application of laser energy has been tested by using a "hot tip" catheter and a laser balloon angioplasty system. Although the hot tip device has received FDA approval for use in peripheral arteries, it appears to have very limited applications in the coronary arteries. Laser balloon angioplasty appears to be beneficial in the setting of threatened acute closure; the device continues to be evaluated for potential beneficial impact on restenosis. Mechanical atherectomy catheters are designed to remove atherosclerotic plaque from the arterial system and include the AtheroCath, the Transluminal Extraction Catheter (TEC), and the Pullback Atherectomy Catheter (PAC). The Rotablator is an atheroablation device which debrides the obstructing plaque material with distal embolization of the particulate debris. Successful removal/debridement of atherosclerotic plaque has been demonstrated with the AtheroCath, Rotablator, and the TEC device. Pre-clinical studies demonstrate successful removal of plaque material with the PAC device. Despite the theoretic advantage of removing plaque material when performing angioplasty with these devices, there has been little or no reduction in restenosis rates based on a significant experience with the AtheroCath and the Rotablator. Intravascular stent devices including one self-expanding device design and two balloon-expandable device designs have been employed successfully in the elective setting to treat recurrent restenosis lesions. Two of the devices have been successfully tested in the setting of threatened acute closure. Early follow-up studies suggest some improvement in restenosis rates in certain clinical settings following intravascular stenting. Acute and subacute thrombosis remain substantial problems for stent devices and very aggressive anticoagulation regimens are necessary to minimize the adverse events. In summary, a number of a new technologic approaches for treatment of atherosclerotic lesions have been developed and are undergoing significant clinical evaluation.(ABSTRACT TRUNCATED AT 400 WORDS)

Stenosis following laser thermal angioplasty--a blinded controlled randomized study between aspirin against Probucol

Long-term patency of vascular angioplasties is limited by stenosis from neointimal hyperplasia or progressive arteriosclerosis. This study evaluated the hypothesis that ASA (an antiprostaglandin) or Probucol (an antioxidant) may be useful in preventing stenosis following laser thermal angioplasty. Aortoiliac arteriosclerosis was induced in 17 female New Zealand white rabbits with a combination of endothelial denudation (4 Fr. Fogarty balloon catheters) and 2% cholesterol-supplemented diet for 6 weeks. All rabbits then underwent arteriography and were immediately randomized to one of three groups: Group I (n = 6), control, laser but no adjunctive therapy; Group II (n = 5), laser and ASA 10 mg/kg/day; Group III (n = 6), laser and 1% Probucol diet. Retrograde laser thermal angioplasty was performed with a 1-mm coronary Laserprobe. Six watts of argon laser energy was delivered for a single 5-sec pulse using a continuous motion from the right common iliac artery to the aorta. Pre- and postlaser arteriography was performed in all groups. Rabbits were sacrificed 1 month following laser angioplasty, and aortoiliac sections were taken after in situ perfusion fixation with paraformaldehyde and 0.05% glutaraldehyde. Serial 5-mm segments, proximal to the aortic bifurcation and distally from the same, were taken, stained, and evaluated by quantitative morphometry. From each segment, lesion area and lesion area/internal elastic laminae area were evaluated and compared. Serum cholesterol increased from 60.8 +/- 19.5 to 1494.7 +/- 12.7 mg% following institution of the cholesterol diet (P less than 0.05). Arteriosclerotic lesions were observed in all rabbits and maximally located around the common iliac artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser angioplasty in miniature swine: advantages of a modified fiber tip delivery system

Laser angioplasty using a spherical lensed fiber-tip laser delivery catheter and a 200 mum bare silica fiber tip was performed in occluded atherosclerotic iliac arteries of miniature swine. Group I consisted of 8 animals with 11 totally occluded arteries in which the bare silica fiber was used. Group II included 22 animals with occlusive lesions in 41 arteries in which the silica lens tip was used. In vivo laser angioplasty was performed in both groups using an argon ion laser delivering 2 to 3 watts of power in 1 to 5 second intervals. Successful recanalization occurred in 7/11 (64%) in group I arteries and 35/41 (85%) in group II arteries. Vascular perforation occurred in 36% (4/11) in group I compared to 10% (4/41) in group II (P less than 0.05). Mechanical perforation due to the bare fiber alone accounted for 50% of the perforations in group I and did not occur with the silica lens-tip device (group II). We conclude that the atraumatic lensed fiber is more effective in recanalizing occlusive lesions and is a safer delivery system than the bare silica fiber.

Histologic and morphologic effects of rotary atherectomy on human cadaver arteries

Intimal splitting and medial dissection caused by balloon angioplasty and thermal burns and subintimal vacuolization caused by laser angioplasty have been proposed as potential causes of failure from these respective procedures. The purpose of this study was to evaluate the histologic and morphologic effects of a new high speed rotary atherectomy device (the Rotoblator) on human cadaver arteries. Fifteen stenotic human cadaver superficial femoral and popliteal arteries were harvested and atherectomized using the Rotoblator. Histologically, on cross-section, the atherectomized arteries exhibited a denuded endothelial layer, a smooth rounded luminal contour, minute plaque separation from the media, absence of plaque fragmentation, and variable remaining rim of atheromatous plaque. The media showed variable loss of the internal elastic lamina, normal remaining elastin, and normal smooth muscle cells. The adventitia was normal and completely intact in all sections with no media/adventitia separation or perforations. Scanning electron microscopy revealed endothelial peeling, etching from the atherectomy devices within the smooth muscle layer, and a tapered atherectomy distal endpoint. The arterial branches were preserved without evidence of any disruption of the branch artery orifice. Compared to balloon angioplasty and laser angioplasty, the Rotoblator atherectomy device appears to leave a smoother, more rounded luminal surface that may result in less risk of embolic complications and arterial wall damage.

Evaluation of clinical results following laser recanalization of the peripheral arteries

As experience is gained with laser-assisted angioplasty and as long-term follow-up results become available, a realistic and objective view of its role in the treatment of patients with occlusive disease of arteries in the peripheral vascular tree is becoming available. Comparison with results of conventional treatment methods is warranted. Experience in treating patients with vascular lesions is helpful in patient selection, management during the procedure, and follow-up care. Evaluation of experience in 169 procedures, with a follow-up time of 1 month to 3 years indicates what direction evolving patency rates are taking.

Randomized trial of laser-assisted passage through occluded femoro-popliteal arteries

A randomized trial was carried out in patients with occlusions of the femoro-popliteal artery to compare the passage of metal-tipped optical fibres with guide wires and catheters through the occlusions, prior to balloon angioplasty. The study was in a provincial English teaching hospital providing a vascular service for the area. Fifty patients were entered; 25 into the "laser" group and 25 into the "control" group. End points were (a) the success in passage through the occlusion and (b) the outcome 1 month after passage. Comparison of the groups showed no appreciable difference between the two methods with regard to age, sex, symptoms, incidence of diabetes, or previous myocardial infarctions. Successful passage through the occlusion followed by dilatation was achieved in 18 (72%) patients in the laser group and 20 (80%) in the control group. After 1 month, 13 (52%) arteries in the laser group were patent compared to 13 (57%) in the control group. Confidence limits for the difference in success of passage are -15% to +31%, and -24% to +33% for patency after 1 month. Since these limits include zero, it is unlikely that a longer trial would alter the difference between the two methods. The results suggest that the laser system currently in use is no better than conventional methods.

Vascular spasm complicates continuous wave but not pulsed laser irradiation

Preliminary clinical experience with laser angioplasty has suggested that arterial spasm may complicate attempts to employ laser light to accomplish vascular recanalization. The present study was designed to investigate the role of energy profile on the development of arterial spasm during laser angioplasty. Laser irradiation was delivered percutaneously in vivo to New Zealand white rabbits and to Yucatan microswine with or without atherosclerotic lesions induced by a combination of balloon endothelial denudation and atherogenic diet. Continuous wave (CW) laser irradiation from an argon ion gas laser (wavelength 488 to 514 nm) was applied to 23 arteries, while 16 arteries were irradiated using a pulsed xenon chloride (308 nm) or xenon fluoride (351 nm) excimer laser. Arterial spasm, defined as greater than 50% reduction in luminal diameter narrowing, complicated delivery of laser light to 17 (74%) of the 23 arteries irradiated with the CW argon laser. Spasm was consistently observed at powers greater than 2 W, at cumulative exposures greater than 200 seconds, and at total energy greater than 200 joules. Spasm was typically diffuse (including the length of the vessel) and protracted (lasting up to 120 minutes). Intra-arterial nitroglycerin (up to 300 micrograms) produced only temporary and incomplete resolution of laser-induced spasm. In contrast, spasm was never observed in any of the 16 arteries in which laser angioplasty was performed using a pulsed laser (0.95 to 6.37 joules/cm2, 10 to 50 Hz, 48 to 370 seconds). Thus CW but not pulsed laser angioplasty may be complicated by arterial spasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Argon ion laser-excited autofluorescence in normal and atherosclerotic aorta and coronary arteries: morphologic studies

Argon ion laser-excited autofluorescence was studied in unstained frozen sections of 47 normal and atherosclerotic human aortas and coronary arteries by means of a bright-field microscope modified for fluorescence microscopy with 476 nm argon ion laser epillumination, and compared to morphology in serial sections stained with H & E, Movat pentachrome, and oil red O. Normal artery autofluorescence correlated morphologically with the structural protein fibers elastin and collagen in the intima, media, and adventitia. Atherosclerotic plaque autofluorescence correlated morphologically with lipid or calcified deposits in the atheroma core. The autofluorescence of these deposits differed from that of elastin and collagen in distribution, intensity, and color, and increased with the severity of the plaque. We conclude that argon ion laser-excited autofluorescence in normal and atherosclerotic arteries correlates with morphology and has diagnostic potential in laser angiosurgery.

Early experiences with laser-assisted thermal angioplasty for peripheral vascular disease

Laser-assisted angioplasty has been used on 47 occasions in 45 patients for the management of atherosclerosis of the superficial femoral and proximal popliteal arteries. Twenty-four procedures were performed to treat disabling intermittent claudication and 23 procedures were performed for a "threatened limb" (rest pain, ischaemic ulceration or digital gangrene). Technical success was achieved in 40 (85%) cases; the mean length of occluded segment was 7.7 cm. The presence of heavily calcified occlusions contributed significantly (P less than 0.001) to technical failure. In 28 (70%) of the successfully treated cases, the recanalized arteries were patent at one month and in 21 (53%) cases they have remained patent during the follow-up period. In five of nine cases with a nine-month follow-up, the arteries still were patent. The mean length of the occluded segments that were treated initially was 7.1 cm in those that remained patent compared with 8.2 cm in those that reoccluded. Thirty-six (77%) patients were discharged from hospital on the day after the procedure. Laser-assisted angioplasty is a promising new technique that is applied best to short-segment, non-calcified occlusions and should reduce the requirement for femoropopliteal arterial bypass surgery.

Intravascular delivery of laser energy with metal-capped optical fibers: the potential hazard of distal embolism

To assess the risk of embolism resulting from plaque fragmentation during laser angioplasty with metal-capped optical fibers, laser energy of 4, 8, and 12 W for 10 or 20 seconds was delivered through these fibers to 60 coronary endarterectomy segments fitted in a silicone tube filled with saline solution. Twenty specimens manipulated in the same way but without delivering laser energy were used as controls. The effluent was filtered through in-line filters of 225, 70, and 25 microns. Treatment with laser energy resulted in weight loss and shortening of the specimens compared to control specimens (23 +/- 4 mg versus 5.4 +/- 0.8 mg; p less than 0.001 and 0.2 +/- 0.02 mm versus 2.5 +/- 0.5 mm; p less than 0.001). However, this also produced significant debris formation for all combinations of power and time (up to 275 +/- 38 micrograms versus 155 +/- 21 micrograms in controls). Results of scanning electron microscopy showed the presence of fragments up to 300 microns in diameter. Another potential hazard of laser angioplasty with metal-capped optical fibers in thromboembolism. This was studied by delivering laser energy through metal-capped fibers during perfusion with aliquots of blood at 5 or 40 ml/min. At each flow rate nine aliquots were treated with either 4, 8, or 12 W for 3, 6, or 9 seconds and a tenth was used as a control aliquot. The effluent was filtered with five filters between 225 microns and 25 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Probe for laser angioplasty radiating a corolla shaped beam

Laser angioplasty is a rapidly widening field. However, at present, the experimental research on human patients is limited by severe technical problems, particularly in the case of coronary arteries. The risk of mechanical or laser-induced perforations is likely the most serious. To get rid of this drawback here a new fiber-optic probe is described, characterized by a corolla shaped output beam and by no axial radiation. The probe consists of a conical fiber tip inserted in a particular quartz microcapsule. Its optical behavior has been studied both experimentally and theoretically, using a ray tracing method. Some preliminary tests carried out on the aorta wall from a cadaver are also described. The results seem to confirm that the new probe minimizes the risk of vessel perforation, while its diameter is suitable even for coronary applications.

Transvascular argon laser ablation of atrioventricular conduction in dogs: feasibility and morphological results

The purpose of this study was to ablate atrioventricular (AV) conduction in dogs with an argon laser using a transvascular approach. Six dogs were anesthetized and underwent a right thoracotomy and atriotomy. A bipolar #7 French lumen catheter containing a 400 u silica fiber was used to map the region of the AV junction. When a stable His deflection was obtained, the silica fiber was extruded from the end of the catheter and argon laser radiation was delivered for up to 20 s at 3.0-4.5 watts. In five of six dogs, complete heart block was successfully created after 3 to 15 lasings. A continuous His bundle electrogram in one dog showed gradual prolongation of the HV interval before the development of complete infrahisian block. The mean R-R intervals in the five dogs with complete heart block increased from 435 +/- 56 ms to 1216 +/- 197 ms (P less than 0.001), and the QRS duration increased from 78 +/- 26 ms to 91 +/- 19 ms (P = ns). Gross inspection showed multiple 1-2 mm2 craters in the atria just above the tricuspid valve ring. Complications included one instance each of aortic root perforation and creation of a small ventricular septal defect. These lesions were so small that there was no hemodynamic compromise in either animal in which they occurred and the lesions themselves were only detected on careful postmortem examination. Histology revealed two patterns of injury involved in conduction ablation. One was direct vaporization of tissue resulting in a wedge shaped incision and the other was formation of a hematoma and thermal necrosis at the lasing site with little evidence of tissue vaporization. Although catheter modifications are necessary to avoid perforation, this study demonstrates that ablation of conduction can be successfully accomplished using an argon laser.

Change in laser-induced arterial fluorescence during ablation of atherosclerotic plague

Analysis of the change in arterial fluorescence during plaque ablation may provide the basis for developing a fluorescence-guided ablation system capable of selective plaque ablation without risk of vessel perforation. Accordingly, fluorescence spectra were recorded from 91 normal and 91 atherosclerotic specimens of cadaveric human aorta. The ratio of the laser-induced fluorescence intensity at 382 nm to 430 nm (LIF ratio) was capable of classifying these specimens with an 89% accuracy with a threshold value of 1.8 (atherosclerotic greater than or equal to 1.8, normal less than 1.8). To characterize the change in fluorescence during plaque ablation, mechanical plaque ablation with a cold microtome was performed on 16 atherosclerotic aortic specimens. Fluorescence spectra were recorded serially after each 100 microns of plaque ablation; recordings revealed a change in fluorescence spectra from atherosclerotic to a normal pattern. With an LIF ratio of 1.8 to signal termination of plaque ablation, 15 of the atherosclerotic plaques had a residual plaque thickness less than 200 microns; one specimen had a residual plaque thickness of 300 microns. No specimen demonstrated ablation of the media. There was a statistically significant correlation between LIF ratio and plaque thickness (r = .73, P less than .001), but considerable variation in LIF ratio existed at each thickness. Therefore, laser-induced fluorescence spectroscopy is capable of discriminating atherosclerotic from normal aorta and of signaling completion of plaque ablation.