Effect of modulated ultrasound parameters on ultrasound-induced thrombolysis

Percutaneous interventions for pulmonary embolism

Pulmonary embolism (PE) ranks as a leading cause of in-hospital mortality and the third most common cause of cardiovascular death. The spectrum of PE manifestations varies widely, making it difficult to determine the best treatment approach for specific patients. Conventional treatment options include anticoagulation, thrombolysis, or surgery, but emerging percutaneous interventional procedures are being investigated for their potential benefits in heterogeneous PE populations. These novel interventional techniques encompass catheter-directed thrombolysis, mechanical thrombectomy, and hybrid approaches combining different mechanisms. Furthermore, inferior vena cava filters are also available as an option for PE prevention. Such interventions may offer faster improvements in right ventricular function, as well as in pulmonary and systemic haemodynamics, in individual patients. Moreover, percutaneous treatment may be a valid alternative to traditional therapies in high bleeding risk patients and could potentially reduce the burden of mortality related to major bleeds, such as that of haemorrhagic strokes. Nevertheless, the safety and efficacy of these techniques compared to conservative therapies have not been conclusively established. This review offers a comprehensive evaluation of the current evidence for percutaneous interventions in PE and provides guidance for selecting appropriate patients and treatments. It serves as a valuable resource for future researchers and clinicians seeking to advance this field. Additionally, we explore future perspectives, proposing "percutaneous primary pulmonary intervention" as a potential paradigm shift in the field.

State of the art on microbubble cavitation monitoring and feedback control for blood-brain-barrier opening using focused ultrasound

Focused ultrasound (FUS) is a non-invasive and highly promising method for targeted and reversible blood-brain barrier permeabilization. Numerous preclinical studies aim to optimize the localized delivery of drugs using this method in rodents and non-human primates. Several clinical trials have been initiated to treat various brain diseases in humans using simultaneous BBB permeabilization and drug injection. This review presents the state of the art ofin vitroandin vivocavitation control algorithms for BBB permeabilization using microbubbles (MB) and FUS. Firstly, we describe the different cavitation states, their physical significance in terms of MB behavior and their translation into the spectral composition of the backscattered signal. Next, we report the different indexes calculated and used during the ultrasonic monitoring of cavitation. Finally, the differentin vitroandin vivocavitation control strategies described in the literature are presented and compared.

Percutaneous treatment options for acute pulmonary embolism: a clinical consensus statement by the ESC Working Group on Pulmonary Circulation and Right Ventricular Function and the European Association of Percutaneous Cardiovascular Interventions

There is a growing clinical and scientific interest in catheter-directed therapy (CDT) of acute pulmonary embolism (PE). Currently, CDT should be considered for patients with high-risk PE, in whom thrombolysis is contraindicated or has failed. Also, CDT is a treatment option for initially stable patients in whom anticoagulant treatment fails, i.e., those who experience haemodynamic deterioration despite adequately dosed anticoagulation. However, the definition of treatment failure (primary reperfusion therapy or anticoagulation alone) remains an important area of uncertainty. Moreover, several techniques for CDT are available without evidence supporting one over the other, and variation in practice with regard to periprocedural anticoagulation is considerable. The aim of this position paper is to describe the currently available CDT approaches in PE patients and to standardise patient selection, the timing and technique of the procedure itself as well as anticoagulation regimens during CDT. We discuss several clinical scenarios of the clinical evaluation of the "efficacy" of thrombolysis and anticoagulation, including treatment failure with haemodynamic deterioration and treatment failure based on a lack of improvement. This clinical consensus statement serves as a practical guide for CDT, complementary to the formal guidelines.

Treatment of Limb Ischemia with Conducted Effects of Catheter-Based Endovascular Ultrasound

Ultrasound (US) is known to stimulate endogenous shear-dependent pathways, and can lower microvascular resistance through mediators that are conducted downstream from US exposure. We hypothesized that endovascular US, already in use for thrombolysis in humans, can improve tissue perfusion in the setting of acute limb ischemia through downstream-conducted effects. Models of severe peripheral arterial disease were developed in mice and in rhesus macaques. An endovascular US catheter (2.3 MHz, 0.5-1.1 MPa) was used to expose the limb adductor in mice for 10 min or the femoral artery distal to stenosis in macaques for 15 min. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess flow augmentation in the adductor muscle of mice and the calf muscle of macaques. Microvascular blood flow in the ischemic limb relative to the contralateral control limb was reduced to 22 ± 8% in mice and 36 ± 20% in macaques. US produced immediate 2.3- and 3-fold increases (p < 0.05) in the murine and macaque ischemic limbs, respectively. In macaques, perfusion in the ischemic limb was increased to a normal level. We conclude that non-cavitating US produced by endovascular catheters that are used to enhance thrombolysis in humans can reduce vascular resistance and increase limb perfusion in the setting of acute ischemia.

Cavitation Emissions Nucleated by Definity Infused through an EkoSonic Catheter in a Flow Phantom

The EkoSonic endovascular system has been cleared by the U.S. Food and Drug Administration for the controlled and selective infusion of physician specified fluids, including thrombolytics, into the peripheral vasculature and the pulmonary arteries. The objective of this study was to explore whether this catheter technology could sustain cavitation nucleated by infused Definity, to support subsequent studies of ultrasound-mediated drug delivery to diseased arteries. The concentration and attenuation spectroscopy of Definity were assayed before and after infusion at 0.3, 2.0 and 4.0 mL/min through the EkoSonic catheter. PCI was used to map and quantify stable and inertial cavitation as a function of Definity concentration in a flow phantom mimicking the porcine femoral artery. The 2.0 mL/min infusion rate yielded the highest surviving Definity concentration and acoustic attenuation. Cavitation was sustained throughout each 15 ms ultrasound pulse, as well as throughout the 3 min infusion. These results demonstrate a potential pathway to use cavitation nucleation to promote drug delivery with the EkoSonic endovascular system.

Safety and efficacy of an endovascular-first approach to acute limb ischemia

BACKGROUND

The optimal techniques to manage acute limb ischemia (ALI) remain unclear. Previous reports have suggested that the decreased morbidity and mortality of endovascular approaches are mitigated by the limited technical success rates relative to open or hybrid approaches for ALI. However, these data failed to include newer technologies that might improve the technical success rates. We, therefore, sought to describe the current outcomes for an endovascular-first approach to ALI.

METHODS

We performed a single-center, single-arm, retrospective cohort study of consecutive patients with ALI from 2015 to 2018. Technical success, limb salvage, survival, patency, and length of stay were quantified using Kaplan-Meier (KM) analysis. Cox regression analysis was used to identify the predictors of amputation-free survival.

RESULTS

During the 3 years, 60 consecutive patients (39 men [65%]; median age, 65 years) presented with ALI. The Rutherford class was I in 15 patients (25%), IIa in 23 (38%), IIb in 13 (22%), and III in 9 patients (15%). Of the 60 patients, 34 had a history of previous failed ipsilateral revascularization (56%), including open bypass for 8 (13%), endovascular for 8 (13%), and both open and endovascular intervention for 18 (30%). The endovascular-first approach procedures included catheter-directed thrombolysis only (n = 19; 3%), catheter-directed thrombolysis plus aspiration and/or rheolytic thrombectomy (n = 19; 32%), and aspiration and/or rheolytic thrombectomy (n = 16; 26%). Six patients (10%) underwent covered stent placement only. The underlying occlusive process was most often thrombosis of a previous bypass graft or stent in 32 patients (53%), followed by native vessel thrombosis in 15 (25%). ALI had resulted from embolism in 13 patients (21.7%), including 2 (3%) with embolization to occlude a previous bypass graft or stent. Technical success was achieved in 58 patients (97%), with open conversion required in two patients (3%). At 30 days postoperatively, 52 patients (87%) survived, and 53 (88%) had successful limb salvage. Five patients (8%) had required four-compartment fasciotomy. No major hemorrhagic complications developed. The median length of stay overall and in the intensive care unit was 9 days (interquartile range, 4-14 days) and 2 days (interquartile range, 1-5 days), respectively. At 1 year, the KM estimates were as follows: amputation-free survival, 58% ± 0.08%; limb salvage, 74.3% ± 0.07%; and survival, 73.3% ± 0.07%. The 1-year KM estimates for primary and secondary patency were 39.4% ± 0.08% and 78.2% ± 0.07%, respectively. On multivariable Cox regression analysis, only age independently predicted for death and/or amputation at the last follow-up (hazard ratio, 1.06; 95% confidence interval, 1.01-1.10; P = .01).

CONCLUSIONS

The current endovascular approaches to ALI have high technical success rates. Survival, limb salvage, perioperative complications, and length of stay were similar to those from previous reports of historical open cohorts. Further prospective, appropriately powered, multicenter cohort studies are warranted to evaluate the efficacy of endovascular vs open approaches to ALI.

Minimally invasive approaches for the management of intraventricular hemorrhage

Adult-onset intraventricular hemorrhage is a potentially life-threatening condition associated with a high morbidity and mortality rates. Intraventricular hemorrhage remains one of the most challenging entities for neurosurgeons to treat. Various medical and surgical modalities have been employed for the management of this entity with variable success and complications rates. In this paper, we review the neurosurgical interventions for the management of intraventricular hemorrhage and describe new approaches and potential therapeutic modalities for the management of this devastating condition.

Examination of Effects of Low-Frequency Ultrasound on Scleral Permeability and Collagen Network

Delivery of therapeutics to the intraocular space or to targeted tissues in the posterior segment is challenging because of the structural and dynamic barriers surrounding the eye. Previously, we reported the feasibility of using ultrasound (US) irradiation to deliver macromolecules to the posterior segment of the eye via the transscleral route, which consists of sclera as the outermost anatomic barrier. In this study, we found that although ultrasound increases scleral permeability for macromolecules, the scleral collagen arrangement remains undisturbed. In an ex vivo experiment, protein permeation across the sclera was significantly enhanced by ultrasound in the stable cavitation regime. The scleral collagen network was further examined by second harmonic generation imaging. Quantitative image analysis techniques were adopted to examine the density, anisotropy and interlacing pattern of collagen fibers before and after ultrasound irradiation. Repeated ultrasound applications did not induce significant changes in the arrangement of collagen fibrils at 40 kHz with a spatial average temporal average intensity (I_SATA) <1.8 W/cm². These parameters correspond to a mechanical index (MI) below 0.8 in our setting. These data suggested that enhanced permeation of macromolecules across the sclera was achieved without disturbing the collagen network of the sclera. This evidence supports that low-frequency, low-intensity ultrasound is a tolerable approach to transscleral drug delivery.

In Vitro Examination of the Thrombolytic Efficacy of Desmoteplase and Therapeutic Ultrasound Compared with rt-PA

The aim of the study described here was to evaluate the thrombolytic efficacy of combined treatment with the fibrin-selective plasminogen activator desmoteplase (DSPA) and therapeutic ultrasound (sonothrombolysis [STL]) compared with conventional rt-PA (recombinant tissue plasminogen activator) treatment in vitro. Lysis rates were determined by the weight loss of platelet-rich plasma (PRP) clots treated with rt-PA (60 kU/mL) or DSPA (2 μg/mL) combined with pulsed wave ultrasound (2 MHz, 0.179 W/cm(2)). To reveal the individual effects of medication and ultrasound, lysis rates were also determined for DSPA monotherapy and for combined treatment with rt-PA and ultrasound. Clots solely placed in plasma served as the control group. Lysis increased significantly with rt-PA (26.5 ± 7.8%) and DSPA (30.5 ± 6%) compared with the control group (18.2 ± 5.9%) (each p < 0.001). DSPA lysis was more effective than rt-PA lysis (without STL: p = 0.015, with STL: p = 0.01). Combined treatment with DSPA and 2-MHz STL significantly exceeded rt-PA lysis (32.8% vs. 26.5%, p < 0.001).

Endovascular Management of Acute Pulmonary Embolism Using the Ultrasound-Enhanced EkoSonic System

Acute, symptomatic pulmonary embolism (PE) in the massive and submassive categories continues to be a healthcare concern with significant risk for increased morbidity and mortality. Despite increased awareness and venous thromboembolism prophylaxis, endovascular treatment is still an important option for many of these patients. There are a variety of techniques and devices used for treating PE, but none have been evaluated as extensively as the EkoSonic endovascular system that is also currently the only FDA-approved device for the treatment of pulmonary embolism. This article describes the use of the EkoSonic device for this patient population.

Molecular mechanisms of the effect of ultrasound on the fibrinolysis of clots

BACKGROUND

Ultrasound accelerates tissue-type plasminogen activator (t-PA)-induced fibrinolysis of clots in vitro and in vivo.

OBJECTIVE

To identify mechanisms for the enhancement of t-PA-induced fibrinolysis of clots.

METHODS

Turbidity is an accurate and convenient method, not previously used, to follow the effects of ultrasound. Deconvolution microscopy was used to determine changes in structure, while fluorescence recovery after photobleaching was used to characterize the kinetics of binding/unbinding and transport.

RESULTS

The ultrasound pulse repetition frequency affected clot lysis times, but there were no thermal effects. Ultrasound in the absence of t-PA produced a slight but consistent decrease in turbidity, suggesting a decrease in fibrin diameter due solely to the action of the ultrasound, likely caused by an increase in protofibril tension because of vibration from ultrasound. Changes in fibrin network structure during lysis with ultrasound were visualized in real time by deconvolution microscopy, revealing that the network becomes unstable when 30-40% of the protein in the network was digested, whereas without ultrasound, the fibrin network was digested gradually and retained structural integrity. Fluorescence recovery after photobleaching during lysis revealed that the off-rate of oligomers from digesting fibers was little affected, but the number of binding/unbinding sites was increased.

CONCLUSIONS

Ultrasound causes a decrease in the diameter of the fibers due to tension as a result of vibration, leading to increased binding sites for plasmin(ogen)/t-PA. The positive feedback of this structural change together with increased mixing/transport of t-PA/plasmin(ogen) is likely to account for the observed enhancement of fibrinolysis by ultrasound.

Usefulness and safety of ultrasound-assisted catheter-directed thrombolysis for submassive pulmonary emboli

The optimal treatment for intermediate-risk pulmonary embolism (PE) remains unclear. Our goal was to describe the safety and efficacy of the EkoSonic ultrasound-assisted catheter-directed thrombolysis system (EKOS Corporation, Bothell, Washington) in a real-world registry of patients with intermediate-risk PE. Fifty-three consecutive patients with intermediate-risk PE treated with ultrasound-assisted catheter-directed thrombolysis at Brigham and Women's Hospital from 2010 to 2014 were analyzed. The primary outcome was a change in directly measured pulmonary artery pressures as assessed using logistic regression with generalized estimating equations to account for serial measurements. Patients received an average of 24.6 ± 9 mg of alteplase using the EKOS catheter with an average treatment time of 15.9 ± 3 hours. After treatment, there was a 7.2- and a 11.4-mm Hg reduction in mean and systolic pulmonary artery pressure (95% confidence interval 4.7 to 9.7 mm Hg, p <0.001, and 95% confidence interval 7.8 to 15.0 mm Hg, p <0.001), respectively. In this cohort, 9.4% had any bleeding complication noted during their hospital stay. One patient's alteplase was prematurely discontinued for access site bleeding although no other interventions were required related to bleeding complications.

Application of cavitation promoting surfaces in management of acute ischemic stroke

High frequency, low intensity ultrasound has the potential to accelerate the clearance of thrombotic occlusion in the absence of cavitation. At high frequency ultrasound, high acoustic pressures, >5.2MPa, are required to generate cavitation in thrombus. The focus of this study was to reduce the cavitation threshold by applying materials with appropriate nucleation sites at the transducer-thrombus boundary to further augment sonothrombolysis. Heterogeneous and homogenous nucleation sites were generated on the outer surface of a polyimide tube (PI) using microfringed (MPI) and laser induced (LPI) microcavities. The cavitation threshold of these materials was determined using a passive cavitation detection system. Furthermore, the biological impact of both materials was investigated in vitro. The results revealed that both MPI and LPI have the potential to induce cavitation at acoustic pressure levels as low as 2.3MPa. In the presence of cavitation, thrombolysis rate could be enhanced by up to two times without any evidence of hemolysis that is generally associated with cavitation activities in blood. A prototype ultrasonic catheter operating at 1.7MHz frequency and acoustic pressure of 2.3MPa with either of MPI or LPI could be considered as a viable option for treatment of acute ischemic stroke.

Removing vascular obstructions: a challenge, yet an opportunity for interventional microdevices

Cardiovascular diseases are the leading cause of death worldwide; they are mainly due to vascular obstructions which, in turn, are mainly caused by thrombi and atherosclerotic plaques. Although a variety of removal strategies has been developed for the considered obstructions, none of them is free from limitations and conclusive. The present paper analyzes the physical mechanisms underlying state-of-art removal strategies and classifies them into chemical, mechanical, laser and hybrid (namely chemo-mechanical and mechano-chemical) approaches, while also reviewing corresponding commercial/research tools/devices and procedures. Furthermore, challenges and opportunities for interventional micro/nanodevices are highlighted. In this spirit, the present review should support engineers, researchers active in the micro/nanotechnology field, as well as medical doctors in the development of innovative biomedical solutions for treating vascular obstructions. Data were collected by using the ISI Web of Knowledge portal, buyer's guides and FDA databases; devices not reported on scientific publications, as well as commercial devices no more for sale were discarded. Nearly 70% of the references were published since 2006, 55% since 2008; these percentages respectively raise to 85% and 65% as regards the section specifically reviewing state-of-art removal tools/devices and procedures.

Minimally invasive evacuation of spontaneous intracerebral hemorrhage using sonothrombolysis

OBJECT

Catheter-based evacuation is a novel surgical approach for the treatment of brain hemorrhage. The object of this study was to evaluate the safety and efficacy of ultrasound in combination with recombinant tissue plasminogen activator (rt-PA) delivered through a microcatheter directly into spontaneous intraventricular (IVH) or intracerebral (ICH) hemorrhage in humans.

METHODS

Thirty-three patients presenting to the Swedish Medical Center in Seattle, Washington, with ICH and IVH were screened between November 21, 2008, and July 13, 2009, for entry into this study. Entry criteria included the spontaneous onset of intracranial hemorrhage ≥ 25 ml and/or IVH producing ventricular obstruction. Nine patients (6 males and 3 females, with an average age of 63 years [range 38-83 years]) who met the entry criteria consented to participate and were entered into the trial. A ventricular drainage catheter and an ultrasound microcatheter were stereotactically delivered together, directly into the IVH or ICH. Recombinant tissue plasminogen activator and 24 hours of continuous ultrasound were delivered to the clot. Gravity drainage was performed. In patients with IVHs, 3 mg of rt-PA was injected; in patients with intraparenchymal hemorrhages, 0.9 mg of rt-PA was injected. The rt-PA was delivered in 3 doses over 24 hours.

RESULTS

All patients had significant volume reductions in the treated hemorrhage. The mean percentage volume reduction after 24 hours of therapy, as determined on CT and compared with pretreatment stability scans, was 59 ± 5% (mean ± SEM) for ICH and 45.1 ± 13% for IVH (1 patient with ICH was excluded from analysis because of catheter breakage). There were no intracranial infections and no significant episodes of rebleeding according to clinical or CT assessment. One death occurred by 30 days after admission. Clinical improvements as determined by a decrease in the National Institutes of Health Stroke Scale score were demonstrated at 30 days after treatment in 7 of 9 patients. The rate of hemorrhage lysis was compared between 8 patients who completed treatment, and patient cohorts treated for IVH and ICH using identical doses of rt-PA and catheter drainage but without the ultrasound (courtesy of the MISTIE [Minimally Invasive Surgery plus T-PA for Intracerebral Hemorrhage Evacuation] and CLEAR II [Clot Lysis Evaluating Accelerated Resolution of Intraventricular Hemorrhage II] studies). Compared with the MISTIE and CLEAR data, the authors observed a faster rate of lysis during treatment for IVH and ICH in the patients treated with sonolysis plus rt-PA versus rt-PA alone.

CONCLUSIONS

Lysis and drainage of spontaneous ICH and IVH with a reduction in mass effect can be accomplished rapidly and safely through sonothrombolysis using stereotactically delivered drainage and ultrasound catheters via a bur hole. A larger clinical trial with catheters specifically designed for brain blood clot removal is warranted.

Introduction of a new model for time-continuous and non-contact investigations of in-vitro thrombolysis under physiological flow conditions

Background

Thrombolysis is a dynamic and time-dependent process influenced by the haemodynamic conditions. Currently there is no model that allows for time-continuous, non-contact measurements under physiological flow conditions. The aim of this work was to introduce such a model.

Methods

The model is based on a computer-controlled pump providing variable constant or pulsatile flows in a tube system filled with blood substitute. Clots can be fixed in a custom-built clot carrier within the tube system. The pressure decline at the clot carrier is measured as a novel way to measure lysis of the clot. With different experiments the hydrodynamic properties and reliability of the model were analyzed. Finally, the lysis rate of clots generated from human platelet rich plasma (PRP) was measured during a one hour combined application of diagnostic ultrasound (2 MHz, 0.179 W/cm²) and a thrombolytic agent (rt-PA) as it is commonly used for clinical sonothrombolysis treatments.

Results

All hydrodynamic parameters can be adjusted and measured with high accuracy. First experiments with sonothrombolysis demonstrated the feasibility of the model despite low lysis rates.

Conclusions

The model allows to adjust accurately all hydrodynamic parameters affecting thrombolysis under physiological flow conditions and for non-contact, time-continuous measurements. Low lysis rates of first sonothrombolysis experiments are primarily attributable to the high stability of the used PRP-clots.

Potentiating intra-arterial sonothrombolysis for acute ischemic stroke by the addition of the ultrasound contrast agents (Optison™ & SonoVue(®))

Transcranial ultrasound in combination with intravenously administered ultrasound contrast agents (UCA) in the presence or absence of recombinant tissue plasminogen activator (rt-PA) has been widely evaluated as a new modality for treatment of ischemic stroke. Despite the successful demonstration of accelerated clot lysis there are inherent limitations associated with this modality such as inconsistency in temporal window thickness and/or potential serious cardiopulmonary reactions to intravenous administration of UCA that prevent broad application to ischemic stroke populations. As a complementary modality, we evaluated potential lysis enhancement by intra-arterial ultrasound with concurrent intra-clot delivery of UCA and rt-PA. To this end, clots were formed with average pore diameter similar to clinically retracted clots by adjusting the thrombin concentration. Physical characteristic and retention of UCA after delivery through the catheter as a function of clinically relevant flow rates of 6, 12, 18 ml/h were determined using a microscopic method. The ability of the UCA employed in this study, Optison and SonoVue, to penetrate into the clot was verified using ultrasound B-mode imaging. Clot lysis as a function of rt-PA concentration, 0.009 through 0.5 mg/ml, in the presence and absence of UCA diluted to 1:10, 1:100, and 1:200 v/v at two Peak rarefaction acoustic pressures of 1.3 and 2.1 MPa were evaluated using a weighing method. The study results suggest the addition of only 0.02 ml of 1:100 diluted UCA to rt-PA of 0.009, 0.05, 0.3, and 0.5 mg/ml can enhance the lysis rate by 3.9, 2.6, 1.9 and 1.8 fold in the presence of peak rarefaction acoustic pressure of 1.3 MPa and by 5.1, 3.4, 2.6, 3.1 in the presence of peak rarefaction acoustic pressure of 2.1 MPa, respectively. In addition, Optison and SonoVue demonstrated comparable effectiveness in enhancing the clot lysis rate. Addition of UCA to intra-arterial sonothrombolysis could be considered as a viable treatment option for ischemic stroke patients.