The value of 64-detector row computed tomography for the exclusion of pulmonary embolism.

Recently, a diagnostic strategy using a clinical decision rule, D-dimer testing and spiral computed tomography (CT) was found to be effective in the evaluation of patients with clinically suspected pulmonary embolism (PE). However, the rate of venous thromboembolic complications in the three-month follow-up of patients with negative CT was still substantial and included fatal events. It was the objective to evaluate the safety of withholding anticoagulants after a normal 64-detector row CT (64-DCT) scan from a cohort of patients with suspected PE. A total of 545 consecutive patients with clinically suspected first episode of PE and either likely pre-test probability of PE (using the simplified Wells score) or unlikely pre-test probability in combination with a positive D-dimer underwent a 64-DCT. 64-DCT scanning was inconclusive in nine patients (1.6%), confirmed the presence of PE in 169 (31%), and ruled out the diagnosis in the remaining 367. During the three-month follow-up of the 367 patients one developed symptomatic distal deep-vein thrombosis (0.27%; 95%CI, 0.0 to 1.51%) and none developed PE (0 %; 95%CI, 0 to 1.0%). We conclude that 64-DCT scanning has the potential to safely exclude the presence of PE virtually in all patients presenting with clinical suspicion of this clinical disorder.

A risk assessment model for the identification of hospitalized medical patients at risk for venous thromboembolism: the Padua Prediction Score.

BACKGROUND: Prophylaxis of venous thromboembolism (VTE) in hospitalized medical patients is largely underused. We sought to assess the value of a simple risk assessment model (RAM) for the identification of patients at risk of VTE. METHODS: In a prospective cohort study, 1180 consecutive patients admitted to a department of internal medicine in a 2-year period were classified as having a high or low risk of VTE according to a predefined RAM. They were followed-up for up to 90 days to assess the occurrence of symptomatic VTE complications. The primary study outcome was to assess the adjusted hazard ratio (HR) of VTE in high-risk patients who had adequate in-hospital thromboprophylaxis in comparison with those who did not, and that of VTE in the latter group in comparison with low-risk patients. RESULTS: Four hundred and sixty-nine patients (39.7%) were labelled as having a high risk of thrombosis. VTE developed in four of the 186 (2.2%) who received thromboprophylaxis, and in 31 of the 283 (11.0%) who did not (HR of VTE, 0.13; 95% CI, 0.04-0.40). VTE developed also in two of the 711 (0.3%) low-risk patients (HR of VTE in high-risk patients without prophylaxis as compared with low-risk patients, 32.0; 95% CI, 4.1-251.0). Bleeding occurred in three of the 186 (1.6%) high-risk patients who had thromboprophylaxis. CONCLUSIONS: Our RAM can help discriminate between medical patients at high and low risk of VTE. The adoption of adequate thromboprophylaxis in high-risk patients during hospitalization leads to longstanding protection against thromboembolic events with a low risk of bleeding.

Von Willebrand factor propeptide makes it easy to identify the shorter Von Willebrand factor survival in patients with type 1 and type Vicenza von Willebrand disease.

Reduced von Willebrand factor (VWF) half-life has been suggested as a new pathogenic mechanism in von Willebrand disease (VWD). The usefulness of VWF propeptide (VWFpp) in exploring VWF half-life was assessed in 22 type 1 and 14 type Vicenza VWD patients, and in 30 normal subjects, by comparing the findings on post-Desmopressin (DDAVP) VWF t(1/2) elimination (t(1/2el)). The VWFpp/VWF antigen ratio (VWFpp ratio) was dramatically increased in type Vicenza VWD (13.02 +/- 0.49) when compared to normal subjects (1.45 +/- 0.06), whereas it appeared to be normal in all type 1 VWD patients (1.56 +/- 0.7), except for the four carrying the C1130F mutation (4.69 +/- 0.67). A very short VWF t(1/2el) was found in type Vicenza VWD (1.3 +/- 0.2 h), while all type 1 VWD patients had a t(1/2el) similar to that of the controls (11.6 +/- 1.4 and 15.4 +/- 2.5 h respectively), except for the four patients carrying the C1130F mutation, who had a significantly shorter VWF survival (4.1 +/- 0.2 h). A significant inverse correlation emerged between VWFpp ratio and VWF t(1/2el) in both VWD patients and normal subjects. The VWFpp ratio thus seemed very useful for distinguishing between type 1 VWD cases with a normal and a reduced VWF survival, as well as for identifying type Vicenza VWD.

Endothelial dysfunction in haemophilia patients.

Haemophilia patients may develop cardiovascular diseases, suggesting that their clotting defect does not protect them completely from atherosclerosis and its complications. We aimed to evaluate cardiovascular risk factors and, for the first time, the presence of endothelial dysfunction in middle-aged haemophilia patients. We studied 40 patients with haemophilia A and B (24 with moderate-severe disease and 16 with mild disease), and 40 healthy controls. Flow-mediated dilation (FMD), carotid ultrasound (US) intima media thickness (IMT), arterial blood pressure, body mass index (BMI), cholesterol, triglycerides, glucose, insulin, lipoprotein(a) and homocysteine levels were measured, and PAI-1 and t-PA levels before and after venous occlusion (VO), and antibodies to HIV, HBV and HCV were assayed. At least one cardiovascular risk factor was detected in 87.5% of patients, and 2 or more in 47.5% of cases. At US exam, none of the patients had significant carotid stenosis or significant differences in IMT compared to controls. In contrast, all the patients had a significant FMD impairment, associated with a reduced t-PA release after VO in 70% of cases. PAI-1 levels significantly correlated with BMI, triglycerides and insulin values. Fifteen haemophilia patients with chronic viral hepatitis and/or HIV infection showed a significantly lower FMD than patients without active infection. We found an endothelial dysfunction with impaired FMD and t-PA release in our haemophilia patients, usually associated with cardiovascular risk factors. Other pathogenic mechanisms, such as chronic viral infections, are likely to be involved in this endothelial damage, however.

Variations in fibrinolytic parameters and inhibin-A in pregnancy: related hypertensive disorders.

BACKGROUND: The mechanisms leading to pregnancy-related hypertensive disorders, and pregnancy-induced hypertension (PIH) and pre-eclampsia (PE) in particular, are still not clear. Diagnostic criteria are clinical because specific markers of the condition are lacking. A role of the fibrinolytic system has been suggested. OBJECTIVES: We aimed to evaluate the behavior of tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor type 1 (PAI-1), PAI-2, and the placental hormone inhibin-A in women with a normal pregnancy vs. women with pregnancies complicated by PIH or PE. METHODS: Blood samples were drawn between the 25th and 30th gestational week (GW) and between the 31st and 36th GW in order to assay t-PA, PAI-1, PAI-2 and inhibin-A; routine biochemical exams, ultrasonography umbilical artery pulsatility index (PI), placental weight and newborn weight were measured. RESULTS: In pregnancies complicated by hypertensive disorders, PAI-1 levels were higher than in controls and increased significantly after the 25th GW, especially in PE, as did inhibin-A. PAI-2 levels were significantly lower after the 30th GW in patients with PIH and PE. The PAI-1/PAI-2 ratio was significantly higher in PE patients than in controls as of the 25th GW, but only after the 30th GW in patients with PIH. Inhibin-A was significantly correlated with fibrinolytic parameters, and inversely with newborn weight. Receiver-operator characteristic curves for PAI-1 and inhibin-A showed a high sensitivity and specificity for PE. PAI-2 correlated with newborn and placental weight, and inversely with PI of the umbilical artery. CONCLUSIONS: Fibrinolytic tests (especially PAI-1) and inhibin-A monitoring during pregnancy may help in the early diagnosis of pregnancy-related hypertensive disorders.

Porphyrin-photosensitized processes: their applications in the prevention of arterial restenosis.

Photodynamic therapy (PDT) is based on the use of a photozensitising compound which is accumulated by rapidly proliferating cells. Subsequent irradiation with light wavelengths specifically absorbed by the photosensitiser promotes the generation of reactive short-lived oxygen species which cause an irreversible and selective damage. Endovascular interventions to correct obstructive arterial disease have been developed worldwide with excellent short term results. However, long term patency is still limited by the onset of restenosis, due to subsequent intimal hyperplasia (IH). IH is characterized by proliferation and migration of smooth muscle cells (SMC) and extracellular matrix production. Targeting of SMC by photozensitisers can be efficiently achieved by taking advantage of the receptors for low density lipoproteins (LDL) expressed by such cells. Thus, preference is given to hydrophobic compounds which readily partition in the lipid matrix of LDL. We developed a liposomal formulation of a highly hydrophobic photozensitising agent, Zn(II)-phthalocyanine (ZnPc). The liposome-delivered ZnPc was readily taken up by cultured SMC cells and preferentially localized in the Golgi apparatus. Red light irradiation of incubated SMC induced cell death. Extension of these investigations to an in vivo rabbit model showed that ZnPc mainly accumulated in the media layer, where PDT induces the main damage through cellular depletion due to apoptosis of SMC, changes in the extracellular matrix with generation of a barrier to cellular migration, and acceleration of re-endothelization. Initial clinical applications showed that PDT safely and effectively prevents restenosis after angioplasty up to a 6 month follow-up.

Identifying carriers of type 2N von Willebrand disease: procedures and significance.

The defective FVIII carrier function of von Willebrand factor (VWF) identifies type 2N von Willebrand disease (VWD), a variant with a pattern resembling hemophilia A. Type 2N characterization is based on the evaluation of the capacity of VWF to bind exogenous FVIII (VWF:FVIIIB). Here we report on a retrospective evaluation of hemostatic laboratory parameters most useful in detecting type 2N carriers. The diagnostic capacity of aPTT, FVIII, VWF:Ag, FVIII/VWF:Ag ratio, VWF:FVIIIB and VWF:FVIIIB/VWF:Ag ratio was evaluated in 21 type 2N VWD carriers. Twenty subjects were heterozygous for the R854Q mutation, one was heterozygous for the R760C missense mutation, which interferes with cleavage of the VWF propeptide. We found that prolongation of aPTT and decrease in FVIII and FVIII/VWF:Ag ratio were not frequent findings in type 2N carriers. The same was true for VWF:FVIIIB which was not always abnormal. On the contrary, VWF:FVIIIB/VWF:Ag ratio was always defective and its values were not related with FVIII and FVIII/VWF:Ag ratio or influenced by plasma VWF concentration. Given these results, we attribute the greatest significance to VWF:FVIIIB/VWF:Ag ratio in the diagnosis of type 2N defects, and only search for type 2N mutations, to validate the diagnosis, if the ratio proves abnormal.

Cardiovascular risk factors and ultrasound evaluation of intima-media thickness at common carotids, carotid bulbs, and femoral and abdominal aorta arteries in patients with classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

CONTEXT: In congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, a tendency for obesity, high insulin, and high 24-h blood pressure levels has been reported in children and adolescents. Increased intima-media thickness (IMT) is considered a measure of subclinical atherosclerosis and a predictor of myocardial infarction and stroke. OBJECTIVE: The objective of the study was to evaluate glucose metabolism, lipid profile, IMT of the abdominal aorta, right and left common carotids, carotid bulbs, and common femoral arteries in adult CAH patients. SUBJECTS: Nineteen (10 females, nine males; 28 +/- 3.5 yr) patients (12 salt wasting and seven simple virilizing) and 19 (10 females, nine males) healthy subjects matched for anthropometric parameters (age, sex, body mass index, smoking habit, waist to hip ratio, and blood pressure). METHODS: Glucose metabolism was studied using the oral glucose tolerance test and the homeostasis model assessment-insulin resistance. The echo-Doppler was used for arterial ultrasound. 17-Hydroxyprogesterone, androstenedione, testosterone, ACTH, plasma renin activity, total and high-density lipoprotein cholesterol, and triglycerides were measured. RESULTS: CAH patients had significantly higher fasting plasma insulin (11.6 +/- 6.20 microU/ml vs 5.18 +/- 2.4 microU/ml; P < 0.0001) and homeostasis model assessment-insulin resistance than controls (2.46 +/- 1.92 vs 1.12 +/- 0.58; P = 0.0033). IMT of the studied arteries was higher in CAH patients than controls. There was no correlation between IMT and cumulative glucocorticoid doses and androgen levels. CONCLUSION: A reduced insulin sensitivity and increased IMT were demonstrated in adults with CAH, who consequently need a follow-up for cardiovascular risk.

Diagnosis and follow-up of thrombotic thrombocytopenic purpura by means of von Willebrand factor collagen binding assay.

Thrombotic thrombocytopenic purpura (TTP) is characterized by intravascular thrombosis leading to consumption of large or unusually large von Willebrand factor (VWF) multimers. The usefulness of VWF collagen binding (VWF:CB) assay was assessed in detecting the decrease/absence of large VWF multimers or the presence of abnormally large forms in patients with TTP. Nine patients with TTP were studied during the acute phase of the disorder and the absence of large VWF multimers was demonstrated by means of the VWF:CB assay. These findings were confirmed by VWF multimer pattern analysis; VWF:CB deficiency appeared to correlate with abnormalities in large VWF multimers. The diagnostic potency of VWF:CB was especially evident when the values were expressed as VWF:CB/VWF:Ag ratio. VWF:CB was also used during the follow-up of the disorder to document improvement or restoration of large VWF multimers. VWF:CB was able to detect the absence or decrease of large VWF multimers better than VWF ristocetin cofactor (VWF:RCo); in fact, VWF:CB was defective when large VWF multimers persisted to be decreased, in contrast with what observed with VWF:RCo. In conclusion, VWF:CB is a simple test that appears to be useful, together with clinical symptoms and reduced platelet count, for the diagnosis and follow-up of TTP.

Venous thromboembolism and the risk of subsequent symptomatic atherosclerosis.

BACKGROUND: Recently, we reported an association between asymptomatic carotid atherosclerosis and venous thromboembolism (VTE) of unknown origin. We hypothesized that patients with VTE of unknown origin would be at a higher risk of developing symptomatic atherosclerosis than patients with VTE induced by known risk factors. METHODS: To examine this hypothesis, we studied 1,919 consecutive patients followed prospectively after their first VTE episode. The primary outcome was non-fatal and fatal symptomatic atherosclerotic disease in patients with VTE of unknown origin as compared to those with secondary VTE. An independent committee assessed all study outcomes, and adjusted hazard ratios (HR) were calculated using the Cox's proportional hazards model. RESULTS: After a median follow-up of 48 and 51 months, respectively, at least one symptomatic atherosclerotic complication was detected in 160 of the 1,063 patients (15.1%) with VTE of unknown origin, and in 73 of the 856 (8.5%) with secondary VTE. After adjusting for age and other risk factors of atherosclerosis, the HR for symptomatic atherosclerotic complications in patients with VTE of unknown origin compared to those with secondary VTE was 1.6 (95% confidence intervals; CI: 1.2-2.0). When the analysis was restricted to patients without previous symptomatic atherosclerosis, the HR became 1.7 (95% CI: 1.1-2.4). CONCLUSIONS: Patients with VTE of unknown origin have a 60% higher risk of developing symptomatic atherosclerotic disease than do patients with secondary venous thrombosis.

Patients with Cushing's syndrome have increased intimal media thickness at different vascular levels: comparison with a population matched for similar cardiovascular risk factors.

Cushing's syndrome (CS) is associated with high cardiovascular risk. The aim of this study was to analyze intimal media thickness (IMT) in patients with CS and compare them with subjects matched for similar conventional and independent cardiovascular risk factors. Twenty eight patients with CS (mean age: 40.7 +/- 2.5 y) and 28 subjects (mean age: 41.1 +/- 14 y) matched for sex, age, smoking habit, body mass index, blood pressure levels, glucose and lipid metabolism were evaluated. IMT was measured at right and left common carotid (CC), carotid bulb (BC), aorta (Ao) and femoral (F) levels by B-echo-Doppler ultrasonography. Although parameters of cardiovascular risk factors did not differ statistically between patients and controls, IMT was significantly increased (right and left CC-IMT, p < 0.05; right and left BC-IMT, p < 0.01, Ao-IMT p < 0.05) and wall plaques were more common (14.2 % VS. 7.1 %) in patients. In CS patients, CC-IMT and F-IMT correlated positively and significantly with fasting glucose (right CC-IMT: r (2) = 0.37, p = 0.05; left CC-IMT: r (2) = 0.43, p = 0.02; right F-IMT: r (2) = 0.57; p < 0.01; left F-IMT: r (2) = 0.47, p = 0.01) and HOMA index (left CC-IMT: r (2) = 0.64, p < 0.01 and left F-IMT: r (2) = 0.48, p < 0.05). The CS patients' waist-to-hip ratio (WHR) was evaluated and correlated positively and significantly with CC-IMT (right: r (2) = 0.53, p = 0.01 and left: r (2) = 0.44, p = 0.05). No correlation was found between IMT and cortisol levels, however. In conclusion, patients with CS have more severe atherosclerotic damage than a population matched for similar cardiovascular risk factors. Multiple events related to long-term cortisol effects on metabolism and at vascular and endothelial sites may increase the risk of cardiovascular damage in patients with CS.

Blood oxidative status and selectins plasma levels in healthy donors receiving granulocyte-colony stimulating factor.

Recombinant human G-CSF (rHuG-CSF) is used for hematopoietic progenitor cells (HPC) mobilization and collection. Activation of polymorphonuclear leukocytes (PMN) is present during rHuG-CSF treatment and is associated with endothelial cell dysfunction and hypercoagulation. We evaluated whether PMN activation by rHuG-CSF may alter the blood oxidative status and subsequently affect the vascular cell function. Fourteen healthy individuals received rHuG-CSF for HPC harvesting. Blood was drawn before starting rHuG-CSF (T0), on the last day of rHuG-CSF (T1) and 1 week after stopping rHuG-CSF (T2). Levels of CD11b, myeloperoxidase (MPO), hydroperoxides, nitric oxide (NO), and soluble endothelium (sES), leukocyte (sLS), and platelet (sPS) selectins were measured. During rHuG-CSF, CD11b, MPO and hydroperoxides significantly increased, while NO levels significantly decreased, compared with T0. At T2 all these markers returned to baseline values. Significant increments of all selectins were observed during rHuG-CSF. At T2 sES and sEP significantly decreased back to pre-treatment values, whereas sLS remained significantly high. These data show that rHuG-CSF induces a transient inflammatory status characterized by circulating activated PMN, which release reactive oxygen species and intracellular proteases, promoting the onset of an abnormal oxidative status. This process may modify the hemostatic balance towards a pro-thrombotic state.

Expression of the normal factor V allele modulates the APC resistance phenotype in heterozygous carriers of the factor V Leiden mutation.

BACKGROUND: Functional defects of the protein C pathway, detectable in plasma as activated protein C (APC) resistance, are a prevalent risk factor for venous thrombosis. The factor V (FV) Leiden mutation causes APC resistance by interfering with the APC-mediated inactivation of both FVa and FVIIIa. Co-inheritance of FV Leiden and quantitative FV deficiency on different alleles, a rare condition known as pseudo-homozygous APC resistance, is associated with pronounced APC resistance and 50% reduced FV levels, because of non-expression of the non-Leiden FV allele. OBJECTIVES: The role of normal FV in modulating the APC resistance phenotype in carriers of FV Leiden was investigated in patients with pseudo-homozygous APC resistance and in model systems. PATIENTS/METHODS: Four functional plasma assays probing both components of APC resistance (susceptibility of FVa to APC and cofactor activity of FV in FVIIIa inactivation) were employed to compare seven clinically and genetically characterized FV Leiden pseudo-homozygotes to 30 relatives with different FV genotypes (including 12 FV Leiden heterozygotes and seven carriers of FV deficiency) and to 32 unrelated FV Leiden homozygotes. RESULTS AND CONCLUSIONS: All assays consistently indicated that FV Leiden pseudo-homozygotes are significantly more APC-resistant than heterozygotes and indistinguishable from homozygotes. Thrombin generation measurements in FV-deficient plasma reconstituted with purified normal FV and FV Leiden confirmed these observations and showed that the expression of the normal FV allele is an important modulator of APC resistance in FV Leiden heterozygotes. These findings provide an explanation for the higher thrombotic risk of FV Leiden pseudo-homozygotes when compared with heterozygotes.

The incidence of venous thromboembolism in carriers of antithrombin, protein C or protein S deficiency associated with the HR2 haplotype of factor V: a family cohort study.

In order to assess whether the HR2 haplotype of the factor V gene (HR2) increases the risk of venous thromboembolism (VTE) in carriers of antithrombin (AT), protein C (PC) or S (PS) defects, we performed this determination in 336 subjects, who were family members of 66 symptomatic patients with clotting inhibitors defects. We first assessed the presence of previous VTE, and then followed prospectively subjects without prior VTE. VTE episodes had occurred in 26 individuals: 18 in 139 carriers of clotting inhibitors defects alone (annual incidence, 0.55%), four in 33 carriers of clotting inhibitors defects combined with HR2 (0.52%) and four in 151 non-carriers (0.1%), resulting in a relative risk (RR) for VTE of 4.9 (95% CI: 1.7-14.4) and 4.62 (95% CI: 1.2-18.4), respectively. After an overall follow-up of 2557 patient-years, VTE episodes developed in 12 subjects: nine in 121 carriers of clotting inhibitors defects alone (annual incidence, 0.92%), three in 29 carriers of clotting inhibitors defects combined with HR2 (1.0%) and none in 147 non-carriers. In family members of patients with AT, PC or PS defects the coinheritance of HR2 haplotype does not seem to increase the thromboembolic risk.

Carotid plaque morphology and cerebrovascular events.

AIM: Beside the degree of stenosis, plaque morphology obtained by the B mode ultrasound technique has been considered to define the plaque at risk for cerebrovascular events, and a subset of patients who deserve more strict surveillance. Our aim was to evaluate the relationship between plaque morphology, progression of stenosis, and the development of new cerebrovascular events. METHODS: We followed up by carotid duplex scan 230 asymptomatic patients, evaluating the degree and progression of internal carotid (ICA) stenoses and plaque morphology of the atherosclerotic lesions. RESULTS: During the follow-up period (median 32 month, range 6-125 months) 7% of patients developed ischemic neurological events of which 1.7% was a stroke. Of these events, only 5.7% correlated with carotid lesions. The new neurological events correlated with the degree and progression of stenoses, with a non homogeneous echographic appearance and irregular surface. The progression of the degree of stenoses was the parameter that correlated the most with the development of new neurologic symptoms. Nevertheless, the lesions that progressed modified their echographic pattern from homogeneous to non homogeneous in 78% of cases. Irregular surface and high degree of stenoses more than the baseline echographic pattern seem to correlate with plaque progression. CONCLUSION: Our follow-up study confirmed that ICA stenosis is a benign condition: very few strokes clearly correlated to the stenosis were observed. Nevertheless, the major predictors of risk for cerebrovascular events, besides the degree of stenoses, are the progression of the degree of stenosis, irregular surface and non-homogeneous echographic appearance.

Psychological aspects and coping in haemophilic patients: a case-control study.

Although enormous progress has been made in recent years in the field of haemophilia, some problems still await solution, such as the risk of sudden haemorrhage, the sequelae of haemophilic arthropathy and social activities. We, therefore, carried out a case-control study in which some psychological dimensions (social expectations, tendency to depression, state of anxiety and self-esteem) were evaluated in a group of 60 haemophiliacs. A control group was formed of 78 healthy subjects matched for age, socio-economic class and level of education. The methodology used was the administration of self-assessment questionnaires which investigate and provide a quantitative measure of psychological dimensions. The results can be subjected to statistical analysis. Three self-assessment questionnaires were used: (i) the Marlowe-Crowne scale, (ii) the Beck Inventory version modified by Cusinato and (iii) the S.T.A.I.-form. Our aim was to evaluate: (i) whether there are significant differences in the considered psychological aspects between haemophiliacs and healthy subjects; (ii) whether there is a significant correlation between the psychological dimensions considered in the haemophiliacs and in the healthy subjects. The results showed that the haemophiliacs have a good psychological adaptation to their disease with the exception of their greater tendency to have less self-esteem than do the healthy subjects. As far as concerns the second aim, we found than self-esteem correlated with all the psychological variables investigated. This information could indicate the enormous importance that the psychological variable 'self-esteem' plays in haemophiliacs with respect to whether or not they develop depressive disorders and/or anxiety states.

[Therapeutic indications for acute venous thromboembolism. Current status and future perspectives]. / Indicazioni di terapia della malattia tromboembolica venosa. Attualità e prospettive.

Except for selected patients requiring aggressive therapies, the large majority of patients with acute venous thromboembolism are currently treated with full doses of unfractionated or low-molecular-weight heparins (LMWH) followed by oral anticoagulants for variable periods of time. LMWHs present a number of potential advantages over unfractionated heparin: a longer plasma half-life, improved subcutaneous bioavailability, and a more predictable dose-response relationship. As a result of these pharmacokinetic properties, these compounds have the potential to greatly simplify the initial treatment of venous thromboembolism, making the treatment of suitable patients feasible in an outpatient setting with considerable saving in costs and improvement in patients' quality of life. The use of unfractionated heparin is still desirable in the initial treatment of acute pulmonary embolism in non-critically ill patients. The use of heparin protocols assures that virtually all patients will promptly achieve the therapeutic range for the activated partial thromboplastin time. Although the optimal duration of anticoagulation in patients suffering an episode of venous thromboembolism is presently unknown, it seems reasonable to administer a short-term course of coumarin drugs to patients with thrombosis associated with transient risk factors, while a longer course should be considered in patients with idiopathic thrombosis and in those with permanent risk factors. At present, indefinite anticoagulant therapy remains a clinical judgment in the individual patient. The efficacy and safety of emerging drugs (pentasaccharide, ximelagatran) in the treatment and secondary prevention of venous thromboembolic disorders is currently under investigation.