Intravenous Targeted Microbubbles Carrying Urokinase versus Urokinase Alone in Acute Peripheral Arterial Thrombosis in a Porcine Model.

BACKGROUND: Standard therapy in acute peripheral arterial occlusion consists of intra-arterial catheter-guided thrombolysis. As microbubbles may be used as a carrier for fibrinolytic agents and targeted to adhere to the thrombus, we can theoretically deliver the thrombolytic medication locally following simple intravenous injection. In this intervention-controlled feasibility study, we compared intravenously administered targeted microbubbles incorporating urokinase and locally applied ultrasound, with intravenous urokinase and ultrasound alone. METHODS: In 9 pigs, a thrombus was created in the left external iliac artery, after which animals were assigned to either receive targeted microbubbles and urokinase (UK + tMB group) or urokinase alone (UK group). In both groups, ultrasound was applied at the site of the occlusion. Blood flow through the iliac artery and microcirculation of the affected limb were monitored and the animals were euthanized 1 hr after treatment. Autopsy was performed to determine the weight of the thrombus and to check for adverse effects. RESULTS: In the UK + tMB group (n = 5), median improvement in arterial blood flow was 5 mL/min (range 0-216). Improvement was seen in 3 of these 5 pigs at conclusion of the experiment. In the UK group (n = 4), median improvement in arterial blood flow was 0 mL/min (-10 to 18), with slight improvement in 1 of 4 pigs. Thrombus weight was significantly lower in the UK + tMB group (median 0.9383 g, range 0.885-1.2809) versus 1.5399 g (1.337-1.7628; P = 0.017). No adverse effects were seen. CONCLUSIONS: Based on this experiment, minimally invasive thrombolysis using intravenously administered targeted microbubbles carrying urokinase combined with local application of ultrasound is feasible and might accelerate thrombolysis compared with treatment with urokinase and ultrasound alone.

Therapeutic application of contrast-enhanced ultrasound and low-dose urokinase for thrombolysis in a porcine model of acute peripheral arterial occlusion.

BACKGROUND: The addition of local ultrasound (US) with a contrast agent to standard intra-arterial thrombolysis can accelerate the thrombolytic treatment of stroke and myocardial infarction. The contrast agent consists of microsized gas-filled bubbles that collapse when exposed to US, causing destabilization of the clot and making the clot surface more susceptible to fibrinolytics. In this study, we investigated the effect of additional US and microbubbles on standard low-dose intra-arterial thrombolysis in a porcine model of extensive peripheral arterial occlusion. METHODS: Extensive arterial thrombosis was induced in 10 pigs in the 4-cm external iliac artery by clamping and injection of 100 IU of bovine thrombin. A transcutaneous laser Doppler flow probe and an ultrasonic perivascular flow probe assessed microcirculation and arterial flow respectively. The urokinase-only (UK) group (n = 4) received standard thrombolytic therapy: intra-arterial bolus injection of 500,000 IU, followed by a continuous low-dose urokinase (50,000 IU/h) infusion through an intra-arterial catheter and local intermittent application of US, 1 second on, 5 seconds off, to visualize vascular patency during the first hour of therapy and to ensure microbubbles replenished the proximal portion of the occluded artery. The urokinase plus microbubbles (UK+) group (n = 6) received the same urokinase therapy with a concomitant intravenous infusion of microbubbles and local intermittent application of US. The contrast infusion protocol consisted of a bolus of two vials of 5 mL in the first 15 minutes and then three times 5 mL slowly hand-injected continuously during the next 45 min. After 3 hours of therapy, the animals were euthanized, and thrombi were harvested and weighed. All organs were cut in thin slices and macroscopically inspected for potential (hemorrhagic) adverse events, and tissue samples were taken. RESULTS: Median thrombus weights were 1.1 g (range, 0.8-1.3 g) in the UK+ group vs 1.6 g (range, 1.3-1.9 g) in the UK group (P = .01). Arterial blood flow increased in four of six pigs in the UK+ group by a mean 61% vs in one of four in the UK group, with 1%. Microcirculation and lower limb arterial pressure levels improved after the start of therapy in the UK+ group, contrary to a trend of decline in the UK group. No signs of bleeding complications were observed in either group. CONCLUSIONS: In this experimental pilot study, the addition of contrast-enhanced US accelerated the thrombolytic effect of low-dose intra-arterial thrombolysis in peripheral arterial occlusions. Further clinical studies are warranted.

General anesthesia with sevoflurane decreases myocardial blood volume and hyperemic blood flow in healthy humans.

BACKGROUND: Preservation of myocardial perfusion during general anesthesia is likely important in patients at risk for perioperative cardiac complications. Data related to the influence of general anesthesia on the normal myocardial circulation are limited. In this study, we investigated myocardial microcirculatory responses to pharmacological vasodilation and sympathetic stimulation during general anesthesia with sevoflurane in healthy humans immediately before surgical stimulation. METHODS: Six female and 7 male subjects (mean age 43 years, range 28-61) were studied at baseline while awake and during the administration of 1 minimum alveolar concentration sevoflurane. Using myocardial contrast echocardiography, myocardial blood flow (MBF) and microcirculatory variables were assessed at rest, during adenosine-induced hyperemia, and after cold pressor test-induced sympathetic stimulation. MBF was calculated from the relative myocardial blood volume multiplied by its exchange frequency (ß) divided by myocardial tissue density (ρT), which was set at 1.05 g·mL(-1). RESULTS: During sevoflurane anesthesia, MBF at rest was similar to baseline values (1.05 ± 0.28 vs 1.05 ± 0.32 mL·min(-1)·g(-1); P = 0.98; 95% confidence interval [CI], -0.18 to 0.18). Myocardial blood volume decreased (P = 0.0044; 95% CI, 0.01-0.04) while its exchange frequency (ß) increased under sevoflurane anesthesia when compared with baseline. In contrast, hyperemic MBF was reduced during anesthesia compared with baseline (2.25 ± 0.5 vs 3.53 ± 0.7 mL·min(-1)·g(-1); P = 0.0003; 95% CI, 0.72-1.84). Sympathetic stimulation during sevoflurane anesthesia resulted in a similar MBF compared to baseline (1.53 ± 0.53 and 1.55 ± 0.49 mL·min(-1)·g(-1); P = 0.74; 95% CI, -0.47 to 0.35). CONCLUSIONS: In otherwise healthy subjects who are not subjected to surgical stimulation, MBF at rest and after sympathetic stimulation is preserved during sevoflurane anesthesia despite a decrease in myocardial blood volume. However, sevoflurane anesthesia reduces hyperemic MBF, and thus MBF reserve, in these subjects.

Contrast-enhanced ultrasound for myocardial perfusion imaging.

Ultrasound contrast agents are gas-filled microbubbles that enhance visualization of cardiac structures, function and blood flow during contrast-enhanced ultrasound (CEUS). An interesting cardiovascular application of CEUS is myocardial contrast echocardiography, which allows real-time myocardial perfusion imaging. The intraoperative use of this technically challenging imaging method is limited at present, although several studies have examined its clinical utility during cardiac surgery in the past. In the present review we provide general information on the basic principles of CEUS and discuss the methodology and technical aspects of myocardial perfusion imaging.