Thrombogenesis

Free Tissue Transfer to the Lower Extremity in the Setting of Thrombocytosis and the Role of Antiplatelet Therapy: A Propensity Score-Matched Analysis

BACKGROUND

 Free tissue transfer (FTT) provides a versatile method to achieve successful lower limb salvage. Thrombocytosis in patients undergoing lower extremity (LE) FTT is associated with increased risk of complications. The aims of this study were to assess the feasibility of performing LE FTT in patients with preoperative thrombocytosis, and whether antiplatelet (AP) therapy on the day of surgery (DOS) affects outcomes.

METHODS

 A retrospective review of thrombocytotic patients who underwent LE FTT between 2011 and 2022 was performed. Patients were stratified into groups based on the receipt of AP therapy on the DOS. Patients were propensity score matched for comorbidity burden and postoperative risk stratification. Outcomes of interest included perioperative transfusion requirements, postoperative flap-related complications, rates of flap success, limb salvage, and ambulatory status.

RESULTS

 Of the 279 patients who underwent LE FTT, 65 (23.3%) were found to have preoperative thrombocytosis. Fifty-three patients remained following propensity score matching; of which, 32 (60.4%) received AP therapy on the DOS and 21 (39.6%) did not. Overall flap success rate was 96.2% (n = 51). The likelihoods of thrombosis and hematoma development were similar between cohorts (p = 0.949 and 0.574, respectively). Receipt of DOS AP therapy was associated an additional 2.77 units and 990.10 mL of transfused blood (p = 0.020 and 0.018, respectively). At a mean follow-up of 20.7 months, overall limb salvage and ambulatory rates were 81.1% (n = 43) and 79.2% (n = 42), respectively, with no differences between cohorts.

CONCLUSION

 Preoperative thrombocytosis is not an absolute contraindication to LE FTT. DOS AP therapy may be protective in comorbid patients with elevated platelet counts but must be weighed against possible short-term bleeding as suggested by significant increases in postoperative transfusion requirements.

Biomimetic nanoparticles in ischemic stroke therapy

Abstract

Ischemic stroke is one of the most severe neurological disorders with limited therapeutic strategies. The utilization of nanoparticle drug delivery systems is a burgeoning field and has been widely investigated. Among these, biomimetic drug delivery systems composed of biogenic membrane components and synthetic nanoparticles have been extensively highlighted in recent years. Biomimetic membrane camouflage presents an effective strategy to prolong circulation, reduce immunogenicity and enhance targeting. For one thing, biomimetic nanoparticles reserve the physical and chemical properties of intrinsic nanoparticle. For another, the biological functions of original source cells are completely inherited. Compared to conventional surface modification methods, this approach is more convenient and biocompatible. In this review, membrane-based nanoparticles derived from different donor cells were exemplified. The prospect of future biomimetic nanoparticles in ischemic stroke therapy was discussed.

Graphic abstract

Management of Patients with Embolic Stroke of Unknown Source: Interpreting the Evidence in the Light of Clinical Judgement

PURPOSE OF REVIEW

To assess the validity of the belief that anticoagulation is not beneficial in patients with embolic stroke of unknown source (ESUS), and to asssess the benefits and safety of direct-acting oral anticoagulants (DOACs).

RECENT FINDINGS

The failure of randomized trials to show benefit of anticoagulation in ESUS is probably due to misclassification of large artery atherosclerosis (LAA) as ESUS, as defined by a stenosis ≥ 50%. There are important differences among DOACs. There are a number of problems with dabigatran, and rivaroxaban and edoxaban are not suitable for once-daily dosing. Recent evidence from real-world practice indicates that apixaban is more effective and safer than rivaroxaban. Plaque burden should be included in the definition of LAA. Patients in whom a cardioembolic source is strongly suspected should be anticoagulated; antiplatelet agents are not significantly safer than DOACs, and are not effective in cardioembolic stroke.

Stroke Etiology and Outcomes after Endovascular Thrombectomy: Results from the SITS Registry and a Meta-Analysis

BACKGROUND AND PURPOSE

The influence of stroke etiology on outcomes after endovascular thrombectomy (EVT) is not well understood. We aimed to investigate whether stroke etiology subgrouped as large artery atherosclerosis (LAA) and cardiac embolism (CE) influences outcomes in large artery occlusion (LAO) treated by EVT.

METHODS

We included EVT treated LAO stroke patients registered in the Safe Implementation of Treatment in Stroke (SITS) thrombectomy register between January 1, 2014 and September 3, 2019. Primary outcome was successful reperfusion (modified Treatment in Cerebral Infarction 2b-3). Secondary outcomes were symptomatic intracranial hemorrhage (SICH), 3-month functional independence (modified Ranking Scale 0-2) and death. Multivariable logistic regression models were used for comparisons. In addition, a meta-analysis of aggregate data from the current literature was conducted (PROSPERO, ID 167447).

RESULTS

Of 7,543 patients, 1,903 (25.2%) had LAA, 3,214 (42.6%) CE, and 2,426 (32.2%) unknown, other, or multiple etiologies. LAA patients were younger (66 vs. 74, P<0.001) and had lower National Institutes of Health Stroke Scale score at baseline (15 vs. 16, P<0.001) than CE patients. Multivariable analyses showed that LAA patients had lower odds of successful reperfusion (odds ratio [OR], 0.70; 95% confidence interval [CI], 0.57 to 0.86) and functional independence (OR, 0.74; 95% CI, 0.63 to 0.85), higher risk of death (OR, 1.44; 95% CI, 1.21 to 1.71), but no difference in SICH (OR, 1.09; 95% CI, 0.71 to 1.66) compared to CE patients. The systematic review found 25 studies matching the criteria. The meta-analysis did not find any difference between etiologies.

CONCLUSIONS

From the SITS thrombectomy register, we observed a lower chance of reperfusion and worse outcomes after thrombectomy in patients with LAA compared to CE etiology, despite more favorable baseline characteristics. In contrast, the meta-analysis did not find any difference between etiologies with aggregate data.

Stroke Prevention: Little-Known and Neglected Aspects

Combining available therapies has the potential to reduce the risk of stroke by 80% or more. A comprehensive review of all aspects of stroke prevention would be very lengthy; in this narrative review, we focus on some aspects of stroke prevention that are little-known and/or neglected. These include the following: (1) implementation of a Mediterranean diet; (2) B vitamins to lower homocysteine; (3) coordinated approaches to smoking cessation; (4) intensive lipid-lowering therapy; (5) lipid lowering in the elderly; (6) physiologically individualized therapy for hypertension based on renin/aldosterone phenotyping; (7) avoiding excessive blood pressure reduction in patients with stiff arteries; (8) treatment of insulin resistance with pioglitazone in stroke patients with prediabetes and diabetes; (9) impaired activation of clopidogrel in patients with variants of CYP2C19; (10) aspirin pseudoresistance due to enteric coating; (11) rationale for anticoagulation in patients with embolic stroke of unknown source; (12) pharmacologic properties of direct-acting oral anticoagulants that should be considered when choosing among them; (13) the identification of which patients with asymptomatic carotid stenosis are at a high enough risk to benefit from carotid endarterectomy or stenting; and (14) the importance of age in choosing between endarterectomy and stenting. Stroke prevention could be improved by better recognition of these issues and by implementation of the principles derived from them.

Rotational Thromboelastometry Derivative Fibrinogen-Platelet Ratio Predicts Thrombosis in Microsurgery

BACKGROUND

 Early detection of thrombotic events is of paramount importance for microsurgical procedures. Here, we present findings that underscore the value of rotational thromboelastometry (ROTEM) to aid in decision-making for pre- and postoperative anticoagulation, as well for patients with suspected hypercoagulability.

METHODS

 We prospectively collected pre- and postoperative ROTEM values on all free flap cases at the University of California, San Francisco, from 2015 to 2016. Patient age, body mass index, comorbidities, operative reports, risk factors, thrombotic complications, and outcomes were collected from electronic medical records. Two-sample t-tests were used to compare ROTEM values between cohorts. Modeling for sensitivity, specificity, and accuracy was done for threshold fibrinogen-to-platelet ratio (FPR).

RESULTS

 Of 52 patients who underwent free-tissue transfer, 15 had a thrombotic event either intraoperatively or postoperatively that required revision of the vascular anastomosis. Eight patients were clinically hypercoagulable preoperatively, seven of which had a thrombotic event. Several pre- and postoperative ROTEM values differed significantly between thrombotic and nonthrombotic cases. Preoperative (p = 0.027) and postoperative (p = 0.013) FPR were statistically significant when comparing the thrombotic to the nonthrombotic cohort. Threshold FPR ≥ 30 was the most sensitive and FPR ≥ 40 was the most specific.

CONCLUSION

 Our study affirms other studies that established ROTEM as an effective predictive tool for thrombotic events during free-tissue transfer. However, a lower threshold for FPR improves catchment of thrombotic events and flap failure with acceptable sensitivity. Our results support the routine use of ROTEM for detecting hypercoagulability in patients who would potentially benefit from intervention to prevent thrombotic complications.

Stroke Prevention in Older Adults: Recent Advances

The risks of stroke and dementia increase steeply with age, and both are preventable. At present, the best way to preserve cognitive function is to prevent stroke. Therapeutic nihilism based on age is common and unwarranted. We address recent advances in stroke prevention that could contribute greatly to prevention of stroke and dementia at a time when the aging of the population threatens to markedly increase the incidence of both. Issues discussed: (1) old patients benefit even more from lipid-lowering therapy than do younger patients; (2) patients with stiff arteries are at risk from a target systolic blood pressure <120 mm Hg; (3) the interaction of the intestinal microbiome, age, and renal function has important dietary implications for older adults; (4) anticoagulation with direct-acting oral anticoagulants should be prescribed more to old patients with atrial fibrillation; (5) B vitamins to lower homocysteine prevent stroke; and (6) most old patients in whom intervention is warranted for carotid stenosis would benefit more from endarterectomy than from stenting. An 80-year-old person has much to lose from a stroke and should not have effective therapy withheld on account of age. Lipid-lowering therapy, a more plant-based diet, appropriate anticoagulation or antiplatelet therapy, appropriate blood pressure control, B vitamins to lower homocysteine, and judicious intervention for carotid stenosis could do much to reduce the growing burden of stroke and dementia.

Recent advances in preventing recurrent stroke

Since a 2017 update, there have been important advances in stroke prevention. These include new evidence about nutrition, antiplatelet therapy, anticoagulation, lipid-lowering therapy, hypertension control, pioglitazone, and carotid endarterectomy and stenting. Evidence regarding toxic metabolites produced by the intestinal microbiome from egg yolk and red meat has important dietary implications, particularly for patients with impaired renal function, including the elderly. They should avoid egg yolk and red meat and limit the intake of animal flesh. Higher doses of folic acid may be needed for patients with the T allele of MTHFR, so it may not be sufficient to give vitamin B12 (methylcobalamin) alone, even in countries with folate fortification. There is now good evidence that lipid-lowering therapy is even more beneficial in the elderly than in younger patients; we should be using lipid-lowering therapy more intensively, often/usually combining statins with ezetimibe. There is new evidence that lower systolic blood pressure targets are better for most patients, but a subgroup with stiff arteries, a wide pulse pressure, and a diastolic pressure of <60 would be more likely to be harmed than helped by aiming for a systolic target of <120 mmHg. There is a better understanding of how the pharmacological properties of direct-acting oral anticoagulants and the metabolism of antiplatelet agents should inform decisions about the use of these agents. Pioglitazone markedly reduces the risk of stroke, both in diabetics and prediabetics; it should be used more widely. It is now clear that carotid endarterectomy is safer than stenting and that the difference is strongly affected by age. Most patients, and in particular older patients, would be better served by endarterectomy than stenting.

Advances in Stroke Prevention

There have been recent advances in stroke prevention in nutrition, blood pressure control, antiplatelet therapy, anticoagulation, identification of high-risk asymptomatic carotid stenosis, and percutaneous closure of patent foramen ovale. There is evidence that the Mediterranean diet significantly reduces the risk of stroke and that B vitamins lower homocysteine, thus preventing stroke. The benefit of B vitamins to lower homocysteine was masked by harm from cyanocobalamin among study participants with impaired renal function; we should be using methylcobalamin instead of cyanocobalamin. Blood pressure control can be markedly improved by individualized therapy based on phenotyping by plasma renin and aldosterone. Loss of function mutations of CYP2D19 impair activation of clopidogrel and limits its efficacy; ticagrelor can avoid this problem. New oral anticoagulants that are not significantly more likely than aspirin to cause severe bleeding, and prolonged monitoring for atrial fibrillation (AF), have revolutionized the prevention of cardioembolic stroke. Most patients (~90%) with asymptomatic carotid stenosis are better treated with intensive medical therapy; the few that could benefit from stenting or endarterectomy can be identified by a number of approaches, the best validated of which is transcranial Doppler (TCD) embolus detection. Percutaneous closure of patent foramen ovale has been shown to be efficacious but should only be implemented in selected patients; they can be identified by clinical clues to paradoxical embolism and by TCD estimation of shunt grade. “Treating arteries instead of treating risk factors,” and recent findings related to the intestinal microbiome and atherosclerosis point the way to promising advances in future.

B vitamins in stroke prevention: time to reconsider

B vitamin therapy lowers plasma total homocysteine concentrations, and might be a beneficial intervention for stroke prevention; however, cyanocobalamin (a form of vitamin B12) can accelerate decline in renal function and increase the risk of cardiovascular events in patients with impaired renal function. Although early trials did not show benefit in reduction of stroke, these results might have been due to harm in participants with impaired renal function. In patients with diabetic nephropathy, cyanocobalamin is harmful, whereas B vitamins appear to reduce cardiovascular events in study participants with normal renal function. Our meta-analysis of individual patient data from two large trials of B vitamin therapy (VISP and VITATOPS) indicates that patients with impaired renal function who are exposed to high-dose cyanocobalamin do not benefit from therapy with B vitamins for the prevention of stroke (risk ratio 1·04, 95% CI 0·84-1·27), however, patients with normal renal function who are not exposed to high-dose cyanocobalamin benefit significantly from this treatment (0.78, 0·67-0·90; interaction p=0·03). The potential benefits of B vitamin therapy with folic acid and methylcobalamin or hydroxycobalamin, instead of cyanocobalamin, to lower homocysteine concentrations in people at high risk of stroke warrant further investigation.

Preoperative Platelet Count Predicts Lower Extremity Free Flap Thrombosis: A Multi-Institutional Experience

BACKGROUND

Thrombocytosis in patients undergoing lower extremity free tissue transfer may be associated with increased risk of microvascular complications. This study assessed whether preoperative platelet counts predict lower extremity free flap thrombosis.

METHODS

All patients undergoing lower extremity free tissue transfer at Duke University from 1997 to 2013 and at the University of Pennsylvania from 2002 to 2013 were retrospectively identified. Logistic regression was used to assess whether preoperative platelet counts independently predict flap thrombosis, controlling for baseline and operative factors.

RESULTS

A total of 565 patients underwent lower extremity free tissue transfer, with an overall flap thrombosis rate of 16 percent (n = 91). Elevated preoperative platelet counts were independently associated with both intraoperative thrombosis (500 ± 120 versus 316 ± 144 × 10/liter; p < 0.001) and postoperative thrombosis (410 ± 183 versus 320 ± 143 × 10/liter; p = 0.040) in 215 patients who sustained acute lower extremity trauma within 30 days before reconstruction. In acute trauma patients, preoperative platelet counts predicted a four-fold increased risk of intraoperative thrombosis (cutoff value, 403 × 10/liter; OR, 4.08; p < 0.001) and a two-fold increased risk of postoperative thrombosis (cutoff value, 361 × 10/liter; OR, 2.16; p = 0.005). In patients who did not sustain acute trauma, preoperative platelet counts predicted a four-fold increased risk of intraoperative thrombosis (cutoff value, 352 × 10/liter; OR, 3.82; p = 0.002).

CONCLUSIONS

Acute trauma patients with elevated preoperative platelet counts are at increased risk for lower extremity free flap complications. Prospective evaluation is warranted for guiding risk stratification and targeted treatment strategies.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

Atrial fibrillation and stroke prevention: is warfarin still an option? Yes: Debate at the Controversies in Neurology Congress, Beijing, October 2011

With the advent of new oral anticoagulants, the place of warfarin for stroke prevention in patients with atrial fibrillation needs re-evaluation. Warfarin is difficult to use, because of large individual differences in response and metabolism, many significant interactions with drugs and foods, and fluctuations in vitamin K absorption. It requires frequent blood testing and dose adjustments, so with good reason patients and physicians are eager for the newer agents that are easier to use. However, the purchase price of the new anticoagulants is so high that warfarin will remain in widespread use. It is important therefore for physicians to know how to use it well. Anticoagulants work much better for stroke prevention in atrial fibrillation than do antiplatelet agents; physicians need to understand the concept of red thrombus (for which anticoagulants are required) versus white thrombus-platelet aggregates-which are the target of antiplatelet agents. Stroke from atrial fibrillation increases steeply with age, and the elderly benefit disproportionately from anticoagulation. It is still necessary for physicians to know how to use warfarin, and to use it better than it has been used in the past.

Effects of some pharmacological agents on the survival of unipedicled venous flaps: an experimental study

Clinical and experimental studies have been conducted to improve the survival of venous flaps. As a result of these studies, although various survival mechanisms were raised, none obtained satisfactory information. Venous stasis, and the resultant venous thrombosis, is a factor that decreases the survival of venous flaps. In this study, we evaluated the effects of two antiinflammatory agents, etodolac and etofenamate, on the survival of unipedicled venous flaps. In this study, 35 male New Zealand white rabbits (3,500-4,000 g) (70 ears) were used. Perichondrocutaneous flaps, 3 x 4.5 cm in size, were designed and raised, keeping the central veins intact in the middle of venous flap. Central arteries and nerves were ligated and transected both proximally and distally, to prepare unipedicled venous flaps. A silicone sheet was placed between the cartilage tissue and flap, to prevent blood flow and revascularization beneath. The subjects were divided into seven groups, consisting of five rabbits (10 ears). In the negative control group (group I), the single vascular pedicle of venous flaps, central veins were ligated and flaps sutured into their own place as the composite graft. In the positive control group (group II), after venous flaps were prepared, normal saline, 0.2 mL, was given subcutaneously. In the first of five experimental groups (group III), unfractionated heparin (100 U/day) was given subcutaneously. In the second experimental group (group IV), etodolac (5 mg/kg/day) was given subcutaneously. In the third experimental group (group V), etophenamate (5 mg/kg/day) was given orally through a feeding tube. In the fourth experimental group (group VI), parnaparin (5 anti-Xa U/kg/day) was given subcutaneously. In the fifth experimental group (group VII), nadroparin (5 anti-Xa U/kg/day) was given subcutaneously, about 7 days postoperatively. At the eighth postoperative day, surviving areas of venous flaps were measured, and the results were evaluated by Kruskal-Wallis ANOVA and Mann-Whitney U-test (P < 0.05). Biopsies were also taken from the flaps for histological evaluation of border of necrotic tissue. Surviving areas of unipedicled venous flaps were larger in experimental groups than those in negative and positive control group (P < 0.05). However, comparison of the experimental groups demonstrated no statistically significant difference (P > 0.05). We concluded that all pharmacological agents used in the experimental groups succeeded in increasing the survival of unipedicled venous flaps. Survival of the unipedicled venous flap was higher in venous flaps than that of composite graft, clearly showing the importance of the venous pedicle.

Characterization of fibronectin and fibrin(ogen) fragments in gingival crevicular fluid

A total of 49 crevicular fluid (CF) samples were collected with paper strips from 12 healthy adults. Each sample was eluted into sterile saline and two aliquots were drawn for SDS-PAGE, one for fibronectin and one for fibrin analysis. Peptides were transferred to nitrocellulose membranes, and fibronectin and fibrin were detected using specific antibodies. The relative amounts of different molecular forms of fibronectin and fibrin were analyzed using a laser densitometer. After the sample collection, Plaque Index, Papilla Bleeding Index and pocket depth were measured. Bone loss was estimated from the orthopanthomograms. Fibronectin fragments were seen in all CF samples. Intact fibronectin was seen in 21 samples, of which 76% were collected from periodontitis-affected sites. There was a positive correlation between the proportion of intact fibronectin and the clinical parameters. Intact fibrin and fibrin fragments were seen in all samples. Fibrin-positive material with larger molecular weight than intact fibrin was also seen in all samples. A negative correlation was found between the proportion of intact fibrin and the clinical parameters. There was no correlation between total amounts and concentrations of fibronectin and fibrin. Molecular forms of fibronectin and fibrin may affect the pathogenesis and healing of periodontal diseases, since the biologic effects of the fragments of these molecules differ from those of the intact molecules.

Quantification of fibrin deposition in flowing blood with peroxidase-labeled fibrinogen. High shear rates induce decreased fibrin deposition and appearance of fibrin monomers

To study fibrin incorporation into thrombi at different wall shear rates, a new method to study fibrin deposition on extracellular matrixes underlying stimulated endothelial cells under flow conditions was developed. For this method, we used fibrinogen labeled with peroxidase (Fg-PO). Fg-PO was fully exchangeable for Fg in the clotting assays tested, and PO activity was bound to fibrin-specific fragments. Fg-PO containing fibrin could be stained for microscopic studies with 3,3'-diaminobenzidine and could be quantified by oxidation of phenylenediamine. The absorbance values at 492 nm were converted to fibrin quantities via a standard curve. To study fibrin deposition, Fg-PO was added in trace amounts to whole blood anticoagulated with low-molecular-weight heparin, and perfusion studies were performed over endothelial cell matrixes containing tissue factor. In parallel perfusion studies, 125I-labeled Fg was added in trace amounts to whole blood instead of Fg-PO. Both quantitative methods demonstrated decreased fibrin deposition after perfusions at 1,300 sec-1 compared with fibrin deposition after perfusions at 300 sec-1, while fibrinopeptide A generation was independent of the wall shear rate. The decrease in fibrin deposition at 1,300 sec-1 was accompanied by the appearance of fibrin monomers in the perfusate. This suggested that the decrease in fibrin incorporation at 1,300 sec-1 was due to the impaired polymerization of fibrin monomers. This impairment was probably due to a decrease in local fibrin monomer concentration as a result of the increased removal of monomers from the surface at 1,300 sec-1.

Characterization of fibrin(ogen) fragments in gingival crevicular fluid

Crevicular fluid (CF) samples were collected by paper strips from healthy and diseased sites. The molecular distribution of fibrin and fibronectin in CF and plasma samples was investigated using SDS-polyacrylamide gel electrophoresis and specific immunoglobulins. Intact fibrin was found in all CF samples. In addition several bands with both lower and higher molecular weights than intact fibrin were seen. These bands were not present in the plasma samples. The low molecular weight bands are suggested to represent degradation products of fibrin. The high molecular bands could be fibrin-fibronectin complexes or fragments of large fibrin polymers. Fibronectin degradation products, but not intact fibronectin, were seen in both healthy and diseased samples.

Mechanisms of tumor necrosis induced by photodynamic therapy

Despite great progress and promising results achieved in cancer treatment by photodynamic therapy (PDT), the exact mechanism of tumor photosensitization in vivo by porphyrins and related phototherapeutic agents has not been fully explored and understood. This review is an attempt to gather available data on various processes occurring in neoplastic cells, microvasculature, non-vascular stroma and circulating blood within PDT-treated tumors. This information is necessary to understand the mechanisms governing the very complex processes which eventually lead to tumor necrosis.

Role of shear rate and platelets in promoting fibrin formation on rabbit subendothelium. Studies utilizing patients with quantitative and qualitative platelet defects

The deposition of platelets on subendothelium of rabbit aortic segments exposed to non-anticoagulated human blood increased progressively with increasing wall shear rates (50-2,600 s-1), whereas fibrin deposition decreased. Studies in normal subjects and patients with platelet disorders suggested that, under the conditions used, platelets were essential for fibrin deposition at intermediate (650 s-1) but not low (50 s-1) shear rates. Fibrin deposition was markedly diminished in a patient with Scott syndrome whose platelets have a diminished capacity to bind Factor Xa and activate Factors IX and II. In glycoprotein IIb-IIIa deficiency, fibrin deposition was normal (or somewhat increased), whereas in glycoprotein Ib deficiency the association of fibrin with platelets, but not subendothelium, was decreased. The findings indicate that platelets, perhaps through surface localization of coagulation proteins, promote fibrin deposition on subendothelium at arterial shear rates and suggest that agents directed against platelet coagulant properties could be antithrombotic.

Detection of hypercoagulability by the measurement of the dynamic loss modulus of clotting blood

The dynamic loss modulus of clotting whole blood was measured in thrombotic patients to characterize the physical properties of coagulation in the hypercoagulable state. The dynamic loss modulus was measured by a Sonoclot. Thrombotic patients consisted of 30 with deep vein thrombosis and 25 with arterial thrombosis. An accelerated increment rate of the dynamic loss modulus at the beginning of gelling was the characteristic of hypercoagulability. This characteristic occurred more frequently than other abnormalities in other tests for hypercoagulability (beta-thromboglobulin, antithrombin III and TEG). Only in deep vein thrombosis, a moderately positive correlation was noted between the increment rate of the dynamic loss modulus and the plasma fibrinogen level.

Ruptured atheromatous plaques in saphenous vein coronary artery bypass grafts: a mechanism of acute, thrombotic, late graft occlusion

Although early occlusion of saphenous vein coronary artery bypass grafts is usually thrombotic, late occlusion is most often a result of progressive intimal fibromuscular proliferation or atheroma formation in the implanted vain. We describe another mechanism of late graft occlusion: atheromatous plaque rupture with superimposed occlusive thrombosis. Four men, ages 48-67 years underwent repeat bypass surgery for recurrent angina. Six of eight vein grafts excised 5-8 years after original bypass showed complete luminal occlusion by recent thrombus superimposed on ruptured atheromatous plaques. Similar findings were present at autopsy in two of three vein grafts from a 66-year-old man who died 7 years after bypass. These lesions are indistinguishable from those that occur in native coronary arteries of many patients with acute myocardial infarction. Unlike previously described graft occlusions, the present lesion represents a mechanism of acute, thrombotic, late graft occlusion. If recognized early, it may be amenable to nonsurgical intervention by angioplasty or thrombolysis.

Combined effect of prostaglandins and an aortic proteoglycan on platelet aggregation and plasma clotting

The individual and combined effects of PGD2, PGI2 and an aortic proteoglycan on human platelet aggregation and plasma clotting were studied. PGI2 was at least 10 times more potent than PGD2 in inhibiting platelet aggregation. Small doses of prostaglandins inhibited ADP- and thrombin-induced aggregation, but only prolonged aggregation time without affecting the extent of arachidonic acid (AA)-induced aggregation. Small doses of prostaglandins did not affect thrombin-induced clotting of PRP. Large doses of prostaglandins abolished platelet aggregation and prolonged the onset of thrombin-induced clotting. The aortic proteoglycan (APG) had no appreciable effect on ADP- or AA-induced aggregation. Small doses of APG abolished thrombin-induced clotting, while large doses of APG suppressed both clotting and aggregation induced by thrombin. PGI2 and PGD2 showed additive inhibition of platelet aggregation regardless how the aggregation was induced. APG and prostaglandins showed additive inhibition of only thrombin-induced aggregation. APG, but not any of the prostaglandins, prolonged clotting time of PPP. This prolongation was not potentiated by PGI2 or PGD2.

Anticoagulation in myocardial infarction: modern approach to an old problem

The role of routine anticogulation in acute myocardial infarction continues to be a source of controversy. There is currently strong evidence to suggest that conventional anticoagulation will prevent the formation of most deep vein thrombi and subsequent pulmonary embolization. Anticoagulant agents also appear to reduce the incidence of emboli from cardiac mural thrombi to peripheral arteries. Patients without a predisposition to bleeding are unlikely to have hemorrhagic complications in the hospital after usual doses of anticoagulant drugs. In patients with severe hypertension, prior gastrointestinal bleeding, carcinoma or advanced age, small dose heparin therapy appears to reduce the incidence of venous thrombosis and probably of pulmonary emboli as well. Its value in preventing peripheral arterial embolization has not been defined. Anticoagulation with standard "large" doses is an effective means of preventing the risks of pulmonary and peripheral emboli during the in-patient phase of acute myocardial infarction. Small dose heparin therapy provides an excellent alternative to conventional anticoagulation when there is more than a negligible risk of hemorrhage. There is little evidence at this time to support the use of long-term anticoagulation beyond the acute phase of myocardial infarction.

Prevention of femoral vein occlusion by local injection of Thrombolysin in the rat

An experimental model was developed that will produce femoral vein occlusion greater than 90% of the time in rats weighing less than 500 grams. This standard venous clot, produced by combining intimal trauma with local venous stasis, can simulate clinical crush and replantation problems. Using this standard clot model, Thrombolysin was injected in the femoral artery after trauma to the vein but before venous stasis. Femoral vein patency was determined at the end of the 30 minute period of venous stasis. With the appropriate dosage, ipsilateral venous occlusion was prevented (P less than 0.00001) without preventing contralateral venous occlusion (P less than 0.02). Except for decreased fibrinogen levels, there was no significant change in the factors studied between the control and experimental groups. It is possible, therefore, to prevent thrombosis in a vein with intimal damage, even in the presence of a low-flow state by the local injection of Thrombolysin, without producing systemic anticoagulation.

Iliac venous thrombosis in infants and children after cardiac catheterization

Twenty-two patients developed thrombosis of the lower abdominal portion of the inferior vena cava, iliac or femoral vein (IVT) after cardiac catheterization. All patients has at least one previous study from 1 day to 11 months of age (mean, 2 months) and seven had two catheterizations before discovery of IVT. Transposition of the great arteries was the most common defect associated with IVT (12/22, 55%). From one to seven catheter changes were made during the time of venous cannulation (mean, 105 minutes). No clinical evidence of IVT was present immediately after the preceding cardiac catheterization. The discovery of significant IVT usually necessitated the use of a vein from the upper extremity to complete the cardiac catheterization. IVT was associated with previous balloon atrial septostomy using either a Fogarty or Rashkind septostomy catheter in 13/22 patients (59%). In addition, 86% of the patients had either of these balloon catheters or a Swan-Ganz catheter used during a previous study. The potential development of IVT should be considered especially in cyanotic infants and small children in whom balloon catheters are used.

Antithrombotic therapy. Rationale and application

Arterial thrombosis and venous thrombosis differ in pathogenesis, morphology, and response to antithrombotic therapy. Antiplatelet therapy usually is aimed at arterial thrombi, in whose formation platelet-mediated reactions predominate, while anticoagulant therapy is effective against venous thrombi, in whose formation coagulation predominates.

Coronary thrombosis in pathogenesis of acute myocardial infarction. Histopathological study of coronary arteries in 108 necropsied cases using serial section

An extensive histopathological study was carried out on the hearts of 108 patients with electrocardiographically proven acute myocardial infarction dying after admission to a coronary care unit. The occluded or the narrowest segments of the coronary arteries were examined at intervals of 100 mu using serial sections. Serial sectioning is important in such a study because the pathology of the lumen can vary considerably within a 2 to 3 mm segment. A high incidence (80.3%) of thrombus formation corresponding to the site of infarction was observed. These thrombi occluded the vessel lumen, were usually found proximally in the coronary arteries, and were associated with a ruptured atheromatous plaque in 90.8 per cent of cases. It is postulated that an increase of intraplaque pressure resulting from a honeycomb-like accumulation of foam cells, cholesterol clefts, and blood infiltration through the injured endothelial cells is the cause of rupture of the atheromatous plaque. This rupture into the vessel lumen may precede, and be responsible for, formation of thrombus and the onset of acute myocardial infarction.

Relationship between myocardial infarction and preinfarction angina: a histopathological study of coronary arteries in two sudden death cases employing serial section

Two patients who had previously experienced old myocardial infarction and who died suddenly after an attack of chest pain were examined and discussed. In both cases two of the three main coronary arteries showed severe stenosis with canalization. Ruptured atheromatous plaque was found in the unblocked coronary artery. Fibrin was already formed and surrounded the fractured intimal collagen fiber, foam cells, and cholesterin clefts, but a luminal thrombi had not yet been formed. Fresh occluding thrombi were formed at the site of the ruptured atheromatous plaque. Coronary thrombi containing abscess components such as foam cells, cholesterin clefts, and the fractured intimal collagen fiber were found in our preliminary study. These views support the supposition that this fracture between the lumen and the plaque might precede and be responsible for the formation of the thrombus and the onset of acute myocardial infarction. It was confirmed that the attack of preinfarction angina occurred at the time of the rupture of the atheromatous plaque. The rupture of the atheromatous plaque plays an important part as an initiating factor of peinfarction angina and myocardial infarction. Thus, it is necessary to examine coronary arteries by serial histopathological section method.

Occurrence of disseminated intravascular coagulation (DIC) in obstructive jaundice and its relation to biliary tract infection

Coagulation studies were done on 78 consecutive cases of obstructive jaundice with or without biliary tract infection. Among 26 cases with biliary tract infection 20 cases showed no bleeding tendency but remarkable hypercoagulability with decreased fibrinolytic activity. Other six cases developed diffuse bleeding tendency in addition to the signs of hypotension and multiorgan dysfunction such as oliguria, respiratory distress and mental confusion. Most showed marked coagulation defects characterized by thrombocytopenia, decreased fibrinogen, antithrombin III and plasminogen levels and narrowing of maximal amplitude in thrombelastogram as well as the increase of fibrin degradation products and positive soluble fibrin monomer complexes. All except one died and three cases were autopsied. In two cases postmortem examination revealed multiple fibrin thrombi in lungs and other organs. A cause of the development of bleeding tendency in obstructive jaundice presently observed may likely to be due to the occurrence of disseminated intravascular coagulation (DIC), i.e. hypercoagulability caused by the biliary tract infection is responsible.

In vivo and in vitro effects of thrombin and plasmin on human factor VIII (AHF)

The relationship between factor VIII (AHF) procoagulant activity and factor VIII-related antigen were examined in patients with disseminated intravascular coagulation (DIC), pulmonary embolism (PE), and coronary artery disease with or without myocardial infarction (MI). It was found that 13 of 13 patients with DIC, 17 of 17 patients with PE, and 10 of 12 patients with MI possessed a significantly elevated factor VIII-related antigen to factor VIII activity ratio (VIII-ratio). The VIII-ratio returned to normal in each of 2 patients with DIC and 1 paitent with PE after treatment with heparin, heparin and alpha-amino-caproic acid, and heparin and coumadin respectively. In contrast, the VIII-ratio was slightly elevated only in 1 of 15 patients with coronary artery insufficiency without MI. In in vitro studies, after treatment of plasma with thrombin or plasmin, factor VIII activity was lost, whereas the amount of factor VIII-related antigen remained the same or was even increased when measured by agarose quantitative immunoelectrophoresis. These observations have led us to conclude that an elevated VIII-ratio is a very sensitive indicator of intravascular coagulation.

An acute effect of cigarette smoking on platelet function. A possible link between smoking and arterial thrombosis

In a controlled, double blind study, the smoking of a single cigarette has been shown to increase the platelet's response to a standard aggregating stimulus. This phenomenon appears to be specifically related to the inhaling of tobacco smoke; it does not follow the smoking of lettuce leaf filled cigarettes. The platelet effect seems independent of the rise in plasma free fatty acids which follows cigarette smoking. Smoking-induced potentiation of platelet aggregation may help to explain the increased incidence of arterial thrombi and/or atheromatous plaques in cigarette smokers.