Site Of Thrombus Formation Research Articles

An Orbiting Scroll Blood Pump Without Valves or Rotating Seals

Valves in blood pumps are expensive and provide modes of failure. Rotating seals offer sites of thrombus formation and infection. In this study, a prototype pump incorporating no valves or rotating seals was constructed and tested. In this device, fluid is pumped by the orbital action of a spiral shaped scroll relative to an identical stationary scroll whose starting axis is rotated 180 degrees with respect to the orbiting scroll. The two scrolls, which are machined integral with scroll plates, form pockets that are filled from the outside and then ejected in the center as the orbiting scroll completes each cycle. The orbiting scroll is driven by a crank mechanism connected to a motor. Fluid is contained in the space around the scrolls by a flexible collar and does not contact the driving mechanism. The prototype pump is approximately 7.6 cm in diameter and 2.5 cm thick and has an orbiting radius of 5.1 mm. The output of the pump was very sensitive to the clearance between the scroll tip and the base of the opposite scroll plate. For a clearance of 51 microns, pressure differences as high as 400 mmHg and flows as high as 7.7 l/min (of water) were produced at 260 rpm. At 450 rpm with a 330 microns clearance, pressure differences as high as 185 mmHg and flows as high as 7.3 l/min resulted. The relationships between pressure difference and flow were very linear in all cases. Volumetric efficiency was as high as 70% and increased with speed.

Pathologic analysis of 34 explanted symbion ventricular assist devices and 10 explanted Jarvik-7 total artificial hearts

Thirty-four Symbion ventricular assist devices and 10 Jarvik-7 total artificial hearts that had been in clinical use for 1 to 164 days (assist devices) and 1 to 176 days (artificial hearts) were analyzed using a detailed protocol for pathological analysis. The major finding was thrombus formation in 85% of the assist devices and 75% of the artificial hearts. Thrombi were generally small and in only one case interfered with pump function. The number of distinct thrombi per device was 2.5 mean (range 0–5) for assist devices and 2.6 mean (range 0–6) for artificial hearts. Major sites of thrombus formation in the assist devices were valves, valve connections, diaphragm, and the inner surface of the deairing port. Artificial heart thrombi were predominantly paravalvular. In order to relate sites of diaphragmatic thrombi to specific design features of the assist device, the pattern was analyzed quantitatively using a polar coordinate mapping technique to measure the average radial thrombus length around the circumference of each diaphragm. The concentration of thrombus was highest between the valve orifices and lateral to the outflow valve. This identified areas particularly susceptible to thrombus formation and thereby targets specific pump features for redesign. Intraluminal infection was seen in 1 assist device and 1 artificial heart (outflow grafts); extraluminal infection was seen in two artificial hearts (infected hematomas around the outflow grafts). Neither device mineralization for mechanical defects were noted. Thus thrombus formation related to (and potential thromboemboli from) valves, their connectors, and the pumping diaphragms represents the major device-associated complication of pneumatic Symbion assist devices and Jarvik-7 artificial hearts. Thrombi associated with other sites and both intra- and extraluminal infection occur less frequently.

Study of platelet-mediated neurotoxicity in rat brain.

The mechanism of ischemic neuronal injury is not fully resolved. The present view is that vascular occlusion per se does not fully account for the extent of neurological dysfunction. We previously hypothesized that platelet secretory products might contribute to neuronal injury in the central nervous system. Our preliminary studies using organotypic rat spinal cord cultures exposed to human platelet and its secretory products revealed that platelet products had neurotoxic properties. Further studies, using the same methods, were conducted, with the addition of several refinements such as use of gel-filtered platelets (as opposed to washed platelets) and adding additional relevant controls including platelet membranes, red blood cells, and washed rat platelets. Exposure of spinal cord explant cultures to platelet secretory products resulted in reduced number of neurons per ventral horn compared with control. Our findings suggest that platelet secretory products have neurotoxic properties. This effect was seen with platelet secretion obtained from physiological platelet concentrations. It appears possible that more abundant release of platelet products at the site of thrombus formation could have pathological significance in vivo.

Deep venous thrombosis and pulmonary embolism

Left untreated, deep venous thrombosis and pulmonary embolism have a high rate of mortality and long-term morbidity. Physicians therefore must maintain a high index of suspicion for these conditions. Accurate diagnosis is facilitated by knowing the most common sites of thrombus formation, the likelihood of propagation, which patients are at greatest risk, signs and symptoms, and which tests to order. Prompt administration of anticoagulants and, in some cases, thrombolytic agents can minimize the consequences of these diseases. Interruption of the inferior vena cava, thrombectomy, and thromboembolectomy are other treatment options.

Thrombosis and the Heart

The heart is an important site for thrombus formation and cardioembolic events are a frequent cause of stroke. Many cardiac factors may contribute to the risk of cardioembolism. Clinicians must be mindful that those cardiac disorders most likely to cause cardioembolic events include atrial fibrillation, left ventricular dysfunction, valvular heart disease, and structural cardiac abnormalities. The presence of many such conditions mandates the use of specific preventive therapies. Improved diagnostic methods, particularly TEE, now allow more accurate identification and follow-up of potential cardiac sources. Embolus detection monitoring has the potential to allow in vivo identification of embolic events and offers the possibility of objective longitudinal assessment of the impact of therapy. Intravascular ultrasound is an invasive test, but it may eventually allow the most accurate evaluation of the cardiac chambers. New therapies, and new combinations of currently available compounds, may ultimately offer more specific and efficacious alternatives to prevent formation of cardiac thrombus and subsequent cardioembolism. The importance of the heart-brain relationship in stroke has finally been appreciated. Improved understanding of this complex interrelationship will have great impact on clinical practice in the future.

Intracoronary thrombus formation causes focal vasoconstriction of epicardial arteries in patients with coronary artery disease.

Experimental studies have demonstrated that intracoronary platelet aggregation and thrombus formation may induce marked vasoconstriction of epicardial arteries with endothelial injury. To examine the effects of intracoronary thrombus formation on coronary vasomotor tone of human epicardial arteries in vivo, we studied 15 patients who developed intracoronary thrombi adherent to the guide wire during balloon dilatation. Epicardial artery luminal area was evaluated by quantitative coronary angiography proximal and distal to the site of intracoronary thrombus formation and in a reference vessel before and after thrombus formation as well as after intracoronary injection of 0.2-0.3 mg nitroglycerin. All artery segments distal to the site of thrombus formation showed vasoconstriction with a luminal area reduction of -27.4 +/- 17.1% (p less than 0.001), whereas proximal vessel segments and reference vessels not manipulated during percutaneous transluminal coronary angioplasty did not demonstrate any significant luminal area changes during thrombus formation. Angiographic measurements after advancing the guide wire with the adherent thrombus (performed in six of the 15 patients) revealed in all patients that vasoconstriction did develop at a new site distal to the thrombus persistence of the initial vasoconstriction now residing proximal to the thrombus. Thus, there was a sequential association between thrombus formation and subsequent distal vasoconstriction. Intracoronary injection of nitroglycerin abolished the thrombus-induced vasoconstriction. No significant luminal area changes were observed in 20 patients without angiographic evidence of intracoronary thrombus formation. Intracoronary thrombus formation during percutaneous transluminal coronary angioplasty causes focal vasoconstriction of epicardial arteries in patients with coronary artery disease. Although caution must be advised in the extrapolation of this phenomenon, which was observed in a manipulated artery during coronary angioplasty, the vasoconstrictor response to intracoronary thrombus formation in vivo may play an important role in the dynamic mechanisms of acute coronary heart disease syndromes.

Role of Serotonin in Arteriolar Thrombosis and Secondary Vasospasm

Platelets are implicated both in the thrombotic reaction to an intimal lesion of the arteriolar wall and to the resulting vasospasm even if the two phenomena are not linked directly. The spastic reaction is a consequence of the thrombotic process because without localized platelet activation (thrombus formation) there is no vasospastic reaction, but by pharmacological manipulation, the thrombotic reaction can develop without resulting vasospasm. We developed an original experimental model that allowed us to study the thrombotic reaction secondary to localized endothelial injury in arterioles of the mesentery of the rat, as well as the vasospastic reaction downstream to the site of thrombus formation. In this setting, we studied the reactivity of Sprague-Dawley rats treated with three 5-HT2 serotonergic antagonists (ketanserin, ritanserin, and naftidrofuryl) and that of Fawn-Hooded rats (a strain affected by a congenital reduction of platelet dense granules, with a resulting decrease in platelet content of serotonin, ADP, and catecholamines). Naftidrofuryl had antithrombotic properties similar to those of ritanserin but was less potent than ketanserin. It possessed antispastic activity against the reaction secondary to intravascular platelet activation. Its potency was similar to that of ketanserin but greater than that of ritanserin. Naftidrofuryl had no significant antispastic activity against platelet-derived agents reaching the ateriolar wall from the adventitial side. Compared to the Sprague-Dawley rat, Fawn-Hooded rats had a minimal reduction of the thrombotic process and of the intraluminal induced vasospasm but a similar response to adventitial stimulation of the arterial wall by vasoactive factors released from a neighboring hemostatic plug.(ABSTRACT TRUNCATED AT 250 WORDS)

Local measurements of thrombus induced vasoconstriction in vivo

No data is available describing the local effect of thrombus formation on the vessel's diameter in vivo. As platelet or thrombus induced vasoconstriction seems to be of clinical importance in various diseases, it is desirable to get insight into the interrelation of thrombus formation and local vasoactivity. With a contactless photochemical process, endothelial cells can be damaged and thrombogenesis may be initiated in vivo. After first platelets stick to endothelial cells, a strong vasoconstriction is observed in arterioles. In venules, no vascular reaction can be observed. Constriction is most pronounced at the site of thrombus formation and decreases at growing distance. The thrombus is squeezed by the vascular constriction and thus mechanically held in place and squeezed out. A slight relaxation follows 30–80 rain later, but the vessel remains constricted during the following three hours. Thrombus induced vasoconstrictions can be reduced by papaverine, EP 092 (a thromboxane A 2 antagonist) and phentolamine in dose dependent manner in vivo. Papaverine was most effective followed by EP 092, Phentolamine was less effective, showing the minor importance of α-receptor stimulation in this model.

The accumulation of a platelet protein, thrombospondin, at the site of arterial thrombus formation: preliminary report.

There are many methods available for the detection of thrombosis, none of which are noninvasive, rapid and accurate. Thrombospondin is a platelet protein that is present in the developing thrombus and may be an effective substance to use for imaging thrombosis. Vascular stenosis and thrombosis were produced in coronary, carotid and femoral arteries in eleven adult mongrel dogs. 131I labeled thrombospondin was administered to each animal to determine whether the radiotracer accumulated at the site of thrombus formation. The radioactivity per gram of vessels with thrombi was significantly different from the control vessels or whole blood (p = 0.0037 and p = 0.0015, respectively, paired t-test). This preliminary work suggests that iodinated thrombospondin accumulates at the site of thrombus formation. Labeled thrombospondin may be a rapid, safe and accurate method of detecting arterial thrombosis.

Effects of vascular constriction on occlusive thrombus formation of rat mesenteric artery

Effects of vascular constriction on thrombotic occlusion was evaluated using rat mesenteric arteries and video-recording system attached to the microscope. Topical application of norepinephrine of 1, 10 and 100 pg/ml reduced the arterial diameter dose dependently from 297 ± 41 μ to 166 ± 50, 87 ± 18 and 84 ± 11 μ(mean ± SD, n=7), respectively. The diameter reduction by the higher 2 doses persisted for more than 30 minutes until the wash out of the agent. But, no thrombus formation was observed. A reproducible thrombus formation was induced by inserting a glass micropipette into the vascular lumen. The maximal percent occlusion by the thrombus was 80 ± 11 % (range; 67 to 95 %, n=7). The topical application of 10 μg/ml norepinephrine induced vasoconstriction and increased the percent occlusion significantly to 97 ± 8 % (p<0.05). Complete occlusion of the lumen developed in 6 of 7 rats after the agent and in 2 rats it was not released until the wash out of the agent for more than 30 minutes. Thrombus formation itself did not change the arterial diameter at the site of thrombus formation as well as at sites of 300 and 600 μ down stream. It is suggested that the vascular constriction alone does not necessarily cause thrombus formation but may aggravate the arterial flow reduction induced by thrombosis.

Coronary vascular occlusion mediated via thromboxane A2-prostaglandin endoperoxide receptor activation in vivo.

The use of enzyme inhibitors to clarify the role of thromboxane A2 in vasoocclusive disease has been complicated by their non-specific action. To address this problem we have examined the effects of thromboxane A2/prostaglandin endoperoxide receptor antagonism in a canine model of platelet-dependent coronary occlusion. Two structurally distinct thromboxane A2/prostaglandin endoperoxide receptor antagonists, 3-carboxyl-dibenzo (b, f) thiepin-5,5-dioxide (L636,499) and (IS-(1 alpha,2 beta(5Z),3 beta,4 alpha))-7-(3-((2-((phenylamino)-carbonyl)hydrazino)methyl)-7- oxabicy-clo(2.2.1)-hept-2-yl)-5-heptenoic acid (SQ 29,548), were studied to ensure that the effects seen in vivo were mediated by receptor antagonism and did not reflect a nonspecific drug effect. Both compounds specifically inhibited platelet aggregation induced by arachidonic acid and by the prostaglandin endoperoxide analogue, U46619, in vitro and ex vivo, and increased the time to thrombotic vascular occlusion in vivo. When an antagonist (L636,499) was administered at the time of occlusion in vehicle-treated dogs, coronary blood flow was restored. In vitro L636,499 and a third antagonist, 13-azaprostanoic acid, specifically reversed endoperoxide-induced platelet aggregation and vascular smooth muscle contraction. Neither compound altered cyclic AMP in platelet-rich plasma before or during disaggregation. Therefore, reversal of coronary occlusion may reflect disaggregation of platelets and/or relaxation of vascular smooth muscle at the site of thrombus formation through specific antagonism of the thromboxane A2/prostaglandin endoperoxide receptor. Thromboxane A2/prostaglandin endoperoxide receptor antagonists are compounds with therapeutic potential which represent a novel approach to defining the importance of thromboxane A2 and/or endoperoxide formation in vivo.

A method for generating obstructive thrombi in the coronary arteries of the conscious dog.

A technique for staging the generation of obstructive thrombi in the coronary arteries of conscious dogs is described. At thoracotomy, electrodes are placed in the lumina of coronary artery branches. When thrombus generation in proximity to the intraluminal electrode tip is desired, anodal current is applied to the exteriorised end of the electrode. In each of nine anaesthetised adult mongrel dogs two to seven intracoronary electrodes were implanted for a total of 35. One to 75 days later, 50 to 800 microA anodal current was applied to 16 electrodes for 30 min to 48 h. Upon autopsy, thrombi in various stages of organisation were found in proximity to the intracoronary portion of 15 electrodes. Six electrodes were found to be damaged or broken. In contrast, only four of the 13 control electrodes were sites of thrombus formation. In seven dogs tissue sections indicated either myocardial ischaemia or infarct in regions whose perfusion was blocked by thrombi. This method may provide for discretionary generation of intracoronary thrombi in the desired quantity, at the preferred site(s), at selected times of onset. Consequently, it offers the possibility of adjusting the onset, severity, and time course of myocardial ischaemia.

Effects of aspirin and dipyridamole on the degradation of adenosine diphosphate by cultured cells derived from bovine pulmonary artery.

To improve understanding of the mechanisms by which ADP is degraded during passage through the pulmonary vascular bed, we examined cultured endothelial and smooth muscle cells of bovine pulmonmary artery for their abilities to metabolize [8-14C]ADP. ADP is rapidly converted to AMP and then to adenosine, hypoxanthine, and inosine. Inosine is the major metabolite produced by endothelial cells. Radioactivity (5-10%) is accumulated intracellularly primarily as ATP. Medium containing 50 micro M ADP incubated with endothelial cells rapidly loses its ability to aggregate platelets and becomes antiaggregatory under conditions in which prostacyclin is absent. The antiaggregatory activity is probably the result of accumulated adenosine. 10 micro M dipyridamole inhibits cellular uptake of radioactivity by greater than 90%, and inosine in the medium is largely replaced by adenosine. This is accompanied by increased anti-aggregatory activity of conditioned medium, which can be matched by authentic adenosine at the same concentration. 1 mM aspirin had no effect on the metabolism of ADP by endothelial cells. Our results suggest: (a) Metabolism of ADP during passage through the lung is mainly the result of endothelial ADPase. (b) ADP released from aggregating platelets can be converted to the antiaggregatory substance, adenosine. Dipyridamole may exert some of its antithrombotic actions by preventing the intracellular uptake of adenosine, thereby increasing its concentration near the site of thrombus formation. (c) The ability of the vessel wall to degrade ADP should not be compromised by the use of aspirin as an antithrombotic drug. (d) Endothelium may retain some of its antithrombogenicity when prostacyclin generation is impaired.

New developments in the detection and prevention of venous thromboembolism

The recent development of relatively noninvasive, sensitive and specific procedures has been responsible for new information in the pathophysiology and epidemiology of venous thrombosis. Primary emphasis has been placed on detection of thrombosis with the radioactive fibrinogen leg scan, Doppler ultrasonic recording and, more recently, electrical impedance plethysmography. The latter procedure is easily performed by trained technicians; it is also sensitive and specific and provides an immediate answer. In 95 percent of patients with angiographically confirmed pulmonary embolism, results of impedance plethysmography were abnormal, indicating deep vein thrombosis and thus establishing the relation between the site of thrombus formation and pulmonary embolism. In 90 percent of patients suspected of having pulmonary embolism, when the plethysmogram indicated deep vein thrombosis, pulmonary anglograms revealed pulmonary embolism; similarly, when the plethysmogram was normal, pulmonary angiograms revealed normal findings in 90 percent of the patients. Hence, objective, noninvasive assessment of the deep venous system can be an excellent diagnostic aid, particularly when ventilation/perfusion scanning or pulmonary angiography is not readily available. The most widely studied measure to prevent venous thrombosis has been treatment with subcutaneous small dose heparin. Although extremely effective in patients undergoing elective general surgery, this treatment has not been as effective or as appropriate in high risk patients, such as those undergoing hip, urologie or neurosurgical procedures, or in patients with malignancy. Among medically treated patients, it has been quite effective in those with acute myocardial infarction. Dextran has not been very effective in patients undergoing general surgery, although its use with relatively large volumes has resulted in favorable results in patients having hip surgery. Platelet antiaggregating agents have generally been disappointing prophylactic agents. The most recent and promising technique is intermittent pneumatic boot compression of the calves, which does not require medications that may alter blood coagulation. The results of this procedure have been impressive in general surgical, neurosurgical and urologie patients, conflicting in patients with hip surgery and poor in patients with malignancy undergoing surgery. In these groups of high risk patients, further investigations with new agents or methods or combined techniques are indicated.

Myeloperoxidase-Mediated Platelet Release Reaction

The ability of the neutrophil myeloperoxidase-hydrogen peroxide-halide system to induce the release of human platelet constituents was examined. Both lytic and nonlytic effects on platelets were assessed by comparison of the simultaneously measured release of a dense-granule marker, [(3)H]serotonin, and a cytoplasmic marker, [(14)C]adenine. Incubation of platelets with H(2)O(2) alone (20 muM H(2)O(2) for 10 min) resulted in a small, although significant, release of both serotonin and adenine, suggesting some platelet lysis. Substantial release of these markers was observed only with increased H(2)O(2) concentrations (>0.1 mM) or prolonged incubation (1-2 h). Serotonin release by H(2)O(2) was markedly enhanced by the addition of myeloperoxidase and a halide. Under these conditions, there was a predominance of release of serotonin (50%) vs. adenine (13%), suggesting, in part, a nonlytic mechanism. Serotonin release by the complete peroxidase system was rapid, reaching maximal levels in 2-5 min, and was active at H(2)O(2) concentrations as low as 10 muM. It was blocked by agents which inhibit peroxidase (azide, cyanide), degrade H(2)O(2) (catalase), chelate Mg(2+) (EDTA, but not EGTA), or inhibit platelet metabolic activity (dinitrophenol, deoxyglucose).These results suggest that the myeloperoxidase system initiates the release of platelet constituents primarily by a nonlytic process analogous to the platelet release reaction. Because components of the peroxidase system (myeloperoxidase, H(2)O(2)) are secreted by activated neutrophils, the reactions described here may have implications for neutrophilplatelet interaction in sites of thrombus formation.

Recent experience with the Baylor left ventricular bypass pump.

The current Baylor left ventricular bypass pump is a pneumatically actuated diaphragm pump lined with segmented polyurethane. It is a swirl design in which blood moves in a circular motion within the pump. It has tilting disc inflow and outflow valves and the stroke volume is 60 ml. It is intended for periods of use up to fourteen days. Eighteen devices have been implanted in normal calves. The mean duration of pump operation was eleven days. The pump-canula junctions and regions of the valve seats have been sites of thrombus formation and are being redesigned to eliminate areas of flow separation and stasis.

Thrombus generation within the artificial heart

The sites of thrombus formation in the Jarvik III artificial heart were studied in 20 consecutive calf experiments. Identical design and implantation procedures were used with two different surfaces. The 10 anticoagulated calves receiving Dacron-fibrilized silicone rubber surfaces survived an average of 296 hours. In contrast, the 10 nonanticoagulated calves with smooth poyurethane hearts survived 545 hours. The polyurethane surfaces were constantly clean. However, the rough surfaces were coated with variable amounts of thrombi. The sharp angle between the diaphragm and housing contained varying amounts of thrombi deposits in 75 per cent of the cases. Thrombe deposition occurred on 41 per cent of the valves. These thrombe were the source of emboli into the kidney, brain, and lungs. Turbulences and stagnation areas generated thrombus formation. Anticoagulation did not prevent thrombus formation. It would appear that heart free of turbulence and stagnation areas must be designed to eliminate thromboembolism.

Chemotherapy in Experimental Cancer: I. Attempts to Produce Intratumoral Clotting by the Combined Action of Lead and Thrombogenic Agents

Chemical agents being tested for their action on tumor growth are usually injected into animals with the hope that they will have a specific action on the malignant cell. While some chemicals have produced necrosis and regression of tumors, the effects often appear to be due to ischemia and cellular starvation resulting from vascular injury and thrombosis, rather than to a selective action of the chemical on the cell itself. Although evidence for the therapeutic value of heavy metals, particularly lead, is contradictory, it may be said that some metals given in sufficiently large doses produce vascular impairment, thrombosis, and necrosis, as was shown by Izar and Basile (1912) for colloidal sulphur, Weil (1913) for copper, and Wood (1926) for lead. Wood states that thrombi are abundantly present in tumor capillaries twenty-four hours after the injection of colloidal lead into rats bearing sarcoma 39. In order to produce extensive injury of the larger vessels and marked destruction of the tumor, the dosage must, however, approach the lethal. The great toxicity of the heavy metals in effective doses seems to be the chief obstacle to their more extensive use.3 Since the inhibitory effect of certain heavy metals would seem ascribable to the results of thrombosis (Cruickshank, 1931), attempts to enhance thrombus formation by the addition of clot-forming agents are warranted. In combination with active thrombogenic agents, such as thrombin, thromboplastin, or cephalin, the dose of the toxic metal might be reduced to a level effective and safe. As rapidly growing endothelial cells of tumor vessels are more susceptible to traumatization than are cells of mature vessels, the site of thrombus formation might be localized to areas of rapid growth.