Effect of 40-kHz ultrasound on acute thrombotic ischemia in a rabbit femoral artery thrombosis model: enhancement of thrombolysis and improvement in capillary muscle perfusion

Influence of Atherosclerotic Risk Factors on the Effectiveness of Therapeutic Ultrasound Cavitation for Flow Augmentation

BACKGROUND

Shear created by inertial cavitation of microbubbles by ultrasound augments limb and myocardial perfusion and can reverse tissue ischemia. Our aim was to determine whether this therapeutic bioeffect is attenuated by atherosclerotic risk factors that are known to impair shear-mediated vasodilation and adversely affect microvascular reactivity.

METHODS

In mice, lipid-stabilized decafluorobutane microbubbles (2 × 108) were administered intravenously while exposing a proximal hind limb to ultrasound (1.3 MHz, 1.3 mechanical index, pulsing interval 5 seconds) for 10 minutes. Murine strains included wild-type mice and severely hyperlipidemic mice at 15, 35, or 52 weeks of age as a model of aging and elevated cholesterol, and obese db/db mice (≈15 weeks) with severe insulin resistance. Quantitative contrast-enhanced ultrasound perfusion imaging was performed to assess microvascular perfusion in the control and ultrasound-exposed limb. An in situ electrochemical probe and in vivo biophotonic imaging were used to assess limb nitric oxide (NO) and adenosine triphosphosphate concentrations, respectively.

RESULTS

Microvascular perfusion was significantly increased by several fold in the cavitation-exposed limb versus control limb for all murine strains and ages (P < .001). In wild-type and hyperlipidemic mice, hyperemia from cavitation was attenuated in the 2 older age groups (P < .01). In young mice (15 weeks), perfusion in cavitation-exposed muscle was less in both the hyperlipidemic mice and the obese db/db mice compared with corresponding wild-type mice. Using young hyperlipidemic mice as a model for flow impairment, limb NO production after cavitation was reduced but adenosine triphosphosphate production was unaltered when compared with age-matched wild-type mice.

CONCLUSIONS

In mice, ultrasound cavitation of microbubbles increases limb perfusion by several fold even in the presence of traditional atherosclerotic risk factors. However, older age, hyperlipidemia, and insulin resistance modestly attenuate the degree of flow augmentation, which could impact the degree of flow response in current clinical trials in patients with critical limb ischemia.

Low-Intensity Ultrasound Reduces Brain Infarct Size by Upregulating Phosphorylated Endothelial Nitric Oxide in Mouse Model of Middle Cerebral Artery Occlusion

OBJECTIVE

There have been attempts to use therapeutic ultrasound (US) for the treatment of both experimental and clinical stroke. We hypothesized that low-intensity US has direct beneficial effects on the brain independent of cerebral blood flow (CBF) during middle cerebral artery occlusion (MCAO).

METHODS

Three groups of mice were studied. Group I included 84 mice with MCAO undergoing US treatment/no treatment at two US frequencies (0.25 and 1.05 MHz) with three different acoustic pressures at each frequency in which infarct size (IS) was measured 24 h later. Group II included 11 mice undergoing treatment based on best US results from group I animals in which the IS/risk area (RA) ratio was measured 24 h later. Group III included 38 normal mice undergoing US treatment/no treatment for assessment of CBF, tissue metabolite and protein expression and histopathology.

DISCUSSION

Ultrasound at both frequencies and most acoustic pressures resulted in reduction in IS in group I animals, with the best results obtained with 0.25 MHz at 2.0 MPa: IS was reduced 4-fold in the cerebral cortex, 1.5-fold in the caudate putamen and 3.5-fold in the cerebral hemisphere compared with control. US application in group III animals elicited only a marginal increase in CBF despite a 2.6-fold increase in phosphorylated endothelial nitric oxide synthase (p-eNOS)-S1177 and a corresponding decrease in p-eNOS-T494. Histopathology revealed no evidence of hemorrhage, inflammation or necrosis.

CONCLUSION

Low-intensity US at specific frequencies and acoustic pressures results in marked neuroprotection in a mouse model of stroke by modulation of p-eNOS independent of its effect on CBF.

Current Status of Sub-micron Cavitation-Enhancing Agents for Sonothrombolysis

Thrombosis in cardiovascular disease is an urgent global issue, but treatment progress is limited by the risks of current antithrombotic approaches. The cavitation effect in ultrasound-mediated thrombolysis offers a promising mechanical alternative for clot lysis. Further addition of microbubble contrast agents introduces artificial cavitation nuclei that can enhance the mechanical disruption induced by ultrasound. Recent studies have proposed sub-micron particles as novel sonothrombolysis agents with increased spatial specificity, safety and stability for thrombus disruption. In this article, the applications of different sub-micron particles for sonothrombolysis are discussed. Also reviewed are in vitro and in vivo studies that apply these particles as cavitation agents and as adjuvants to thrombolytic drugs. Finally, perspectives on future developments in sub-micron agents for cavitation-enhanced sonothrombolysis are shared.

Diagnostic ultrasound-mediated microbubble cavitation dose-dependently improves diabetic cardiomyopathy through angiogenesis

Ultrasound-mediated microbubble cavitation (UMMC) induces therapeutic angiogenesis to treat ischemic diseases. This study aimed to investigate whether diagnostic UMMC alleviates diabetic cardiomyopathy (DCM) and, if so, through which mechanisms. DCM model was established by injecting streptozocin into rats to induce hyperglycemia, followed by a high-fat diet. The combined therapy of cation microbubble with low-intensity diagnostic ultrasound (frequency = 4 MHz), with a pulse frequency of 20 Hz and pulse length (PL) of 8, 18, 26, or 36 cycles, was given to rats twice a week for 8 consecutive weeks. Diagnostic UMMC therapy with PL at 8, 18, and 26 cycles, but not 36 cycles, dramatically prevented myocardial fibrosis, improved heart functions, and increased angiogenesis, accompanied by increased levels of PI3K, Akt, and eNOS proteins in the DCM model of rats. In cultured endothelial cells, low-intensity UMMC treatment (PL = 3 cycles, sound pressure level = 50%, mechanical index = 0.82) increased cell viability and activated PI3K-Akt-eNOS signaling. The combination of diagnostic ultrasound with microbubble destruction dose-dependently promoted angiogenesis, thus improving heart function through PI3K-Akt-eNOS signaling in diabetes. Accordingly, diagnostic UMMC therapy should be considered to protect the heart in patients with diabetes.

Enhanced thrombolysis by endovascular low-frequency ultrasound with bifunctional microbubbles in venous thrombosis: in vitro and in vivo study

There is a need to improve the efficacy and safety of endovascular techniques in venous thrombotic diseases, and microbubble enhanced sonothrombolysis is a promising approach. However, whether endovascular low-frequency ultrasound (LFUS) can be utilized in microbubble enhanced sonothrombolysis is unclear. Here, we present a catheter-based thrombolytic system that combines unfocused low-frequency low-intensity ultrasound with novel fibrin-targeted drug-loaded bifunctional microbubbles. We develop an in vitro flow model and an in vivo rabbit inferior vena cava (IVC) thrombosis model to evaluate the safety and efficacy of the thrombolytic system. The results indicate that microbubble enhanced sonothrombolysis with endovascular LFUS treatment for 30 min is equally effective compared to pure pharmacologic treatment. Furthermore, the thrombolytic efficacy of this system is safely and substantially improved by the introduction of a fibrin-targeted drug-loaded bifunctional microbubble with a reduction of the fibrinolytic agent dosage by 60%. The microbubble enhanced endovascular LFUS sonothrombolysis system with excellent thrombolytic efficacy may serve as a new therapeutic approach for venous thrombotic diseases.

Sonothrombolysis Promotes Improvement in Left Ventricular Wall Motion and Perfusion Scores after Acute Myocardial Infarction

BACKGROUND

It has recently been demonstrated that the application of high-energy ultrasound and microbubbles, in a technique known as sonothrombolysis, dissolves intravascular thrombi and increases the angiographic recanalization rate in patients with ST-segment-elevation myocardial infarction (STEMI).

OBJECTIVE

To evaluate the effects of sonothrombolysis on left ventricular wall motion and myocardial perfusion in patients with STEMI, using real-time myocardial perfusion echocardiography (RTMPE).

METHODS

One hundred patients with STEMI were randomized into the following 2 groups: therapy (50 patients treated with sonothrombolysis and primary coronary angioplasty) and control (50 patients treated with primary coronary angioplasty). The patients underwent RTMPE for analysis of left ventricular ejection fraction (LVEF), wall motion score index (WMSI), and number of segments with myocardial perfusion defects 72 hours after STEMI and at 6 months of follow-up. P < 0.05 was considered statistically significant.

RESULTS

Patients treated with sonothrombolysis had higher LVEF than the control group at 72 hours (50% ± 10% versus 44% ± 10%; p = 0.006), and this difference was maintained at 6 months of follow-up (53% ± 10% versus 48% ± 12%; p = 0.008). The WMSI was similar in the therapy and control groups at 72 hours (1.62 ± 0.39 versus 1.75 ± 0.40; p = 0.09), but it was lower in the therapy group at 6 months (1.46 ± 0.36 versus 1.64 ± 0.44; p = 0.02). The number of segments with perfusion defects on RTMPE was similar in therapy and control group at 72 hours (5.92 ± 3.47 versus 6.94 ± 3.39; p = 0.15), but it was lower in the therapy group at 6 months (4.64 ± 3.31 versus 6.57 ± 4.29; p = 0.01).

CONCLUSION

Sonothrombolysis in patients with STEMI resulted in improved wall motion and ventricular perfusion scores over time.

Contrast Ultrasound, Sonothrombolysis and Sonoperfusion in Cardiovascular Disease: Shifting to Theragnostic Clinical Trials

Contrast ultrasound has a variety of applications in cardiovascular medicine, both in diagnosing cardiovascular disease as well as providing prognostic information. Visualization of intravascular contrast microbubbles is based on acoustic cavitation, the characteristic oscillation that results in changes in the reflected ultrasound waves. At high power, this acoustic response generates sufficient shear that is capable of enhancing endothelium-dependent perfusion in atherothrombotic cardiovascular disease (sonoperfusion). The oscillation and collapse of microbubbles in response to ultrasound also induces microstreaming and jetting that can fragment thrombus (sonothrombolysis). Several preclinical studies have focused on identifying optimal diagnostic ultrasound settings and treatment regimens. Clinical trials have been performed in acute myocardial infarction, stroke, and peripheral arterial disease often with improved outcome. In the coming years, results of ongoing clinical trials along with innovation and improvements in sonothrombolysis and sonoperfusion will determine whether this theragnostic technique will become a valuable addition to reperfusion therapy.

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.

Low-Intensity Continuous Ultrasound Therapies—A Systematic Review of Current State-of-the-Art and Future Perspectives

Therapeutic ultrasound has been studied for over seven decades for different medical applications. The versatility of ultrasound applications are highly dependent on the frequency, intensity, duration, duty cycle, power, wavelength, and form. In this review article, we will focus on low-intensity continuous ultrasound (LICUS). LICUS has been well-studied for numerous clinical disorders, including tissue regeneration, pain management, neuromodulation, thrombosis, and cancer treatment. PubMed and Google Scholar databases were used to conduct a comprehensive review of all research studying the application of LICUS in pre-clinical and clinical studies. The review includes articles that specify intensity and duty cycle (continuous). Any studies that did not identify these parameters or used high-intensity and pulsed ultrasound were not included in the review. The literature review shows the vast implication of LICUS in many medical fields at the pre-clinical and clinical levels. Its applications depend on variables such as frequency, intensity, duration, and type of medical disorder. Overall, these studies show that LICUS has significant promise, but conflicting data remain regarding the parameters used, and further studies are required to fully realize the potential benefits of LICUS.

Time- and Dose-Dependent Effects of Pulsed Ultrasound on Dermal Repair in Diabetic Mice

Chronic wounds, including diabetic, leg and pressure ulcers, impose a significant health care burden worldwide. Some evidence indicates that ultrasound can enhance soft tissue repair. However, therapeutic responses vary among individuals, thereby limiting clinical translation. Here, effects of pulsed ultrasound on dermal wound healing were assessed using a murine model of chronic, diabetic wounds. An ultrasound exposure system was developed to provide daily ultrasound exposures to full-thickness, excisional wounds in genetically diabetic mice. Wounds were exposed to 1 MHz ultrasound (2 ms pulse, 100 Hz pulse repetition frequency, 0-0.4 MPa) for 2 or 3 wk. Granulation tissue thickness and wound re-epithelialization increased as a function of increasing ultrasound pressure amplitude. At 2 wk after injury, significant increases in granulation tissue thickness and epithelial ingrowth were observed in response to 1 MHz pulsed ultrasound at 0.4 MPa. Wounds exposed to 0.4 MPa ultrasound for 3 wk were characterized by collagen-dense, revascularized granulation tissue with a fully restored, mature epithelium. Of note, only half of wounds exposed to 0.4 MPa ultrasound showed significant granulation tissue deposition after 2 wk of treatment. Thus, the db+/db+ mouse model may help to identify biological variables that influence individual responses to pulsed ultrasound and accelerate clinical translation.

Ultrasound therapy for treatment of lower extremity intermittent claudication

BACKGROUND

While often thought of as a diagnostic tool, ultrasound (US) can also potentially be used as a therapeutic modality. US applies mechanical stress on endothelial cells and induces nitric oxide synthase, which regulates the secretion of nitric oxide, a potent vasodilator. In animal ischemic models, US has been shown to improve hindlimb, myocardial, and cerebral perfusion. We performed a pilot trial of US therapy in the lower extremities of human subjects with intermittent claudication.

METHODS

10 subjects (5 male, 5 female, mean age 69.7 ± 10.3) with intermittent claudication were recruited. Both legs were placed in a specially designed boot with a water interface between US transducers and the legs. Subjects underwent pulsed US therapy at 250 kHz frequency for 30 min for three treatments a week for six weeks. Pre and post treatment ankle:brachial index (ABI), 6-min walk (6 MW), Walking Impairment Questionnaire (WIQ), and Short Form 36 (SF36) were performed. Pre and post-treatment results were compared with paired t-test.

RESULTS

Six minute walking distance at baseline was 352 ± 70 m, after one treatment session 353 ± 70 m (p = 0.99), and at completion 372 ± 71 m (p = 0.015). There was a trend toward improved ABI after 6 weeks of treatment (0.53 ± 0.17 vs 0.64 ± 0.12, p = 0.083). After six weeks, significant improvements were noted in overall WIQ score (2.00 ± 1.48 vs 2.63 ± 1.38, p = 0.0001), WIQ (distance) 2.07 ± 1.54 vs 2.73 ± 1.42 (p = 0.036), and WIQ (stair) 2.00 ± 1.67 vs 2.62 ± 1.24, p = 0.034, with a trend in WIQ (speed), 1.89 ± 1.26 vs 2.46 ± 1.43, p = 0.069. In the SF-36, significant improvements were noted in the domains of physical functioning (44.0 ± 41.6 vs 50.5 ± 41.1, p = 0.009) and role limitations - physical (35.0 ± 48.3 vs 60.0 ± 49.6, p = 0.006) after six weeks.

CONCLUSIONS

Therapeutic US is a potential noninvasive treatment for intermittent claudication. Pilot study patients noted significant improvements in 6 MW and WIQ results after 6 weeks of treatment. A nonsignificant improvement in ABI was noted. Further research will be needed to clarify optimal treatment frequency and duration.

Hypotension and Bradycardia Produced by Transthoracic Application of Low-Intensity Ultrasound Therapy in Hearts of Healthy Rats - A Preclinical Study

Objective

To investigate the cardiovascular effects produced by transthoracic application of low-intensity pulsed ultrasound therapy (LIPUST).

Methods

Three-month-old male Wistar rats (± 300 g, N=16) were randomly allocated in two groups, namely SHAM (control group, faked procedures) and UST (animals treated with LIPUST). These animals, under anesthesia, were instrumented (femoral artery and vein catheterization) for hemodynamic recordings (mean blood pressure [MBP], heart rate [HR]) and blood biochemical profile (lipids, creatine kinase-myocardial band [CK-MB]). Then, LIPUST (spatial average-temporal average [ISATA] 1-MHz, power 0.1 to 1.2 W/cm2, pulsed 2:8 ms, cycle at 30%, for three minutes) was applied to animals from the UST group, externally to their thorax. SHAM animals were equally manipulated, but without application of ultrasound energy. After the hemodynamic and biochemical measurements, animals were sacrificed, and their hearts were mounted in a Langendorff apparatus for coronary reactivity evaluation. Standard histology techniques were employed to analyze the hearts.

Results

LIPUST application caused statistically significant reductions in MBP (92±4 vs. 106±1 mmHg) and HR (345±14 vs. 380±17 rpm) when compared with SHAM procedures. UST rats exhibited higher CK-MB levels (318±55 vs. 198±26 U/dL) and lower plasma triglycerides levels (38±7 vs. 70±10 mg/dL) than SHAM animals. Coronary reactivity was not significantly changed by LIPUST. Cardiac histopathology showed an increase in capillary permeability in treated animals when compared with SHAM animals.

Conclusion

Noninvasive LIPUST induces significant metabolic and hemodynamic changes, including intensity-dependent bradycardia and hypotension, indicating a possible therapeutic effect for cardiac events.

Effect of Low-Frequency Therapeutic Ultrasound on Induction of Nitric Oxide in CKD: Potential to Prevent Acute Kidney Injury

Introduction

Post-contrast acute kidney injury (PC-AKI) develops in a significant proportion of patients with CKD after invasive cardiology procedures and is strongly associated with adverse outcomes.

Objective

We sought to determine whether increased intrarenal nitric oxide (NO) would prevent PC-AKI.

Methods

To create a large animal model of CKD, we infused 250 micron particles into the renal arteries in 56 ± 8 kg pigs. We used a low-frequency therapeutic ultrasound device (LOTUS - 29 kHz, 0.4 W/cm²) to induce NO release. NO and laser Doppler probes were used to assess changes in NO content and blood flow. Glomerular filtration rate (GFR) was measured by technetium-diethylene-triamine-pentaacetic acid (Tc-99m-DTPA) radionuclide imaging. PC-AKI was induced by intravenous infusion of 7 cm³/kg diatrizoate. In patients with CKD, we measured GFR at baseline and during LOTUS using Tc-99m-DTPA radionuclide imaging.

Results

In the pig model, CKD developed over 4 weeks (serum creatinine [Cr], mg/dL, 1.0 ± 0.2-2.6 ± 0.9, p < 0.01, n = 12). NO and renal blood flow (RBF) increased in cortex and medulla during LOTUS. GFR increased 75 ± 24% (p = 0.016, n = 3). PC-AKI developed following diatrizoate i.v. infusion (Cr 2.6 ± 0.7 baseline to 3.4 ± 0.6 at 24 h, p < 0.01, n = 3). LOTUS (starting 15 min prior to contrast and lasting for 90 min) prevented PC-AKI in the same animals 1 week later (Cr 2.5 ± 0.4 baseline to 2.6 ± 0.7 at 24 h, p = ns, n = 3). In patients with CKD (n = 10), there was an overall 25% increase in GFR in response to LOTUS (p < 0.01).

Conclusions

LOTUS increased intrarenal NO, RBF, and GFR and prevented PC-AKI in a large animal model of CKD, and significantly increased GFR in patients with CKD. This novel approach may provide a noninvasive nonpharmacological means to prevent PC-AKI in high-risk patients.

A thrombolytic therapy using diagnostic ultrasound combined with RGDS-targeted microbubbles and urokinase in a rabbit model

This study aimed to explore thrombolysis therapy based on ultrasound combined with urokinase and Arg–Gly–Asp sequence (RGDS)-targeted microbubbles by evaluating the histological changes in a thrombotic rabbit model. Forty-two New Zealand rabbits featuring platelet-rich thrombi in the femoral artery were randomized to (n = 6/group): ultrasound alone (US); urokinase alone (UK); ultrasound plus non-targeted microbubbles (US + M); ultrasound plus RGDS-targeted microbubbles (US + R); RGDS-targeted microbubbles plus urokinase (R + UK); ultrasound, non-targeted microbubbles and urokinase (US + M + UK); and ultrasound, RGDS-targeted microbubbles and urokinase (US + R + UK) groups. Diagnostic ultrasound was used transcutaneously over the thrombus for 30 min. We evaluated the thrombolytic effect based on ultrasound thrombi detection, blood flow, and histological observations. Among all study groups, complete recanalization was achieved in the US + R + UK group. Hematoxylin and eosin staining showed that the thrombi were completely dissolved. Scanning electron microscopy examination demonstrated that the fiber network structure of the thrombi was damaged. Transmission electron microscopy showed that the thrombus was decomposed into high electron-dense particles. Histology for von Willebrand factor and tissue factor were both negative in the US + R + UK group. This study revealed that a thrombolytic therapy consisting of diagnostic ultrasound together with RGDS-targeted and urokinase coupled microbubbles.

Therapeutic Ultrasound Improves Myocardial Blood Flow and Reduces Infarct Size in a Canine Model of Coronary Microthromboembolism

BACKGROUND

Therapeutic ultrasound (TUS) has been used to lyse infarct-related coronary artery thrombus. There has been no study examining the effect of TUS specifically on myocardial microthromboemboli seen in acute myocardial infarction and acute coronary syndromes. The aim of this study was to test the hypothesis that TUS improves myocardial blood flow (MBF) and reduces infarct size (IS) in this situation by dissolving myocardial microthrombi.

METHODS

An open-chest canine model of myocardial microthromboembolism was created by disrupting a thrombus in the left anterior descending coronary artery, and 1.05- and 0.25-MHz TUS (n = 7 each) delivered epicardially for 30 min was compared with control (n = 6). MBF and IS (as a percentage of left anterior descending coronary artery perfusion bed size) were measured 60 min after treatment. In addition, immunohistochemistry was performed to assess microthrombi, and histopathology was performed to define inflammation.

RESULTS

Transmural, epicardial, and endocardial myocardial blood volume and MBF (measured using myocardial contrast echocardiography) and percentage wall thickening were significantly higher 60 min after receiving TUS compared with control. The ratio of IS to left anterior descending coronary artery perfusion bed size was significantly smaller (P = .03) in the 1.05-MHz TUS group (0.14 ± 0.04) compared with the control (0.31 ± 0.06, P = .04) and 0.25-MHz (0.36 ± 0.08) groups. MBF versus percentage wall thickening exhibited a linear relation (r = 0.65) in the control and 1.05-MHz TUS groups but not in the 0.25-MHz TUS group (r = 0.29). The presence of myocardial microemboli in vessels >10 μm in diameter was significantly reduced in the 1.05-MHz TUS group compared with the other two groups. The distribution and intensity of inflammation was higher in the 0.25-MHz TUS group compared with the other groups.

CONCLUSIONS

TUS at 1.05 MHz is effective in restoring myocardial blood volume and MBF, thus reducing IS by clearing the microcirculation of microthrombi. IS reduction is not seen at 0.25 MHz, despite improvement in MBF, which may be related to the increased inflammation noted at this frequency. Because both acute myocardial infarction and acute coronary syndromes are associated with microthromboembolism, these results suggest that TUS could have a potential adjunctive role in the treatment of both conditions.

Therapeutic Ultrasound Increases Myocardial Blood Flow in Ischemic Myocardium and Cardiac Endothelial Cells: Results of In Vivo and In Vitro Experiments

BACKGROUND

Therapeutic ultrasound can reduce infarct size in a model of coronary thrombosis even when sonothrombolysis is ineffective. The aim of this study was to test the hypothesis that ultrasound-induced cardioprotection is mediated by molecules released from the vascular endothelium that increase myocardial blood flow (MBF) and also have direct tissue-salvaging effects.

METHODS

In vivo and in vitro experiments were performed using a 1.05-MHz transducer. For the in vivo experiments 10 control and 10 ultrasound-treated dogs undergoing occlusion of the left anterior descending coronary artery were studied. MBF was measured using myocardial contrast echocardiography. For the in vitro experiments, primary mouse cardiac endothelial cells were exposed to ultrasound at baseline or following oxygen-glucose deprivation and endothelial nitric oxide synthase phosphorylation as well as adenosine and the eicosanoids epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids, and hydroxyl-eicosatetraenoic acids were measured.

RESULTS

In vivo, ultrasound treatment caused higher MBF (20 ± 10 vs 10 ± 8, P = .03) and higher wall thickening (3 ± 3% vs 1 ± 0.4%, P = .01) in the collateral-derived border zone compared with control. Epicardial MBF in the left anterior descending coronary artery bed also tended to be higher (17 ± 17 vs 5 ± 4, P = .05) in ultrasound-treated versus control animals; however, endocardial MBF in this region was similar to that in controls (13 ± 14 vs 14 ± 7). In vitro, phosphorylated endothelial nitric oxide synthase and adenosine increased (by 129 ± 11% and 286 ± 63%, respectively, P < .01) with ultrasound compared with unstimulated cells. Similar results were obtained with epoxyeicosatrienoic acids. After oxygen-glucose deprivation, phosphorylated endothelial nitric oxide synthase decreased and was restored with application of ultrasound. Similar changes were noted with epoxyeicosatrienoic acids. Cell viability decreased with oxygen-glucose deprivation and returned to near baseline with ultrasound.

CONCLUSIONS

Ultrasound increases MBF in ischemic tissue in vivo. This effect is likely mediated by the release of a plethora of coronary vasodilators during ultrasound treatment that also have direct tissue-salvaging effects. Therapeutic ultrasound, therefore, has potential for treatment of acute and chronic myocardial ischemia independent of its effect on thrombolysis.

Review of Protocols Used in Ultrasound Thrombolysis

OBJECTIVES

This paper focuses on the review of protocols used in thrombolysis studies with ultrasound.

MATERIALS AND METHODS

Data from peer-review articles were acquired.

RESULTS

The protocols of several published reports are summarized in 3 tables (in vitro, in vivo, and clinical), providing detailed information concerning clot model, thrombolytic drug, treatment mode, sonication parameters, evaluation method, thrombolysis outcome, side effects, and conclusions.

CONCLUSIONS

The aim of this review was to give an overview of the different protocols used so far in the field of sonothrombolysis and investigate the impact of several aspects involved on sonothrombolysis outcome.

Comparative lytic efficacy of rt-PA and ultrasound in porcine versus human clots

Introduction

Porcine thrombi are employed routinely in preclinical models of ischemic stroke. In this study, we examined the differential lytic susceptibility of porcine and human whole blood clots with and without the use of microbubbles and ultrasound (US) as an adjuvant.

Materials and methods

An in vitro system equipped with time-lapse microscopy was used to evaluate recombinant tissue-plasminogen activator (rt-PA) lysis of porcine and human clots in the same species or cross species plasma. Human and porcine whole blood clots were treated with rt-PA and an echo contrast agent, Definity^®, and exposed to intermittent 120 kHz US.

Results and conclusions

The rt-PA lytic efficacy observed for porcine clots in porcine plasma was 22 times lower than for human clots in human plasma reported previously. Further, porcine clots did not exhibit increased lysis with adjuvant Definity^® and US exposure. However, the rt-PA lytic susceptibility of the porcine clots in human plasma was similar to that of human clots in human plasma. Human clots perfused with porcine plasma did not respond to rt-PA, but adjuvant use of Definity^® and US enhanced lysis. These results reveal considerable differences in lytic susceptibility of porcine clots and human clots to rt-PA. The use of porcine clot models to test new human thrombolytic therapies may necessitate modulation of coagulation and thrombolytic factors to reflect human hemostasis accurately.

The effect of ultrasound for increasing neural differentiation in hBM-MSCs and inducing neurogenesis in ischemic stroke model

AIMS

This study's purpose was to evaluate the effect of ultrasound in air at a frequency of 0.04MHz and an intensity of 50mW/cm² on neural differentiation of hBM-MSCs in vitro and on neurogenesis in an ischemic stroke model.

MATERIALS AND METHODS

hBM-MSCs were exposed to 0.04MHz ultrasound and then compared with no exposed one in cell morphology, lactate dehydrogenase (LDH) activity, RT-PCR, and Western blot. In addition, we made stroke model mice by means of the photothrombosis (PT) method and these models were exposed to 0.04MHz ultrasound after hBM-MSCs injection. We compared with sham group in histological and immunohistochemical analysis and western blot.

KEY FINDINGS

Ultrasound induced neural differentiation without cell death. In stroke models, inflammatory cells were observed around the infarct area in the Cell, Cell/Ultrasound group and the brain infarct volume in the Cell/Ultrasound group was smaller than in the sham group. Further, the expression of neural proteins in the Cell/Ultrasound group was increased relative to the sham group.

SIGNIFICANCE

The present study showed that ultrasound promotes neural differentiation of hBM-MSC and neurogenesis in a mouse stroke model. This may be applicable as a therapeutic device with the aim of inducing neurogenesis following stroke.

Salutary Effects of Cepharanthine against Skeletal Muscle and Kidney Injuries following Limb Ischemia/Reperfusion

Limb ischemia/reperfusion (I/R) causes oxidation and inflammation and subsequently induces muscle and kidney injuries. Cepharanthine, a natural plant alkaloid, possesses anti-inflammatory and antioxidative properties. We elucidated the salutary effects of cepharanthine against muscle and kidney injuries following limb I/R. Adult male rats were randomized to receive I/R or I/R plus cepharanthine. I/R was achieved by applying tourniquet high around each thigh for 3 hours followed by reperfusion for 24 hours. Cepharanthine (10 mg/kg, intraperitoneal) was injected immediately before reperfusion. After euthanization, degrees of tissue injury, inflammation, and oxidation were examined. Our data revealed that the I/R group had significant increases in injury biomarker concentrations of muscle (creatine kinase and lactate dehydrogenase) and kidney (creatinine, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1). Histological assays revealed moderate muscle and kidney injury characteristics in the I/R group. The I/R group also had significant increases in concentrations of inflammatory molecules (interleukin-6, macrophage inflammatory protein-2, and prostaglandin E₂) and reactive nitrogen species (nitric oxide) as well as lipid peroxidation (malondialdehyde). Of note, these effects of limb I/R could be mitigated by cepharanthine. These data confirmed that cepharanthine attenuated muscle and kidney injuries induced by limb I/R. The mechanisms may involve its anti-inflammatory and antioxidative capacities.

Augmentation of limb perfusion and reversal of tissue ischemia produced by ultrasound-mediated microbubble cavitation

BACKGROUND

Ultrasound can increase tissue blood flow, in part, through the intravascular shear produced by oscillatory pressure fluctuations. We hypothesized that ultrasound-mediated increases in perfusion can be augmented by microbubble contrast agents that undergo ultrasound-mediated cavitation and sought to characterize the biological mediators.

METHODS AND RESULTS

Contrast ultrasound perfusion imaging of hindlimb skeletal muscle and femoral artery diameter measurement were performed in nonischemic mice after unilateral 10-minute exposure to intermittent ultrasound alone (mechanical index, 0.6 or 1.3) or ultrasound with lipid microbubbles (2×10(8) IV). Studies were also performed after inhibiting shear- or pressure-dependent vasodilator pathways, and in mice with hindlimb ischemia. Ultrasound alone produced a 2-fold increase (P<0.05) in muscle perfusion regardless of ultrasound power. Ultrasound-mediated augmentation in flow was greater with microbubbles (3- and 10-fold higher than control for mechanical index 0.6 and 1.3, respectively; P<0.05), as was femoral artery dilation. Inhibition of endothelial nitric oxide synthase attenuated flow augmentation produced by ultrasound and microbubbles by 70% (P<0.01), whereas inhibition of adenosine-A2a receptors and epoxyeicosatrienoic acids had minimal effect. Limb nitric oxide production and muscle phospho-endothelial nitric oxide synthase increased in a stepwise fashion by ultrasound and ultrasound with microbubbles. In mice with unilateral hindlimb ischemia (40%-50% reduction in flow), ultrasound (mechanical index, 1.3) with microbubbles increased perfusion by 2-fold to a degree that was greater than the control nonischemic limb.

CONCLUSIONS

Increases in muscle blood flow during high-power ultrasound are markedly amplified by the intravascular presence of microbubbles and can reverse tissue ischemia. These effects are most likely mediated by cavitation-related increases in shear and activation of endothelial nitric oxide synthase.

Diagnostic ultrasound induced inertial cavitation to non-invasively restore coronary and microvascular flow in acute myocardial infarction

Ultrasound induced cavitation has been explored as a method of dissolving intravascular and microvascular thrombi in acute myocardial infarction. The purpose of this study was to determine the type of cavitation required for success, and whether longer pulse duration therapeutic impulses (sustaining the duration of cavitation) could restore both microvascular and epicardial flow with this technique. Accordingly, in 36 hyperlipidemic atherosclerotic pigs, thrombotic occlusions were induced in the mid-left anterior descending artery. Pigs were then randomized to either a) ½ dose tissue plasminogen activator (0.5 mg/kg) alone; or same dose plasminogen activator and an intravenous microbubble infusion with either b) guided high mechanical index short pulse (2.0 MI; 5 usec) therapeutic ultrasound impulses; or c) guided 1.0 mechanical index long pulse (20 usec) impulses. Passive cavitation detectors indicated the high mechanical index impulses (both long and short pulse duration) induced inertial cavitation within the microvasculature. Epicardial recanalization rates following randomized treatments were highest in pigs treated with the long pulse duration therapeutic impulses (83% versus 59% for short pulse, and 49% for tissue plasminogen activator alone; p<0.05). Even without epicardial recanalization, however, early microvascular recovery occurred with both short and long pulse therapeutic impulses (p<0.005 compared to tissue plasminogen activator alone), and wall thickening improved within the risk area only in pigs treated with ultrasound and microbubbles. We conclude that although short pulse duration guided therapeutic impulses from a diagnostic transducer transiently improve microvascular flow, long pulse duration therapeutic impulses produce sustained epicardial and microvascular re-flow in acute myocardial infarction.

Exploratory analysis of estimated acoustic peak rarefaction pressure, recanalization, and outcome in the transcranial ultrasound in clinical sonothrombolysis trial

PURPOSE

Acoustic peak rarefaction pressure (APRP) is the main factor that influences ultrasound-enhanced thrombolysis. We sought to determine whether recanalization rate and functional outcomes in the Transcranial Ultrasound in Clinical SONothrombolysis (TUCSON) trial could be predicted by estimated in vivo APRP.

METHODS

We developed an acoustic attenuation model to estimate the in vivo APRP at the arterial occlusion site in each subject of the TUCSON trial with CT scans eligible for measurements. Variables included temporal bone thickness, depth of arterial occlusion site, and average attenuation of skin and brain tissues. Recanalization was defined as partial or complete using the Thrombolysis in Brain Infarction flow grades. Functional independence was assessed at 3 months using the modified Rankin Scale score (mRS, 0-1).

RESULTS

APRP was calculated in 20 acute ischemic stroke patients treated with sonothrombolysis (mean age, 64 ± 15 years, 65% men; median NIHSS score, 13; IQR, 6-17). The mean APRP was 30.2 ± 15.5 kPa (range, 8-68 kPa). Patients with persisting occlusion had nonsignificantly lower APRP than patients with partial or complete recanalization (25.2 ± 8.0 versus 32.3 ± 17.7 kPa; p = 0.228). Patients who were functionally independent at 3 months had nonsignificantly higher APRP than patients with worse outcome (35.1 ± 19.5 versus 25.9 ± 11.2 kPa; p = 0.217).

CONCLUSIONS

Our exploratory analysis suggests a potentially important role of successful energy delivery to augment thrombolysis with 2-MHz ultrasound in acute ischemic stroke patients.

Safety and efficacy of endovascular sonolysis using the EkoSonic endovascular system in patients with acute stroke

BACKGROUND AND PURPOSE

Sonolysis is a new therapeutic procedure for arterial recanalization. The aim of this study was to confirm the safety and efficacy of endovascular sonolysis by using the EkoSonic Endovascular System in subjects with acute ischemic stroke.

MATERIALS AND METHODS

Patients with acute ischemic stroke with occlusion of the middle cerebral artery or basilar artery were enrolled consecutively in this prospective study. The control group (44 MCA and 12 BA occlusions) was selected from historical controls. EkoSonic Endovascular System was started within 8 hours after stroke onset. The NIHSS score at hospital admission, after 24 hours, and at 7 days; arterial recanalization; early neurologic improvement; symptomatic intracerebral hemorrhage; and favorable 3-month clinical outcome defined as a modified Rankin Scale score of 0-2 were evaluated by statistical means.

RESULTS

Fourteen patients (10 men; mean age, 65.1 ± 11.2 years; median NIHSS score, 16.5) underwent EkoSonic endovascular sonolysis. Arterial recanalization after endovascular treatment was achieved in 6 of 7 (85.7%) patients with MCA occlusion (4 complete recanalizations) and in all 7 (100%) patients with BA occlusion (6 complete recanalizations). No (0%) symptomatic intracerebral hemorrhage or periprocedural complications occurred. Seven (50%) patients were independent at 3 months (median mRS score, 2). Early neurologic improvement and favorable clinical outcome were significantly more frequent in patients with MCA occlusion undergoing EkoSonic endovascular sonolysis than in controls (100% and 71.4% versus 4.6% and 13.6% of patients; P = .0001 and P = .003, respectively). Three-month mortality was significantly lower in patients with BA occlusion undergoing EkoSonic endovascular sonolysis than in controls (0% versus 66.7% patients, P = .013).

CONCLUSIONS

In this small study, EkoSonic endovascular sonolysis allowed safe and potentially effective revascularization in patients experiencing acute ischemic stroke.

Mechanical clot damage from cavitation during sonothrombolysis

Recent studies have shown that high intensity focused ultrasound (HIFU) accelerates thrombolysis for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role. The goal of this paper is to investigate the potential for cavitation to cause mechanical damage to a blood clot. The amount of damage to the fiber network caused by a single bubble expansion and collapse is estimated by two independent approaches: One based on the stretch of individual fibers and the other based on the energy available to break individual fibers. The two methods yield consistent results. The energy method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating an impinging jet. This leads to significantly more damage compared to a bubble embedded within the clot structure. Finally, as an example of how one can apply the theory, a simulation of the propagation of HIFU waves through model calvaria of varying density is explored. The maximum amount of energy available to cause damage to a blood clot increases as the density of the calvaria decreases.

The role of sonolysis and sonothrombolysis in acute ischemic stroke: a systematic review and meta-analysis of randomized controlled trials and case-control studies

OBJECTIVES

To assess the evidence on the safety and efficacy of sonothrombolysis in acute stroke.

SEARCH METHODS

Electronic databases and grey literature were searched under different MeSH terms from 1970 to present.

SELECTION CRITERIA

Randomized control trials (RCTs) and case control studies (CCSs) on sonolysis and sonothrombolysis alone or with microsphere in acute stroke patients (>18 old). Outcome measures included complete recanalization (CR) at 1-2 and 24 hours, 3 months modified Rankin Scale (mRS), and symptomatic intracerebral hemorrhage (sICH). Data was extracted to Review Manager software.

RESULTS

Fifty-seven studies were retrieved and analyzed. Ten studies (7 RCTs and 3 CCSs) were included in our meta-analysis, which revealed that sonolysis and sonothrombolysis are safe (OR of sICH: 1.14; 95% confidence interval (CI): 0.56- 2.34;P=0.71) and effective (OR of CR at 1-2 hours: 2.95;95% CI: 1.81-4.81;P<0.00001) and have more than two-fold higher likelihood of favourable long-term outcome (3-month mRS 0-2; OR: 2.20; CI:1.52-3.19;P<0.0001). Further subgroup analysis based on the presence of microsphere revealed that it is safe (OR of sICH: 1.18; CI:0.433.24;P=0.75) and effective (OR of CR: 2.61; CI: 1.36-4.99;P=0.004). Subgroup analysis based on sonolysis revealed to be safe and effective.

CONCLUSIONS

This novel treatment appears safe and effective. The evidence of microsphere as an enhancement of sonothrombolysis is evolving.

Safety and efficacy of sonothrombolysis using bilateral TCD monitoring by diagnostic 2 MHz probes - a pilot study

INTRODUCTION

Sonothrombolysis is a new treatment method for patients with acute ischemic stroke (IS). Various ultrasound frequencies and intensities are being tested these days. The aim of this pilot study was to assess the safety and efficacy of sonothrombolysis using 2 diagnostic probes and bilateral monitoring in patients with acute occlusion of the middle cerebral artery (MCA).

PATIENTS AND METHODS

Twelve consecutive IS patients (7 males; age 47 - 78, average 64.1 ± 9.4 years) with acute MCA occlusion and contraindication of thrombolysis were included in the study. 60-min bilateral 2-MHz pulsed-wave Doppler monitoring of the area of occlusion was performed in all patients (Group 1). The control group consisted of 37 IS patients (20 males; age 32 - 78, average 62.2 ± 12.1 years) treated with standard sonothrombolysis and selected from the Thrombotripsy Study database (Group 2). The differences in number of recanalized arteries after a 1 h treatment, independent patients (modified Rankin scale [mRS] value of 0 - 2) after 90 days and symptomatic intracerebral hemorrhages (SICH) were statistically evaluated.

RESULTS

Complete recanalization was found in 4 (30.0%) Group 1 and in 12 (32.4%) Group 2 patients. Seven (58.3%) Group 1 and 22 (59.5%) Group 2 patients were independent after 90 days. SICH was found in none of Group 1 patients and in 1 (2.7%) of the Group 2 patients (P>0.05 in all cases).

CONCLUSION

In this pilot study, sonothrombolysis using 2 probes and bilateral monitoring is safe but not more effective than standard sonothrombolysis in acute IS patients with MCA occlusion.

Changes in middle cerebral artery blood flow velocity during sonolysis using a diagnostic transcranial probe with a 2-MHz Doppler frequency in healthy volunteers

OBJECTIVES

Ultrasound has various biological effects in the human body. The effects of continuous monitoring with ultrasound (sonolysis) on vasodilatation of the radial artery were described recently. We wanted to ascertain whether similar changes in the blood flow velocity during sonolysis could also be detected in the middle cerebral artery.

METHODS

Fifteen healthy volunteers (6 male and 9 female; age range, 23-68 years; mean ± SD, 47.1 ± 15.1 years) were subjected to 1 hour of middle cerebral artery sonolysis using a diagnostic transcranial probe with a 2-MHz Doppler frequency and measurement of the blood flow velocity at 2-minute intervals. During a second session, a flow curve was recorded for 10 seconds at 2-minute intervals. The peak systolic velocity, end-diastolic velocity, mean flow velocity, pulsatility index, and resistive index were recorded during both measurements.

RESULTS

Irregular changes in the measured blood flow parameters were recorded during both sessions. Changes in particular hemodynamic parameters during both measurements were similar. The changes in the peak systolic velocity, end-diastolic velocity, mean flow velocity, pulsatility index, and resistive index were not significantly different between the two measurements (P < .05 in all cases).

CONCLUSIONS

As opposed to sonolysis of the radial artery, sonolysis of the middle cerebral artery using a diagnostic 2-MHz frequency in healthy volunteers did not lead to changes in the flow curve or peripheral vasodilatation.

Taboos and opportunities in sonothrombolysis for stroke

Systemic thrombolysis with tissue plasminogen activator (tPA) is the only approved treatment for acute ischaemic stroke that improves functional outcome if given up to 4.5 h from symptom onset. At least half of treated patients have unfavourable outcomes long-term though, emphasising the need to amplify the only approved acute stroke therapy. Ultrasound targeting of an intra-arterial occlusive clot and delivering mechanical pressure to its surrounding fluids (referred to as sonothrombolysis) accelerates the thrombolytic effect of tPA. Higher recanalisation rates produce a trend towards better functional outcomes that could be safely achieved with the combination of 2 MHz frequency ultrasound and systemic tPA. To further accelerate the clot-dissolving effect of ultrasound, a variety of frequencies and intensities as well as other adjuvant treatment elements are being studied. However, literature reports argue efficacy and safety of these novel approaches doubting promptly translation into the clinical practice. This review will summarise our current knowledge about potentially harmful (taboos) directions and what we think are promising avenues for these future stroke therapies. We also give a prospect for novel technologies such as operator-independent devices that aim to further spread the use of sonothrombolysis for stroke.

Evaluation of ultrasound-assisted thrombolysis using custom liposomes in a model of retinal vein occlusion

PURPOSE

To study the potential efficacy of ultrasound (US) assisted by custom liposome (CLP) destruction as an innovative thrombolytic tool for the treatment of retinal vein occlusion (RVO).

METHODS

Experimental RVO was induced in the right eyes of 40 rabbits using laser photothrombosis; the US experiment took place 48 hours later. Rabbits were randomly divided into four equal groups: US+CLP group, US+saline group, CLP+sham US group, and no treatment group. The latter three groups acted as controls. Fundus fluorescein angiography and Doppler US were used to evaluate retinal blood flow.

RESULTS

CLP-assisted US thrombolysis resulted in restoration of flow in seven rabbits (70%). None of the control groups showed significant restoration of retinal venous blood flow.

CONCLUSIONS

US-assisted thrombolysis using liposomes resulted in a statistically significant reperfusion of retinal vessels in the rabbit experimental model of RVO. This approach might be promising in the treatment of RVO in humans. Further studies are needed to evaluate this approach in patients with RVO. Ultrasound assisted thrombolysis can be an innovative tool in management of retinal vein occlusion.

Ultrasound enhanced prehospital thrombolysis using microbubbles infusion in patients with acute ST elevation myocardial infarction: pilot of the Sonolysis study

In animal studies, transthoracic ultrasound and microbubbles have shown to dissolve thrombi in ST elevation myocardial infarction (STEMI). To examine this effect in patients, we have initiated the Sonolysis trial. In this pilot study of 10 patients with a first acute STEMI, we investigated the safety and feasibility of this trial. After pretreatment in the ambulance, five patients were randomized to receive microbubbles with three-dimensional (3-D) guided high mechanical index impulses (1.18) for 15 min, whereas the control group received placebo without ultrasound. Subsequently, primary percutaneous coronary intervention (PPCI) was performed, if indicated. All patients successfully underwent study treatment and PPCI. No significant difference between treatment and control group in safety (minor adverse events 2/5 vs. 2/5, p = NS) and outcome (TIMI III flow 3/5 vs. 1/5 respectively, p = 0.23) was recorded. These results demonstrate that the study protocol is feasible in the acute cardiac care setting and safe during treatment and follow-up.

Effects of low frequency ultrasound on some properties of fibrinogen and its plasminolysis

Background

Pharmacological thrombolysis with streptokinase, urokinase or tissue activator of plasminogen (t-PA), and mechanical interventions are frequently used in the treatment of both arterial and venous thrombotic diseases. It has been previously reported that application of ultrasound as an adjunct to thrombolytic therapy offers unique potential to improve effectiveness. However, little is known about effects of the ultrasound on proteins of blood coagulation and fibrinolysis. Here, we investigated the effects of the ultrasound on fibrinogen on processes of coagulation and fibrinogenolysis in an in vitro system.

Results

Our study demonstrated that low frequency high intensity pulse ultrasound (25.1 kHz, 48.4 W/cm2, duty 50%) induced denaturation of plasminogen and t-PA and fibrinogen aggregates formation in vitro. The aggregates were characterized by the loss of clotting ability and a greater rate of plasminolysis than native fibrinogen. We investigated the effect of the ultrasound on individual proteins. In case of plasminogen and t-PA, ultrasound led to a decrease of the fibrinogenolysis rate, while it increased the fibrinogenolysis rate in case of fibrinogen. It has been shown that upon ultrasound treatment of mixture fibrinogen or fibrin with plasminogen, t-PA, or both, the rate of proteolytic digestion of fibrin(ogen) increases too. It has been shown that summary effect on the fibrin(ogen) proteolytic degradation under the conditions for combined ultrasound treatment is determined exclusively by effect on fibrin(ogen).

Conclusions

The data presented here suggest that among proteins of fibrinolytic systems, the fibrinogen is one of the most sensitive proteins to the action of ultrasound. It has been shown in vitro that ultrasound induced fibrinogen aggregates formation, characterized by the loss of clotting ability and a greater rate of plasminolysis than native fibrinogen in different model systems and under different mode of ultrasound treatment. Under ultrasound treatment of plasminogen and/or t-PA in the presence of fibrin(ogen) the stabilizing effect fibrin(ogen) on given proteins was shown. On the other hand, an increase in the rate of fibrin(ogen) lysis was observed due to both the change in the substrate structure and promoting of the protein-protein complexes formation.

Coronary and microvascular thrombolysis with guided diagnostic ultrasound and microbubbles in acute ST segment elevation myocardial infarction

BACKGROUND

During a microbubble infusion, guided high-mechanical index impulses from a diagnostic two-dimensional transducer improve microvascular recanalization in acute ST-segment elevation myocardial infarction. The purpose of this study was to further elucidate the mechanism of improved microvascular flow in normal and hyperlipidemic atherosclerotic pigs.

METHODS

In 14 otherwise normal pigs, acute left anterior descending thrombotic coronary occlusions were created. Pigs subsequently received aspirin, heparin, and half-dose fibrinolytic agent (tenecteplase or tissue plasminogen activator), followed by randomization to either no additional treatment (group I) or a continuous infusion of nontargeted microbubbles and guided high-mechanical index impulses from a three-dimensional transducer (group II). Epicardial recanalization rates, ST-segment resolution, microsphere-derived myocardial blood flow, and ultimate infarct size using myocardial contrast echocardiography were compared. The same coronary thrombosis was created in a set of 12 hypercholesterolemic pigs, which were then treated with the same pharmacologic and ultrasound regimen (group III, n = 6) or the pharmacologic regimen alone (group IV, n = 6).

RESULTS

Epicardial recanalization rates in groups I and II were the same (29%), but peri-infarct myocardial blood flow and ultimate infarct size improved after treatment in group II (P < .01 vs group I). In group III, epicardial recanalization was 100% (vs. 50% in group IV), and there were significant reductions in ultimate infarct size (P = .02 compared with group IV).

CONCLUSIONS

Guided high-mechanical index impulses from a diagnostic transducer and nontargeted microbubbles improve peri-infarct microvascular flow in acute ST-segment elevation myocardial infarction, even when epicardial recanalization does not occur.

Successful microbubble sonothrombolysis without tissue-type plasminogen activator in a rabbit model of acute ischemic stroke

BACKGROUND AND PURPOSE

Microbubbles (MB) combined with ultrasound (US) have been shown to lyse clots without tissue-type plasminogen activator (tPA) both in vitro and in vivo. We evaluated sonothrombolysis with 3 types of MB using a rabbit embolic stroke model.

METHODS

New Zealand White rabbits (n=74) received internal carotid angiographic embolization of single 3-day-old cylindrical clots (0.6 × 4.0 mm). Groups included: (1) control (n=11) embolized without treatment; (2) tPA (n=20); (3) tPA+US (n=10); (4) perflutren lipid MB+US (n=16); (5) albumin 3 μm MB+US (n=8); and (6) tagged albumin 3 μm MB+US (n=9). Treatment began 1 hour postembolization. Ultrasound was pulsed-wave (1 MHz; 0.8 W/cm²) for 1 hour; rabbits with tPA received intravenous tPA (0.9 mg/kg) over 1 hour. Lipid MB dose was intravenous (0.16 mg/kg) over 30 minutes. Dosage of 3 μm MB was 5 × 10⁹ MB intravenously alone or tagged with eptifibatide and fibrin antibody over 30 minutes. Rabbits were euthanized at 24 hours. Infarct volume was determined using vital stains on brain sections. Hemorrhage was evaluated on hematoxylin and eosin sections.

RESULTS

Infarct volume percent was lower for rabbits treated with lipid MB+US (1.0%± 0.6%; P=0.013), 3 μm MB+US (0.7% ± 0.9%; P=0.018), and tagged 3 μm MB+US (0.8% ± 0.8%; P=0.019) compared with controls (3.5%± 0.8%). The 3 MB types collectively had lower infarct volumes (P=0.0043) than controls. Infarct volume averaged 2.2% ± 0.6% and 1.7%± 0.8% for rabbits treated with tPA alone and tPA+US, respectively (P=nonsignificant).

CONCLUSIONS

Sonothrombolysis without tPA using these MB is effective in decreasing infarct volumes. Study of human application and further MB technique development are justified.

Effects of attenuation and thrombus age on the success of ultrasound and microbubble-mediated thrombus dissolution

The purpose of this study was to examine the effects of applied mechanical index, incident angle, attenuation and thrombus age on the ability of 2-D vs. 3-D diagnostic ultrasound and microbubbles to dissolve thrombi. A total of 180 occlusive porcine arterial thrombi of varying age (3 or 6 h) were examined in a flow system. A tissue-mimicking phantom of varying thickness (5 to 10 cm) was placed over the thrombosed vessel and the 2-D or 3-D diagnostic transducer aligned with the thrombosed vessel using a positioning system. Diluted lipid-encapsulated microbubbles were infused during ultrasound application. Percent thrombus dissolution (%TD) was calculated by comparison of clot mass before and after treatment. Both 2-D and 3-D-guided ultrasound increased %TD compared with microbubbles alone, but %TD achieved with 6-h-old thrombi was significantly less than 3-h-old thrombi. Thrombus dissolution was achieved at 10 cm tissue-mimicking depths, even without inertial cavitation. In conclusion, diagnostic 2-D or 3-D ultrasound can dissolve thrombi with intravenous nontargeted microbubbles, even at tissue attenuation distances of up to 10 cm. This treatment modality is less effective, however, for older aged thrombi.

Adjunctive transcutaneous ultrasound with thrombolysis: results of the PLUS (Perfusion by ThromboLytic and UltraSound) trial

OBJECTIVES

We investigated whether transcutaneous ultrasound (TUS) augments coronary thrombolysis and achieves higher rates of Thrombolysis In Myocardial Infarction (TIMI) flow grade 3 and ST-segment resolution in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

In animal coronary and peripheral artery thrombosis models, low-frequency TUS enhances and accelerates thrombolysis.

METHODS

In a double-blind, randomized, controlled international clinical trial, 396 patients with STEMI < or =6 h were randomized to thrombolysis alone or thrombolysis plus TUS. The 60 minute TIMI flow grade, ST-segment resolution (primary end points) and other angiographic, electrocardiographic, and clinical outcomes were compared between treatment groups.

RESULTS

The trial was halted after Safety and Efficacy Monitoring Committee interim analysis that demonstrated lack of treatment efficacy. In total, 360 patients were evaluable for angiographic, electrocardiographic, or clinical end points. Sixty minutes after thrombolytic administration, the proportion of patients achieving TIMI flow grade 3 did not differ between TUS and control groups (40.7% vs. 48.5%, respectively; p = 0.10). Achievement of >50% ST-segment resolution at 60 min did not differ between TUS and control groups (53.2% vs. 50.0%; p = 0.93). Thirty-day mortality and composite clinical events-death, reinfarction, recurrent ischemia, stroke, major bleed, left ventricular rupture (9.7 % vs. 10.2%; p = 0.88)-did not differ between TUS and control patients.

CONCLUSIONS

Thrombolysis plus TUS failed to improve 60-min TIMI flow grade or ST-segment resolution versus thrombolysis alone.

Sonoporation, drug delivery, and gene therapy

Ultrasound is a very effective modality for drug delivery and gene therapy because energy that is non-invasively transmitted through the skin can be focused deeply into the human body in a specific location and employed to release drugs at that site. Ultrasound cavitation, enhanced by injected microbubbles, perturbs cell membrane structures to cause sonoporation and increases the permeability to bioactive materials. Cavitation events also increase the rate of drug transport in general by augmenting the slow diffusion process with convective transport processes. Drugs and genes can be incorporated into microbubbles, which in turn can target a specific disease site using ligands such as the antibody. Drugs can be released ultrasonically from microbubbles that are sufficiently robust to circulate in the blood and retain their cargo of drugs until they enter an insonated volume of tissue. Local drug delivery ensures sufficient drug concentration at the diseased region while limiting toxicity for healthy tissues. Ultrasound-mediated gene delivery has been applied to heart, blood vessel, lung, kidney, muscle, brain, and tumour with enhanced gene transfection efficiency, which depends on the ultrasonic parameters such as acoustic pressure, pulse length, duty cycle, repetition rate, and exposure duration, as well as microbubble properties such as size, gas species, shell material, interfacial tension, and surface rigidity. Microbubble-augmented sonothrombolysis can be enhanced further by using targeting microbubbles.

Opening of the blood-brain barrier by low-frequency (28-kHz) ultrasound: a novel pinhole-assisted mechanical scanning device

Disruption of the blood-brain barrier (BBB) may be transiently achieved via high-frequency focused spherical ultrasound in the presence of microbubbles. In this experimental animal study, we sought to determine whether focal reversible opening of the BBB may be achieved using low-frequency (i.e., 20-30 kHz) planar ultrasonic waves. In the presence of microbubbles, we were able to obtain BBB opening using non-focused ultrasound irradiation with a frequency as low as 28 kHz. We also achieved a tight regulation of the ultrasound patterns by using a mechanical scanning device equipped with a pinhole. Histologic examination of the brains supported the feasibility of our system. The areas of BBB disruption obtained with this method were large enough to cover a typical circumscribed cerebral tumor mass. The inherent advantages of our BBB opening method include an improved portability, the possibility to obtain fairly wide areas of BBB opening and a low incidence of hemorrhagic complications. In addition, our system has the potential to reduce the need for image guidance for treating superficial brain lesions.

Fibrinolytic effects of transparietal ultrasound associated with intravenous infusion of an ultrasound contrast agent: study of a rat model of acute cerebral stroke

The aim of this study was to evaluate the thrombolytic effect of focused transparietal ultrasound in combination with a specific contrast agent (microbubbles) in acute cerebral ischemia. Acute cerebral ischemia was induced in 10 rats by intra-arterial clots injection. Five rats (group 1) were treated with a combination of transparietal ultrasound (probe 2 MHz, acoustic power 500 mW/cm(2)) and intravenous injection of 0.6 mL of the ultrasound contrast agent (UCA) sulfur hexafluoride. Five rats (group 2) were treated by fibrinolytic intravenous infusion (recombinant tissue plasminogen activator). Cerebral cellular energy production was determined by measuring the cellular phosphorylation using phosphorus magnetic spectroscopy before and during ischemia induction and after treatment. Measures were performed on a dedicated 2.35T magnet. The ratio phosphocreatine (P(Cr)) on inorganic phosphate (P(i)), P(Cr)/P(i), estimation of the oxidative phosphorylation metabolism and the intracellular pH (pHi) were measured in the two groups. Compared with the ischemia induction period, both treatments were associated with an increase of P(Cr)/P(i) and pHi values, respectively, +80% and +100% in group 1 (p=0.07) and +100% and +80% in group 2 (p=0.04). There was no significant difference between the two groups for the response treatment. To conclude, treatment with intravenous fibrinolytic infusion and treatment with focused ultrasound in combination with UCA seems to be equally effective in treating acute cerebral ischemia in rats. (E-mail: j.p.tasu@chu-poitiers.fr).

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.

Therapeutic Ultrasound-Enhanced Thrombolysis in Patients With Acute Myocardial Infarction

Thrombolytic therapy is widely used to treat the patients with ST elevation acute myocardial infarction (STE-MI). Due to logistic and economic reasons, only 10% of patients with acute myocardial infarction can be treated with the percutaneous coronary intervention (PCI). Optimal flow (TIMI (Thrombolysis In Myocardial Infarction) 3 flow) is achieved in only about 60% of cases by enzymatic thrombolysis. Therapeutic ultrasound (US) exerts an effect on thrombolysis by micromechanical processes or indirectly by supporting enzymatic thrombolysis. This review examines relevant experimental and clinical published data. Technical issues in therapeutic US-enhanced thrombolysis in patients with acute myocardial infarction and advancements of the techniques during recent 10 years are discussed.

Early iNOS impairment and late eNOS enhancement during reperfusion following 2.49 MHz continuous ultrasound exposure after ischemia

OBJECTIVE

Ischemia reperfusion (IR) injury, occurring during heart attacks, hemorrhagic shock, and bypass and transplant surgeries, impairs microcirculatory function and nitric oxide (NO) synthesis. We report the regulation of endothelial and inducible NO synthase (eNOS and iNOS) proteins as a consequence of the application of continuous mode diagnostic frequency ultrasound application following IR injury.

METHODS

Animals were assigned to one of five groups for microcirculatory assessment or Western blot analysis (WB) as follows: (1) IR+iNOS inhibition (1400W); and (2) IR+1400W+ultrasound for microcirculatory assessment, (3) Control; (4) IR; and (5) IR+ultrasound for WB. Functional capillary density and microvascular diameter, flow velocity, and flow were monitored for microcirculatory assessment. Skin tissue samples were harvested for WB. 2.49MHz continuous ultrasound was used for application.

RESULTS

Both the inhibition of iNOS alone and iNOS inhibition with ultrasound irradiation positively influenced the microcirculation of observed animals relative to baseline values. Ultrasound exposure resulted in a significant production of eNOS protein in skin tissue harvested 24h into reperfusion (p<0.01). iNOS levels from the same tissue of ultrasound exposed animals were found to be significantly decreased 0.5h into reperfusion (p<0.05).

CONCLUSION

Protection from lasting IR injury effects in the microcirculation, with continuous mode diagnostic frequency ultrasound, results from augmented eNOS protein levels during late reperfusion. Ultrasound inhibited iNOS protein production during early reperfusion may also confer protection from IR injury.

Safety and efficacy of the sonographic acceleration of the middle cerebral artery recanalization: results of the pilot thrombotripsy study

The aim was to demonstrate the safety and efficacy of continuous ultrasound monitoring of the artery occlusion area (sonothrombotripsy) in patients with acute middle cerebral artery (MCA) occlusion. A total of 52 consecutive patients with acute MCA occlusion were included in the thrombotripsy group. Doppler monitoring of the region of occlusion was performed for up to 45 min. The control group was created from the NAIS study database. Patients were matched for their vascular status, age, sex, artery occlusion, NIHSS at admission, rt-PA treatment and time to the first ultrasound examination. The number of recanalized arteries at 6 and 24 h after the onset of symptoms, the number of independent patients (mRS 0-2 versus 3-6) after 90 d, and the number of serious adverse events were statistically evaluated. In the thrombotripsy group, 19 patients (36.5%) had complete recanalization and 27 (51.9%) patients had partial recanalization at 1 h after the start of the TCCS monitoring. Higher recanalization rates at 6 and 24 h after stoke onset were also seen compared with controls (69.2% versus 7.7% and 92.3% versus 61.5% complete recanalizations, respectively, p < 0.05). Independence (mRS 0-2) at day 90 was achieved by 61.5% of the thrombotripsy patients and 32.7% controls, p < 0.05, odds ratio 1.88 (95% confidence interval = 1.23 - 2.90). In both groups, two symptomatic intracerebral hemorrhages and one symptomatic brain edema occurred. Sonothrombotripsy with diagnostic transcranial duplex technology is safe and may offer benefit in addition to standard of care stroke treatment.

Ultrasound enhanced thrombolysis in acute arterial ischemia

In vitro and animal studies have shown that thrombolysis with intravenous tissue plasminogen activator (tPA) can be enhanced with ultrasound. Ultrasound delivers mechanical pressure waves to the clot, thus exposing more thrombus surface to circulating drug. Moreover, intravenous gaseous microspheres with ultrasound have been shown to be a potential alternative to fibrinolytic agents to recanalize discrete peripheral thrombotic arterial occlusions or acute arteriovenous graft thromboses. Small phase I-II randomized and non-randomized clinical trials have shown promising results concerning the potential applications of ultrasound-enhanced thrombolysis in the setting of acute cerebral ischemia. CLOTBUST was an international four-center phase II trial, which demonstrated that, in patients with acute ischemic stroke, transcranial Doppler (TCD) monitoring augments tPA-induced arterial recanalization (sustained complete recanalization rates: 38% vs. 13%) with a non-significant trend toward an increased rate of clinical recovery from stroke, as compared with placebo. The rates of symptomatic intracerebral hemorrhage (sICH) were similar in the active and placebo group (4.8% vs. 4.8%). Smaller single-center clinical trials using transcranial color-coded sonography (TCCD) reported recanalization rates ranging from 27% to 64% and sICH rates of 0-18%. A separate clinical trial evaluating the safety and efficacy of therapeutic low-frequency ultrasound was discontinued because of a concerning sICH rate of 36% in the active group. To further enhance the ability of tPA to break up thrombi, current ongoing clinical trials include phase II studies of a single beam 2 MHz TCD with perflutren-lipid microspheres. Moreover, potential enhancement of intra-arterial tPA delivery is being clinically tested with 1.7-2.1 MHz pulsed wave ultrasound (EKOS catheter) in ongoing phase II-III clinical trials. Intravenous platelet-targeted microbubbles with low-frequency ultrasound are currently investigated as a rapid noninvasive technique to identify thrombosed intracranial and peripheral vessels. Multi-national dose escalation studies of microspheres and the development of an operator independent ultrasound device are underway.