William C. Culp

Intracranial Clot Lysis With Intravenous Microbubbles and Transcranial Ultrasound in Swine

Background and Purpose— Destruction of microbubbles by transcutaneous low-frequency ultrasound (LFUS) has been used to lyse adjacent clot and recanalize acutely thrombosed vessels. LFUS with intraarterial microbubbles has been shown to lyse cerebral clot rapidly in pigs without thrombolytic drugs. We hypothesized that intravenous platelet-targeted microbubbles with LFUS may be a rapid noninvasive technique to recanalize thrombosed intracerebral vessels. Methods— After angiography, 0.5 cc of autogenous thrombus was injected into 1 ascending pharyngeal artery of a pig, occluding it and the rete mirabile. These vessels connect the carotid to the internal carotid and are the main cerebral blood supply. Saline control or intravenous decafluorobutane-sonicated dextrose albumin microbubbles tagged with a subtherapeutic quantity of glycoprotein 2b/3a receptor inhibitor eptifibatide (75 U/kg plus 12 cc of microbubbles administered over 21 minutes), or eptifibatide control, was given with transcutaneous temporal LFUS (1 MHz at 2.0 W/cm2) for 24 minutes. Angiography followed with scoring of declotting and flow. The same protocol was repeated on the contralateral side with the other test fluid so each animal received a saline control and either tagged microbubble or eptifibatide alone. Results— Fifteen pigs completed the protocol with a mean clot age of 4.6 hours. Using tagged microbubbles, 6 of 8 achieved success compared with 0 of 7 receiving eptifibatide alone (P=0.007) and 1 of 15 receiving saline alone (P=0.02). Conclusions— Intravenous platelet-targeted microbubbles combined with transcranial LFUS can rapidly open acute intracranial thrombotic occlusions. Further development for ischemic stroke therapy is justified.

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 &mgr;m MB+US (n=8); and (6) tagged albumin 3 &mgr;m 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 &mgr;m 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 &mgr;m MB+US (0.7%±0.9%; P=0.018), and tagged 3 &mgr;m 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.

Changes in Ultrasonographic Echogenicity and Visibility of Needles with Changes in Angles of Insonation

PURPOSE To objectively compare the echogenicity of several types of needles at clinically important angles of insonation. MATERIALS AND METHODS Four commercial needles (Echotip, Mini-Stick, Echo-Coat, Surflo) and a prototype dimpled needle were tested in a liver phantom at angles of insonation ranging from 90 degrees to 15 degrees. Photodensity measurement determined echogenicity levels in arbitrary echogenicity units (EU). RESULTS At 90 degrees angles of insonation all needles were easily seen (60-76 EU) and echogenic levels were similar (P =.264). All values decreased with angulation. From the 35 degrees to 15 degrees angles, the prototype and Echotip needles were superior (P <.05). At 15 degrees the values were 43 EU for the prototype needle, 40 EU for the Echotip needle, 9.0 EU for the Echo-Coat needle, and 5.0 EU for the Surflo needle. CONCLUSION With angulation, all needles drop in echogenicity, with prototype dimpled and Echotip best maintaining visibility at clinically important angles.

Microbubbles Improve Sonothrombolysis In Vitro and Decrease Hemorrhage In Vivo in a Rabbit Stroke Model

Introduction:Tissue plasminogen activator (tPA) is the thrombolytic standard of care for acute ischemic stroke, but intracerebral hemorrhage (ICH) remains a common and devastating complication. We investigated using ultrasound (US) and microbubble (MB) techniques to reduce required tPA doses and to decrease ICH. Materials and Methods:Fresh blood clots (3–5 hours) were exposed in vitro to tPA (0.02 or 0.1 mg/mL) plus pulsed 1 MHz US (0.1 W/cm2), with or without 1.12 × 108/mL MBs (Definity or albumin/dextrose MBs [adMB]). Clot mass loss was measured to quantify thrombolysis. New Zealand white rabbits (n = 120) received one 3- to 5-hour clot angiographically delivered into the internal carotid artery. All had transcutaneous pulsed 1 MHz US (0.8 W/cm2) for 60 minutes and intravenous tPA (0.1–0.9 mg/kg) with or without Definity MBs (0.16 mL/mg/kg). After killing the animals, the brains were removed for histology 24 hours later. Results:In vitro, MBs (Definity or adMB) increased US-induced clot loss significantly, with or without tPA (P < 0.0001). At 0 and 0.02 mg/mL, tPA clot loss was greater with adMBs compared with Definity (P ≤ 0.05). With MB, the tPA dose was reduced 5-fold with good efficacy. In vivo, both Definity MB and tPA groups had less infarct volume compared with controls at P < 0.0183 and P = 0.0003, respectively. Definity MB+tPA reduces infarct volume compared with controls (P < 0.0001), and ICH incidence outside of strokes was significantly lower (P = 0.005) compared with no MB. However, infarct volume in Definity MB versus tPA was not different at P = 0.19. Conclusion:Combining tPAand MB yielded effective loss of clot with very low dose or even no dose tPA, and infarct volumes and ICH were reduced in acute strokes in rabbits. The ability of MBs to reduce tPA requirements may lead to lower rates of hemorrhage in human stroke treatment.

Microbubble-augmented Ultrasound Declotting of Thrombosed Arteriovenous Dialysis Grafts in Dogs

PURPOSE Transcutaneous low-frequency ultrasound (LFUS) can effectively lyse clots in the presence of microbubbles. This study was designed to test the commercially available human albumin microspheres injectable suspension octafluoropropane formulation, Optison, to establish efficacy and assess US parameters of intensity and wave modes in a canine model of a thrombosed arteriovenous (dialysis) graft. MATERIALS AND METHODS Arteriovenous grafts in five dogs were cannulated, temporarily ligated, and thrombosed. Different declotting techniques were randomized to treat nine groups. Control groups involved direct saline (4.5 mL) clot injection in 0.5-1.0-mL increments. One group underwent peripheral intravenous microbubble injection (13.5 mL). Six groups underwent direct incremental clot injection of 4.5 mL of microspheres with LFUS for 30 minutes in 3-5-minute increments with use of various intensity settings in continuous-wave and pulsed-wave (PW) modes. At each increment, angiography was used to grade flow, declotting, and overall success. RESULTS One hundred four procedures showed success in all 24 high-intensity PW modes (1.2-2.0 W/cm(2)); only one of 20 control experiments was successful (P <.0001). Medium-intensity modes yielded intermediate success rates. Lowest-intensity direct-injection groups and intravenous and control groups ranked lower. Results at 30 minutes were better than at 15 minutes (P <.0001). CONCLUSIONS LFUS with direct injection of microbubbles is effective in lysing moderate-sized clots and recanalizing thrombosed arteriovenous grafts. It best succeeds at the higher range of intensity settings tested in PW mode. Further development is justified.

Microbubble Potentiated Ultrasound as a Method of Stroke Therapy in a Pig Model: Preliminary Findings

PURPOSE Low-frequency ultrasound (LFUS) with intraarterial or intravenous microbubbles can recanalize thrombosed dialysis grafts and arteries. A similar method for declotting intracranial arteries in an animal model has been developed. MATERIALS AND METHODS Swine underwent selective cerebral angiography, and 1 mL of 2-6 hour old clot was placed in one ascending pharyngeal artery and rete mirabile. This occluded the primary brain blood supply from the rete mirabile in the base of the skull. Human albumin octafluoropropane microbubbles were injected through the same catheter in 0.5-1.0-mL doses for a total of 4.5 mL in 21 minutes. Transcutaneous pulsed-wave 1-MHz ultrasound was administered through a temporal approach using 2.2 W/cm(2). Repeated angiography was performed through 24 minutes. Saline controls underwent an identical process on the opposite side. Declotting was graded on a scale of 0-4, and flow used the 0-3 thrombolysis in myocardial infarction (TIMI) scale. Success was defined as declotting of grade >/= 3 (>70% clearing) with flow of >/= 2. RESULTS Seven pigs received 14 declotting sequences. Average clot age was 217 minutes. Average declotting score was 3.1, and flow was 2.1 for microbubbles and 1.4 and 0.1 for saline controls, P =.016 in each. Success occurred with microbubbles in six of seven attempts and in controls in zero of seven attempts, P =.031. CONCLUSIONS LFUS with microbubble augmentation rapidly lyses intracranial clot and restores flow at ultrasound ranges similar to those required in humans. Further development of this possible acute stroke therapy is justified.

Microbubbles for Thrombolysis of Acute Ischemic Stroke

Improved treatment of acute ischemic stroke with ultrasound and microbubbles in combination with thrombolytic drugs shows great promise, but the optimal techniques, indications, and contraindications have not yet been well defined. Moreover, details such as microbubble dosage, delivery, required thrombolytic drug dosage, and optimal ultrasound characteristics all remain uncertain. Recent results suggest that ultrasound and microbubbles may be effective in clot lysis of ischemic stroke without additional thrombolytic drugs. Moreover, targeting thrombus with specific immunobubbles may improve the efficacy of sonothrombolysis. Safety remains a major concern in the further development of ultrasound-enhanced thrombolysis and extensive animal work is required to define the most promising methods to translate into human application.

Utility of magnetic resonance arteriography for distal lower extremity revascularization

PURPOSE Magnetic resonance arteriography (MRA) of the lower extremities affords several possible advantages over conventional contrast arteriography (CA). We hypothesized that MRA of the infrageniculate vessels was sufficiently accurate to replace CA before revascularization procedures in patients with limb-threatening ischemia. METHODS Fifty-three extremities in 49 patients were prospectively evaluated before attempted infrageniculate revascularization procedures with preoperative infrageniculate time-of-flight MRA (cost,

Ultrasound enhanced thrombolysis in acute arterial ischemia.

170/study) and standard contrast arteriography (cost,

The Pocket Echocardiograph: Validation and Feasibility

1310/study) of the aortoiliac and runoff vessels. Independent operative plans were formulated based on the MRA and CA results before the revascularization procedure. Intraoperative, prebypass arteriograms (IOA; cost,