Clinical trial of percutaneous peripheral ultrasound angioplasty

Sonothrombolysis: State-of-the-Art and Potential Applications in Children

In recent years, advances in ultrasound therapeutics have been implemented into treatment algorithms for the adult population; however, the use of therapeutic ultrasound in the pediatric population still needs to be further elucidated. In order to better characterize the utilization and practicality of sonothrombolysis in the juvenile population, the authors conducted a literature review of current pediatric research in therapeutic ultrasound. The PubMed database was used to search for all clinical and preclinical studies detailing the use and applications of sonothrombolysis, with a focus on the pediatric population. As illustrated by various review articles, case studies, and original research, sonothrombolysis demonstrates efficacy and safety in clot dissolution in vitro and in animal studies, particularly when combined with microbubbles, with potential applications in conditions such as deep venous thrombosis, peripheral vascular disease, ischemic stroke, myocardial infarction, and pulmonary embolism. Although there is limited literature on the use of therapeutic ultrasound in children, mainly due to the lower prevalence of thrombotic events, sonothrombolysis shows potential as a noninvasive thrombolytic treatment. However, more pediatric sonothrombolysis research needs to be conducted to quantify the safety and ethical considerations specific to this vulnerable population.

Focused Ultrasound, an Emerging Tool for Atherosclerosis Treatment: A Comprehensive Review

Focused ultrasound (FUS) has emerged as a promising noninvasive therapeutic modality for treating atherosclerotic arterial disease. High-intensity focused ultrasound (HIFU), a noninvasive and precise modality that generates high temperatures at specific target sites within tissues, has shown promising results in reducing plaque burden and improving vascular function. While low-intensity focused ultrasound (LIFU) operates at lower energy levels, promoting mild hyperthermia and stimulating tissue repair processes. This review article provides an overview of the current state of HIFU and LIFU in treating atherosclerosis. It focuses primarily on the therapeutic potential of HIFU due to its higher penetration and ability to achieve atheroma disruption. The review summarizes findings from animal models and human trials, covering the effects of FUS on arterial plaque and arterial wall thrombolysis in carotid, coronary and peripheral arteries. This review also highlights the potential benefits of focused ultrasound, including its noninvasiveness, precise targeting, and real-time monitoring capabilities, making it an attractive approach for the treatment of atherosclerosis and emphasizes the need for further investigations to optimize FUS parameters and advance its clinical application in managing atherosclerotic arterial disease.

Kinetics of fibrin clots destruction under ultrasonic cavitation

We studied the kinetic features of fibrin clot destruction in vitro under the action of ultrasonic cavitation generated by low-frequency (36 kHz) ultrasound (US) with the intensity I0  of 4.4–51.2 W/cm2, using a flexible waveguide concentrator. It was established that the rate of US destruction of clots immersed in saline at the initial stage of the process is proportional to I0 in the range of 12–51 W/cm2, corresponds to first-order kinetics, and is determined by the erosive processes without the formation of D-dimers and other fibrinolysis products at a minimum contribution of sonochemical reactions. The clot destruction rate is maximum at the initial time moment and decreases with increasing the US exposure duration (by 35 % in 1 min and by 72 % by the end of the second minute at I0 = 51.2 W/cm2). It was shown that in order to increase the completeness of clot destruction at a minimum administered US dose, it is advisable to minimize the US exposure time when using the highest values of the US intensity limited by the level of safe cavitation exposure to the vascular wall, hemostasis, and blood cells.

A narrative review on the application of high-intensity focused ultrasound for the treatment of occlusive and thrombotic arterial disease

Objectives

High-intensity focused ultrasound (HIFU) is a noninvasive therapeutic modality with a variety of applications. It is approved for the treatment of essential tremors, ablation of prostate, hepatic, breast, and uterine tumors. Although not approved for use in the treatment of atherosclerotic arterial disease, there is a growing body of evidence investigating applications of HIFU. Currently, percutaneous endovascular techniques are predominant for the treatment of arterial pathology; however, there are no endovascular techniques of HIFU available. This study aims to review the state of current evidence for the application of HIFU in atherosclerotic arterial disease.

Methods

All English-language articles evaluating the effect of HIFU on arterial occlusive and thrombotic disease until 2021 were reviewed. Both preclinical and human clinical studies were included. Study parameters such as animal or clinical model and outcomes were reviewed. In addition, details pertaining to settings on the HIFU device used were also reviewed.

Results

In preclinical models, atherosclerotic plaque progression was inhibited by HIFU, through decreases in oxidized low-density lipoprotein cholesterol and increases in macrophage apoptosis. Additionally, HIFU promotes angiogenesis in hindlimb ischemic models by the upregulation of angiogenic and antiapoptotic factors, with increased angiogenesis at higher line densities of HIFU. HIFU also promotes thrombolysis and conversely induces platelet activation at low frequencies and higher intensities. Various clinical studies have attempted to translate some of these properties and demonstrated positive clinical outcomes for arterial recanalization after thrombotic stroke, decreased atherosclerotic plaque burden in carotid arteries, increase in tissue perfusion and a decrease in diameter stenosis in patients with atherosclerotic arterial disease.

Conclusions

In current preclinical and clinical data, the safety and efficacy of HIFU shows great promise in the treatment of atherosclerotic arterial disease. Future focused studies are warranted to guide the refinement of HIFU settings for more widespread adoption of this technology.

Dependence of the Rate and Completeness of Fibrin Clot Destruction on the Acoustic Dose and Ultrasound Intensity

The kinetics of fibrin clot destruction under catheter-delivered 32- to 45-kHz ultrasound (US) has been studied at 36°C-38°C in isotonic saline solution. A pseudo-first-order rate constant increased linearly from 0.06/min to 0.57/min with increasing US intensity I₀ from 21.6 to 51.2 W/cm². At I₀ = 4.4 and 11.4 W/cm², the degree of clot destruction did not exceed 11%-15% regardless of the time of US exposure. Starting from I₀ = 21.6 W/cm², the maximum achievable level of clot destruction increased linearly with US intensity, reaching 68% at I₀ = 51.2 W/cm² after 3 min of US exposure. Thus, US intensity is a key parameter determining the maximum achievable level of clot destruction. However, an increase in US intensity above 30 W/cm² is limited by the intensified negative sonochemical effect on the enzymatic system of hemostasis caused by an increase in inertial cavitation. The best effect can be achieved with ultrasound of a sufficiently high intensity that ensures a large contribution of stable cavitation, generating microstreaming flows, and a minimum contribution of inertial cavitation, generating microjets and shock waves.

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.

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.

Blood clot disruption in vitro using shockwaves delivered by an extracorporeal generator after pre-exposure to lytic agent

The standard methods for recanalyzing thrombosed vessels are vascular stenting or administration of thrombolytic drugs. However, these methods suffer from uncertain success rate and side-effects. Therefore, minimally-invasive ultrasound methods have been investigated. In this article, we propose to use shockwaves after pre-exposure to fibrinolytic agent for disrupting thrombus. Shockwaves were delivered by an extracorporeal piezocomposite generator (120 mm in diameter, focused at 97 mm, pulse length = 1.4 micros). In vitro blood clots, made from human blood, were placed at the focal point of the generator. The clots were exposed to shockwaves either with or without prior immersion in a solution of streptokinase. The percentage of lysed clot was determined by weighing the clot before and after treatment. The proportion of lysed clot increased with the pressure at the focus and with the number of shocks. A mean clot reduction of 91% was obtained for 42 MPa in 4-min treatment duration only, without using streptokinase. For a treatment of 2 min at 29 MPa, the clot reduction increased significantly (p < 0.01) from 47% without streptokinase to 82% when streptokinase was used prior to shockwaves. These results also showed no significant damage to streptokinase due to exposure to shockwaves. This study suggests that extracorporeal shockwaves combined with streptokinase is a promising pharmaco-mechanical method for treating occlusive thrombus, and should be confirmed by in vivo trials. Additional studies must also be conducted with other fibrinolytic agents, whose abilities to penetrate clots are different.

Effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold

The study was to investigate thrombolysis in vivo with ultrasound, and to discuss effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold, under different ultrasound intensity and exposure time. The structure of erythrocyte in thrombus was evaluated under light microscope. The relationship between the structure of erythrocyte in thrombus and ultrasound intensity and exposure time was obtained. The results showed that ultrasound eliminated the thrombus. According to the change of the structure of erythrocyte in thrombus and ultrasound intensity and exposure time, the effects of thrombolysis with ultrasound could be divided into three kinds of areas: the A, B, C area. The area A was the safe area, the area B was the relatively safe area, and the area C was the irreversible damage area. The study suggested that ultrasound intensity and exposure time had significant impact on the structure of erythrocyte. Too much ultrasound intensity or too long exposure time could cause erythrocytes irreversible damaged. It could accelerate thrombolysis and shorten the exposure time that the ultrasound intensity was little bit increased. This study of effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold were important for practical applications.

Ultrasound angioplasty: an update review

The use of therapeutic ultrasound to treat atherosclerosis and thrombosis has been appreciated for decades. However, it was only the explosive growth of angioplasty in the 1980s that brought real momentum to the development of therapeutic catheter ultrasound. The idea behind this technique was that ultrasound, by its bioselectivity, might provide a solution to some of the shortcomings of balloon angioplasty. In the late 1980s, two groups, headed by Rosenschein and Siegel, began serious work to address the technical challenge of developing a catheter that would provide efficient external ultrasound energy to the lesion. Current catheters from both groups consist of a solid metal probe which is connected to a piezoelectric transducer. In the distal segment, the wire is specially designed to increase energy delivery. Initial in vitro studies concentrated on understanding the mechanisms of ablation and the effects of mechanical vibration, thermal phenomena and cavitation. Clinical studies of ultrasound ablation were initially performed in peripheral vessels. Later, after safety had been assured, clinical studies involving the coronary arteries began to take place. In this article we aim to update the reader about the experimental and limited clinical experience in this novel technique for treating different kinds of arterial obstruction.

Ultrasound and thrombolysis

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

Cavitational mechanisms in ultrasound-accelerated thrombolysis at 1 MHz

Inertial cavitation is hypothesized to be a mechanism by which ultrasound (US) accelerates the dissolution of human blood clots when the clot is exposed to a thrombolytic agent such as tissue plasminogen activator (t-PA). To test this hypothesis, radiolabeled fibrin clots were exposed or sham-exposed in vitro to 1 MHz c.w. US in a rotating sample holder immersed in a water-filled tank at 37 degrees C. Percent clot dissolution after 60 min of US exposure was assessed by removing the samples, centrifuging, and measuring the radioactivity of the supernatant fluid relative to the pelletized material. To suppress acoustic cavitation, the exposure tank was contained within a hyperbaric chamber capable of pneumatic pressurization to 10 atmospheres (gauge). Various combinations of static pressure (0, 2, 5, and 7.5 atm gauge), US (0 or 4 W/cm(2) SATA), and t-PA (0 or 10 microg/mL) were employed, showing statistically significant reductions in thrombolytic activity as static pressure increased. To gain further insight, an active cavitation detection scheme was employed in which 1-micros duration tonebursts of 20-MHz US (< 1 kPa peak negative pressure, 1 Hz PRF) were used to interrogate clots subjected to US and static pressure. Results of this cavitation detection scheme showed that scattering from within the clot and broadband acoustic emissions that were both present during insonification were significantly reduced with application of static pressure. However, only about half of the acceleration of thrombolysis due to US could be removed by static pressure, suggesting the possibility of other mechanisms in addition to inertial cavitation.

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

BACKGROUND

We have shown previously that 40-kHz ultrasound (US) at low intensity accelerates fibrinolysis in vitro with little heating and good tissue penetration. These studies have now been extended to examine the effects of 40-kHz US on thrombolysis and tissue perfusion in a rabbit model.

METHODS AND RESULTS

Treatment was administered with either US alone at 0.75 W/cm(2), streptokinase alone, or the combination of US and streptokinase. US or streptokinase resulted in minimal thrombolysis, but reperfusion was nearly complete with the combination after 120 minutes. US also reversed the ischemia in nonperfused muscle in the absence of arterial flow. Tissue perfusion decreased after thrombosis from 13. 7+/-0.2 to 6.6+/-0.8 U and then declined further to 4.5+/-0.4 U after 240 minutes. US improved perfusion to 10.6+/-0.5 and 12.1+/-0. 5 U after 30 and 60 minutes, respectively. This effect was reversible and declined to pretreatment values after US was discontinued. Similarly, tissue pH declined from normal to 7.05+/-0. 02 after thrombosis, but US improved pH to 7.34+/-0.03 after 60 minutes. US-induced improvement in tissue perfusion and pH also occurred after femoral artery ligation, indicating that thrombolysis did not cause these effects.

CONCLUSIONS

40-kHz US at low intensity markedly accelerates fibrinolysis and also improves tissue perfusion and reverses acidosis, effects that would be beneficial in treatment of acute thrombosis.

Platelet aggregation and change in intracellular Ca(2+) induced by low frequency ultrasound in vitro

Treatment of platelet-rich plasma and washed platelets with low frequency ultrasound (US, 22 kHz) at intensity range of 1.0-8.8 W/cm(2) resulted in intensity- and time-dependent platelet aggregation. The effect was absent in calcium-free medium and was initiated by adding supernatant from sonicated suspension (16 W/cm(2), 2 min) to non-treated platelets. A marked decrease in the rate of US-induced aggregation was observed in the presence of specific inhibitors of platelet activation dipyridamole, pentoxifillin, aspirin and verapamil. Concentration of intracellular calcium in washed platelets evaluated with fluorescent probe quin-2 acetoxymethyl ester (quin-2) increased upon sonication in both the calcium containing and calcium free media. It is suggested that US increase of [Ca(2+)](i) is involved in platelet aggregation induced by low frequency US.

Enhancement of fibrinolysis with 40-kHz ultrasound

BACKGROUND

Ultrasound at frequencies of 0.5 to 1 MHz and intensities of > or =0.5 W/cm2 accelerates enzymatic fibrinolysis in vitro and in some animal models, but unacceptable tissue heating can occur, and limited penetration would restrict application to superficial vessels. Tissue heating is less and penetration better at lower frequencies, but little information is available regarding the effect of lower-frequency ultrasound on enzymatic fibrinolysis. We therefore examined the effect of 40-kHz ultrasound on fibrinolysis, tissue penetration, and heating.

METHODS AND RESULTS

125I-fibrin-radiolabeled plasma clots in thin-walled tubes were overlaid with plasma containing tissue plasminogen activator (tPA) and exposed to ultrasound. Enzymatic fibrinolysis was measured as solubilization of radiolabel. Tissue attenuation and heating were examined in samples of porcine rib cage. Fibrinolysis was increased significantly in the presence of 40-kHz ultrasound at 0.25 W/cm2, reaching 39+/-7% and 93+/-11% at 60 minutes and 120 minutes, compared with 13+/-8% and 37+/-4% in the absence of ultrasound (P<0.0001). The acceleration of fibrinolysis increased at higher intensities. Attenuation of the ultrasound field was only 1.7+/-0.5 dB/cm through the intercostal space and 3.4+/-0.9 dB/cm through rib. Temperature increments in rib were <1 C/(W/cm2).

CONCLUSIONS

These findings indicate that 40-kHz ultrasound significantly accelerates enzymatic fibrinolysis at intensities of > or =0.25 W/cm2 with excellent tissue penetration and minimal heating. Externally applied 40-kHz ultrasound at low intensities is a potentially useful therapeutic adjunct to enzymatic fibrinolysis with sufficient tissue penetration for both peripheral vascular and coronary applications.

Ultrasound inhibits the adhesion and migration of smooth muscle cells in vitro

This study investigated in vitro the effect of therapeutic ultrasound (ULS) on smooth muscle cell (SMC) function as adhesion, migration and proliferation. Experiments were conducted on aortic SMC in culture. The LD50 was established (1.5 W for 15 s at a frequency of 20 kHz) and used as standard dose in all experiments. Control SMC and viable sonicated SMC were compared in each experiment. Migratory capacity decreased 2.4-fold after sonication and stayed reduced for up to 24 h. Adhesion capacity decreased 5.5-fold after ULS. The proliferative capacity was similar to that of nonsonicated SMC. Sonication was accompanied by the disorganization of alpha-SM actin fibers and diminished distribution of vinculin; tyrosinated alpha tubulin and vimentin appeared unaffected. These changes might be responsible for the observed inhibition of SMC adhesion and migration. Sonicated cells exhibited less lamellipodia, membrane collapse and bleb formation. The signal transduction cascade, which involves activation of the phospholipase-C pathway, was unaffected by ULS.

[Ultrasound coronary angioplasty: state of the art and new clinical aspects]

Therapeutic ultrasound was shown to ablate thrombi and to disrupt atherosclerotic plaques in vitro and recently to recanalize occluded coronary arteries in acute myocardial infarction (AMI). The goal of this article is to update collective experience and to weigh the promising and unresolved aspects of this newly developed technology and its clinical results. As therapeutic ultrasound was for long known a synonym for lithotripsy of calculi diseases, it lastly received high attention as a catheter-based ultrasound method to ablate thrombi and disrupt atherosclerotic plaques in interventional cardiology (Figure 1). The effect of therapeutic ultrasound to ablate selectively pathological tissue depends on its bioselectivity for elastic fibers: After ultrasound sonication, healthy tissue-rich in elastin and collagen-including arterial wall remains intact whereas thrombus and plaque with their minimal elastic support are found to be highly susceptible to ablation. Our catheter for coronary ultrasound thrombolysis (Figure 2) consists of a solid metal probe and is connected to a piezo-electric transducer at its proximal end. The distal part ends in a three-wire flexible segment with a 1.6 mm tip ball to guarantee maximal wire flexibility and optimal transmission of ultrasound energy. The initial in vitro studies resulted in a fundamental understanding of the destructive effect of ultrasound on tissue based on 4 factors: mechanical vibration, thermal effects, microcurrents, and cavitation. The first studies on human peripheral vessels were published in 1991 being performed during femoral bypass surgery on occluded and partially obstructed arteries. The procedure was performed without perforation, no adverse side effects emerged, restenosis rate was 20%. The clinical application of coronary ultrasound angioplasty was initiated in 1991; Siegel published his data on 44 patients. In his study, 30 patients with chronic atherosclerotic occlusive lesions and 14 with unstable or stable angina or AMI were treated by ultrasound angioplasty. Residual stenosis after ultrasound treatment was 71%, after balloon dilation reduced to 34%. In the 6-month follow-up angiograms showed no major adverse effect or restenosis. Our experience with coronary ultrasound thrombolysis (CUT) is based on the analysis of 33 patients' data in the feasibility (Table 1) plus multicenter phase of the ACUTE trial (Analysis of Coronary Ultrasound Thrombolysis Endpoints) (Figure 3). Our patients were exclusively treated for AMI by ultrasound angioplasty and afterwards by PTCA if required (Figure 4). The average final percent stenosis was 20% (Figure 5). The main efficacy parameters, device success and angiographic success rates were 100%, clinical success rate was 91.7% (Figure 6 and Table 2). The adverse clinical events of CUT are limited--at least in our studies--to reocclusion of infarct-related artery and ischemia and could be reversed by additional PTCA. No adverse clinical side effects were observed during sonication of the coronary tree. Final angiography revealed residual stenosis of 20% without morphological signs. These excellent results suggest that bioselectivity of ultrasound together with the developed skills of the catheter system induces rapid and selective thrombolysis with no need to cross the target lesion before sonication. But what is the better solution for thrombosis and which for plaque disruption? The development of transluminal balloon catheter really modified therapeutic approach to obstructive coronary and peripheral arterial disease but it is still accompanied by a high rate of abrupt closure, AMI and death. Although the use of intravenous thrombolytic agents is well established in the treatment of AMI and these agents are widely used, a large patient collective remains (up to 33% and more) in whom their use is inadvisable due to recent stroke, surgery, trauma or other contraindications. (ABSTRACT TRUNCATED)

Dissolution of thrombotic arterial occlusion by high intensity, low frequency ultrasound and dodecafluoropentane emulsion: an in vitro and in vivo study

OBJECTIVES

We examined the effectiveness of the microbubbles of an echo contrast agent, dodecafluoropentane (DDFP) emulsion, to enhance low frequency ultrasound clot disruption in vitro and in vivo.

BACKGROUND

Ultrasound is reported to facilitate clot dissolution, and microbubbles could theoretically enhance ultrasound clot dissolution by augmenting cavitational effects.

METHODS

IN VITRO STUDIES

The disruption rate of fresh human clots by ultrasound (24 kHz, 2.9 W/cm2) was examined in saline and DDFP emulsion. In vivo studies: Using a rabbit iliofemoral thrombotic occlusion model, recanalization rate and histopathologic findings were compared among groups treated with DDFP emulsion alone, transcutaneous ultrasound (20 kHz, 1.5 W/cm2) alone and with DDFP emulsion and ultrasound combined.

RESULTS

The ultrasound clot disruption rate was significantly (p < 0.01) increased, from 72 +/- 18% (mean +/- SD) in saline to 98 +/- 4% in DDFP emulsion in 3 min in vitro. No vessel was recanalized by DDFP emulsion alone (0%), and only a single artery was patent after ultrasound treatment alone (9%). In contrast, 82% of iliofemoral arteries were angiographically recanalized after ultrasound treatment with DDFP emulsion. Histologically, the patent arteries had only minimal focal mural thrombus, with no evidence of vessel wall damage. However, substantial damage was observed in rabbit dermis and subcutaneous tissue.

CONCLUSIONS

1) DDFP emulsion, an echo contrast agent, significantly enhances the clot-disrupting effect of low frequency ultrasound in vitro and in an in vivo rabbit iliofemoral occlusion model. 2) This simple combination therapy has potential for clinical application in patients with thrombotic arterial occlusions.

Ultrasonic coronary angioplasty during coronary artery bypass grafting

This preliminary study in 20 patients demonstrated that ultrasonic coronary angioplasty in the setting of bypass grafting is feasible, safe, and able to recanalize atherosclerotic vessels. Shorter monorail probes were superior to longer probes without guidewires in terms of success of vessel recanalization; >95% of particle debris was <25 microm in size.

High intensity, low frequency catheter-delivered ultrasound dissolution of occlusive coronary artery thrombi: an in vitro and in vivo study

OBJECTIVES

This study assessed the efficacy of a new high intensity, low frequency therapeutic coronary ultrasound catheter for thrombus dissolution in vitro and in vivo in canine coronary arteries.

BACKGROUND

Therapeutic ultrasound has been shown to dissolve thrombi in vitro and in peripheral arteries in vivo. There have been no previous studies on in vivo coronary thrombus dissolution by ultrasound.

METHODS

In vitro, we exposed 1- to 4-h old human blood clots for 3 min to pulsed-wave ultrasound. Clot dissolution under various conditions was evaluated. In vivo occlusive coronary thrombi were induced in 18 dogs.

RESULTS

In vitro irrigation alone (10 ml/min of normal saline solution) and ultrasound alone each contributed to a reduction of clot weight by 47.1 +/- 11.4 mg and 84.6 +/- 25.6 mg, respectively, after 3 min (p < 0.001). Ultrasound plus irrigation resulted in a reduction of clot weight by 216.5 +/- 31.5 mg after 3 min (p < 0.001). The magnitude of clot dissolution was considerably amplified when ultrasound energy was combined with irrigation, probably because of cavitational effects. In vivo, in three dogs mechanical passage of the unactivated probe failed to recanalize the artery, and the arteries remained thrombotically occluded. After passage of the activated ultrasound probe, angiography revealed widely patent coronary arteries in 13 of 15 dogs and partial recanalization with filling defects indicative of residual thrombus in 2 of 15 dogs. Three of 15 coronary arteries were histologically free of residual thrombi. Mural thrombi extending to < or = 10% of the vessel circumference were seen in 10 of 15 dogs. Residual thrombi > or = 50% of the vessel circumference were found in two cases. There was no histologic evidence of ultrasound-mediated vessel damage.

CONCLUSIONS

Catheter-delivered therapeutic ultrasound effectively dissolves clots in vitro and in canine coronary arteries in vivo. Thus, therapeutic catheter-delivered ultrasound has the potential to serve as an adjunct or alternative treatment for thrombus-mediated coronary ischemic syndromes or myocardial infarction.

In vitro study of a radiofrequency guidewire aimed at recanalization of totally occluded peripheral arteries

A novel radiofrequency ablative system (40 msec-train pulses with twenty 200 msec pulses at the carrier frequency of 750 KHz and 1 Hz repetition rate) aimed at recanalizing totally occluded peripheral arteries was investigated by means of in vitro tissue ablation from human postmortem arterial wall samples. The samples were submitted to irradiation with a guidewire 150 cm long, maximum diameter of ceramic tip 0.033 inch positioned perpendicular to the tissue surface in saline, contrast medium or blood using varying generator power. Ablation efficacy was determined as the depth of vaporization per pulse delivered. Electrical current for the train duration was measured as voltage at the 1 ohm-resistor. In saline, the ablation efficacy increased from 8 to 65 microns/pulse with generator power increasing from 11 W to 27.5 W. There was no significant difference in the ablation efficacy between saline and blood. In contrast medium, the ablation efficacy was significantly lower. For the same generator power, the electrical current varied during the ablation procedure from 1.3 +/- 0.2 A at the beginning of the procedure to 1.1 +/- 0.2 A after the first pulses and to 2.0 A before artery wall perforation occurred. Neither tissue ablation nor current variations were observed when radiofrequency energy was emitted on calcified tissue. The diameter of craters was 0.89 +/- 0.1 mm (range: 0.85-0.96 mm). No major thermal injury such as carbonization or charring was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of therapeutic ultrasound in percutaneous coronary angioplasty. Experimental in vitro studies and initial clinical experience

BACKGROUND

Previous studies have shown the feasibility of peripheral arterial ultrasound angioplasty.

METHODS AND RESULTS

In this report, we describe the use of percutaneous therapeutic ultrasound for coronary angioplasty. In vitro, 11 postmortem, atherosclerotically occluded coronary arteries were obtained to assess catheter-delivered ultrasound for arterial recanalization as well as for assessment of the size of particulate debris. Clinically, coronary ultrasound angioplasty was performed in 19 patients (mean age, 56 years) to assess safety and feasibility for the treatment of obstructive coronary atherosclerosis. Three patients with unstable angina and 16 with exercise-induced myocardial ischemia were treated with a prototype 4.6F coronary catheter ultrasound ablation device with a 1.7-mm diameter ball tip. The ultrasound coronary catheter delivered ultrasound energy at 19.5 kHz, with a power output of 16 to 20 W at the transducer. Energy is delivered in a pulsed mode with a 50% duty cycle of 30 milliseconds. Patients were treated for a mean of 493 seconds (range, 130 to 890) with intracoronary ultrasound ablation. All lesions were treated with adjunctive balloon angioplasty. All 11 postmortem coronary occlusions were recanalized, and 99% of the particulates generated were < 10 microns in diameter. We found that after ultrasound, mean (+/- SD) coronary arterial stenosis fell from 80 +/- 12% to 60 +/- 18% (P < .001) and to 26 +/- 11% (P < .001) after adjunctive balloon angioplasty. Mean pressures required to achieve full balloon inflation were 2.7 atm (range, 1 to 5.5) with a median of 3.0-mm balloon size (2.5 to 3.5). No ultrasound-related complications were identified.

CONCLUSIONS

Intracoronary ultrasound plaque ablation appears to be safe. Our findings suggest that catheter-delivered high-intensity, low-frequency ultrasound may be useful for lesion debulking and enhancing arterial distensibility, allowing balloon dilation at relatively low pressures.