Percutaneous transluminal therapy of occluded saphenous vein grafts: can the challenge be met with ultrasound thrombolysis?

Interventional Microbubble Enhanced Sonothrombolysis on Left Ventricular Assist Devices

The left ventricular assist device (LVAD) is often used in the treatment of heart failure. However, 4% to 9% implanted LVAD will have thrombosis problem in one year, which is fatal to the patient's life. In this work, an interventional sonothrombolysis (IST) method is developed to realize the thrombolysis on LVAD. A pair of ultrasound transducer rings is installed on the shell of LVAD, and drug-loaded microbubbles are injected into the LVAD through the interventional method. The microbubbles are adhere on the thrombus with the coated thrombus-targeted drugs, and the thrombolytic drugs carried by the bubbles are brought into the thrombus by the cavitation of bubbles under the ultrasound. In a proof-of-concept experiment in a live sheep model, the thrombus on LVAD is dissolved in 30 min, without damages on LVADs and organs. This IST exhibits to be more efficient and safer compared with other thrombolysis methods on LVAD.

Molecular magnetic resonance imaging of deep vein thrombosis using a fibrin-targeted contrast agent: a feasibility study

PURPOSE

To evaluate the value of a fibrin-specific MR contrast agent (EP-2104R; EPIX Pharmaceuticals) for detection of deep vein thrombosis (DVT) and monitoring of percutaneous intervention for treatment.

MATERIALS AND METHODS

In 6 domestic swine, DVT was induced in an iliac/femoral vein using an occlusion-balloon catheter and subsequent injection of thrombin. The occluded vessels were recanalized by mechanical thrombectomy using a Fogarty catheter and an Arrow rotating thrombectomy device. Magnetic resonance imaging of the pelvis and lung was repeated 4 times (before and after DVT induction, after contrast agent administration, and after intervention) using a 1.5-T whole-body XMR system (ACS-NT, Philips Medical Systems, Best, NL). The visualization of the thrombi and contrast-to-noise ratio (CNR) was assessed.

RESULTS

EP-2104R allowed selective visualization of thrombi with accurate determination of the extent of DVT with high contrast (CNR: 65.3 +/- 17.2). After intervention, dislodged thrombus fragments were selectively visualized in the lung (CNR: 27.9 +/- 9.3).

CONCLUSIONS

Molecular magnetic resonance imaging using fibrin-specific MR contrast agent EP-2104R allowed for selective visualization of DVT and monitoring of percutaneous intervention.

The consequences of a new software package for the quantification of gated-SPECT myocardial perfusion studies

Purpose

Semiquantitative analysis of myocardial perfusion scintigraphy (MPS) has reduced inter- and intraobserver variability, and enables researchers to compare parameters in the same patient over time, or between groups of patients. There are several software packages available that are designed to process MPS data and quantify parameters. In this study the performances of two systems, quantitative gated SPECT (QGS) and 4D-MSPECT, in the processing of clinical patient data and phantom data were compared.

Methods

The clinical MPS data of 148 consecutive patients were analysed using QGS and 4D-MSPECT to determine the end-diastolic volume, end-systolic volume and left ventricular ejection fraction. Patients were divided into groups based on gender, body mass index, heart size, stressor type and defect type. The AGATE dynamic heart phantom was used to provide reference values for the left ventricular ejection fraction.

Results

Although the correlations were excellent (correlation coefficients 0.886 to 0.980) for all parameters, significant differences (p < 0.001) were found between the systems. Bland-Altman plots indicated that 4D-MSPECT provided overall higher values of all parameters than QGS. These differences between the systems were not significant in patients with a small heart (end-diastolic volume <70 ml). Other clinical factors had no direct influence on the relationship. Additionally, the phantom data indicated good linear responses of both systems.

Conclusion

The discrepancies between these software packages were clinically relevant, and influenced by heart size. The possibility of such discrepancies should be taken into account when a new quantitative software system is introduced, or when multiple software systems are used in the same institution.

Sonothrombolysis: an emerging modality for the management of stroke

OBJECTIVE

Ischemic stroke and intracranial hemorrhage remain a persistent scourge in Western civilization. Therefore, novel therapeutic modalities are desperately needed to expand the current limitations of treatment. Sonothrombolysis possesses the potential to fill this void because it has experienced a dramatic evolution from the time of early conceptualization in the 1960s. This process began in the realm of peripheral and cardiovascular disease and has since progressed to encompass intracranial pathologies. Our purpose is to provide a comprehensive review of the historical progression and existing state of knowledge, including underlying mechanisms as well as evidence for clinical application of ultrasound thrombolysis.

METHODS

Using MEDLINE, in addition to cross-referencing existing publications, a meticulous appraisal of the literature was conducted. Additionally, personal communications were used as appropriate.

RESULTS

This appraisal revealed several different technologies close to broad clinical use. However, fundamental questions remain, especially in regard to transcranial high-intensity focused ultrasound. Currently, the evidence supporting low intensity ultrasound's potential in isolation, without tissue plasminogen, remains uncertain; however, possibilities exist in the form of microbubbles to allow for focal augmentation with minimal systemic consequences. Alternatively, the literature clearly demonstrates, the efficacy of high-intensity focused ultrasound for independent thrombolysis.

CONCLUSION

Sonothrombolysis exists as a promising modality for the noninvasive or minimally invasive management of stroke, both ischemic and hemorrhagic. Further research facilitating clinical application is warranted.

Cardiovascular therapeutic uses of targeted ultrasound contrast agents

The therapeutic use of ultrasound contrast agents (UCAs) is an emerging methodology with high potential for enhanced directed therapeutic gene, bioactive gas, drug, and stem cell delivery. Ultrasound-targeted microbubble destruction has already demonstrated feasibility for plasmid DNA delivery. Similarly, therapeutic ultrasound for thrombolysis treatment has been taken into the clinical setting, and the addition of UCAs for therapeutic delivery or enhanced effect through cavitation is a natural progression to this investigation. However, as with any new technique, safety needs to be first demonstrated before translation into clinical practice. This review article will focus on the development of UCAs for cardiac and vascular therapeutics as well as the limitations/concerns for the use of therapeutic ultrasound in clinical medicine in order to lay a foundation for investigators planning to enter this exciting field or for those who want to broaden their understanding.

The utilization of ultrasound and microbubbles for therapy in acute coronary syndromes

Ultrasound has become a useful high resolution imaging modality for examining the cardiac microcirculation. With the use of microbubbles as an ultrasound contrast agent, ultrasound can be utilized to image the microcirculation and detect capillary flow abnormalities in acute ischaemia. A wide range of ultrasound frequencies (including those used for diagnostic transthoracic imaging) have also been utilized therapeutically to augment the effectiveness of fibrinolytic therapy in ST-segment elevation myocardial infarction (STEMI). Ultrasound and microbubbles are now being explored as methods of improving both microcirculatory and epicardial flow in acute STEMI. This article will review the mechanisms by which ultrasound and microbubbles assist in thrombus detection and dissolution. In addition, the pre-clinical studies utilizing transthoracic ultrasound as a therapeutic entity in acute STEMI will be reviewed. Clinical studies, completed and ongoing, will also be presented.

A porcine deep vein thrombosis model for magnetic resonance-guided monitoring of different thrombectomy procedures

PURPOSE

To establish a porcine model of deep iliac vein thrombosis, which allows monitoring of thrombectomy and thrombolytic procedures by magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Deep iliac vein thrombosis was induced in 12 domestic swine using an occlusion-balloon catheter and subsequent injection of thrombin distal to the occluded vessel site. Thrombosis induction was successfully achieved in all animals after 1 hour as verified by MRI. In addition, x-ray fluoroscopy was performed for comparison. Subsequently, thrombectomy was performed using a Fogarty catheter, an Arrow-Trerotola percutaneous thrombolytic device as well as electrical discharge-induced shock waves. The latter procedure was carried out with and without additional administration of Actilyse. MRI and x-ray fluoroscopy were repeated to monitor therapy.

RESULTS

After successful thrombosis induction within the deep iliac veins in all cases, thrombus material could be completely removed using the Fogarty catheter and the Arrow-Trerotola percutaneous thrombolytic device, whereas electrical discharge-induced shock wave failed to recanalize the occluded vessel even if additional Actilyse was administered. The actual burden of thrombotic material could be reliably visualized using MRI.

CONCLUSIONS

A porcine model of deep iliac vein thrombosis model is presented, which permits reliable visualization of thrombotic material. This model might be a useful tool to compare different thrombectomy devices or to evaluate the effectiveness of new thrombolytic approaches.

Pulsed-high intensity focused ultrasound enhanced tPA mediated thrombolysis in a novel in vivo clot model, a pilot study

INTRODUCTION

Thrombotic disease continues to account for significant morbidity and mortality. Ultrasound energy has been investigated as a potential primary and adjunctive treatment for thrombotic disease. We have previously shown that pulsed-high intensity focused ultrasound (HIFU) enhances thrombolysis induced by tissue plasminogen activator (tPA) in vitro, including describing the non-destructive mechanism by which tPA availability and consequent activity are increased. In this study we aimed to determine if the same effects could be achieved in vivo.

MATERIALS AND METHODS

In this study, pulsed-HIFU exposures combined with tPA boluses were compared to treatment with tPA alone, HIFU alone and control in a novel in vivo clot model. Clots were formed in the rabbit marginal ear vein and verified using venography and infrared imaging. The efficacy of thrombolytic treatment was monitored via high resolution ultrasonography for 5 h post-treatment. The cross-sectional area of clots at 4 points along the vein was measured and normalized to the pre-treatment size.

RESULTS

At 5 h the complete recanalization of clots treated with pulsed-HIFU and tPA was significantly different from the partial recanalization seen with tPA treatment alone. tPA treatment alone showed a significant decrease in clot versus control, where HIFU was not significantly different than control. Histological analysis of the vessel walls in the treated veins showed no apparent irreversible damage to endothelial cells or extravascular tissue.

CONCLUSIONS

This study demonstrates that tPA mediated thrombolysis can be significantly enhanced when combined with non-invasive pulsed-HIFU exposures.

Treatment of Acute Iliofemoral Deep Venous Thrombosis: A Strategy of Thrombus Removal

Patients with acute iliofemoral deep vein thrombosis (DVT) suffer the most severe postthrombotic sequelae. The majority of physicians treat all patients with acute DVT with anticoagulation alone, despite evidence that postthrombotic chronic venous insufficiency, leg ulceration, and venous claudication are common in patients treated only with anticoagulation. The body of evidence to date in patients with iliofemoral DVT suggests that a strategy of thrombus removal offers these patients the best long-term outcome. Unfortunately, currently published guidelines use outdated experiences to recommend against the use of techniques designed to remove thrombus, ignoring recent clinical studies showing significant benefit in patients who have thrombus eliminated. Contemporary venous thrombectomy, intrathrombus catheter-directed thrombolysis, and pharmacomechanical thrombolysis are all options that can be offered to successfully remove venous thrombus with increasing safety. The authors review evidence supporting the rationale for thrombus removal and discuss the most effective approaches for treating patients with acute iliofemoral DVT.

Therapeutic applications of ultrasound

Therapeutic applications of ultrasound predate its use in imaging. A range of biological effects can be induced by ultrasound, depending on the exposure levels used. At low levels, beneficial, reversible cellular effects may be produced, whereas at high intensities instantaneous cell death is sought. Therapy ultrasound can therefore be broadly divided into "low power" and "high power" applications. The "low power" group includes physiotherapy, fracture repair, sonophoresis, sonoporation and gene therapy, whereas the most common use of "high power" ultrasound in medicine is probably now high intensity focused ultrasound. Therapeutic effect through the intensity spectrum is obtained by both thermal and non-thermal interaction mechanisms. At low intensities, acoustic streaming is likely to be significant, but at higher levels, heating and acoustic cavitation will predominate. While useful therapeutic effects are now being demonstrated clinically, the mechanisms by which they occur are often not well understood.

Effects of simultaneous application of ultrasound and microbubbles on intracerebral hemorrhage in an animal model

Microbubble-enhanced sonothrombolysis (MEST) may be an alternative therapeutic option in ischemic stroke. Clinical study of the efficacy of MEST as an adjunct stroke therapy, before imaging with CT or MRI, requires experimental data on the safety of this approach in the presence of hemorrhagic stroke. We, therefore, investigated the effect of diagnostic transcranial ultrasound combined with microbubbles (US + MB) in an experimental animal model of intracerebral hemorrhage (ICH). ICH was induced in anesthetized rats by intracerebral collagenase injection. Transcranial ultrasound (2 MHz, mechanical index 1.3, 1051 kPa) was applied 3 h after ICH induction to rat brains for 30 min during a continuous IV infusion of sulfur hexafluoride microbubbles (SonoVue). The size of cerebral hemorrhage, the extent of brain edema, and the amount of apoptosis were compared with those from control rats with ICH but without US + MB. Results showed no significant effect of US + MB on hemorrhage size (control 23.3 +/- 10.7 mm(3), US + MB 20.3 +/- 5.8 mm(3)), on the extent of brain edema (control 3.3 +/- 2.0%, US +MB 3.5 +/- 1.9%), or on the rate of apoptosis (control 5.2 +/- 1.5%, US + MB 5.2 +/- 1.0%). We conclude that diagnostic ultrasound in combination with microbubbles does not cause additional damage to the rat brain during ICH in our experimental set-up. This finding provides support for the use of MEST as an early stroke therapy.

Treatment of deeply located acute intravascular thrombi with therapeutic ultrasound guided by diagnostic ultrasound and intravenous microbubbles

OBJECTIVE

We sought to determine the added value of simultaneous imaging of intravenously infused microbubbles that are being used to dissolve an intravascular thrombus with therapeutic ultrasound (TUS).

METHODS

In a chronic canine arteriovenous graft occluded by a thrombus, TUS (1 MHz) was applied through a 6-cm-thick tissue-mimicking phantom (measured mean +/- SD peak negative pressure through the phantom, 958 +/- 104 kPa) during an intravenous infusion of either saline (n = 6 occlusions) or lipid-encapsulated microbubbles (ImaRx Therapeutics, Inc, Tucson, AZ). Therapeutic ultrasound was intermittently applied during the microbubble infusion either at set time intervals (n = 6 occlusions) or when simultaneous diagnostic ultrasound (DUS) indicated a sustained presence of microbubbles (n = 12 occlusions). Success was defined as return of rapid flow within the graft (grade 3 flow).

RESULTS

Diagnostic ultrasound showed microbubbles moving through small channels within the thrombus before angiographic evidence of flow in the graft. This guided the timing of TUS application better than using set time intervals. Angiographic clearance of the thrombus and restoration of grade 3 flow at 45 minutes of treatment were seen in 33% of deeply located thrombosed grafts treated with TUS at set time intervals and 92% of grafts treated with TUS guided by DUS (P < .001 compared with set time intervals).

CONCLUSIONS

The use of TUS with intravenous microbubbles has a high success rate in recanalizing deeply located thrombosed arteriovenous grafts when performed with DUS guidance.

Distal protection in cardiovascular medicine: current status

Iatrogenic and spontaneous downstream microembolization of atheromatous material is increasingly recognized as a source of cardiovascular morbidity and mortality. Devising ways of reducing this distal embolization using a variety of mechanical means--distal protection--is currently under intense and diverse investigation. This review therefore summarizes the present status of distal protection. It examines the problem of distal embolization, describes the available distal protection devices, reviews those areas of cardiovascular medicine where distal protection devices are being investigated, and discusses potential future developments.

Pulsed high-intensity focused ultrasound enhances thrombolysis in an in vitro model

PURPOSE

To evaluate the use of pulsed high-intensity focused ultrasound exposures to improve tissue plasminogen activator (tPA)-mediated thrombolysis in an in vitro model.

MATERIALS AND METHODS

All experimental work was compliant with institutional guidelines and HIPAA. Clots were formed by placing 1 mL of human blood in closed-off sections of pediatric Penrose tubes. Four experimental groups were evaluated: control (nontreated) clots, clots treated with pulsed high-intensity focused ultrasound only, clots treated with tPA only, and clots treated with pulsed high-intensity focused ultrasound plus tPA. The focused ultrasound exposures (real or sham) were followed by incubations of the clots in tPA with saline or in saline only. Thrombolysis was measured as the relative reduction in the mass of the clot. D-Dimer assays also were performed. Two additional experiments were performed and yielded dose-response curves for two exposure parameters: number of pulses per raster point and total acoustic power. Radiation force-induced displacements caused by focused ultrasound exposures were simulated in the clots. A Tukey-Kramer honestly significant difference test was performed for comparisons between all pairs of experimental groups.

RESULTS

The clots treated with focused ultrasound alone did not show significant increases in thrombolysis compared with the control clots. The clots treated with focused ultrasound plus tPA showed a 50% ([30.2/20.1]/20.1) increase in the degree of thrombolysis compared with the clots treated with tPA only (P < .001), further corroborating the d-dimer assay results (P < .001). Additional experiments revealed how increasing both the number of pulses per raster point and the total acoustic power yielded corresponding increases in the thrombolysis rate. In the latter experiment, simulations performed at a range of power settings revealed a direct correlation between increased displacement and observed thrombolysis rate.

CONCLUSION

The rate of tPA-mediated thrombolysis can be enhanced by using pulsed high-intensity focused ultrasound exposure in vitro.

Low power ultrasound delivered through a PTCA-like guidewire: preclinical feasibility and safety of a novel technology for intracoronary thrombolysis

BACKGROUND

Low power ultrasound delivered through an angioplasty-like guidewire may be effective for intracoronary thrombolysis. We evaluated the preclinical feasibility and safety of such wire.

METHODS AND RESULTS

In 15 anesthetized Yucatan minipigs, the ultrasonic wire was advanced percutaneously into all three coronaries. Each coronary was randomized to long activation (6 minutes), short activation (3 minutes), or control (3 minutes indwelling, no activation). The energy delivered was 0.14 +/- 0.01 W/cm of active length (20 kHz). No changes in heart rate, rhythm, or arterial pressure occurred during wire positioning or activation. Mean lumen diameter (MLD) by quantitative angiography was not significantly different pre- and postintervention (2.36 +/- 0.12 mm vs 2.36 +/- 0.11 mm for long activation, P = 0.96; 2.33 +/- 0.15 mm vs 2.34 +/- 0.14 mm for short activation, P = 0.54; 2.30 +/- 0.12 mm vs 2.33 +/- 0.12 mm for control, P = 0.21). There were no angiographic stenoses at 60 or 90 days follow-up. Compared with baseline, MLD at follow-up increased in all the three groups (2.40 +/- 0.13 mm vs 2.53 +/- 0.11 mm, P = 0.004 for long activation; 2.37 +/- 0.17 mm vs 2.52 +/- 0.14 mm, P = 0.023 for short activation; 2.20 +/- 0.12 mm vs 2.33 +/- 0.11 mm, P = 0.001 for the control group). By histology, there were no clinically significant pathologic changes in coronary morphology.

CONCLUSION

Use of a transverse cavitation therapeutic wire is feasible and well tolerated acutely in the normal porcine coronary. At 60 and 90 days, no angiographically apparent damage, no clinically significant pathologic changes, and no adverse events were seen. This technology may be safely used during percutaneous coronary intervention. Further studies are justified to evaluate its efficacy for intracoronary thrombus ablation.

Influence of ultrasound operating parameters on ultrasound-induced thrombolysis in vitro

The effect of operating parameters on the thrombolytic potency of ultrasound (US) is important for potential therapeutic applications, but is not fully understood. Fresh human whole-blood thrombi were exposed in vitro to focused US from a diagnostic transducer driven by an impulse generator via an amplifier to vary duration (10 to 60 min), intensity (7 to 90 W/cm(2)), frequency (2 to 4.5 MHz), pulsed wave duty cycle (1:5 to 1:100 and continuous wave mode) and pulse length (100 to 400 micros). Segments of thrombi (498 +/- 73 mg) were submersed and insonated in saline solution. Thrombolytic efficiency was expressed as percentage loss of mass compared with controls (noninsonified thrombi). Ultrasound exposure achieved a significantly higher thrombolysis than no US, 56 +/- 16 % vs. 29 +/- 11 % (n = 232, p < 10(-6)). There was an exponential saturation-type correlation with duration of insonation (r(2) = 0.64) and intensity (r(2) = 0.97), an inverse correlation with US frequency at matched intensities (r(2) = 0.76, p < 10(-5)), a logarithmic relationship with duty cycle in pulsed mode (r(2) = 0.86) and a modest direct effect of pulse length (r(2) = 0.57, p < 10(-5)). Thus, thrombolytic efficiency of US depends directly on duration, intensity, duty cycle and pulse length and inversely, on frequency.

Perspectives on the role of ultrasonic devices in thrombolysis

Reperfusion strategies in acute myocardial infarction and thrombotic vascular occlusion are focused on rapid and complete restoration of antegrade flow in the infarct-related artery in order to maximize myocardial salvage. Due to the limitations of fibrinolytic agents in restoration of vascular flow, ultrasonic clot dissolution alone and concomitantly with fibrinolytic, anti-thrombotic and echocardiographic contrast agents has been intensively studied during the last 2 decades. Ultrasound thrombolysis has been tested in-vitro and in-vivo as well as in patients with acute thrombotic occlusions. We review currently available techniques and methods of ultrasonic thrombolysis and present recent clinical and experimental data. The future role of ultrasonic thrombolysis and the strategy of "power thrombectomy" for treatment of acute coronary syndromes is also discussed.

Drug and gene delivery and enhancement of thrombolysis using ultrasound and microbubbles

This article reviews some important characteristics of microbubbles that give them therapeutic properties. It discusses the use of microbubbles and ultrasound for targeted delivery of adenovirus and nonviral vectors to myocytes and endothelial cells and for the dissolution of thrombus or potentiation of fibrinolytic agents for acutely thrombosed vessels. Potential applications, such as induction of angiogenesis, inhibition of neointimal hyperplasia, and in the setting of acute myocardial infarction and ischemic stroke,are discussed briefly.

Clinical perspectives and therapeutics of thrombolysis

Reperfusion therapy with thrombolytic agents has been a significant advancement in the management of patients with acute ST elevation myocardial infarction. The outcome of acute myocardial infarction has significantly improved by early application of thrombolytic therapy. Intracoronary streptokinase has been used for >30 years, but reawakening interest occurred in the early 1980s in the use of thrombolytic therapy to establish rapid reperfusion during an acute myocardial infarction. Initial studies aimed at direct intracoronary thrombolysis, but owing to its cumbersome process and requirement of an active round the clock cardiac catheterization laboratory, it has been replaced by regimens of intravenous thrombolytic therapy which is as efficacious as intracoronary administration. Consideration of thrombolytic therapy has become a standard treatment for patients presenting with acute ST elevation myocardial infarction and various well-controlled trials have demonstrated the importance of both early and full reperfusion in improving clinical outcome in the setting of acute myocardial infarction. The subject of intravenous thrombolysis is perhaps the most rapidly evolving area in the management of acute myocardial infarction patients in the past decade. The current review focuses on the thrombolysis in the treatment of myocardial infarction and other conditions.

Noninvasive Extracorporeal Thrombolysis Using Electrical Discharge-Induced Shock Waves

RATIONALE AND OBJECTIVES

Many thrombectomy approaches have been developed for the treatment of venous thrombosis; however, no reference standard exists at this time. The aim of this study was to evaluate the efficacy of the transcutaneous application of electrical discharge-induced shock waves for thrombolysis in an in vitro model.

METHODS

Shock waves were applied on a thrombus positioned in a plasma-containing silicon tube using 2 different energy flux densities (0.53 and 2.26 mJ/mm). Depending upon the specific experiment, the thrombus was slightly moved to mimic pulsatory motions or/and additional Actilyse was added. Plasma samples were taken to determine the d-dimers before and after the application of shock waves.

RESULTS

Energy of 0.53 mJ/mm was insufficient for thrombolysis whereas the energy of 2.26 mJ/mm yielded a removal rate of up to 76.4% when the thrombus was slightly moved during the procedure. The amount of d-dimers correlated well with the addition of Actilyse. However, this did not affect the removal rate significantly.

CONCLUSION

The results demonstrate the potential of electrical discharge-induced shock waves for thrombolysis.

An experimental study of surgical ultrasonic angioplasty: its effect on atherosclerosis and normal arteries

BACKGROUND

We have developed a new hand-held probe for surgically open ultrasonic angioplasty. Two experimental studies were conducted to determine the optimal power range for carrying out ultrasonic angioplasty.

METHODS

The probe measured 2.5 mm in diameter and 5 cm in length. The amplitude was 210 microm at 100% power. One of the studies was designed to determine the power range that is effective for removal of atherosclerotic lesions. Human cadaveric arteries were used in the study. The other study was designed to investigate the long-term adverse effect on normal arteries. Canine arteries were used in this study.

RESULTS

In the study using cadaveric arteries, the amplitude ranging from 90 to 110 microm was effective for soft atheroma, the range from 110 to 130 microm was effective for mild arteriosclerosis, and 150 microm was effective for calcified lesions. The other study of the long-term effect on canine normal arteries indicated that each incidence of stenosis and occlusion was 0% at amplitude ranging from 90 to 110 microm, 13% at 130 microm, and 25% at 150 microm.

CONCLUSIONS

The surgically open ultrasonic angioplasty with a new hand-held probe was effective for various kinds of atherosclerotic lesions, whereas the angioplasty at high amplitude had a problem with the long-term effect on normal arteries.

Power thrombectomy in acute ischemic coronary syndromes

Intracoronary thrombi are commonly found in patients with acute coronary syndromes. A large thrombus burden or a platelet-rich thrombus frequently resists pharmacologic therapy ("thrombolytic ceiling"). In such cases restoration of adequate antegrade coronary flow necessitates application of a mechanical force. Power thrombectomy is a revascularization strategy incorporating a mechanical device for removal of occlusive coronary thrombi in conjunction with or following administration of either platelet glycoprotein IIb/IIIa receptor inhibitors or thrombolytic agents, or both. Mechanical devices for power thrombectomy include ultrasound sonication, rheolytic thrombectomy (Angiojet), laser, transluminal extraction catheter, aspiration catheter, and to a limited extent, balloon angioplasty. In acute coronary syndromes the strategy of power thrombectomy aims to achieve the clinical advantages of more nearly complete vessel patency, improved antegrade flow, and enhanced preservation of myocardial tissue.

Augmentation of low-frequency ultrasound-induced clot disruption by hydroxyethyl starch is dependent on the duration and intensity of ultrasound exposure; an in vitro study

We investigated the synergistic effect between low-frequency ultrasound (US) and hydroxyethyl starch (HAES) on blood clot disruption, using different HAES concentrations, US duration and intensity. Human blood clots, 200 to 400 mg in weight, were placed in tubes containing 10 mL of normal saline alone or with HAES 0.1%, 1% or 2%. Clots were randomized to four intensities of US exposure: none, low, medium and high (maximal amplitude of motion at the tip of the horn: 0, 96, 144 and 192 micro m, respectively), and for three durations of US exposure (10, 20 and 40 s). After treatment, the clots were reweighed, and the percent differences in weights were calculated. US intensity, US duration and HAES concentration had a significant effect on the blood clot dissolution (p < 0.001 for all three variables). HAES augmented clot dissolution only when US intensity was medium or high. With low intensity, HAES did not augment clot lysis.

CONCLUSIONS

microparticle-containing solutions, such as HAES, have a potential for augmenting clot disruption by US. This effect is highly dependent on US intensity.

Stent deployment with distal vascular protection for the culprit vein graft stenosis in a patient with an acute infarct and cardiogenic shock

A case of emergency stent deployment to a critical vein graft lesion in a patient with an acute myocardial infarction and cardiogenic shock is described. An Angioguard vascular protection device was used, retrieving a large amount of atheromatous debris. Use of filter-type protection devices to prevent distal atheroembolism may be lifesaving in such patients.

Distal emboli protection in patients undergoing percutaneous coronary intervention after a recent myocardial infarction

Devices to prevent distal atheroembolization are an important addition to the armamentarium of an interventional cardiologist. We report the use of PercuSurge, a distal balloon occlusion device, in two patients with recent myocardial infarction of differing etiologies. The first case is a patient with an old degenerated vein graft with thrombotic occlusion of greater than 48-hr duration and the second case is a patient with an embolic myocardial infarction in a native coronary artery. In both cases, significant thromboembolic debris was aspirated with technical success and no complications. These cases illustrate use of the PercuSurge device in patients after a recent myocardial infarction for preserving distal myocardial perfusion and microvascular integrity.

Distal occluder and rheolytic thrombectomy of a saphenous vein graft lesion with a large associated thrombus

Percutaneous intervention in thrombus-containing lesions is frequently associated with complications, including distal embolization and no-reflow. In saphenous vein bypass grafts (SVG), friable atheroma and associated thrombus make interventions particularly difficult. Distal protection strategies are in development, but complete protection with removal of all potentially embolic material is challenging. This case illustrates a novel technique using a distal occluder balloon and rheolytic thrombectomy followed by stent deployment to treat a SVG lesion. This combination therapy was technically feasible, resulted in no angiographic complications and normal creatine kinase levels throughout follow-up, and can be used during high risk SVG interventions.

Coronary perforation as a potential complication derived from coronary thrombectomy with the X-Sizer device

We report a case of coronary perforation after failed atherectomy with a 2 mm X-Sizer catheter in recent totally occluded right coronary artery. The perforation was successfully managed with a polytetrafluoroethylene-covered stent with satisfactory final angiographic results. Possible predictors of this complication with this new device are discussed.

Ultrasound and thrombolysis

Thrombolytic therapy and mechanical interventions are frequently used in the treatment of both arterial and venous thrombotic disease. Limitations to these approaches include failure to achieve reperfusion and complications including bleeding and vessel wall damage. Increasing evidence indicates that the use of ultrasound offers potential therapeutic advantages. This review considers two distinct approaches which include the use of high intensity ultrasound to mechanically fragment clots and also the use of low intensity ultrasound to augment enzymatic fibrinolysis. High intensity ultrasound can be delivered via catheter or transcutaneously to disrupt clots in vitro or in animal models into small fragments. Initial clinical studies demonstrate potential clinical value in peripheral and coronary arterial thrombosis and occluded saphenous vein bypass grafts treated with the catheter approach. Studies in vitro indicate that low intensity ultrasound accelerates enzymatic thrombolysis through non-thermal mechanisms involving improvement in drug transport. The effect is larger at low frequencies, which also offer better tissue penetration and less heating. The ability to accelerate thrombolysis has been confirmed in animal models demonstrating markedly increased reperfusion and minimal toxicity. The use of ultrasound to mechanically disrupt occlusive thrombi or to accelerate enzymatic thrombolysis offers a new approach to treating occlusive thrombotic disease.

Extraction of large intracoronary thrombus in acute myocardial infarction by percutaneous Fogarty maneuver: intentional abuse of a novel interventional device

Intracoronary thrombus in the infarct-related artery remains a challenge for interventional catheter-based techniques in acute myocardial infarction and may result in severe complications due to distal embolization. We describe a patient with acute myocardial infarction in whom a large intracoronary thrombus of the left anterior descending coronary artery was successfully removed by percutaneous Fogarty maneuver using an expanded filter protection device.

Percutaneous transluminal therapeutic ultrasound for high-risk thrombus-containing lesions in native coronary arteries

We assessed the short-term outcome of percutaneous coronary ultrasound thrombolysis (CUT) for high-risk thrombus-containing lesions in native coronaries in the setting of acute coronary syndromes (ACS). Data were prospectively collected in a multicenter (n = 32) registry of consecutive ACS patients. The study population (n = 126) had mostly (84%) totally occluded vessels. The mean age of clot was 5.7 +/- 9.5 days (range, 0-60 days). CUT (41 kHz, 18 W) led to device success in 112 (89%) patients, with a residual stenosis of 69% +/- 20%. Adjunct PTCA or stenting was used in 97% of the patients. Procedural success was achieved in 124 (98%) patients, with a final residual stenosis of 6% +/- 10%. There were no major adverse clinical events during hospitalization. Ultrasound thrombolysis is a feasible procedure that offers a safe and probably effective adjuvant device solution for the treatment of high-risk, thrombus-containing lesions in the native coronary arteries.

Percutaneous intervention of old degenerated saphenous vein grafts

The treatment of failing bypass grafts is difficult because repeat surgery carries a higher mortality rate than a first operation. Percutaneous intervention is more difficult because mechanical manipulation of these soft, friable atherosclerotic plaques have been associated with a significant rate of distal embolization, myocardial infarction, late restenosis and death. Balloon angioplasty alone has proven to have serious limitations in the treatment of older degenerated saphenous vein grafts (SVG). Although directional atherectomy yielded a higher angiographic success in a randomized trial, the restenosis rate was similar, and the procedural complications higher. The transluminal extraction catheter (TEC) has also shown significant limitations for the treatment of degenerated or thrombotic vein grafts with a significant procedural complication rate. A randomized trial comparing stenting versus balloon angioplasty in focal SVG lesions showed a higher freedom from major adverse cardiovascular events in the stent group, but there was no significant difference in the angiographic restenosis rates. More recently, rheolytic thrombectomy and mechanical thrombolysis have proven useful in treating thrombotic lesions in SVG. In addition, the recent development of distal protection devices appears very promising and will probably contribute to decreased distal embolization during percutaneous revascularization of these conduits.

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.

Ultrasound, microbubbles, and thrombolysis

Although dissolution of thrombus using ultrasound has been attempted for over 25 years, the clinical use of this technique remains limited. The ability of microbubbles to potentiate ultrasound-induced thrombolysis has renewed interest in this technique, which recanalizes occluded vessels without the need for fibrinolytic therapy. In this article, the potential mechanisms by which ultrasound and microbubbles produce thrombus dissolution are explored. In vitro and in vivo studies using ultrasound alone and ultrasound in combination with microbubbles to cause thrombolysis are reviewed. Potential clinical implications of more recent findings are explored.

The use of mechanical devices as adjuncts to intracoronary stenting

A number of mechanical adjuncts to intracoronary stenting are now available to the interventional cardiologist. These devices have assisted in the development of a safer and more effective stenting practice. Intravascular ultrasound-guided stenting has been shown to reduce the rate of subacute thrombosis and subsequent restenosis. It allows a greater appreciation of lesion structure and severity so that an appropriate intervention strategy can be devised. Debulking techniques may allow the optimal deployment of stents so that restenosis is reduced; however, the results of large randomized studies are still awaited. The use of thrombectomy and distal embolization protection devices is emerging as a safer alternate to stenting alone in difficult patient subsets, such as those with thrombus-laden lesions and degenerated vein grafts. Doppler and pressure wires may be useful in determining optimal stent deployment and predict subsequent patient outcomes. An understanding of the indications and limitations of these devices is of increasing importance to the interventional cardiologist as the coming decade threatens to yield an impressive array of high-tech innovations.

Arterial thrombus dissolution in vivo using a transducer-tipped, high-frequency ultrasound catheter and local low-dose urokinase delivery

PURPOSE

To examine the hypothesis that a transducer-tipped high-frequency ultrasound drug-delivery catheter may augment the thrombolytic effects of locally delivered low-dose urokinase and result in improved recanalization rates and reduced residual thrombotic burden.

METHODS

Thrombi were induced in situ bilaterally in 5- to 6-cm-long segments of the superficial femoral arteries in 9 dogs by intraluminal thermal damage and injection of thrombin. A transducer-tipped high-frequency local drug-delivery catheter was applied at 1.1 MHz and 0.6 W for 60 minutes to one superficial femoral artery segment, and an identical catheter with an inactivated ultrasound transducer was used to treat the contralateral control segment. Urokinase (5000 IU/kg) was delivered bilaterally into the thrombi during the treatment interval.

RESULTS

Angiography documented TIMI grade 2 or 3 flow in 9 (100%) segments in the ultrasound-treated group versus 6 (67%) of the controls (no ultrasound) (p = 0.058). Angiographically detected distal embolization was found in 2 ultrasound-treated segments compared with 5 controls (p = 0.02). Protruding or occlusive thrombi were seen angioscopically in 8 (89%) control segments but in only 1 (11%) of the ultrasound-treated arteries (p < 0.001). By histopathology, 7 (78%) segments in the control group had occlusive thrombi, whereas only 3 nonocclusive thrombi were found in the ultrasound-treatment group (p < 0.001).

CONCLUSIONS

Catheter-delivered high-frequency ultrasound and local low-dose urokinase infusion is efficacious for the treatment of acute thrombotic occlusions as evaluated by angiography, angioscopy, and histopathology.

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.

Ultrasound thrombolysis in hemodialysis access: in vitro investigation

PURPOSE

To evaluate the effectiveness of ultrasound thrombolysis in occluded hemodialysis access shunts using an in vitro model.

METHODS

Thrombosed hemodialysis accesses were simulated by clotted bovine blood in a flow model (silicone tubing; inner diameters 4, 6, and 9 mm). After retrograde and antegrade sheath placement (7 Fr), mechanical thrombolysis was performed using an ultrasound probe (Acolysis, Angiosonics, Morrisville, NC, USA). The tip of the device measured 2.2 mm in diameter. During sonication, the catheter was moved slowly back and forth using an over-the-wire system. Thirty complete occlusions [tubing diameters 4 mm (n = 12), 6 mm (n = 12), 9 mm (n = 6)] were treated. Initial thrombus weights were 3.5 (+/- 0.76) g, 7.7 (+/- 1.74) g, and 19.4 (+/- 2.27) g for the three diameters. Maximum sonication time was 15 min for each probe.

RESULTS

With this device, we were able to restore a continuous lumen in all 12 occluded 4 approximately mm silicone tubes. No wall-adherent thrombi remained after sonication for 3.5--9.6 min. In hemodialysis access models with diameters of 6 mm, thrombus fragments persisted in 25% (3/12 accesses). These were located in the medial portion of the access loop and near to the puncture sites. However, flow was re-established after 5.0--13.0 min of treatment in all settings. Mechanical dissolution of thrombus material failed in five of six access models with diameters of 9 mm, even though ultrasound energy was applied for the maximum of 15 min.

CONCLUSION

In a clotted hemodialysis shunt model, successful ultrasound thrombolysis was limited to small access diameters and small amounts of thrombus.

Ultrasound thrombolysis in stent thrombosis

Recent refinement in stent implantation technique and peri-procedural pharmacological treatment has lowered the incidence of stent thrombosis significantly. Still, all stent thromboses are associated with major adverse events. In previous studies it has been suggested that intravascular ultrasound fibrinolysis is safe and effective. In this report, ultrasound successfully reperfused thrombotically occluded stents. These observations suggest that ultrasound may dissolve occlusive platelet-rich thrombus effectively and safely. Cathet. Cardiovasc. Intervent. 51:332-334, 2000.

Balloon occlusion and transluminal aspiration of saphenous vein grafts to prevent distal embolization

Distal embolization is a common complication of percutaneous intervention in saphenous vein grafts. This may lead to the "no reflow" phenomenon and subsequent myocardial infarction. We describe a case in which we occluded the distal portion of a saphenous vein graft with a balloon to prevent distal embolization, performed percutaneous transluminal coronary angioplasty, and then successfully aspirated the particulate debris with a Dorros/Probing catheter.

Long-term clinical outcome after endoluminal reconstruction of diffusely degenerated saphenous vein grafts with less-shortening wallstents

OBJECTIVES

This study was designed to evaluate the immediate and long-term clinical results of patients undergoing endoluminal reconstruction in diffusely degenerated saphenous vein grafts (SVGs) with elective implantation of one or more less-shortening Wallstents.

BACKGROUND

The optimal treatment strategy for patients with diffusely degenerated SVGs is controversial. Endoluminal reconstruction by stent implantation is one proposed strategy; however, there are few data regarding long-term clinical outcome.

METHODS

Between May 1995 and September 1998, 6,534 consecutive patients underwent angioplasty in our institution, including 440 who were treated for SVG lesions. Of these, 126 (115 men, 11 women, median age 69.5 years, range: 33-86 years) with old SVGs (mean age: 13+/-5 years) diffusely degenerated stenosed or occluded (mean lesion length: 27+/-12 mm) were treated electively with implantation of one or multiple (total 197) less-shortening Wallstents.

RESULTS

Before discharge, 13 patients (10.3%) sustained at least one major cardiovascular event, including 4 deaths (3.2%), 11 myocardial infarctions (MI) (8.7%), and 3 repeat revascularizations (target vessel = 1, nontarget vessel = 2, 2.4%). Surviving patients were followed for 22+/-11 months: 13 patients (11.1%) died, 11 (9.4%) sustained an MI, 37 underwent angioplasty (31.6%), and 4 (3.4%) underwent bypass surgery. The estimated three-year event-free survival rates (freedom from death, and freedom from death/MI/target vessel revascularization) were (mean +/- SE) 81.1+/-7.8% and 43.2+/-18.5%, respectively.

CONCLUSIONS

The long-term clinical outcome of patients undergoing endoluminal reconstruction in diffusely degenerated SVG is relatively poor, mainly because of a high incidence of death or MI and the frequent need for repeat angioplasty. It is unlikely that percutaneous intervention alone will provide a satisfactory or definitive solution for these patients.

Ultrasound thrombolysis for the treatment of thrombotic occlusion of degenerated saphenous vein grafts

Despite improvements in catheter-based revascularization outcomes, coronary interventionalists face difficult challenges in the treatment of the thrombus-laden coronary lesion. In this report, we describe the use of the Acolysis device, which utilizes high-frequency (41.9 kHz) ultrasonic energy to vibrate a small metal tip at the end of a 4.5 Fr catheter to treat two thrombotically occluded saphenous vein grafts in two patients. In both cases, the Acolysis device provided normalization of flow with angiographically evident dissolution of thrombus and excellent acute angiographic and clinical results. We conclude that in these two selected cases the Acolysis device was used safely and effectively for thrombus debulking as an adjunct to stenting in diseased saphenous vein bypass grafts.