Laser for optical thrombolysis and facilitation of balloon angioplasty in acute myocardial infarction following failed pharmacologic thrombolysis

The feasibility of ultrasound-assisted endovascular laser thrombolysis in an acute rabbit thrombosis model

PURPOSE

This study aimed to test the feasibility of combined ultrasound and laser technique, namely, ultrasound-assisted endovascular laser thrombolysis (USELT), for thrombolysis by conducting in vivo tests in a rabbit thrombosis model.

MATERIALS AND METHODS

An acute thrombus was created in the right jugular vein of rabbit and then was treated with ultrasound only, laser only, and USELT to dissolve the blood clot. A total of 20 rabbits were used. Out of which, the first three rabbits were used to titrate the laser and ultrasound parameters. Then, five rabbits were treated with ultrasound only, five rabbits were treated with laser only, and seven rabbits were treated with USELT. During USELT, 532-nm laser pulses were delivered endovascularly directly to the clot through a fiber optic, and 0.5 MHz ultrasound pulses were applied noninvasively to the same region. A laser fluence of 4 to 12 mJ/cm² and ultrasound amplitude of 1 to 2 MPa were used. Recanalization of the jugular vein was assessed by performing ultrasound Doppler imaging immediately after the treatment. The maximum blood flow speed after the treatment as compared to its value before the treatment was used to calculate the blood flow recovery in vessel.

RESULTS

The blood flow was fully recovered (100%) in three rabbits, partially recovered in two rabbits (more than 50% and less than 100%) with mean percentage recovery of 69.73% and poorly recovered in two rabbits (<50%) with mean percentage recovery of 6.2% in the USELT group. In contrast, the treatment group with ultrasound or laser alone did not show recanalization of vein in any case, all the five rabbits were poorly/not recovered with a mean percentage recovery of 0%.

CONCLUSIONS

The USELT technology was shown to effectively dissolve the blood clots in an acute rabbit jugular vein thrombosis model.

Ultrasound-assisted laser thrombolysis with endovascular laser and high-intensity focused ultrasound

PURPOSE

The combination of laser and ultrasound can significantly improve the efficiency of thrombolysis through an enhanced cavitation effect. We developed a fiber optics-based laser-ultrasound thrombolysis device and tested the feasibility and efficiency of this technology for restoring blood flow in an in vitro blood clot model.

METHODS

An in vitro blood flow-clot model was setup, and then an endovascular laser thrombolysis system was combined with high-intensity focused ultrasound to remove the clot. The laser and ultrasound pulses were synchronized and delivered to the blood clot concurrently. The laser pulses of 532 nm were delivered to the blood clot endovascularly through an optical fiber, whereas the ultrasound pulses of 0.5 MHz were applied noninvasively to the same region. Effectiveness of thrombolysis was evaluated by the ability to restore blood flow, which was monitored by ultrasound Doppler.

RESULTS

As laser powers increased, the ultrasound threshold pressures for effective thrombolysis decreased. For laser fluence levels of 0, 2, and 4 mJ/cm² , the average negative ultrasound threshold pressures were 1.26 ± 0.114, 1.05 ± 0.181, and 0.59 ± 0.074 MPa, respectively. The periods of time needed to achieve effective thrombolysis were measured at 0.8, 2, and 4 mJ/cm² laser fluence levels and 0.42, 0.70, and 0.98 MPa negative ultrasound pressures. In general, thrombolysis could be achieved more rapidly with higher laser powers or ultrasound pressures.

CONCLUSIONS

Effective thrombolysis can be achieved by combining endovascular laser with noninvasive ultrasound at relatively low power and pressure levels, which can potentially improve both the treatment efficiency and safety.

A reconstituted in vitro clot model for evaluating laser thrombolysis

BACKGROUND/OBJECTIVE

Laser thrombolysis is the selective removal of thrombus from occluded blood vessels using laser energy. A reconstituted clot model with reproducible optical absorption properties was developed to evaluate the effect of various laser parameters on thrombus removal rate.

STUDY DESIGN/MATERIALS AND METHODS

Reconstituted clots were made with known fibrinogen concentrations and hematocrits. Ex vivo clots were collected from ten swine. Four red gelatin phantoms were prepared. Mass removal rates and ablation efficiencies were determined using a 577 nm, 1 microsec pulsed dye laser. The ablation efficiencies of the three clot models were compared at an energy of 25 mJ and a repetition rate of 4 Hz. In addition, the reconstituted clot model was ablated as pulse energy and repetition rate were varied with average power held constant at 100 mW.

RESULTS

The mean ablation efficiency for ex vivo clots ranged from 0.4 +/- 0.1 to 3.4 +/- 0.7 microg/mJ/pulse, with significant differences between groups (ANOVA p < 0.05). Reconstituted clots of varied fibrinogen content had ablation efficiencies of 1.5 +/- 0.2 to 1.6 +/- 0.3 microg/mJ/pulse at this energy and repetition rate. Gelatin ablation efficiency was inversely proportional to protein content and ranged from 0.5 +/- 0.3 to 2.0 +/- 0.7 microg/mJ/pulse. Reconstituted clot mass removal rates (in microg/s) were clinically similar for settings ranging from 13 mJ at 8 Hz to 33 mJ at 3 Hz.

CONCLUSIONS

The reconstituted model clot is a reproducible and biologically relevant thrombolysis target. Ex vivo clot lacks reproducibility between individuals and gelatin phantoms lack clinical relevance. At a constant average power, varying laser parameters did not affect mass removal rates to a clinically significant degree.

Enhancement of fibrinolytics with a laser-induced liquid jet

BACKGROUND AND OBJECTIVE

There are several problems inherent in the treatment of cerebral embolisms, such as the narrow therapeutic time window and the severe side effects of fibrinolytic drugs. There is thus need of a new method of removing a cerebral thrombus more rapidly using smaller amounts of fibrinolytics.

STUDY DESIGN/MATERIALS AND METHODS

The liquid-jet generator was made by insertion of an optical fiber (diameter: 0.6 mm) into a balloon catheter (6 Fr). A pulsed holmium (Ho) YAG laser (pulse duration time = 350 micros) was used as a laser source. The maximum penetration depth of a liquid jet generated with this device into a gelatin artificial thrombus was measured at various stand-off distances (L; distance between the optical fiber end and the catheter exit). Based on the result, a stand-off distance of 13 mm was chosen to investigate the enhancement of urokinase (UK) efficacy by only a single operation of the liquid-jet device in artificial thrombi made of human blood.

RESULTS

Maximum penetration depth increased in proportion to L and reached a maximum value (9 mm) when L was around 13 mm. Fibrinolysis rates (%) after incubation with a small amount of UK for 10 and 30 minutes were predominantly raised by a single use of the laser-induced liquid jet (5.4 +/- 2.4 vs. 22.6 +/- 6.1 and 7.3 +/- 3.8 vs. 38.3 +/- 5.6, respectively (mean +/- SD, P < 0.001)).

CONCLUSIONS

A laser-induced liquid jet effectively promoted fibrinolysis in vitro with use of only a small amount of fibrinolytics.

Engineering design of optimal strategies for blood clot dissolution

Blood clots form under hemodynamic conditions and can obstruct flow during angina, acute myocardial infarction, stroke, deep vein thrombosis, pulmonary embolism, peripheral thrombosis, or dialysis access graft thrombosis. Therapies to remove these clots through enzymatic and/or mechanical approaches require consideration of the biochemistry and structure of blood clots in conjunction with local transport phenomena. Because blood clots are porous objects exposed to local hemodynamic forces, pressure-driven interstitial permeation often controls drug penetration and the overall lysis rate of an occlusive thrombus. Reaction engineering and transport phenomena provide a framework to relate dosage of a given agent to potential outcomes. The design and testing of thrombolytic agents and the design of therapies must account for (a) the binding, catalytic, and systemic clearance properties of the therapeutic enzyme; (b) the dose and delivery regimen; (c) the biochemical and structural aspects of the thrombotic occlusion; (d) the prevailing hemodynamics and anatomical location of the thrombus; and (e) therapeutic constraints and risks of side effects. These principles also impact the design and analysis of local delivery devices.

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.

Coronary revascularization in heart transplant recipients by excimer laser angioplasty

BACKGROUND AND OBJECTIVE

Aggressive development of allograft coronary artery disease is a major cause of death in heart transplant recipients. Percutaneous balloon angioplasty is considered suboptimal for complex lesions in native coronary vessels and heart transplant recipients, alike. Excimer laser energy (308-nm wavelength) can successfully remove and vaporize atherosclerotic plaques in native coronary vessels; however, its application in heart transplant recipients has not been studied clinically yet.

STUDY DESIGN/MATERIALS AND METHODS

Six heart transplant recipients underwent percutaneous excimer laser (CVX-300, Spectranetics, Colorado Springs, CO) coronary angioplasty for treatment of a total of 10 discrete, obstructive coronary artery lesions. By using concentric or eccentric multifiber laser catheters, energy parameters were set at a fluence of 45 mJ/mm(2) or 60 mJ/mm(2) with a frequency of 25 Hz and 40 Hz, respectively, with a pulse duration of 135 ns and output of 200 mJ/pulse. The "saline flush" and "pulse and retreat" lasing techniques were used. In each case, adjunct balloon angioplasty was performed; in five lesions, an intracoronary stent was implanted. Angiographic evaluation was performed by visual assessment.

RESULTS

Each procedure was successful as defined by laser recanalization of the target lesion (reduction of target lesion stenosis in more than 20%) and subsequent adequate final luminal patency (reduction of target lesion stenosis to less than 50%) and absence of any major in-cardiac catheterization complication (such as perforation, acute closure, dissection, emergency coronary artery bypass surgery), or in-hospital complications (such as death, myocardial infarction, cardiac enzyme elevation, major bleeding), or need for surgical revascularization. A 92 +/- 5% preprocedural percent diameter stenosis was reduced by laser to 35 +/- 16% and by adjunct balloon angioplasty in all lesions and stenting in five lesions, to final residual stenosis of 2 +/- 6%. Angiographic follow-up between 2 and 6 months after the procedure demonstrated a target lesion restenosis rate of 22%.

CONCLUSION

Percutaneous excimer laser is safe and efficacious in the treatment of focal obstructive lesions caused by allograft coronary artery disease. These data represent an early clinical experience; thus, the long-term outcome of this revascularization method in recipients of heart transplantation will have to be determined by a large scale prospective, randomized, multicenter clinical study.

Failed thrombolysis in myocardial infarction

Prompt treatment with thrombolytic therapy in acute myocardial infarction has been proven to reduce infarct size and mortality. However, reperfusion fails to occur in 30-50% of patients, either due to impaired epicardial artery flow or microvascular occlusion, with these patients experiencing a higher morbidity and mortality. We review the diagnosis and management of failed thrombolysis in acute myocardial infarction.

Enhanced laser thrombolysis with photomechanical drug delivery: an in vitro study

BACKGROUND AND OBJECTIVE

Current techniques for laser thrombolysis are limited because they can not completely clear thrombotic occlusions in arteries, typically leaving residual thrombus on the walls of the artery. The objective of this study was to investigate the possibility of using photomechanical drug delivery to enhance laser thrombolysis by delivering drugs into mural thrombus during laser thrombolysis.

STUDY DESIGN/MATERIALS AND METHODS

Three experimental protocols were performed in vitro to quantitatively compare the effectiveness of thrombolysis by 1) constant infusion of drug, 2) laser thrombolysis, and 3) photomechanical drug delivery. A fiber-optic flushing catheter delivered drug (a solution of 1 microm fluorescent microspheres) and light ( a 1 micros pulsed dye laser) into a gelatin-based thrombus model. The process of laser-thrombus interaction was visualized using flash photography and the laser-induced pressure waves were measured using an acoustic transducer.

RESULTS

Lumen sizes generated by mechanically manipulating the catheter through the thrombus were smaller than those generated by laser ablation. The microspheres could be driven several hundred microns into the mural thrombus.

CONCLUSION

Photomechanical drug delivery has potential for enhancement of laser thrombolysis. Two mechanisms seem to be involved in photomechanical drug delivery: 1) mural deposition of the drug at the ablation site and 2) increased exposure of the thrombus surface area to the drug.

Laser thrombolysis using long pulse frequency-doubled Nd:YAG lasers

BACKGROUND AND OBJECTIVE

Laser thrombolysis is a means for clearing blood clots in occluded arteries. Many researchers have studied the mechanisms of clot ablation, and research clinicians have used the technique to treat myocardial infarction with a number of different laser systems. Specifically, a 1-microsec pulsed dye laser has been used clinically to remove blood clots in coronary arteries. As a comparative study, the ablation characteristics of lasers with pulse durations in the ranges of 50-150 microsec and 2-10 msec were investigated. Two frequency-doubled Nd:YAG lasers at 532 nm were used in this study. Ablation threshold and ablation efficiency of gel phantoms and thrombus using these two lasers were measured and compared with the results of the pulsed dye laser. The pulsed dye laser in this study operated at 522 nm.

STUDY DESIGN/MATERIALS AND METHODS

Gelatin samples with 150 cm(-1) absorption coefficient at 532 nm and animal clot were confined to 3-mm silicone tubes to measure ablation parameters. Additional samples with 150 cm(-1) absorption coefficient at 522 nm were prepared for use with the pulsed dye laser. A fluorescence technique and photographic bubble detection were used to determine ablation threshold. A spectrophotometric technique was used to determine ablation efficiency.

RESULTS

The ablation threshold of the gel phantoms for all three lasers was determined to be 17 +/- 2 mJ/mm(2). Ablation efficiency for the gel phantoms was 1.7 +/- 0.1 microg/mJ. Clot had an ablation efficiency of 2.9 +/- 1.0 microg/mJ.

CONCLUSIONS

Ablation threshold and efficiency are independent of laser pulse duration for 1-microsec, 50-150-microsec, and 2-10-msec pulses (P < 0.05).

Percutaneous revascularization modalities in heart transplant recipients

Accelerated allograft vasculopathy significantly limits the survival of heart transplant recipients. The prevalence of allograft coronary artery disease is as high as 18% by 1 year and 50% by 5 years following heart transplant. Heart failure and sudden cardiac death are the two most common clinical presentations. In heart transplant recipients with severe, discrete focal allograft vascular disease, percutaneous balloon angioplasty is a viable palliative option. However, its application is limited by a significant restenosis rate and progression of allograft disease in nontreated segments. Diffuse disease with tapering of vessels may be approached by debulking devices. Emerging revascularization modalities for focal stenoses and some of the diffuse tapering vessels include coronary stents, rotational atherectomy, various wavelength lasers, and, to a lesser extent, directional atherectomy. Conceivably, stents will reduce restenosis rates related to focal, discrete plaques; yet it is unknown whether they will be efficacious in short- and long-term treatment of diffusely diseased segments affected by allograft disease. Accurate assessment of clinical outcomes and long-term evaluation is imperative prior to acceptance of these devices as fundamental interventional tools for treatment of allograft coronary artery disease.

Prospective, randomized, multicenter comparison of laser-facilitated balloon angioplasty versus stand-alone balloon angioplasty in patients with obstructive coronary artery disease. The Laser Angioplasty Versus Angioplasty (LAVA) Trial Investigators

OBJECTIVES

The goal of this study was to examine the relative safety and efficacy of laser-facilitated percutaneous transluminal coronary angioplasty (PTCA) versus "stand-alone" PTCA.

BACKGROUND

Plaque debulking with lasing before PTCA may result in improved lumen dimensions and decreased rates of periprocedural ischemic complications, thus improving short- and long-term outcomes after percutaneous intervention. The mid-infrared holmium:yttrium-aluminum-garnet (YAG) laser has been shown to be effective in a variety of plaque subtypes and may be particularly useful in high risk acute ischemic syndromes.

METHODS

A total of 215 patients (mean [+/-SD] age 61 +/- 12 years) with 244 lesions were prospectively randomized at 14 clinical centers to laser versus stand-alone PTCA. After laser treatment, all patients underwent PTCA; 148 patients (69%) had unstable angina.

RESULTS

The procedural success rate without major catheterization laboratory complications was similar in patients assigned to laser treatment or PTCA alone (96.6% vs. 96.9%, p = 0.88), as was the in-hospital clinical success rate (89.7% vs. 93.9%, p = 0.27). There was no difference in postprocedural diameter stenosis after laser treatment compared with PTCA (18.3% +/- 13.6% vs. 19.5% +/- 15.1%, p = 0.50). However, use of the laser, versus PTCA alone, did result in significantly more major and minor procedural complications (18.0% vs. 3.1%, p = 0.0004), myocardial infarctions (4.3% vs. 0%, p = 0.04) and total in-hospital major adverse events (103% vs. 4.1%, p = 0.08). At a mean follow-up time of 11.2 +/- 7.7 months, there were no differences in late or event-free survival in patients assigned to laser treatment versus PTCA alone.

CONCLUSIONS

Compared with stand-alone PTCA, laser-facilitated PTCA results in a more complicated hospital course, without immediate or long-term benefits.