Factors associated with thrombotic complications after the Fontan procedure: a secondary analysis of a multicenter, randomized trial of primary thromboprophylaxis for 2 years after the Fontan procedure.

OBJECTIVES: The study sought to identify factors associated with increased risk of thrombosis after Fontan. BACKGROUND: The Fontan procedure is the culmination of staged palliation for patients with univentricular physiology. Thrombosis is an important complication after this procedure. METHODS: An international multicenter randomized controlled trial of acetylsalicylic acid versus warfarin for thromboprophylaxis after the Fontan procedure was conducted in 111 patients, and did not show a significant difference regarding thrombotic complications. We performed a secondary analysis of this previously published manuscript to identify factors associated with thrombosis in this population. Standardized prospective data collection included independent adjudication of all events. RESULTS: At 2.5 years after randomization, time-related freedom from thrombosis was 69% (all venous, no arterial events), with 28% of thrombosis presenting with clinical signs or events. Hazard of thrombosis was highest immediately after Fontan with a gradual increase in risk during late follow-up. In multivariable models, factors associated with higher risk of thrombosis were pulmonary atresia with intact ventricular septum (hazard ratio [HR]: 3.64, 95% confidence interval [CI]: 1.04 to 12.70, p = 0.04), pulmonary artery distortion (HR: 2.35, 95% CI: 0.96 to 5.73, p = 0.06), lower pre-operative unconjugated bilirubin (HR: 0.84 µmol/l, 95% CI: 0.72 to 0.99, p = 0.04), use of central venous lines for >10 days or until hospital discharge (HR: 17.8, 95% CI: 3.97 to 79.30, p < 0.001), and lower FiO(2) 24 h after the procedure (HR: 0.67/10%, 95% CI: 0.45 to 1.00, p = 0.06). Patients on warfarin who consistently achieved minimum target international normalized ratio levels or those on acetylsalicylic acid had a decrease in risk of thrombosis compared with patients who often failed to meet target international normalized ratio level (HR: 3.53, 95% CI: 1.35 to 9.20, p = 0.01). CONCLUSIONS: More favorable thromboprophylaxis strategies are needed in light of the difficulties in controlling warfarin therapy and the high prevalence of thrombosis in this population.

A multicenter, randomized trial comparing heparin/warfarin and acetylsalicylic acid as primary thromboprophylaxis for 2 years after the Fontan procedure in children.

OBJECTIVES: The purpose of this study was to compare the safety and efficacy of acetylsalicylic acid (ASA) and warfarin for thromboprophylaxis after the Fontan procedure. BACKGROUND: Fontan surgery is the definitive palliation for children with single-ventricle physiology. Thrombosis is an important complication; the optimal thromboprophylaxis strategy has not been determined. METHODS: We performed a multicenter international randomized trial of primary prophylactic anticoagulation after Fontan surgery. Patients were randomized to receive for 2 years either ASA (5 mg/kg/day, no heparin phase) or warfarin (started within 24 h of heparin lead-in; target international normalized ratio: 2.0 to 3.0). Primary endpoint (intention to treat) was thrombosis, intracardiac or embolic (all events adjudicated). At 3 months and 2 years after the Fontan procedure, transthoracic and transesophageal echocardiograms were obtained as routine surveillance. Major bleeding and death were primary adverse outcomes. RESULTS: A total of 111 eligible patients were randomized (57 to ASA, 54 to heparin/warfarin). Baseline characteristics for each group were similar. There were 2 deaths unrelated to thrombosis or bleeding. There were 13 thromboses in the heparin/warfarin group (3 clinical, 10 routine echo) and 12 thromboses in the ASA group (4 clinical, 8 routine echo). Overall freedom from thrombosis 2 years after Fontan surgery was 19%, despite thrombosis prophylaxis. Cumulative risk of thrombosis was persistent but varying and similar for both groups (p = 0.45). Major bleeding occurred in 1 patient in each group. CONCLUSIONS: There was no significant difference between ASA and heparin/warfarin as primary thromboprophylaxis in the first 2 years after Fontan surgery. The thrombosis rate was suboptimal for both regimens, suggesting alternative approaches should be considered. (International Multi Centre Randomized Clinical Trial Of Anticoagulation In Children Following Fontan Procedures; NCT00182104).

The influence of age on in vitro plasmin generation in the presence of fibrin monomer.

BACKGROUND AND OBJECTIVES: The components of the fibrinolytic system interact to generate plasmin from its zymogen form, plasminogen. At birth, all the components of the fibrinolytic system are present but with differing plasma concentrations. The present study was undertaken to explore the effect of physiological, age-dependent factors of the fibrinolytic system during childhood on the capacity to generate plasmin. DESIGN AND METHODS: Total plasmin generation was measured in venous plasma from umbilical cords and adults, on plastic and cell surfaces, in the presence of fibrin monomer, Desafib. Plasminogen, its inhibitors alpha2-antiplasmin and plasminogen activator inhibitor type 1, and plasmin-alpha2-antiplasmin complex in the time samples were assayed by enzyme-linked immunosorbent assay. The effect of addition of plasminogen on the plasmin generation in cord plasma and the effect of lipoprotein on adult and cord plasmin generation were measured. RESULTS: On the surface of human umbilical vein endothelial cells, onset of plasmin generation was earlier (40 min) compared to plastic (60 min) but total plasmin generation was similar on both surfaces. The addition of plasminogen to cord plasma increased plasmin generation. Supplementation of lipoprotein in adult plasma had an inhibitory effect, but there was no significant effect in cord plasma. INTERPRETATIONS AND CONCLUSIONS: Plasmin generation is reduced in newborn compared to adult plasma. Decreased plasmin generation in cord plasma is likely due to decreased plasminogen concentration. The antifibrinolytic effect of lipoprotein is more pronounced in adults as compared to newborns due to the presence of higher plasminogen concentration.

Urgent clinical challenges in children with ischemic stroke: analysis of 1065 patients from the 1-800-NOCLOTS pediatric stroke telephone consultation service.

BACKGROUND AND PURPOSE: Clinical trials are lacking in pediatric stroke. As a result, physicians caring for children with stroke face significant challenges. The patient characteristics and specific nature of clinical challenges facing practicing clinicians can inform the design of and priorities for developing relevant clinical trials. METHODS: Physicians consulted the 1-800-NOCLOTS toll-free pediatric stroke telephone consultation service on children (birth to 18 years) with ischemic stroke. Pediatric neurologist or hematologists provided telephone consultation and documented caller and patient characteristics, antithrombotic treatments and callers' questions for entry into a computerized database. Children referred from January 1, 1995 to January 1, 2004, comprised the study cohort. RESULTS: Stroke consults were completed on 1065 children located predominantly in the United States (76%). Children had arterial ischemic stroke (AIS; 679; 64%) or cerebral sinovenous thrombosis (CSVT; 386; 36%) and were 54% male and 16% neonates. Risk factors and antithrombotic agents (none, aspirin, warfarin, and heparins) differed by stroke type. In 60% of patients, callers had not initiated antithrombotic therapy. Callers' questions for both stroke types usually concerned treatment selection (83%), but for AIS, questions more frequently (P<0.0001) concerned the selection and interpretation of etiological investigations. CONCLUSIONS: Research is urgently needed in pediatric stroke to provide direction for management in "real-life" settings. Research efforts should address the unique challenges within different stroke types and include observational studies addressing investigation of the child with AIS. For AIS and CSVT, randomized controlled trials investigating the efficacy of antithrombotic treatment are urgently needed.

Impaired fibrinolytic activity is present in children with dyslipidemias.

Dyslipidemias are major risk factors for atherosclerosis and cardiovascular disease. Abnormalities of fibrinolytic and coagulation components are considered useful predictors of cardiovascular morbidity and mortality in adults. This study examined whether fibrinolytic and coagulation components are abnormal in children with dyslipidemia. Thirty-six children with asymptomatic dyslipidemia, and 26 control subjects underwent venous occlusion stress testing with collection of preocclusion and postocclusion blood samples. All samples were assayed for tissue plasminogen activator, plasminogen, plasminogen activator inhibitor-1, alpha(2)-antiplasmin, alpha(2)-macroglobulin, D-dimer, fibrinogen, and von Willebrand factor. Children with dyslipidemia had significantly decreased levels of tissue plasminogen activator in both preocclusion and postocclusion samples compared with control subjects, reflecting decreased fibrinolytic activity. Children with dyslipidemia also had significantly increased levels of plasminogen, alpha(2)-macroglobulin, and fibrinogen in preocclusion and postocclusion samples compared with control subjects. In conclusion, decreased fibrinolytic activity is present in asymptomatic children with dyslipidemias, potentially reflecting endothelial dysfunction and increased risk of cardiovascular disease in early adult life. Further studies are required to determine the usefulness of this marker in predicting disease progression or response to therapy.

A cross-sectional study evaluating post-thrombotic syndrome in children.

BACKGROUND: Post-thrombotic syndrome (PTS) in adults, characterized by swelling, skin pigmentation, pain, and ulceration of the limb, is secondary to deep vein thrombosis (DVT). In contrast to the extensive documentation on PTS in adults, little is known about the risk of PTS in children. OBJECTIVE: To determine the incidence, clinical characteristics, and predictors of PTS in children. METHODS: A cross-sectional study in 153 nonselected children with objectively confirmed DVT. All children were assessed for PTS using a standardized score. As per the PTS score, severity was classified as: absent, mild, moderate, or severe. RESULTS: Post-thrombotic syndrome was present in 96/153 children (63%), in which 80 (83%) were mild and 16 (17%) were moderate. Swelling was the most frequently recorded subjective symptom (43%) while increased limb circumference (71%) and presence of collateral circulation (53%) were the most frequently recorded objective symptoms. Risk factors for development of PTS were: lack of resolution of the DVT by radiographic assessment (OR 3.96, 95% CI 1.68-9.30), number of vessels involved in the initial DVT (OR 2.05, 95% CI 1.52-2.77), and length of follow-up (OR 1.22, 95% CI 1.08-1.39). CONCLUSIONS: These findings demonstrate that PTS is a clinically significant disease in children with previous DVT.

Trend to efficacy and safety using antithrombin concentrate in prevention of thrombosis in children receiving l-asparaginase for acute lymphoblastic leukemia. Results of the PAARKA study.

An association has been reported between thrombotic events and the use of L-asparaginase (ASP) in children with acute lymphoblastic leukaemia (ALL). The mechanism for thrombosis is likely related to an acquired antithrombin deficiency. Since a primary prophylaxis using antithrombin concentrates may prevent thrombosis, the PARKAA (Prophylactic Antithrombin replacement in kids with ALL treated with L-asparaginase) study was performed. The objectives of PARKAA were to determine if there was a trend to efficacy and safety of antithrombin treatment as assessed by 1) incidence of thrombosis 2) incidence of bleeding and 3) plasma markers of endogenous thrombin generation as surrogate outcomes for thrombosis. The study was not powered to answer the question of efficacy and safety, but rather to detect a trend. PARKAA was an open, randomised, controlled study in children with ALL being treated with ASP. Children were randomised to receive antithrombin infusions or no antithrombin treatment. All thrombotic events were confirmed using bilateral venography, ultrasound, echocardiography and MRI. The incidence of thrombosis in patients treated with antithrombin was 28% (95% CI 10-46%), compared to 37% (95% CI 24-49%) in the non treated arm. Two minor bleeds occurred in patients in the treated arm, but were not considered to be related to antithrombin. No significant differences were seen in plasma markers by the treatment group. In conclusion, treatment with antithrombin concentrate shows a trend to efficacy and safety. In contrast, there was no difference in surrogate markers for thrombosis. Carefully designed clinical trials are needed to test the efficacy and safety of antithrombin in this population.

Dose-finding and pharmacokinetic profiles of prophylactic doses of a low molecular weight heparin (reviparin-sodium) in pediatric patients.

INTRODUCTION: The low molecular weight heparin (LMWH), reviparin-sodium was studied in dose-finding and pharmacokinetic studies in children with central venous lines (CVLs). MATERIALS AND METHODS: The dose-finding study was performed in 24 patients aged 3 days to 16 years. Dose adjustments were made using a nomogram based on anti-factor Xa levels (units (U)/ml) (target of 0.1-0.3 U/ml). The pharmacokinetic study was performed in 19 patients, 9 less than or equal to 5 kg (7 of whom were less than 3 months) and 10 greater than 5 kg (all more than 3 months). RESULTS: The dose-finding study demonstrated that children over 5 kg required 30 International Units (IU)/kilogram (kg), subcutaneous (SC) twice daily (BID), and children less than or equal to 5 kg required 50 IU/kg, SC BID, to achieve target levels. The pharmacokinetic study demonstrated that 80% of anti-factor Xa levels were within the target range with both patient groups having similar peak (average=0.26 U/ml) and trough (average=0.13 U/ml) levels. CONCLUSIONS: Peak anti-factor Xa levels (0.1-0.3 U/ml) using reviparin-sodium are achieved by administering 50 IU/kg in children greater than 3 months of age and 30 U/kg in children less than 3 months of age.

An open-label randomized controlled trial of low molecular weight heparin compared to heparin and coumadin for the treatment of venous thromboembolic events in children: the REVIVE trial.

OBJECTIVE(S): Venous thromboembolic events (VTE) are serious complications in children and for which the standard of care, unfractionated heparin followed by oral anticoagulation (UFH/OA), is problematic. The objective of REVIVE was to compare the efficacy and safety of a low molecular weight heparin (reviparin-sodium) to UFH/OA for the treatment of VTE in children. STUDY DESIGN: This multicenter, open-label study, with blinded central outcome adjudication, randomized patients with objectively confirmed VTE to receive either reviparin-sodium or UFH/OA. Dose adjustments were made using nomograms. The efficacy outcome was based on recurrent VTE and death due to VTE during the 3-month treatment period. The safety outcomes were major bleeding, minor bleeding and death. Due to slow patient accrual, REVIVE was closed prematurely. RESULTS: At 3 months, with reviparin-sodium, 2/36 patients (5.6%) had recurrent VTE or death compared to 4/40 patients (10.0%) receiving UFH/OA (odds ratio=0.53; 95% CI=(0.05, 4.00); Fisher's exact test: 2P=0.677). There were 7 major bleeds, 2/36 (5.6%) in the reviparin-sodium group and 5/40 (12.5%) in UFH/OA group (odds ratio=0.41; 95% confidence interval 0.04, 2.76); Fisher's exact test: P=0.435). There were 5 deaths during the study period, 1 (2.8%) in the reviparin-sodium group and 4 (10.0%) in the UFH/OA group. All five deaths were unrelated to VTE but one was due to an intracranial hemorrhage in the UFH/OA group. CONCLUSIONS: Although limited by small sample size, REVIVE provides valuable information on the incidence of recurrent VTE, major bleeding and problematic issues associated with therapy of VTE in children.

An open-label randomized controlled trial of low molecular weight heparin for the prevention of central venous line-related thrombotic complications in children: the PROTEKT trial.

OBJECTIVE(S): Central venous lines (CVLs) are major risk factors for venous thromboembolism (VTE) in children. The objective of PROTEKT was to determine if a low molecular weight heparin (reviparin-sodium) safely prevents CVL-related VTE. STUDY DESIGN: This multi-center, open-label study, with blinded central outcome adjudication, randomized patients with new CVLs to twice-daily reviparin-sodium or standard care. The efficacy outcome was based on an exit venogram at Day 30 (+14 days), or earlier in case of CVL removal, or confirmed symptomatic VTE. The safety outcomes were major bleeding and death. Due to slow and restricted patient accrual, PROTEKT was closed prematurely. RESULTS: With reviparin-sodium, 14.1% (11:78) of patients had VTE compared to 12.5% (10:80) of control patients (odds ratio=1.15; 95% confidence interval 0.42, 3.23); 2P=0.82). One patient had a major bleed and there were two deaths, all three events occurring in the standard care group. CONCLUSIONS: The use of reviparin-sodium for short-term prophylaxis of CVL-related VTE in children was safe but its efficacy remains unclear. Although underpowered, PROTEKT provided valuable information on event rates and predictors of CVL-related VTE.

Fibrinolytic response to venous occlusion is decreased in patients after Kawasaki disease.

Impaired fibrinolysis is considered a sensitive marker of endothelial dysfunction. Persistent endothelial dysfunction occurs in some patients following Kawasaki disease. The aim of the present study was to assess whether impaired fibrinolysis is present in long-term survivors of Kawasaki disease. The study included 42 children with a documented history of Kawasaki disease presenting with or without coronary lesions, and 26 healthy controls. Blood samples were collected from patients and controls prior to and following venous occlusion stress testing. Significantly decreased fibrinolytic response to venous occlusion was detected in patients compared with controls due to decreased tissue plasminogen activator. In addition, patients had significantly increased plasma concentrations of plasminogen and fibrinogen, which were related to similar increases of alpha2 -macroglobulin. Decreased fibrinolytic response was found in patients with coronary aneurysms but also in those without coronary lesions. In summary, a decreased fibrinolytic response to venous occlusion may reflect persistent endothelial damage following acute Kawasaki disease, potentially predisposing these patients to accelerated atherosclerosis and cardiovascular disease in early adult life.

Central venous line-related thrombosis in children: association with central venous line location and insertion technique.

Venous thromboembolic events (VTEs) in children are associated with central venous lines (CVLs). The study objective was to assess whether CVL location and insertion technique are associated with the incidence of VTE in children. We hypothesized that VTE would be more frequent with (1). CVL location on the left body side, (2). CVL location in the subclavian vein rather than the jugular vein, and (3). CVL insertion by percutaneous technique rather than venous cut-down. This was a prospective, multicenter cohort study in children with acute lymphoblastic leukemia who had a CVL placed in the upper venous system during induction chemotherapy. Characteristics of CVL were documented prospectively. All children had outcome assessment for VTE by objective radiographic tests, including bilateral venography, ultrasound, echocardiography, and cranial magnetic resonance imaging. Among 85 children, 29 (34%) had VTE; 28 VTEs appeared in the upper venous system, and 1 was sinovenous thrombosis. Left-sided CVL (odds ratio [OR], 2.5; 95% confidence interval, 1.0-6.4; P =.048), subclavian CVL (OR, 3.1; 95% CI, 1.2-8.5; P =.025), and percutaneous CVL insertion (OR, 3.5; 95% CI, 1.3-9.2; P =.011) were associated with an increased incidence of VTE. Interaction occurred between CVL vein location and insertion technique. Subclavian vein CVL inserted percutaneously had an increased incidence (54%) of VTE compared with any other combination (P =.07). For CVL in the upper venous system, CVL placement on the right side and in the jugular vein may reduce the risk for CVL-related VTE. If subclavian vein placement is necessary, CVL insertion by venous cut-down appears preferable over percutaneous insertion.

Fibrinolytic system in adolescents: response to venous occlusion stress tests.

Recent studies indicate that the incidence of thromboembolic events is increasing as a secondary complication in children with serious underlying diseases. The mechanism to eliminate these thrombi via the thrombolytic system in children is unknown. The baseline fibrinolytic system is age dependent, with significant variation between children and adults. Adult studies would suggest that the fibrinolytic response to venous occlusion has more clinical relevance than the baseline fibrinolytic system. The aim of this study was to determine whether the fibrinolytic response to venous occlusion stress testing in healthy adolescents differs from the response in healthy adults. Healthy adolescents (13-18 y) from a school population and normal adults were recruited. Pre- and postvenous occlusion blood samples were collected using standard techniques. Plasma tissue plasminogen activator, plasminogen activator inhibitor-1, plasminogen, alpha(2)-antiplasmin, alpha(2)-macroglubulin, D-dimers, euglobulin lysis time, and fibrinogen were measured on each sample. Adolescents had significantly decreased tissue plasminogen activator antigen levels and increased plasminogen activator inhibitor-1 activity levels after venous occlusion, resulting in significantly prolonged euglobulin lysis times. The results of our study confirm developmental differences in the fibrinolytic response to venous occlusion stress testing. The age-related differences in fibrinolytic response to venous occlusion of younger children and the significance of these differences on the pathophysiology of thromboembolic events in children require further studies.

Effect of covalent serpin-heparinoid complexes on plasma thrombin generation on fetal distal lung epithelium.

Extravascular coagulation within the lung airspace is a hallmark of respiratory distress syndrome (RDS) in premature infants. We previously showed that covalent antithrombin-heparin complex (ATH) is superior to noncovalent antithrombin (AT) + heparin (H) mixtures at inhibiting plasma thrombin generation on rat fetal distal lung epithelium (FDLE) in vitro. However, heparin cofactor II (HC) has been shown to selectively inhibit thrombin, which may be advantageous if other enzyme activities are present in the airspace. We compared the abilities of ATH, covalent HC-heparin complex (HCH), and covalent HC-dermatan sulfate (HCD) to inhibit thrombin generation on FDLE in plasmas from either adults or newborns. In the presence of ATH, peak free thrombin generation in adult plasma on the cell surface was reduced by 92% compared with controls (no anticoagulant). However, whereas HCH reduced peak free thrombin generation in adult plasma by 81%, HCD was only able to reduce activity by 33%. All covalent complexes caused a greater decrease in thrombin activity compared with that with the corresponding noncovalent serpin + heparinoid mixtures. Experiments in plasma from newborns resulted in peak free thrombin that was less than or equal to that in adult plasma when covalent conjugates were added. Relative peak free thrombin was proportional to rate of prothrombin consumption and amount of thrombin-inhibitor complexes formed. In vivo, experiments in newborn rats showed that a greater percentage of intratracheally instilled ATH and HCH could be recovered in lung lavage fluid compared withwith that for HCD. In summary, ATH, HCH, and HCD are inhibitors of thrombin generation on FDLE superior to the corresponding noncovalent mixtures, with ATH and HCH being more potent than HCD. Covalent conjugates of AT or HC with H may be preferred in treatment of extravascular coagulation.

A prospective cohort study determining the prevalence of thrombotic events in children with acute lymphoblastic leukemia and a central venous line who are treated with L-asparaginase: results of the Prophylactic Antithrombin Replacement in Kids with Acute Lymphoblastic Leukemia Treated with Asparaginase (PARKAA) Study.

BACKGROUND: Thrombotic events (TEs) are serious secondary complications in children with acute lymphoblastic leukemia (ALL) who receive L-asparaginase (ASP) therapy; however, the prevalence of TEs has not been established. The primary objective of the Prophylactic Antithrombin Replacement in Kids with Acute Lymphoblastic Leukemia Treated with Asparaginase (PARKAA) Study was to determine the prevalence of TEs. The secondary objective was to detect any association of TEs with the presence of congenital or acquired prothrombotic disorders. METHODS: Children with ALL were screened for TEs at the end of ASP treatment using bilateral venograms, ultrasound, magnetic resonance imaging, and echocardiography. Symptomatic TEs were confirmed by appropriate radiographic tests. All tests were read by a blinded central adjudication committee. RESULTS: Twenty-two of 60 children had TEs, a prevalence of 36.7% (95% confidence interval, 24.4-48.8%). TEs were located in the sinovenous system of the brain in 1 patient, the right atrium in 3 patients, and the upper central venous system in 19 patients. TEs detected by venography resulted in 1) 25-100% occlusion, with 1 in 3 patients showing occlusion of > 75% of the greatest vessel dimension, and 2) the presence of collaterals in 60% of patients, with 40% categorized as major. No children with TEs were positive for factor V Leiden or prothrombin gene 20201A, and four of eight children with antiphospholipid antibodies had a TE. CONCLUSIONS: The prevalence of TEs is exceedingly high in this population, and it is likely that the extent of occlusion is likely clinically significant. No trend was seen toward an association between TEs and the presence of congenital prothrombotic disorders. A trend was seen toward an association between TEs and antiphospholipid antibodies. Carefully designed clinical trials of primary prophylaxis for the prevention of TEs are required in this patient population.

Comparison of venography and ultrasound for the diagnosis of asymptomatic deep vein thrombosis in the upper body in children: results of the PARKAA study. Prophylactic Antithrombin Replacement in Kids with ALL treated with Asparaginase.

Deep vein thrombosis (DVT) in children occurs primarily in the upper body venous system. This prospective diagnostic study compared bilateral venography and ultrasound for detection of DVT in the upper venous system in 66 children with acute lymphoblastic leukemia. Results were interpreted by central blinded adjudication. Deep venous thrombosis occurred in 29% (19/66) patients. While 15/19 DVT were detected by venography (sensitivity 79%), only 7/19 were detected by ultrasound (sensitivity 37%). The 12 DVT detected by venography but not by ultrasound were located in the subclavian vein or more central veins. Three of 4 DVT detected by ultrasound but not by venography were in the jugular vein. We conclude that ultrasound is insensitive for DVT in the central upper venous system but may be more sensitive than venography in the jugular veins. A combination of both venography and ultrasound is required for screening for DVT in the upper venous system.

Decreased concentrations of heparinoids are required to inhibit thrombin generation in plasma from newborns and children compared to plasma from adults due to reduced thrombin potential.

Thrombin generation is decreased and delayed in plasma from newborns and children compared to adults. We hypothesized that lower doses of heparinoid anticoagulants are required to give similar thrombin generation in newborn (umbilical cord) and child plasmas compared to that of adults. Thrombin generation was performed in either the absence or presence of unfractionated heparin (UFH), low molecular weight heparin (LMWH) or a covalent antithrombin-heparin complex (ATH). After contact activation and recalcification of each plasma, thrombin activity was measured by periodic sub-sampling into chromogenic substrate. UFH inhibited thrombin generation to a greater extent compared to LMWH in all plasmas. Cord plasma was more sensitive to inhibition and displayed a greater difference in the effectiveness of UFH compared to LMWH than other plasmas. Lower concentrations of UFH and LMWH were required to inhibit thrombin generation in cord and child plasmas compared to adult plasma. In comparison, ATH strongly inhibited thrombin generation in all 3 plasmas. Similar peak thrombin concentrations were observed at lower ATH concentrations (0.1 U/mL) compared to either UFH (0.25 U/mL) or LMWH (0.25 U/mL). As with UFH and LMWH, cord plasma was more sensitive to inhibition by ATH than the other plasmas and lower ATH concentrations inhibited thrombin generation in cord and child plasmas compared to adult plasma. Decreased thrombin generation with heparinoids in cord and child plasmas compared to adult plasma coincided with decreased rates of prothrombin consumption and increased proportion of thrombin-alpha2-macroglobulin inhibitor complexes. In summary, lower doses of UFH, LMWH or ATH result in similar peak thrombin generation in newborn and child plasmas compared to adult plasma. Cord plasma was the most sensitive to inhibition, with ATH being more effective than UFH or LMWH.

Effective treatment of ligneous conjunctivitis with topical plasminogen.

PURPOSE: The etiology of ligneous conjunctivitis is now known to be due to an underlying type 1 plasminogen deficiency. We hereby report the clinical features of three cases and their response to topically administered plasminogen. DESIGN: Observational case series. METHODS: Two Caucasian females aged 5 years and an 18-month male of north African descent presented with a membranous conjunctivitis, which recurred after surgical excision. Case 1 presented before the association with plasminogen deficiency was known with a bilateral chronic membranous mucopurulent conjunctivitis from the age of 14 months associated with bronchiolitis and gingival hyperplasia. A diagnosis of ligneous conjunctivitis was entertained and a number of drops were instituted. At the age of 4 years plasminogen levels were ordered. Case 2 presented at the age of 4 years with a unilateral chronic membranous conjunctivitis. Plasminogen levels were requested as soon as a diagnosis of ligneous conjunctivitis was suspected. Case 3 was born with congenital hydrocephalus. Conjunctivitis was treated with antibiotics from the age of 1 month. He presented to the eye clinic at the age of 5 months when a clinical diagnosis of ligneous conjunctivitis was entertained and treated with a number of medications. Plasminogen levels were available at 9 months of age. RESULTS: The two female patients returned plasminogen levels of 0.25 U/ml and 0.3 U/ml, well below the normal level of 0.7-1.0 U/ml. Functional plasminogen levels in the male infant were not recordable with plasminogen antigen levels of 0.125 U/ml (normal range, 0.52-1.82). All cases have responded well to excision of the membranes and institution of topical plasminogen drops. There has been no recurrence with more than 12 months' follow-up. CONCLUSIONS: With the knowledge of the etiology of ligneous conjunctivitis, efforts are underway to identify the best method of delivery of plasminogen. Topical plasminogen concentrate from fresh frozen plasma holds promise as the definitive treatment for this chronic membranous conjunctivitis

Low molecular weight heparin in children.

UNLABELLED: Low molecular weight heparins potentially have significant advantages over unfractionated heparin and oral anticoagulants for both the prevention and treatment of thromboembolic events in children. Compared to standard heparin, low molecular weight heparins have superior bioavailability, a longer half-life, and a dose-independent clearance, which results in a more predictable anticoagulant response. Low molecular weight heparins are administered subcutaneously and require minimal laboratory monitoring and dose adjustment, offering important benefits to children with poor venous access. In addition, complications including osteoporosis and heparin-induced thrombocytopenia are relatively rare with low molecular weight heparins compared to unfractionated heparin. CONCLUSION: based on the available data, low molecular weight heparins seem to be an efficient and safe alternative to standard anticoagulation therapy with unfractionated heparin and oral anticoagulants for both treatment and prevention of thromboembolic events in children of varying ages and underlying disorders.