Clot Debris Research Articles

Decreased clot debris size and increased efficiency of acoustic vortex assisted high intensity focused ultrasound thrombolysis

High intensity focused ultrasound (HIFU) thrombolysis is a non-pharmacological, non-invasive treatment option for the restoration of blood flow through occluded vessels. This study demonstrated that the combination of an acoustic vortex with HIFU thrombolysis can decrease the size of clot debris, while simultaneously increasing the thrombolysis efficiency. The detected stable and inertial cavitation doses were lower in acoustic vortex assisted HIFU thrombolysis than in HIFU thrombolysis alone or in HIFU thrombolysis combined with regular focused ultrasound. Additionally, optical images indicated that these positive effects can be attributed to the aggregation of the generated clot debris and cavitation microbubbles in the focal region. This effectively enhances the interaction between the microbubbles and the clot, as well as its debris. Furthermore, the proposed method was effective under a flow velocity of up to 6 cm/s. This study demonstrated that the combination of an acoustic vortex and HIFU may provide a safer and more efficient thrombolysis approach by decreasing the debris size and by increasing the efficiency.

Designing a multifunctional staphylokinase variant (SAK-2RGD-TTI) with appropriate thrombolytic activity in vitro.

Thrombin, platelets, and plasmin are three key factors involved in hemostasis and thrombolysis. Thrombolytic therapy with clinically approved drugs is often followed by recurrent thrombosis caused by thrombin-induced platelet aggregation from the clot debris. In order to minimize these problems, new constructs were designed for the expression of recombinant staphylokinase (rSAK) and also a fusion protein composed of staphylokinase, 20 amino acids containing 2 RGD followed by tsetse thrombin Inhibitor (SAK-2RGD-TTI) in Pichia pastoris. Modeling the tertiary structure of SAK-2RGD-TTI showed that the linker containing RGD and TTI did not interfere with proper folding of SAK. In laboratory testing, the purified SAK-2RGD-TTI (420μg/mL) dissolved an average of 45% of the blood clot. The activity of the SAK-2RGD-TTI was also confirmed in various tests including human plasminogen activation assay, fibrin clot lysis assay, well diffusion method, activated partial thromboplastin time and platelet rich clot lysis assay. Our findings suggest that SAK-2RGD-TTI has improved therapeutic properties preventing reocclussion. It further confirms that it is practicable to assemble and produce a hybrid multifunctional protein that targets hemostatic process at various stages.

Phospholipid-Coated Hydrophobic Mesoporous Silica Nanoparticles Enhance Thrombectomy by High-Intensity Focused Ultrasound with Low Production of Embolism-Inducing Clot Debris.

Here we report the efficacy of a nanoparticle-assisted high-intensity focused ultrasound (HIFU) treatment that selectively destroys blood clots while minimizing generation of microparticles, or microemboli, that can cause further complications postsurgery. Treatment of malignant blood clots (thrombi) and the resulting emboli are critical problems for numerous patients, and treatments addressing these conditions would benefit from advancements in noninvasive procedures such as HIFU. While recanalization of occlusive blood clots is currently addressed with surgical intervention that seeks to minimize formation of large emboli, there is a danger of microemboli (micrometer-size particles) that have been theorized to be responsible for the poor correlation between apparent surgical success and patient outcome. Here, the addition of phospholipid-coated hydrophobically modified silica nanoparticles (P@hMSNs) improved the efficacy of HIFU treatment by serving as cavitation nuclei for mechanical disruption of thrombi. This treatment was evaluated for the ability to clear the HIFU focal area of a thick and dense thrombus within 10 min. Moreover, it was found that the use of P@hMSN+HIFU treatment generated a significantly smaller microembolic load as compared to comparison techniques, including a HIFU + microbubble contrast agent, HIFU alone, and direct mechanical disruption. This reduction in the microembolic load can occur either with primary removal of the clot by P@hMSN+HIFU or by insonation of the clot fragments after mechanical thrombectomy. Lastly, this method was evaluated in a flow model, where nonocclusive model thrombi and model emboli were mechanically ablated within the focal area within 15 s. Together, these results represent a combination therapy capable of resolving thrombi and microembolisms resulting from thrombectomy through localized destruction of clotted material.

Reduced clot debris size in sonothrombolysis assisted with phase-change nanodroplets

Thrombosis-related diseases such as stroke, deep vein thrombosis, and others represent leading causes of mortality and morbidity around the globe. Current clinical thrombolytic treatments are limited by either slow reperfusion (drugs) or invasiveness (catheters) and carry significant risks of bleeding. High intensity focused ultrasound (HIFU) has been demonstrated to be a non-pharmacological, non-invasive but yet efficient thrombolytic approach. However, clinical concerns still remain related to the clot debris produced via fragmentation of the original clot potentially being too large and hence occluding downstream vessels, causing hazardous emboli. In this study, we introduced phase-change nanodroplets into pulse HIFU-mediated thrombolysis. The size distribution of the clot debris generated in sonothrombolysis with and without nanodroplets was compared. The effects of nanodroplet concentration, acoustic power and pulse repetition frequency on the clot debris size were further evaluated. It was found that the volume percentage of the large clot debris particles (above 10 μm in diameter) was smaller and the average diameter of the clot debris reduced significantly in nanodroplets-assisted sonothrombolysis. The stable cavitation dose was higher in sonothrombolysis without nanodroplets but the inertial cavitation dose showed no significant differences under two conditions. Besides, the average diameter decreased with increasing nanodroplet concentration and acoustic power when calculated by number percentage, but was found to be similar when calculated by volume percentage. In addition, the number percentage of the clot debris above 30 μm was demonstrated to be larger upon applying a higher pulse repetition frequency. Taken in concert, this study demonstrated that the introduction of phase-change nanodroplets could provide a safer sonothrombolysis method by reducing the overall clot debris size.

Integrated Histotripsy and Bubble Coalescence Transducer for Thrombolysis

After the collapse of a cavitation bubble cloud, residual microbubbles can persist for up to seconds and function as weak cavitation nuclei for subsequent pulses in a phenomenon known as cavitation memory effect. In histotripsy, the cavitation memory effect can cause bubble clouds to repeatedly form at the same discrete set of sites. This effect limits the efficacy of histotripsy-based tissue fractionation. Our previous studies have indicated that low-amplitude bubble-coalescing (BC) ultrasound sequences interleaved with high-amplitude histotripsy pulses can coalesce the residual bubbles into one large bubble quickly. This reduces the cavitation memory effect and may increase treatment efficacy. Histotripsy has been investigated for thrombolysis by breaking up clots into debris smaller than red blood cells. However, this treatment has low efficacy for aged or retracted clots. In this study, we investigate the use of histotripsy with BC to improve the efficacy of treatment of retracted clots. An integrated histotripsy and bubble-coalescing (HBC) transducer system with specialized electronic driving system was built in-house. One high-amplitude (32 MPa), one-cycle histotripsy pulse followed by 36 low-amplitude (2.4 MPa), one-cycle BC pulses formed one HBC sequence. Results indicate that HBC sequences successfully generated a flow channel through the retracted clots at scan speeds of 0.2–0.5 mm/s. The channel size created using the HBC sequence was 128% to 480% larger than that created using histotripsy alone. The clot debris particles generated during HBC treatments were within the tolerable range. These results illustrate the concept that BC improves the treatment efficacy of histotripsy thrombolysis for retracted clots.

TCT-546 Microvascular dysfunction after immediate versus deferred stenting in patients with acute myocardial infarction

Conventional immediate stenting (IS) in highly pro-thrombotic and inflammatory milieu of infarct related arteries (IRA) during primary percutaneous coronary intervention (PCI) would increase distal embolization of clot and atheromatous plaque debris, and provoke subsequent microvascular obstruction

Reduced clot debris size using standing waves formed via high intensity focused ultrasound

The feasibility of utilizing high intensity focused ultrasound (HIFU) to induce thrombolysis has been demonstrated previously. However, clinical concerns still remain related to the clot debris produced via fragmentation of the original clot potentially being too large and hence occluding downstream vessels, causing hazardous emboli. This study investigates the use of standing wave fields formed via HIFU to disintegrate the thrombus while achieving a reduced clot debris size in vitro. The results showed that the average diameter of the clot debris calculated by volume percentage was smaller in the standing wave mode than in the travelling wave mode at identical ultrasound thrombolysis settings. Furthermore, the inertial cavitation dose was shown to be lower in the standing wave mode, while the estimated cavitation bubble size distribution was similar in both modes. These results show that a reduction of the clot debris size with standing waves may be attributed to the particle trapping of the acoustic potential well which contributed to particle fragmentation.

Histotripsy Thrombolysis on Retracted Clots

Retracted blood clots have been previously recognized to be more resistant to drug-based thrombolysis methods, even with ultrasound and microbubble enhancements. Microtripsy, a new histotripsy approach, has been investigated as a non-invasive, drug-free and image-guided method that uses ultrasound to break up clots with improved treatment accuracy and a lower risk of vessel damage compared with the traditional histotripsy thrombolysis approach. Unlike drug-mediated thrombolysis, which is dependent on the permeation of the thrombolytic agents into the clot, microtripsy controls acoustic cavitation to fractionate clots. We hypothesize that microtripsy thrombolysis is effective on retracted clots and that the treatment efficacy can be enhanced using strategies incorporating electronic focal steering. To test our hypothesis, retracted clots were prepared in vitro and the mechanical properties were quantitatively characterized. Microtripsy thrombolysis was applied on the retracted clots in an in vitro flow model using three different strategies: single-focus, electronically-steered multi-focus and dual-pass multi-focus. Results show that microtripsy was used to successfully generate a flow channel through the retracted clot and the flow was restored. The multi-focus and the dual-pass treatments incorporating the electronic focal steering significantly increased the recanalized flow channel size compared to the single-focus treatments. The dual-pass treatments achieved a restored flow rate up to 324 mL/min without cavitation contacting the vessel wall. The clot debris particles generated from microtripsy thrombolysis remained within the safe range. The results of this study show the potential of microtripsy thrombolysis for retracted clot recanalization with the enhancement of electronic focal steering.

Noninvasive thrombolysis using microtripsy: a parameter study.

Histotripsy fractionates soft tissue by well-controlled acoustic cavitation using microsecond-long, high-intensity ultrasound pulses. The feasibility of using histotripsy as a noninvasive, drug-free, and image-guided thrombolysis method has been shown previously. A new histotripsy approach, termed microtripsy, has recently been investigated for the thrombolysis application to improve treatment accuracy and avoid potential vessel damage. In this study, we investigated the effects of pulse repetition frequency (PRF) on microtripsy thrombolysis. Microtripsy thrombolysis treatments using different PRFs (5, 50, and 100 Hz) and doses (20, 50, and 100 pulses) were performed on blood clots in an in vitro vessel flow model. To quantitatively evaluate the microtripsy thrombolysis effect, the location of focal cavitation, the incident rate of pre-focal cavitation on the vessel wall, the size and location of the resulting flow channel, and the generated clot debris particles were measured. The results demonstrated that focal cavitation was always well confined in the vessel lumen without contacting the vessel wall for all PRFs. Pre-focal cavitation on the front vessel wall was never observed at 5Hz PRF, but occasionally observed at PRFs of 50 Hz (1.2%) and 100 Hz (5.4%). However, the observed pre-focal cavitation was weak and did not significantly affect the focal cavitation. Results further demonstrated that, although the extent of clot fractionation per pulse was the highest at 5 Hz PRF at the beginning of treatment (<20 pulses), 100 Hz PRF generated the largest flow channels with a much shorter treatment time. Finally, results showed fewer large debris particles were generated at a higher PRF. Overall, the results of this study suggest that a higher PRF (50 or 100 Hz) may be a better choice for microtripsy thrombolysis to use clinically due to the larger resulting flow channel, shorter treatment time, and smaller debris particles.

Non-invasive thrombolysis using histotripsy beyond the “intrinsic” threshold (microtripsy)

Histotripsy has been demonstrated as a non-invasive, drug-free, image-guided thrombolysis method using cavitation alone. Microtripsy is a new histotripsy approach, where cavitation is generated using 1-cycle ultrasound pulses with negative pressure exceeding a threshold intrinsic to the medium. We hypothesize that, using microtripsy, cavitation can be generated entirely within the vessel lumen, without contacting the vessel wall. Microtripsy was used to create a flow channel through a clot in a vessel-mimicking phantom by scanning the therapy focus through the clot at a pre-set interval. Different scan intervals, doses, and strategies (single focus vs. electrical-steered multi-foci) were tested in both unretracted and retracted clots. The flow channel size, thrombolysis rate, and clot debris particle sizes were measured. A cavitation cloud and flow channel was successfully generated and completely confined within the 6.5 mm-diameter vessel lumen through unretracted and retracted clots. A 1-4 mm channel was created in unretracted clots, at thrombolysis rate of 3.3 min/cm. Using an electrical-steered multi-foci method, a 1–2.5 mm channel was generated through retracted clots, at thrombolysis rate of 5.5 min/cm. The debris particles generated were no greater than 150 μm. The results show the potential of microtripsy for precise and effective clot recanalization, minimizing risks of vessel damage and embolism.

Noninvasive thrombolysis using histotripsy beyond the intrinsic threshold (microtripsy).

Histotripsy has been investigated as a noninvasive, drug-free, image-guided thrombolysis method that fractionates blood clots using acoustic cavitation alone. In previous histotripsy-mediated thrombolysis studies, cavitation clouds were generated using multi-cycle pulses and tended to form on vessel wall. To avoid potential cavitational damage to the vessel wall, a new histotripsy approach, termed microtripsy, has been recently discovered in which cavitation is generated via an intrinsic-threshold mechanism using single-cycle pulses. We hypothesize that microtripsy can generate and confine cavitation in vessel lumen without contacting the vessel wall, which results in recanalization within the clot and potentially eliminating vessel damage. To test our hypothesis, microtripsy was investigated for clot recanalization in an in vitro flow model. Clots were formed inside a vessel phantom (6.5 mm inner diameter) in line with a flow system. Microtripsy was applied by a 1-MHz transducer at a pulse repetition frequency of 50 Hz with a peak negative pressure (P-) of 30 MPa or 36 MPa. To create a flow channel through a clot, the cavitation focus was scanned through the clot at an interval of 0.3 or 0.7 mm. The treated clots were 3-D-scanned by a 20-MHz ultrasound probe to quantify the channels. Restored flow rates were measured and clot debris particles generated from the treatments were analyzed. In all treatments, the cavitation cloud was consistently generated in the center of the vessel lumen without contacting the vessel wall. After each treatment, a flow channel was successfully generated through and completely confined inside the clot. The channels had a diameter up to 60% of the vessel diameter, with restored flow up to 500 mL/min. The debris particles were small with more than 99.9% <10 μm and the largest at 153 um. Each clot (2 cm long) was recanalized within 7 min. The size of the flow channels increased by using higher P- and was significantly larger by using the 0.3 mm scan interval than those using 0.7 mm. The results in this study show the potential of this new microtripsy thrombolysis method for fast, precise, and effective clot recanalization, minimizing risks of vessel damage and embolism.

Dependence of pulsed focused ultrasound induced thrombolysis on duty cycle and cavitation bubble size distribution

In this study, we investigated the relationship between the efficiency of pulsed, focused ultrasound (FUS)-induced thrombolysis, the duty cycle (2.3%, 9%, and 18%) and the size distribution of cavitation bubbles. The efficiency of thrombolysis was evaluated through the degree of mechanical fragmentation, namely the number, mass, and size of clot debris particles. First, we found that the total number and mass of clot debris particles were highest when a duty cycle of 9% was used and that the mean diameter of clot debris particles was smallest. Second, we found that the size distribution of cavitation bubbles was mainly centered around the linear resonance radius (2.5μm) of the emission frequency (1.2MHz) of the FUS transducer when a 9% duty cycle was used, while the majority of cavitation bubbles became smaller or larger than the linear resonance radius when a 2.3% or 18% duty cycle was used. In addition, the inertial cavitation dose from the treatment performed at 9% duty cycle was much higher than the dose obtained with the other two duty cycles. The data presented here suggest that there is an optimal duty cycle at which the thrombolysis efficiency and cavitation activity are strongest. They further indicate that using a pulsed FUS may help control the size distribution of cavitation nuclei within an active size range, which we found to be near the linear resonance radius of the emission frequency of the FUS transducer.

O-033 Aspiration Efficacy of Suction Catheter in the Management of Distal Embolization During Interventional Treatment of Acute Ischemic Stroke

IntroductionImproved recanalization rate and immediate flow restoration have been achieved by the latest clot retrieval (thrombectomy) systems in the acute ischemic stroke treatment. However, clot debris generated during mechanical thrombectomy...

In VitroCharacterization of a Multifunctional Staphylokinase Variant with Reduced Reocclusion, Produced from Salt InducibleE. coliGJ1158

The thrombolytic therapy with clinically approved drugs often ensues with recurrent thrombosis caused by thrombin-induced platelet aggregation from the clot debris. In order to minimize these problems, a staphylokinase (SAK)-based bacterial friendly multifunctional recombinant protein SRH (staphylokinase (SAK) linked with tripeptide RGD and dodecapeptide Hirulog (SRH)) was constructed to have Hirulog as an antithrombin agent and RGD (Arg-Gly-Asp) as an antiplatelet agent in the present study. This multifunctional fusion protein SRH was expressed in osmotically inducible E. coli GJ1158 as soluble form and purified with a yield of 0.27 g/L and functionally characterized in vitro. SRH retained the fibrinolytic activity and plasminogen activation rate comparable to the parental counterpart SAK. The antithrombin activity of SRH was significantly higher than SAK. The platelet rich clot lysis assay indicated that SRH had enhanced platelet binding activity and T 50% and C50 of SRH were significantly lower than that of SAK. Furthermore, SRH inhibited the ADP-induced platelet aggregation in dose-dependent manner while SAK had no significant effect on platelet aggregation. Thus, the current study suggests that the SAK variant produced from osmotically inducible GJ1158 is more potent thrombolytic agent with antithrombin and antiplatelet aggregation activities for reduction of reocclusion in thrombolytic therapy.

Thrombose veineuse profonde aiguë: Place de la thrombolyse

Acute Deep Venous Thrombosis (DVT) therapies have been judged primarily on their ability to prevent symptomatic pulmonary embolism, early thrombus progression, and recurrent VTE. The cornerstones of current management of DVT, supported by the 2008 American College of Chest Physicians (ACCP) guidelines, are the routine use of anticoagulant therapy, graduated elastic compression stockings, and early ambulation. For selected appropriate patients with extensive acute proximal DVT, while the French recommendations (Afssaps 2009) still consider thrombolysis not indicated, ACCP guidelines now suggest in-situ thrombolysis in addition to anticoagulation to reduce the risk of subsequent postthrombotic syndrome (PTS) and recurrent DVT (Grade 2 B recommendation). Contemporary invasive endovascular treatments, called pharmacomechanical treatment, mitigate the drawbacks (major bleeding) historically associated with systemic thrombolytic approaches, by means of intra-thrombus delivery of drugs, followed by mechanical dispersion to accelerate lysis and then aspiration of remaining drug and clot debris. The proof of concept for the "open vein" hypothesis - that a strategy of early thrombus removal can reduce the incidence of PTS long term - comes incrementally and randomized trials (ATTRACT trial with a 2016 target completion date) are currently under way and might lead to a shift of the paradigms of the management of acute DVT focused on active thrombus removal.

Combined Low-Frequency Ultrasound and Streptokinase Intravascular Destruction of Arterial Thrombi In Vivo

To prevent a distal embolization in the course of ultrasound (US) angioplasty, we combined US thrombus disruption in peripheral artery in vivo with simultaneous administration of streptokinase (SK). Acute thrombosis was induced in the femoral arteries of 23 dogs. Two hours after thrombus formation, thrombus destruction was performed using US (36 kHz) and by a combined US+SK (75,000 U/kg) administration. The results showed that thrombi were disrupted completely by 1.5 ± 0.5 min US. A combined US+SK action resulted in activation of fibrinolysis, as indicated by the increase in the content of fibrinogen and fibrin degradation products and D-dimers by a factor of 1.5–2.0 after 120 min from start of treatment compared with the SK lysis. The duration of clot destruction did not change; the distal embolization was not indicated; platelet aggregation activity dropped after thrombus destruction. In summary, intravascular thrombus destruction by a combined US and SK action in vivo is accompanied by enhancing the enzymatic fibrinolysis and lowering the platelet aggregation activity that assists in preventing the distal embolization of the resulting clot debris.

Ischemic Strokes After Cardiac Catheterization

Stroke is an important complication after cardiac catheterization procedures, resulting in death and disability for thousands of patients each year. Common risk factors include advanced age, vascular comorbidities, and more complicated and invasive procedures. Several lines of evidence suggest that these strokes are embolic, from either dislodgement of a clot or atheromatous debris off the aortic arch or from thrombus formation on the tip of a guide catheter. These strokes are likely amenable to thrombolysis, although the current literature regarding the use of thrombolysis in this setting is limited to case reports and series. Whether thrombolysis is safe and efficacious remains to be determined, but the existing evidence seems favorable for individual circumstances.

Editorial Comment—Plaque Pathology and Patient Selection for Carotid Endarterectomy

Experienced carotid surgeons know that when performing a carotid endarterectomy, it is important to avoid excessive manipulation of the carotid bifurcation during dissection, especially when the patient has had recent symptoms from an “active” plaque. This study by Fisher et al comparing the pathology of carotid plaques obtained from the asymptomatic carotid endarterectomy trial, ACAS, to those taken from the symptomatic trial, NASCET, helps explain the danger. Plaques resected from symptomatic patients are more frequently ulcerated and have attached thrombus compared with asymptomatic plaques and, therefore, are at greater risk to embolize clot and atherosclerotic debris into the cerebral circulation during surgical mobilization. During carotid endarterectomy, the tube-like carotid plaque is cut length-wise and not infrequently torn, preventing a highly accurate gross or microscopic assessment. This might …

Ultrasound fibrin clot destruction in vitro in the presence of fibrinolytic agent

Ultrasound fibrin clot destruction was investigated in vitro using electron microscopy and by monitoring the changes in the light transmission of clot debris suspension. It has been established that in the course of a combined action of ultrasound and fibrinolytic agent at high ultrasound intensities and short sonification periods, fibrin clot is disrupted mainly due to sonomechanical treatment, while fermentative lysis takes place in parallel and at a significantly lower rate. However, the streptokinase action prevails after ultrasound switching off and results in the prevention of clot debris conglomeration.

Percutaneous mitral valvuloplasty in an adult patient with calcitic rheumatic mitral stenosis

A 75 year old man with long-standing rheumatic mitral stenosis who refused surgical intervention was treated with percutaneous balloon valvuloplasty. Prevalvuloplasty evaluation revealed a heavily calcified mitral valve, a mean transvalvular gradient of 18 mm Hg, a Fick cardiac index of 1.7 liters/min per m2, a mitral valve area of 0.6 cm2 and 1 + mitral regurgitation. After transeptal catheterization and balloon dilation of the interatrial septum with an 8 mm angioplasty balloon, a 25 mm valvuloplasty balloon was advanced over a guide wire across the interatrial septum and positioned across the mitral anulus. Subsequent balloon inflation at 3 atm pressure resulted in a reduction of the mean mitral valve gradient to 12 mm Hg, an increase in cardiac index to 2.5 liters/min per m2, an increase in mitral valve area in 1.4 cm2 and an increase in mitral regurgitation from 1 + to 2 +. Valvuloplasty was well tolerated without embolization of clot or valvular debris, and resulted in marked clinical improvement with decreased dyspnea and increased exercise tolerance. Repeat catheterization 2 months after valvuloplasty showed further resolution of pulmonary hypertension and no evidence of valvular restenosis or worsening mitral regurgitation, but detected a small atrial septal defect with a pulmonary to systemic blood flow ratio of 1.8. It is concluded that percutaneous valvuloplasty is possible in the adult patient with calcific rheumatic mitral stenosis, and may result in a significant improvement in valvular function without producing life-threatening complications.