Fibrinolytic Agents in Thromboembolic Diseases: Historical Perspectives and Approved Indications

Fibrinolytic agents catalyze the conversion of the inactive proenzyme plasminogen into the active protease plasmin, degrading fibrin within the thrombus and recanalizing occluded vessels. The history of these medications dates to the discovery of the first fibrinolytic compound, streptokinase, from bacterial cultures in 1933. Over time, researchers identified two other plasminogen activators in human samples, namely urokinase and tissue plasminogen activator (tPA). Subsequently, tPA was cloned using recombinant DNA methods to produce alteplase. Several additional derivatives of tPA, such as tenecteplase and reteplase, were developed to extend the plasma half-life of tPA. Over the past decades, fibrinolytic medications have been widely used to manage patients with venous and arterial thromboembolic events. Currently, alteplase is approved by the U.S. Food and Drug Administration (FDA) for use in patients with pulmonary embolism with hemodynamic compromise, ST-segment elevation myocardial infarction (STEMI), acute ischemic stroke, and central venous access device occlusion. Reteplase and tenecteplase have also received FDA approval for treating patients with STEMI. This review provides an overview of the historical background related to fibrinolytic agents and briefly summarizes their approved indications across various thromboembolic diseases.

Antithrombotic management of patients with deep vein thrombosis and venous stents: an international registry

BACKGROUND

In patients with acute deep vein thrombosis (DVT) treated with catheter-based thrombolysis and venous stenting, poststenting anticoagulant management is uncertain.

OBJECTIVES

To determine the type and duration of antithrombotic therapy used in patients who have received venous stents for treatment of acute lower extremity DVT.

METHODS

We created an international registry of patients with leg DVT from 2005 to 2019 who received venous stents as part of their acute management. We collected data on baseline clinical characteristics and pre-venous and post-venous stent antithrombotic therapy.

RESULTS

We studied 173 patients with venous stents: 101 (58%) were aged ≤50 years, 105 (61%) were female, and 128 (74%) had risk factors for thrombotic disease. DVT was iliofemoral in 150 (87%) patients, and catheter-based treatment was given within 7 days of diagnosis in 92 (53%) patients. After venous stenting, 109 (63%) patients received anticoagulant-only therapy with a direct oral anticoagulant (29%), warfarin (22%), or low-molecular-weight heparin (10%), and 59 (34%) received anticoagulant-antiplatelet therapy. In patients taking anticoagulant-only therapy, 29% received indefinite treatment; in patients on anticoagulant-antiplatelet therapy, 19% received indefinite treatment. Factors associated with combined anticoagulant-antiplatelet therapy vs anticoagulant-only therapy were use of thrombolytic, thrombectomy, and aspiration interventions (odds ratio [OR], 5.11; 95% CI, 1.45-18.05); use of balloon angioplasty (OR, 2.62; 95% CI, 1.20-5.76); and immediate stent restenosis (OR, 7.2; 95% CI, 1.45-5.89).

CONCLUSION

Anticoagulant therapy without concomitant antiplatelet therapy appears to be the most common antithrombotic strategy in patients with DVT and venous stenting. More research is needed to determine outcomes of venous stenting in relation to antithrombotic therapy.

Heparin Monitoring with an Anti-Xa Protocol Compared to Activated Clotting Time in Patients on Temporary Mechanical Circulatory Support

BACKGROUND

Temporary mechanical circulatory support (tMCS) devices are used for patients with severe cardiac or respiratory failure; however, these patients are at high risk for clotting and bleeding. The best method to monitor heparin in these patients has not been established.

OBJECTIVE

To determine the risks for bleeding and clotting while monitoring heparin with either anti-Xa or activated clotting time (ACT) in tMCS patients.

METHODS

A retrospective cohort study was conducted on tMCS patients who received heparin adjusted according to an anti-Xa or ACT protocol. The primary outcome was incidence of major bleeding. Pertinent secondary outcomes were individual components of the primary outcome, clotting events, and time to therapeutic range.

RESULTS

There were 103 patients included in the study: 53 in the ACT group and 50 in the anti-Xa group. Overall, there were 30 (56.6%) patients with major bleeding in the ACT group, compared with 16 (32%) patients in the anti-Xa group (P = 0.017). An anti-Xa-based protocol was associated with a decreased hazard of major bleeding (hazard ratio = 0.388 [0.215-0.701]; P = 0.002) in the univariate analysis. In the multivariable analysis, an anti-Xa protocol remained associated with a significantly lower hazard of bleeding. Findings were similar when broken down into more discrete subgroups of the entire cohort, extracorporeal membrane oxygenation life support (ECMO), and non-ECMO groups.

CONCLUSION AND RELEVANCE

Anti-Xa monitoring was associated with a lower hazard of bleeding during tMCS compared to an ACT-based protocol. Further studies should evaluate if anti-Xa monitoring should be preferentially used in tMCS.

Adequacy of hemostatic resuscitation improves therapeutic efficacy of recombinant activated factor VII and reduces reexploration rate for bleeding in postoperative cardiac surgery patients with refractory hemorrhage

Background:

Excessive bleeding and surgical reexploration are common complications that increase the risk of multi-organ failure and prolonged hospitalization after cardiac surgery. Off-label use of recombinant activated factor VII (rFVIIa) is a recommended treatment for refractory bleeding.

Objective:

The objective of the study is to determine if the adequacy of hemostatic resuscitation enhances the efficacy of rFVIIa.

Methods:

This retrospective, observational, cohort study included patients who received rFVIIa for refractory postoperative bleeding after cardiac surgery. Patients were divided into two groups based on the presence or absence of adequate coagulation resuscitation before rFVIIa administration, defined as international ratio (INR) ≤1.5, platelet count ≥100 K/mL, and fibrinogen ≥200 mg/dL. The failure of rFVIIa treatment was defined as surgical reexploration within 24 h, thoracostomy drainage >400 mL/h within 6 h or transfusion of additional blood products or another rFVIIa dose within 6 h after initial rFVIIa dose.

Results:

Of the 3833 patients, screened who underwent cardiothoracic surgery procedures, 58 patients received rFVIIa for refractory postoperative bleeding. Successful hemostasis with rFVIIa was more likely in patients who were adequately resuscitated compared with those who were not (20 [71.4%] vs. 10 [33.3%], respectively; P = 0.0046). Multiple logistic regression analysis indicated that patients who were adequately resuscitated before rFVIIa were less likely to fail treatment (odds ratio, 0.16; 95% confidence interval [0.04–0.62]; P = 0.007).

Conclusions:

The therapeutic efficacy of rFVIIa is dependent on the adequacy of hemostatic resuscitation; restoration of normal serum fibrinogen, INR, and platelet counts >100 K/mL may provide an adequate substrate for rFVIIa to be effective in managing refractory postoperative cardiac surgical bleeding.

Blocking inhibition of prothrombinase by tissue factor pathway inhibitor alpha: a procoagulant property of heparins

Unfractionated heparin (UFH) has procoagulant activity in antithrombin/heparin cofactor II (HCII)-depleted plasma. UFH prevents tissue factor pathway inhibitor alpha (TFPIα) from inhibiting the procoagulant enzyme complex, prothrombinase, providing a possible mechanism for its procoagulant activity. The procoagulant potential of UFH and various low molecular weight heparins (LMWHs) were characterized for TFPIα dependence, using thrombin generation assays performed with antithrombin/HCII-depleted plasma. UFH, the LMWHs enoxaparin and dalteparin, and the low anticoagulant LMWH 2-O, 3-O desulphated heparin (ODSH) all promoted thrombin generation, but fondaparinux did not, and this activity was blocked by a TFPIα antibody. UFH, enoxaparin, and dalteparin were anticoagulant in reactions containing 1-2% normal plasma. In prothrombinase activity assays, UFH, enoxaparin, dalteparin and ODSH blocked prothrombinase inhibition by TFPIα, while again fondaparinux did not. In both the plasma and purified assays, LMWHs displayed greater procoagulant potential than UFH, even when normalized to saccharide concentration. These biochemical data reveal that UFH and LMWHs, but not fondaparinux, block prothrombinase inhibition by TFPIα, thereby producing their paradoxical procoagulant activity observed in the absence of antithrombin/HCII. The findings may help to understand the complex pathophysiology and treatment of patients that are simultaneously bleeding and clotting, such as those with disseminated intravascular coagulation.

Abstract 43: Prothrombinase Assembled with Factor V Leiden is Resistant to Inhibition by Tissue Factor Pathway Inhibitor α Lowering the Procoagulant Threshold for Initiation of Coagulation

Factor V (FV) assembles with factor Xa (FXa) into prothrombinase, the enzymatic complex that converts prothrombin to thrombin. Tissue factor pathway inhibitor α (TFPIα) inhibits prothrombinase by high affinity interactions with FXa-activated FV and the FXa active site, thereby blocking the initiation of coagulation. FV Leiden (FVL) is strongly linked to venous thrombosis through its resistance to degradation by activated protein C (aPC), which enhances the propagation of coagulation. FVL combined with a 50% reduction in TFPI causes severe thrombosis and perinatal lethality in mice, suggesting that FVL also promotes the initiation of coagulation. To examine this possibility, thrombin generation assays initiated with limiting FXa were performed with control or FVL plasma and platelet-rich plasma (PRP). The activation threshold for thrombin generation was 10 to 20 pM FXa in 10 control plasmas, but was 5 pM in 4 of 10 homozygous FVL plasmas. FVL PRP had a similar decrease in the activation threshold. The differences in activation threshold were totally normalized by an anti-TFPI antibody, while exogenous TFPIα and a FV-binding peptide that mimics TFPIα had reduced anticoagulant activity in FVL plasma, revealing that the procoagulant effects of FVL in these assays rely on TFPIα. Next, FVL plasmas were studied in fibrin clot formation assays, as they are sensitive to small amounts of thrombin. In reactions activated with 0.5 pM FXa, 1 of 8 control plasmas, compared to 7 of 8 homozygous FVL plasmas, clotted within 60 minutes, with differences again normalized by the anti-TFPI antibody. In prothrombinase activity assays using purified proteins, TFPIα was a 1.7-fold weaker inhibitor of prothrombinase assembled with FVL compared to FV. Thus, in addition to its aPC-mediated effect on the propagation of coagulation, FVL is resistant to TFPIα inhibition, exerting a procoagulant effect on coagulation initiation. This is evident in responses to small stimuli, where TFPIα blocks clotting in plasmas with FV but not FVL. The TFPIα-mediated modulation of the procoagulant threshold may explain the severe perinatal thrombosis in FVL mice with decreased TFPI and be clinically relevant in the clotting associated with oral contraceptives, which cause acquired TFPI deficiency.

Not only in trauma patients: hospital-wide implementation of a massive transfusion protocol

OBJECTIVES

To review outcomes of massive transfusion protocol (MTP) activation and determine the impact of MTP implementation on blood bank use.

BACKGROUND

MTP has been established to rapidly provide plasma and packed red blood cells in ratios approaching 1 : 1. Due to availability, MTP has been utilised in non-traumatic haemorrhage despite evidence of benefit in this population. Our hospital-wide implementation of MTP was reviewed for propriety, outcomes and effect on blood bank resources.

METHODS

Retrospective cohort study of patients receiving transfusion after MTP activation from October 2009 to 2011. Underlying medical conditions and baseline medication use were determined. In-hospital and 24-h mortality were compared with evaluation for confounding by Acute Physiology And Chronic Health Evaluation (APACHE) score and duration of MTP activation. Blood product use before and after MTP implementation was reviewed.

RESULTS

MTP activation occurred in 62 trauma and 63 non-trauma patients. Non-trauma patients were older, had more underlying medical conditions and higher APACHE scores compared with trauma patients; 24-h mortality was higher in trauma compared with non-trauma patients (27·4 vs 11·1%, P = 0·02). There was no significant difference of in-hospital mortality. Transfusion ratio did not differ between trauma and non-trauma patients and was not associated with mortality even when MTP activation duration and APACHE score were considered. Hospital-wide blood product use did not change with MTP implementation.

CONCLUSIONS

MTP may be successfully used in trauma and non-trauma settings without significantly impacting overall blood product utilisation. Inclusion of non-trauma patients into prospective studies of resuscitation with blood products is warranted to ensure benefit in these patients.

Is prophylaxis required for delivery in women with factor VII deficiency?

Factor VII (fVII) deficiency is a rare congenital bleeding disorder in which fVII activity level and bleeding tendency do not completely correlate. Pregnancy and delivery present a significant haemostatic challenge to women with fVII deficiency. Treatment with recombinant factor VIIa (rfVIIa) carries a thrombotic risk and the literature is not clear whether prophylaxis is necessary prior to delivery. The aim of this study was to define management, haemorrhagic and thrombotic complications of pregnant women with fVII deficiency through a systematic review. Medical databases (PubMed, MEDLINE, CINAHL, Academic Search Premier, Cochrane Library, Web of Science and Scopus) were searched using "factor VII deficiency" and "pregnancy" or "surgery." Overall 34 articles, four abstracts, and three institutional cases were reviewed. Literature from 1953 to 2011 reported 94 live births from 62 women with fVII deficiency. The median fVII activity was 5.5%. Haemostatic prophylaxis was used in 32% of deliveries. Without prophylaxis, 40 vaginal deliveries and 16 caesarean sections were completed. The odds of receiving prophylaxis were 2.9 times higher in women undergoing caesarean section compared to vaginal delivery. Post-partum haemorrhage occurred in 10% of deliveries with prophylaxis and 13% of deliveries without prophylaxis. The fVII level did not significantly differ between women who did and did not receive prophylaxis. We present the only systematic review of the management of pregnancy in fVII deficient women. No difference in post-partum haemorrhage was seen in deliveries with and without prophylaxis. Therefore, we recommend that rfVIIa be available in the case of haemorrhage or surgical intervention, but not as mandatory prophylaxis.

The impact of Agent Orange exposure on presentation and prognosis of patients with chronic lymphocytic leukemia

Exposure to Agent Orange (AO) and the contaminating chemical 2,3,7,8-tetrachlorodibenzodioxin (TCDD) has been associated with the development of chronic lymphocytic leukemia (CLL). Of the 195 veterans diagnosed with CLL from 2001 to 2010 in a retrospective cohort from the Minneapolis Veterans Affairs Medical Center, 33 (17%) were exposed to AO. Prognostic factors including Rai stage, lymphocyte doubling time and cytogenetics did not differ between exposed and unexposed patients. Exposed patients were younger at diagnosis (61 vs. 72 years, p < 0.0001) and time to CLL treatment was shorter (9.6 vs. 30.2 months, p = 0.02). Overall survival did not differ between exposed and unexposed patients on Kaplan-Meier analysis, but when adjusted for age, AO exposure had a hazard ratio of death of 1.8 compared to non-exposure (95% confidence interval 0.7-4.5, p = 0.24). The high estimate of the mortality hazard combined with the relatively low numbers in the exposure group suggests that further examination in a larger patient population is warranted.

Lack of efficacy of pyridoxine (vitamin B6) treatment in acquired idiopathic sideroblastic anaemia, including refractory anaemia with ring sideroblasts

Pyridoxine, or vitamin B6, is commonly used to treat acquired idiopathic sideroblastic anaemia (AISA, including refractory anaemia with ring sideroblasts), but the efficacy of this therapy in an unselected AISA population (i.e. patients without confirmed ALAS2 or other pyridoxine-responsive germline mutations) has not been established. We reviewed clinical data from 231 patients with AISA and found that 42% of 203 evaluable patients had been treated with pyridoxine. Only 6.8% of pyridoxine-treated patients experienced a haemoglobin improvement (≥ 1.5 g/dL) meeting 2006 International Working Group for Myelodysplastic Syndromes standardised response criteria. As some patients received combination therapy with erythropoietin or other agents, improvement could be attributed to pyridoxine monotherapy in only one patient (1.4%). Smaller, less meaningful increments in haemoglobin levels of 0.5 g/dL were observed in 13.5% of patients. Response to therapy did not correlate with International Prognostic Scoring System (IPSS) risk group or multilineage vs unilineage dysplasia. New symptomatic peripheral neuropathy was noted in 2.3% of patients treated with pyridoxine. In this large series of unselected patients with sideroblastic anaemia, pyridoxine therapy was ineffective and was associated with a risk of adverse effects. Pyridoxine therapy should be reserved for patients with known or suspected pyridoxine-responsive mutations.

Selection criteria for internal medicine residency applicants and professionalism ratings during internship

OBJECTIVE

To determine whether standardized admissions data in residents' Electronic Residency Application Service (ERAS) submissions were associated with multisource assessments of professionalism during internship.

PARTICIPANTS AND METHODS

ERAS applications for all internal medicine interns (N=191) at Mayo Clinic entering training between July 1, 2005, and July 1, 2008, were reviewed by 6 raters. Extracted data included United States Medical Licensing Examination scores, medicine clerkship grades, class rank, Alpha Omega Alpha membership, advanced degrees, awards, volunteer activities, research experiences, first author publications, career choice, and red flags in performance evaluations. Medical school reputation was quantified using U.S. News & World Report rankings. Strength of comparative statements in recommendation letters (0 = no comparative statement, 1 = equal to peers, 2 = top 20%, 3 = top 10% or "best") were also recorded. Validated multisource professionalism scores (5-point scales) were obtained for each intern. Associations between application variables and professionalism scores were examined using linear regression.

RESULTS

The mean ± SD (minimum-maximum) professionalism score was 4.09 ± 0.31 (2.13-4.56). In multivariate analysis, professionalism scores were positively associated with mean strength of comparative statements in recommendation letters (β = 0.13; P = .002). No other associations between ERAS application variables and professionalism scores were found.

CONCLUSION

Comparative statements in recommendation letters for internal medicine residency applicants were associated with professionalism scores during internship. Other variables traditionally examined when selecting residents were not associated with professionalism. These findings suggest that faculty physicians' direct observations, as reflected in letters of recommendation, are useful indicators of what constitutes a best student. Residency selection committees should scrutinize applicants' letters for strongly favorable comparative statements.

An MLL-SEPT9 fusion and t(11;17)(q23;q25) associated with de novo myelodysplastic syndrome

Rearrangements of the MLL gene at chromosome 11q23 are uncommon in de novo myelodysplastic syndrome (MDS). Here, we describe molecular findings in a patient with multilineage dysplasia and t(11;17)(q23;q25) who responded to decitabine therapy. Fluorescent in situ hybridization (FISH) demonstrated rearrangement of MLL, while RT-PCR analysis and sequencing identified the transcript fusion partner as SEPT9, a member of the septin family of GTPases. MLL-SEPT9 fusion appears to be rare, having been described to date in only seven cases of AML and not, to our knowledge, in MDS. Analysis of MLL-septin family member fusion products such as the one seen here may provide further insights into the etiology of myeloid neoplasia, and MLL-SEPT9 fusion may be worth seeking in other cases of MLL rearrangements with a translocation partner on chromosome 17q.