Dependence of blood clot lysis on the mode of transport of urokinase into the clot--a magnetic resonance imaging study in vitro

Magnetic resonance imaging was employed to study the dependence of clot lysing patterns on two different modes of transport of urokinase into whole blood clots. In one group of clots (nonperfused clots, n1 = 10), access of urokinase to the fibrin network was possible by diffusion only, whereas in the other group (perfused clots, n2 = 10) bulk flow of plasma containing urokinase was instituted through occlusive clots by a pressure difference of 3.7 kPa (37 cm H2O) across 3 cm long clots with a diameter of 4 mm. It was determined separately that this pressure difference resulted in a volume flow rate of 5.05 +/- 2.4 x 10(-2) ml/min through occlusive clots. Perfused clots diminished in size significantly in comparison to nonperfused ones already after 20 min (p less than 0.005). Linear regression analysis of two-dimensional clot sizes measured by MRI showed that the rate of lysis was more than 50-times faster in the perfused group in comparison to the nonperfused group. It was concluded that penetration of the thrombolytic agent into clots by perfusion is much more effective than by diffusion. Our results might have some implications for understanding the differences in lysis of arterial and venous thrombi.     

Magnetic resonance imaging of retracted and nonretracted blood clots during fibrinolysis in vitro.

Magnetic resonance imaging (MRI) of retracted blood clots embedded in nonretracted clots was used to follow their lysis with urokinase in a plasma milieu in vitro. The two types of clots that were imaged in the same plane differed in signal intensity on T2-weighted spin echo MR images throughout the 20-hour observation period. It was thus possible to delineate the contours of both clot types and measure their relative sizes by digital image processing. Lysis of retracted clots proceeded significantly slower than lysis of nonretracted clots. Our in vitro results suggest that MRI might prove useful in detecting thrombus retraction in vivo and in predicting the outcome of thrombolytic therapy.     

Pharmacological prevention of atherothrombotic events in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is strongly associated with atherosclerosis in the coronary and carotid arteries, leading to a highly increased incidence of myocardial infarction, ischaemic stroke and cardiovascular death. Fortunately, pharmacological interventions in large clinical trials have been as effective in subgroups of patients with PAD as in subjects with other atherosclerotic disease. Antiplatelet treatment is indicated in virtually all patients with PAD. Aspirin 75-325 mg day(-1) is considered as first-line treatment, and clopidogrel 75 mg day(-1) is an effective alternative. Statin therapy is indicated to achieve a target low-density lipoprotein cholesterol level of < or = 2.5 mmol L(-1) in patients with PAD and there is emerging evidence that even lower levels are beneficial. Lowering of plasma homocysteine by supplementing folic acid, vitamin B(12) and vitamin B(6) is not recommended in patients with mild to moderate hyperhomocysteinaemia in the 12-25 micromol L(-1) range, since it does not reduce the incidence of cardiovascular events. Antihypertensive treatment is indicated to achieve a goal blood pressure of < or = 140/90 mmHg or < or = 130/80 mmHg in the presence of diabetes or chronic kidney disease. All classes of antihypertensive drugs are acceptable for treatment of hypertension in patients with PAD, but angiotensin-converting enzyme inhibitors ramipril or perindopril are especially appropriate because they reduce the incidence of cardiovascular events beyond their blood pressure-lowering effects. Beta-blockers should not be used as first-line antihypertensive treatment. Diabetic patients with PAD should reduce their glycosylated haemoglobin to < or = 7%. In conclusion, pharmacological secondary prevention of cardiovascular morbidity and mortality in patients with PAD should be as comprehensive as that in patients with established coronary or cerebrovascular disease.     

A case of pseudothrombocytopenia after infusion of abciximab in vivo and anticoagulant-independent platelet clumping after rechallenge with abciximab in vitro

A 45-year old man was treated for unstable angina pectoris with percutaneous transluminal angioplasty and stenting of his left anterior descending coronary artery. The procedure was followed by infusion of abciximab. The patient's automated platelet count in an EDTA-anticoagulated blood sample at admission to the hospital was normal, but dropped to 5 x 10(9)/l three hours after the procedure. The infusion of abciximab was stopped and the patient received platelet transfusions although there were no signs of bleeding. Two days later his platelet count was still low (37 x 10(9)/l) in an EDTA-anticoagulated blood sample, but normal (193 x 10(9)/l) in a heparin-anticoagulated sample. Platelet clumps were present only in the sample anticoagulated with EDTA, and pseudothrombocytopenia was diagnosed. The patient's recovery was uneventful. At follow-up visits four months and one year after discharge from hospital, the patient's blood samples were anticoagulated with three different anticoagulants: EDTA, citrate and heparin. The platelet count was normal in all three samples but after mixing with abciximab in vitro it dropped profoundly due to platelet clumping, regardless of the choice of the anticoagulant. Our report raises two points: (a) one needs to consider the possibility of pseudothrombocytopenia in a patient with a low automated platelet count after infusion of abciximab but without signs of bleeding, and (b) the in vitro results suggest that our patient who had initially responded to abciximab with pseudothrombocytopenia could develop true thrombocytopenia after repeated exposure.     

Microscopic clot fragment evidence of biochemo-mechanical degradation effects in thrombolysis

Introduction

Although fibrinolytic treatment has been used for decades, the interactions between the biochemical mechanisms and the mechanical forces of the streaming blood remain incompletely understood. Analysis of the blood clot surface in vitro was employed to study the concomitant effect of blood plasma flow and recombinant tissue plasminogen activator (rt-PA) on the degradation of retracted, non-occlusive blood clots. Our hypothesis was that a faster tangential plasma flow removed larger fragments and resulted in faster overall thrombolysis.

Materials and Methods

Retracted model blood clots were prepared in an optical microscopy chamber and connected to an artificial perfusion system with either no-flow, or plasma flow with a velocity of 3 cm/s or 30 cm/s with or without added rt-PA at 2 µg/ml. The clot surface was dynamically imaged by an optical microscope for 30 min with 15 s intervals.

Results

The clot fragments removed during rt-PA mediated thrombolysis ranged in size from that of a single red blood cell to large agglomerates composed of more than a thousand red blood cells bound together by partly degraded fibrin. The average and the largest discrete clot area change between images in adjacent time frames were significantly higher with the faster flow than with the slow flow (14,000 μm² and 160,000 μm² vs. 2200 μm² and 10,600 μm²).

Conclusions

On the micrometer scale, thrombolysis consists of sequential removal of clot fragments from the clot surface. With increasing tangential plasma flow velocity, the size of the clot fragments and the overall rate of thrombolysis increases.     

Serum amyloid A in autoimmune thrombosis

The objectives of this study were (1) to determine how levels of serum amyloid A (SAA), high sensitivity C-reactive protein (CRP) and interleukin-6 (IL-6) correlate to autoimmune diseases in patients with or without thrombosis, and (2) to discuss the parameters that influence the relative SAA values. SAA, CRP and IL-6 concentrations were determined by enzyme linked immunosorbent assay (ELISA). 84 patients with secondary antiphospholipid syndrome (SAPS), primary antiphospholipid syndrome (PAPS), systemic lupus erythematosus with antiphospholipid antibodies (SLE+aPL), SLE, venous thrombosis (VT), arterial thrombosis (AT) were compared to healthy donors (n=60). The percentages of patients above cut-off were highest in the SAPS, SLE and SLE+aPL groups. Significant differences were observed between healthy donors and inflammatory groups of patients (SAPS and SLE+aPL) in all three measured parameters. SAA and CRP were shown to be correlated to a greater extent in SAPS patients than SLE+aPL patients. In summary, this cross-sectional, retrospective, small study and accompanying clinical considerations limit the ability to make definite conclusions. SAA would not serve as a useful marker for venous, arterial thrombosis or PAPS (pro-coagulant events). It could however, be a good predictor of progression from a non-inflammatory thrombotic condition to an inflammatory one.