Algorithm for Rapid Exclusion of Clinically Relevant Plasma Levels of Direct Oral Anticoagulants in Patients Using the DOAC Dipstick: An Expert Consensus Paper

BACKGROUND

 With the widespread use of direct oral anticoagulants (DOACs), there is an urgent need for a rapid assay to exclude clinically relevant plasma levels. Accurate and rapid determination of DOAC levels would guide medical decision-making to (1) determine the potential contribution of the DOAC to spontaneous or trauma-induced hemorrhage; (2) identify appropriate candidates for reversal, or (3) optimize the timing of urgent surgery or intervention.

METHODS AND RESULTS

 The DOAC Dipstick test uses a disposable strip to identify factor Xa- or thrombin inhibitors in a urine sample. Based on the results of a systematic literature search followed by an analysis of a simple pooling of five retrieved clinical studies, the test strip has a high sensitivity and an acceptably high negative predictive value when compared with levels measured with liquid chromatography tandem mass spectrometry or calibrated chromogenic assays to reliably exclude plasma DOAC concentrations ≥30 ng/mL.

CONCLUSION

 Based on these data, a simple algorithm is proposed to enhance medical decision-making in acute care indications useful primarily in hospitals not having readily available quantitative tests and 24/7. This algorithm not only determines DOAC exposure but also differentiates between factor Xa and thrombin inhibitors to better guide clinical management.

Single chest drain is not inferior to double chest drain after robotic esophagectomy: a propensity score-matched analysis

Background

Chest drain management has a significant influence on postoperative recovery after robot-assisted minimally invasive esophagectomy (RAMIE). The use of chest drains increases postoperative pain by irritating intercostal nerves and hinders patients from early postoperative mobilization and recovery. To our knowledge, no study has investigated the use of two vs. one intercostal chest drains after RAMIE.

Methods

This retrospective cohort study evaluated patients undergoing elective RAMIE with gastric conduit pull-up and intrathoracic anastomosis. Patients were divided into two groups according to placement of one (11/2020-08/2022) or two (08/2018-11/2020) chest drains. Propensity score matching was performed in a 1:1 ratio, and the incidences of overall and pulmonary complications, drainage-associated re-interventions, radiological diagnostics, analgesic use, and length of hospital stay were compared between single drain and double drain groups.

Results

During the study period, 194 patients underwent RAMIE. Twenty-two patients were included after propensity score matching in the single and double chest drain group, respectively. Time until removal of the last chest drain [postoperative day (POD) 6.7 ± 4.4 vs. POD 9.4 ± 2.7, p = 0.004] and intensive care unit stay (4.2 ± 5.1 days vs. 5.3 ± 3.5 days, p = 0.01) were significantly shorter in the single drain group. Overall and pulmonary complications, drainage-associated events, re-interventions, number of diagnostic imaging, analgesic use, and length of hospital stay were comparable between both groups.

Conclusion

This study is the first to demonstrate the safety of single intercostal chest drain use and, at least, non-inferiority to double chest drains in terms of perioperative complications after RAMIE.

Ensuring privacy protection in the era of big laparoscopic video data: development and validation of an inside outside discrimination algorithm (IODA)

BACKGROUND

Laparoscopic videos are increasingly being used for surgical artificial intelligence (AI) and big data analysis. The purpose of this study was to ensure data privacy in video recordings of laparoscopic surgery by censoring extraabdominal parts. An inside-outside-discrimination algorithm (IODA) was developed to ensure privacy protection while maximizing the remaining video data.

METHODS

IODAs neural network architecture was based on a pretrained AlexNet augmented with a long-short-term-memory. The data set for algorithm training and testing contained a total of 100 laparoscopic surgery videos of 23 different operations with a total video length of 207 h (124 min ± 100 min per video) resulting in 18,507,217 frames (185,965 ± 149,718 frames per video). Each video frame was tagged either as abdominal cavity, trocar, operation site, outside for cleaning, or translucent trocar. For algorithm testing, a stratified fivefold cross-validation was used.

RESULTS

The distribution of annotated classes were abdominal cavity 81.39%, trocar 1.39%, outside operation site 16.07%, outside for cleaning 1.08%, and translucent trocar 0.07%. Algorithm training on binary or all five classes showed similar excellent results for classifying outside frames with a mean F1-score of 0.96 ± 0.01 and 0.97 ± 0.01, sensitivity of 0.97 ± 0.02 and 0.0.97 ± 0.01, and a false positive rate of 0.99 ± 0.01 and 0.99 ± 0.01, respectively.

CONCLUSION

IODA is able to discriminate between inside and outside with a high certainty. In particular, only a few outside frames are misclassified as inside and therefore at risk for privacy breach. The anonymized videos can be used for multi-centric development of surgical AI, quality management or educational purposes. In contrast to expensive commercial solutions, IODA is made open source and can be improved by the scientific community.

Drainless robot-assisted minimally invasive oesophagectomy-randomized controlled trial (RESPECT)

BACKGROUND

The purpose of this randomized trial is to evaluate the early removal of postoperative drains after robot-assisted minimally invasive oesophagectomy (RAMIE). Evidence is lacking about feasibility, associated pain, recovery, and morbidity.

METHODS/DESIGN

This is a randomized controlled multicentric trial involving 72 patients undergoing RAMIE. Patients will be allocated into two groups. The "intervention" group consists of 36 patients. In this group, abdominal and chest drains are removed 3 h after the end of surgery in the absence of contraindications. The control group consists of 36 patients with conventional chest drain management. These drains are removed during the further postoperative course according to a standard algorithm. The primary objective is to investigate whether postoperative pain measured by NRS on the second postoperative day can be significantly reduced in the intervention group. Secondary endpoints are the intensity of pain during the first week, analgesic use, number of postoperative chest X-ray and CT scans, interventions, postoperative mobilization (steps per day as measured with an activity tracker), postoperative morbidity and mortality.

DISCUSSION

Until now, there have been no trials investigating different intraoperative chest drain strategies in patients undergoing RAMIE for oesophageal cancer with regard to perioperative complications until discharge. Minimally invasive approaches combined with enhanced recovery after surgery (ERAS) protocols lower morbidity but still include the insertion of chest drains. Reduction and early removal have been proposed after pulmonary surgery but not after RAMIE. The study concept is based on our own experience and the promising current results of the RAMIE procedure. Therefore, the presented randomized controlled trial will provide statistical evidence of the effectiveness and feasibility of the "drainless" RAMIE.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05553795. Registered on 23 September 2022.

Analysis of predictors for postoperative complications after pancreatectomy--what is new after establishing the definition of postpancreatectomy acute pancreatitis (PPAP)?

PURPOSE

We aimed to analyze the predictive value of hyperamylasemia after pancreatectomy for morbidity and for the decision to perform rescue completion pancreatectomy (CP) in a retrospective cohort study.

METHODS

Data were extracted from a retrospective clinical database. Postoperative hyperamylasemia (POH) and postoperative hyperlipasemia (POHL) were defined by values greater than those accepted as the upper limit at our institution on postoperative day 1 (POD1). The endpoints of the study were the association of POH with postoperative morbidity and the possible predictors for postpancreatectomy acute pancreatitis (PPAP) and severe complications such as the necessity for rescue CP.

RESULTS

We analyzed 437 patients who underwent pancreaticoduodenectomy over a period of 7 years. Among them, 219 (52.3%) patients had POH and 200 (47.7%) had normal postoperative amylase (non-POH) levels. A soft pancreatic texture (odds ratio [OR] 3.86) and POH on POD1 (OR 8.2) were independent predictors of postoperative pancreatic fistula (POPF), and POH on POD1 (OR 6.38) was an independent predictor of rescue CP. The clinically relevant POPF (49.5% vs. 11.4%, p < 0.001), intraabdominal abscess (38.3% vs. 15.3%, p < 0.001), postoperative hemorrhage (22.8% vs. 5.1%, p < 0.001), major complications (Clavien-Dindo classification > 2) (52.5% vs. 25.6%, p < 0.001), and CP (13% vs. 1.8%, p < 0.001) occurred significantly more often in the POH group than in the non-POH group.

CONCLUSION

Although POH on POD1 occurs frequently, in addition to other risk factors, it has a predictive value for the development of postoperative morbidity associated with PPAP and CP.

How we do it-the use of peritoneal patches for reconstruction of vena cava inferior and portal vein in hepatopancreatobiliary surgery

PURPOSE

Extended resections in hepatopancreatobiliary (HPB) surgery frequently require vascular resection to obtain tumor clearance. The use of alloplastic grafts may increase postoperative morbidity due to septic or thrombotic complications. The use of suitable autologous venous interponates (internal jugular vein, great saphenous vein) is frequently associated with additional incisions. The aim of this study was to report on our experience with venous reconstruction using the introperative easily available parietal peritoneum, focusing on key technical aspects.

METHODS

All patients who underwent HPB resections with venous reconstruction using peritoneal patches at our department between January 2017 and November 2021 were included in this retrospective analysis with median follow-up of 2 months (IQR: 1-8 months). We focused on technical aspects of the procedure and evaluated vascular patency and perioperative morbidity.

RESULTS

Parietal peritoneum patches (PPPs) were applied for reconstruction of the inferior vena cava (IVC) (13 patients) and portal vein (PV) (4 patients) during major hepatic (n = 14) or pancreatic (n = 2) resections. There were no cases of postoperative bleeding due to anastomotic leakage. Following PV reconstruction, two patients showed postoperative vascular stenosis after severe pancreatitis with postoperative pancreatic fistula and bile leakage, respectively. In patients with reconstruction of the IVC, no relevant perioperative vascular complications occurred.

CONCLUSIONS

The use of a peritoneal patch for reconstruction of the IVC in HPB surgery is a feasible, effective, and low-cost alternative to alloplastic, xenogenous, or venous grafts. The graft can be easily harvested and tailored to the required size. More evidence is still needed to confirm the safety of this procedure for the portal vein regarding long-term results.

[Highlights of pancreatic surgery: extended indications in pancreatic neuroendocrine tumors]

Advanced pancreatic neuroendocrine tumors (paNET) are mostly characterized by infiltration of vascular structures and/or neighboring organs. The indications for resection in these cases should be measured based on the possibility of an R0 resection. Although the data situation for this rare entity is limited, small case series have shown a significant survival advantage in patients who underwent a radical resection in locally advanced stages of paNET. Both vascular reconstruction and multivisceral resection, when performed at experienced centers, should be considered as curative treatment options. The very special biological behavior of the paNET and the often young patient age justify a much more aggressive approach compared to the pancreatic ductal adenocarcinoma.

Short-term preoperative drainage is associated with improved postoperative outcomes compared to that of long-term biliary drainage in pancreatic surgery

Purpose

The treatment of choice for patients presenting with obstructive cholestasis due to periampullary carcinoma is oncologic resection without preoperative biliary drainage (PBD). However, resection without PBD becomes virtually impossible in patients with obstructive cholangitis or severely impaired liver cell function. The appropriate duration of drainage by PBD has not yet been defined for these patients.

Methods

A retrospective analysis was conducted on 170 patients scheduled for pancreatic resection following biliary drainage between January 2012 and June 2018 at the University Hospital Dresden in Germany. All patients were deemed eligible for inclusion, regardless of the underlying disease entity. The primary endpoint analysis was defined as the overall morbidity (according to the Clavien-Dindo classification). Secondary endpoints were the in-hospital mortality and malignancy adjusted overall and recurrence-free survival rates.

Results

A total of 170 patients were included, of which 45 (26.5%) and 125 (73.5%) were assigned to the short-term (< 4 weeks) and long-term (≥ 4 weeks) preoperative drainage groups, respectively.

Surgical complications (Clavien-Dindo classification > 2) occurred in 80 (47.1%) patients, with significantly fewer complications observed in the short-term drainage group (31.1% vs. 52%; p = 0.02). We found that long-term preoperative drainage (unadjusted OR, 3.386; 95% CI, 1.507–7.606; p < 0.01) and periampullary carcinoma (unadjusted OR, 5.519; 95% CI, 1.722–17.685; p-value < 0.01) were independent risk factors for postoperative morbidity, based on the results of a multivariate regression model. The adjusted overall and recurrence-free survival did not differ between the groups (p = 0.12).

Conclusion

PBD in patients scheduled for pancreatic surgery is associated with substantial perioperative morbidity. Our results indicate that patients who have undergone PBD should be operated on within 4 weeks after drainage.

[Preoperative diagnostics and typing of abdominal soft tissue sarcomas]

BACKGROUND

Abdominal sarcomas are a heterogeneous group of rare soft tissue tumors and can be localized intraperitoneally or retroperitoneally. A pretherapeutic differentiated subtyping is essential for planning an individual, multimodal treatment concept in an interdisciplinary team of experts.

OBJECTIVE

The central aspects of histology acquisition, imaging diagnostics and (molecular) pathological subtyping of abdominal soft tissue sarcomas are described in detail.

MATERIAL AND METHODS

Imaging and pathological diagnostics are depicted based on the German S3 guidelines on adult soft tissue sarcomas, a current literature search and personal experiences at the Sarcoma Center at the National Center for Tumor Diseases in Dresden (NCT/UCC).

RESULTS

Preoperative imaging and (molecular) pathological subtyping of abdominal soft tissue sarcomas place high demands on surgeons, radiologists and pathologists. Genome analyses of sarcomas have the potential to identify points of attack for individualized treatment options. The limitations of resectability can only be assessed by experienced sarcoma surgeons at specialized centers.

CONCLUSION

The treatment of abdominal soft tissue sarcomas at an experienced center is associated with a better prognosis. Even at the first suspicion of an abdominal sarcoma, a referral to an experienced center should be made in order to guarantee optimal expertise in diagnostics and treatment.

Perioperative Blood Management of Preoperative Anemia Determines Long-Term Outcome in Patients with Pancreatic Surgery

BACKGROUND/PURPOSE

Anemia affects the postoperative course of patients undergoing a major surgical procedure. However, it remains unclear whether anemia has a different impact on the long-term outcome of patients with malignant or benign pancreatic disease.

METHODS

A retrospective analysis of patients undergoing pancreatic surgery for pancreatic malignancies or chronic pancreatitis was conducted between January 2012 and June 2018 at the University Hospital Dresden, Germany. The occurrence of preoperative anemia and the administration of pre-, intra-, and postoperative blood transfusions were correlated with postoperative complications and survival data by uni- and multivariate analysis.

RESULTS

A total of 682 patients were included with 482 (70.7%) undergoing surgical procedures for pancreatic malignancies. Univariate regression analysis confirmed preoperative anemia as a risk factor for postoperative complications > grade 2 according to the Clavien-Dindo classification. Multivariate regression analyses indicated postoperative blood transfusion as an independent risk factor for postoperative complications in patients with a benign (OR 20.5; p value < 0.001) and a malignant pancreatic lesion (OR 4.7; p value < 0.01). Univariate and multivariate analysis revealed preoperative anemia and pre-, intra-, and postoperative blood transfusions as independent prognostic factors for shorter overall survival in benign and malignant patients (p value < 0.001-0.01).

CONCLUSION

Preoperative anemia is a prevalent, independent, and adjustable factor in pancreatic surgery, which poses a significant risk for postoperative complications irrespective of the entity of the underlying disease. It should therefore be understood as an adjustable factor rather than an indicator of underlying disease severity.

[The suffering surgeon-How do German surgeons protect themselves? : Survey of the German Society of General and Visceral Surgery on the extent of occupational safety measures and health burden among German surgeons]

BACKGROUND

There are few data on how surgeons implement occupational safety measures to protect their own health and how they assess their subjective health burden.

OBJECTIVE

In times of a shortage of surgeons it makes sense to examine these relationships in order to evaluate future-oriented adjustments to increase the attractiveness of the profession of "surgeon".

MATERIAL AND METHODS

An online questionnaire was sent to the registered members of the German Society for General and Visceral Surgery (DGAV) in October 2016. The members were asked about the application of occupational safety measures, individual living conditions, working conditions and the subjective health burden depending on the level of training and type of hospital (basic, standard, maximum care).

RESULTS

The response rate was 21% (1065/5011). Occupational safety measures were not strictly implemented: routine use of dosimeters, thyroid radiation protection, smoke extraction and protective goggles only took place in 40% (427/1065), 39% (411/1065), 10% (104/1065) and 5% (55/1065), respectively. The majority of surgeons (51%, 548/1065) rated their lifestyle as unhealthy. The majority of them are senior physicians, 46% (250/548) consider their job to be a health hazard. The proportion of chief physicians and assistant physicians is only 21% (115/548) and 18% (98/548).

CONCLUSION

Guidelines for standardizing the perioperative protection of German surgeons are desirable. Health-promoting behavior could have a positive effect on the occupational safety of surgeons and ultimately also on patient safety. This can contribute to increasing the attractiveness of the profession "surgeon" in the long term.

[Process management in surgery]

Process management is defined as the concept of identifying processes in a company or healthcare organization, analyzing them and improving productivity and efficiency. In hospitals, process management focuses on patient safety, an increase in economic resources and employee satisfaction. The integration of process management into clinical pathways helps to accelerate workflows and to improve the quality of patient service. The different types of process management encompass the radical concept of process renewal (revolutionary renewal) as well as the concept of evolutionary optimization. Process management in surgery is applied to preoperative, perioperative and postoperative procedures. The development and implementation of evidence-based treatment pathways can help to standardize and structure treatment processes in a surgical department. In this context, the operating room (OR) plays a particularly central role as the most important part of the healthcare provision of perioperative services. Process management is indispensable for the utilization of an optimal OR capacity taking a maximum patient safety and the desired optimal satisfaction of employees into account. The benefits of process management in the OR area are illustrated in an exemplary case study, demonstrating how innovative process management results in an increase of the operation capacity with a simultaneous reduction in costs.

Extended treatment with edoxaban in cancer patients with venous thromboembolism: A post-hoc analysis of the Hokusai-VTE Cancer study

BACKGROUND

Patients with active cancer and venous thromboembolism (VTE) are at high risk of recurrence. Therefore, continued anticoagulant therapy beyond the initial 6 months is suggested in this patient population, but evidence supporting this approach is limited.

METHODS

The Hokusai VTE Cancer trial compared edoxaban with dalteparin for VTE treatment in patients with active cancer. This post hoc analysis focused on the follow-up period from 6 to 12 months. The primary outcome was the composite of adjudicated first recurrent VTE or major bleeding. Secondary outcomes included recurrent VTE, major bleeding, and clinically relevant bleeding.

RESULTS

Of the 522 and 524 patients randomized to edoxaban or dalteparin, 294 (56%) received edoxaban and 273 (52%) received dalteparin for more than 6 months (median duration of 318 and 211 days, respectively). Between 6 and 12 months, the primary outcome during study treatment occurred in seven patients (2.4%) in the edoxaban group and six patients (2.2%) in the dalteparin group (unadjusted hazard ratio 1.05; 95% confidence interval, 0.36-3.05). Recurrent VTE occurred in two patients (0.7%) in the edoxaban group and in three patients (1.1%) in the dalteparin group, whereas major bleeding occurred in 5 (1.7%) and three patients (1.1%), respectively.

CONCLUSIONS

The rates of recurrent VTE or major bleeding are relatively low among patients with active cancer receiving extended anticoagulant therapy beyond 6 months. Extended treatment with oral edoxaban appears as effective and safe as subcutaneous dalteparin.

[Transanal total mesorectal excision-a critical appraisal]

INTRODUCTION

Total mesorectal excision (TME) is the international standard for rectal cancer surgery. In addition to laparoscopic TME (lapTME), transanal TME (taTME) was developed in recent years to reduce the rate of incomplete TME, conversion to open surgery and postoperative functional impairment. Despite limited evidence, this technique is becoming increasingly more popular and is already routinely used by many hospitals for rectal cancer in varying tumor level locations. The aim of this review was to evaluate the taTME compared to anterior rectal resection with lapTME as the standard of care in rectal cancer surgery based on currently available evidence.

METHOD

The databases PubMed and Medline were systematically searched for publications on transanal total mesorectal excision (taTME) and transanal minimally invasive surgery (TAMIS). Relevant studies were selected and further research based on the reference lists was undertaken.

RESULTS

A total of 16 studies analyzing 3782 patients were identified. The taTME does not lead to a higher rate of complete TME-resected specimens compared to the standard procedure. So far, superiority could not be demonstrated for complication rates or for functional or oncological results. Serious complications secondary to dissection in incorrect planes were observed. The anastomotic level generally seems to be closer to the sphincter after taTME versus anterior lapTME.

CONCLUSION

Considering current evidence, taTME failed to show superiority compared to conventional anterior lapTME. Although taTME has some potential advantages, it carries substantial risks. If performed outside of clinical trials, it should therefore only be used in carefully selected patients with a high possibility of conversion, following adequate patient informed consent and after intense and systematic training of the surgeon.

[Evidence for robotic surgery in oncological visceral surgery]

The superiority of minimally invasive operative methods compared to open surgery with respect to various parameters of short-term outcome with adequate oncological long-term results has already been confirmed for many tumor entities in high-quality studies. The continuously expanding robotic surgery offers certain additional benefits in minimally invasive oncological visceral surgery, such as a high-resolution stable 3‑dimensional view, optimal freedom of movement in situ, elimination of natural tremor and better ergonomics. This article evaluates whether these postulated advantages are reflected in an improvement of the short-term perioperative and long-term oncological results compared to conventional minimally invasive surgery in oncological visceral surgery (rectum, colon, stomach, esophagus, pancreas, liver) according to the criteria of evidence-based medicine. With the exception of colorectal surgery, there are currently no randomized controlled studies comparing robotic to laparoscopic surgery in oncological visceral surgery. There is still a clear imbalance between the exponentially expanding application of robotic surgery and the existing lack of high-quality evidence. Further randomized controlled clinical trials urgently need to be performed especially considering the great technological development potential of robotic surgery.

Influence of Molecular Status on Recurrence Site in Patients Treated for a Stage III Colon Cancer: a Post Hoc Analysis of the PETACC-8 Trial

BACKGROUND

Recurrence patterns in stage III colon cancer (CC) patients according to molecular markers remain unclear. The objective of the study was to assess recurrence patterns according to microsatellite instability (MSI), RAS and BRAF^V600E status in stage III CC patients.

METHODS

All stage III CC patients from the PETACC-8 randomized trial tested for MSI, RAS and BRAF^V600E status were included. The site and characteristics of recurrence were analyzed according to molecular status. Survival after recurrence (SAR) was analyzed.

RESULTS

A total of 1650 patients were included. Recurrence occurred in 434 patients (26.3%). Microsatellite stable (MSS) patients had a significantly higher recurrence rate (27.2% vs. 18.7%, P = 0.02) with a trend to more pulmonary recurrence (28.8% vs. 12.9%, P = 0.06) when compared to MSI patients. MSI patients experienced more regional lymph nodes compared to MSS (12.9% vs. 4%, P = 0.046). In the MSS population, the recurrence rate was significantly higher in RAS (32.2%) or BRAF (32.3%) patients when compared to double wild-type patients (19.9%) (p < 0.001); no preferential site of recurrence was observed according to RAS and BRAF^V600E mutations. Finally, decreased SAR was observed in the case of peritoneal recurrence or more than two recurrence sites.

CONCLUSIONS

Microsatellite, RAS and BRAF^V600E status influences recurrence rates in stage III CC patients. However, only microsatellite status seems to be associated with specific recurrence patterns. More than two recurrence sites and recurrence in the peritoneum were associated with poorer SAR.

Randomized clinical trial of stapler hepatectomy versus LigaSure™ transection in elective hepatic resection

BACKGROUND

Previous studies have demonstrated stapler hepatectomy and use of various energy devices to be safe alternatives to the clamp-crushing technique in elective hepatic resection. In this randomized trial, the effectiveness and safety of stapler hepatectomy were compared with those of parenchymal transection with the LigaSure™ vessel sealing system.

METHOD

Patients scheduled for elective liver resection at two tertiary-care centres were randomized during surgery to stapler hepatectomy or transection with the LigaSure™ device. Total intraoperative blood loss was the primary efficacy endpoint. Transection time, duration of operation, perioperative complications and length of hospital stay were recorded as secondary endpoints.

RESULTS

A total of 138 patients were analysed, 69 in the LigaSure™ and 69 in the stapler hepatectomy group. Baseline characteristics were well balanced between the groups. Mean intraoperative blood loss was significantly higher in the LigaSure™ group than the stapler hepatectomy group: 1101 (95 per cent c.i. 915 to 1287) versus 961 (752 to 1170) ml (P = 0·028). The parenchymal transection time was significantly shorter in the stapler group (P = 0·005), as was the total duration of operation (P = 0·027). Surgical morbidity did not differ between the groups, nor did the grade of complications.

CONCLUSION

Stapler hepatectomy was associated with reduced blood loss and a shorter duration of operation than the LigaSure™ device for parenchymal transection in elective partial hepatectomy. Registration number: NCT01858987 (http://www.clinicaltrials.gov).

The Non-Vitamin K Antagonist Oral Anticoagulants in Heart Disease: Section V—Special Situations

Non-vitamin K antagonist oral anticoagulants (NOACs) include dabigatran, which inhibits thrombin, and apixaban, betrixaban, edoxaban and rivaroxaban, which inhibit factor Xa. In large clinical trials comparing the NOACs with the vitamin K antagonist (VKA) warfarin, dabigatran, apixaban, rivaroxaban and edoxaban were at least as effective for stroke prevention in atrial fibrillation and for treatment of venous thromboembolism, but were associated with less intracranial bleeding. In addition, the NOACs are more convenient to administer than VKAs because they can be given in fixed doses without routine coagulation monitoring. Consequently, the NOACs are now replacing VKAs for these indications, and their use is increasing. Although, as a class, the NOACs have a favourable benefit–risk profile compared with VKAs, choosing among them is complicated because they have not been compared in head-to-head trials. Therefore, selection depends on the results of the individual trials, renal function, the potential for drug–drug interactions and preference for once- or twice-daily dosing. In addition, several ‘special situations’ were not adequately studied in the dedicated clinical trials. For these situations, knowledge of the unique pharmacological features of the various NOACs and judicious cross-trial comparison can help inform prescription choices. The purpose of this position article is therefore to help clinicians choose the right anticoagulant for the right patient at the right dose by reviewing a variety of special situations not widely studied in clinical trials.

Clinical Impact of Bleeding in Cancer-Associated Venous Thromboembolism: Results from the Hokusai VTE Cancer Study

In the Hokusai VTE Cancer study, edoxaban was non-inferior to dalteparin for the composite outcome of recurrent venous thromboembolism (VTE) and major bleeding in 1,050 patients with cancer-associated VTE. The absolute rate of recurrent VTE was 3.4% lower with edoxaban, whereas the absolute rate of major bleeding was 2.9% higher. The present analysis focuses on the sites, clinical presentation, course and outcome of bleeding events, and the associated tumour types. Major bleeds and their severity (categories 1–4) were blindly adjudicated by a committee using a priori defined criteria, and data were analysed in the safety population. Major bleeding occurred in 32 of 522 patients given edoxaban (median treatment duration, 211 days) and in 16 of 524 patients treated with dalteparin (median treatment duration, 184 days); no patients had more than one major bleed. There were no fatal bleeds with edoxaban, and two with dalteparin. Severe bleeding at presentation (category 3 or 4) occurred in 10 (1.9%) and 11 (2.1%) patients in the edoxaban and dalteparin groups, respectively. The excess of major bleeding with edoxaban was confined to patients with gastrointestinal cancer. However, severe major bleeding at presentation (category 3 or 4) in this sub-group occurred in 5 of 165 (3.0%) and in 3 of 140 (2.1%) patients given edoxaban or dalteparin, respectively.

In conclusion, this analysis suggests that while oral edoxaban is an appropriate alternative to subcutaneous dalteparin for treatment of cancer-associated VTE, the use of edoxaban in patients with gastrointestinal cancer requires careful benefit–risk weighting.

Comparison of the Accuracy of Impedance Plethysmography and Compression Ultrasonography in Outpatients with Clinically Suspected Deep Vein Thrombosis

Impedance plethysmography (IPG) and compression ultrasonography (CUS) have been reported to be highly accurate for the diagnosis of deep vein thrombosis (DVT) in symptomatic patients. In many centres CUS has become the method of choice. However, direct comparisons of the accuracy of IPG to CUS have not been performed. To determine the test of choice we performed a two centre prospective comparison of IPG and CUS, with venography, and determined how the size and distribution of thrombi influenced the accuracy of each test. 495 symptomatic outpatients with suspected DVT had evaluable venograms. The prevalence of DVT was 27% (130/495), 84% (109) of which were proximal. The sensitivity of IPG and CUS for proximal vein thrombosis was 77% and 90% respectively (p = .002). The specificity of IPG was 93% whereas the specificity of CUS was 98% (p = 0.04). There were significant differences in accuracy between the two centres as a consequence of differences in the size and location of thrombi. The majority of proximal thrombi not detected by IPG and CUS involved less than 5 cm of the distal half of the popliteal vein and most of these thrombi occurred in one centre. Exclusion of these thrombi from the analysis increases the sensitivity of CUS to 99% (86/87) and IPG to 91% (72/79), for proximal thrombi (p = .019). The positive predictive value of CUS was strongly influenced by the number of abnormal venous segments (three sites were examined); 100% (80/80) if two or three sites were abnormal, but only 68% if a single site was involved. We conclude that: 1) CUS is more accurate than the IPG for the diagnosis of DVT in symptomatic outpatients, and this relationship holds true regardless of the size or location of the DVT, 2) the sensitivities of IPG and CUS are much lower for small proximal DVT, and 3) confirmatory venography is warranted if the abnormality with CUS is limited to one venous segment.

Do Coagulation Screening Tests Detect Increased Generation of Thrombin and Plasmin in Sick Newborn Infants?

Background: Disseminated intravascular coagulation (DIC) is usually diagnosed in sick infants who have prolonged clotting times, depletion of platelets and coagulation factors, and elevated levels of fibrin derivatives. However, the diagnostic accuracy of abnormal coagulation profiles in neonates at risk of DIC has been uncertain. Since DIC is characterized by activation of both the coagulation and fibrinolytic systems, the objective of this study was to determine whether coagulation screening tests correctly identify infants with biochemical evidence of increased thrombin and plasmin generation.

Methods: Non-surgical patients in a tertiary care nursery who were sick enough to require an indwelling arterial catheter for monitoring purposes, were enrolled in a prospective cohort study. Blood samples for thrombin/antithrombin III (TAT) complexes and the plasmin-derived fibrinopeptide Bβ1-42 were drawn 36 to 72 h after birth from a free-flowing arterial line. Platelet counts, D-Dimer levels, plasma fibrinogen concentrations and prothrombin times, expressed as International Normalized Ratios or INR, were measured at the same time.

Results: One hundred patients were studied. Fifty-seven infants had elevated levels of TAT (≥4 μg/l) and Bβ1-42 (≥4 nmol/l). The sensitivities of platelets <150 × 109/l, D-Dimer >500 ng/ml, fibrinogen <1.5 g/l, and INR >1.5 were 39%, 30%, 12%, and 11%, respectively. Corresponding specificities were 88%, 91%, 98%, and 95%.

Conclusions: Abnormal coagulation screens in sick newborn infants strongly support a diagnosis of DIC. However, normal screens do not exclude activation of the coagulation and fibrinolytic systems.

Effects of Intermittent Pneumatic Calf Compression On Postoperative Thrombin and Plasmin Activity

A previous study of neurosurgical patients demonstrated an imbalance between thrombin and plasmin action following surgery. The present study was designed to determine the effect of intermittent pneumatic calf compression on postoperative enzyme activity. Fibrinopeptide A (FPA) and Bβ 1-42 levels, reflecting thrombin and plasmin action respectively, were measured daily in patients undergoing elective craniotomy. Two of 9 patients not receiving calf compression developed positive fibrinogen leg scans, while none of 5 patients receiving prophylaxis had positive scans. Calf compression was associated with a markedly altered pattern of changes in the fibrinopeptide values following surgery. Without compression, there was perturbation of the balance between thrombin and plasmin action on the day after surgery as reflected by an increase in the FPA/Bβ 1-42 ratio. In contrast, in those receiving prophylaxis there was no change in this ratio on the first postoperative day. Calf compression both blunted the mean postoperative increase in the FPA level (1.8 nM vs 4.7 nM; p <.05) and augmented the mean Bβ 1-42 value (3.0 nM vs 0.2 nM; p <.05) so that the mean increase in the FPA/ Bβ 1-42 ratio was only 0.1 with calf compression as compared to 2.2 without it (p <.05). Systemic modulation of both the coagulation and fibrinolytic pathways thus occurred in association with calf compression.

Free Protein S Deficiency May Be Found in Patients with Antiphospholipid Antibodies who Do not Have Systemic Lupus Erythematosus

In order to determine if there is a relationship between antiphospholipid antibodies and reduced free protein S levels, we evaluated 21 patients who had an antiphospholipid antibody but had neither a history of venous thromboembolism nor systemic lupus erythematosus (cases) and 55 matched controls, who did not have an antiphospholipid antibody, a history of thrombosis or systemic lupus erythematosus. Cases and controls had similar protein C and antithrombin levels. Six of 21 cases had reduced free protein S antigen levels, compared to 5 of 55 controls (x 2 = 5.823 p <0.025). In addition, the mean free protein S level was significantly lower in cases than in controls (0.30 ± 0.09 units vs 0.39 ± 0.13 units, p <0.01, two-tailed Student’s t-test). We conclude that antiphospholipid antibodies are associated with a significant decrease in free protein S levels, and that this acquired free protein S deficiency may contribute to the thrombotic diathesis seen in patients with antiphospholipid antibodies.

Ex-Vivo and In-Vitro Evidence that Low Molecular Weight Heparins Exhibit Less Binding to Plasma Proteins than Unfractionated Heparin

We have compared the non-specific binding of unfractionated heparin (UFH) with that of low molecular weight heparin (LMWFl) to plasma proteins both ex vivo and in vitro. Non specific binding to plas ma proteins was assessed by comparing the heparin levels measured as anti-factor Xa activity before and after the addition of low affinity heparin, which is essentially devoid of anti-factor Xa activity, in order to displace heparin bound to plasma proteins. For the ex-vivo studies, we compared the recovery of UFH and a LMWH (ardeparin) from the plasma of patients participating in a randomized trial of post operative venous thrombosis prophylaxis. For the in-vitro studies, we compared the recovery of UFH and 4 different LMWHs when added to the plasma from healthy volunteers and from patients with suspected venous thromboembolic disease. The results indicate that the recovery of LMWH is much less affected by nonspecific binding to plasma proteins both ex-vivo and in-vitro. In addition, there are differences between the LMWHs with respect to their plasma protein-binding.

Effects on Thrombin Generation of Single Injections of Hirulog™ in Patients with Calf Vein Thrombosis

1. Study objective: To determine whether single injections of Hirulog, a direct thrombin inhibitor, can inhibit thrombin generation in patients with calf vein thrombosis and, if so, if the inhibition is sustained.

2. Design: Phase II open label cohort study.

3. Setting: Tertiary-care referral centres, university affiliated hospitals.

4. Patients: 10 patients with venographically-demonstrated calf vein thrombosis.

5. Intervention: Patients received a single injection of Hirulog, either 1.0 mg/kg subcutaneously or 0.6 mg/kg as a 15 min intravenous infusion. Prothrombin fragment (F1+2) levels, as an index of thrombin generation, were measured before as well as 6 h post- and 24 h post-Hirulog administration. Patients were followed with non-invasive tests to detect thrombus extension into the proximal veins.

6. Results: There was a significant reduction in the levels of F1+2 with both regimens, 6 h after Hirulog. The Fl+2 levels 24 h post-Hirulog showed a significant increase relative to the 6 h post-Hirulog results. One patient developed thrombus extension into the popliteal vein and was treated with conventional anticoagulants.

7. Conclusion: The single injections of Hirulog used in the study produced incomplete and temporary suppression of F1+2. Complete and permanent inhibition of thrombin generation with Hirulog in patients with calf vein thrombosis may require higher doses, multiple subcutaneous injections and/or prolonged intravenous infusion.

Comparison of the Non-Specific Binding of Unfractionated Heparin and Low Molecular Weight Heparin (Enoxaparin) to Plasma Proteins

The non-specific binding of anticoagulantly-active heparin to plasma proteins may influence its anticoagulant effect. We used low affinity heparin (LAH) essentially devoid of anti-factor Xa activity to investigate the extent and possible mechanism of this non-specific binding. The addition of excess LAH to platelet-poor plasma containing a fixed amount of unfractionated heparin doubled the anti-factor Xa activity presumably because it displaces anticoagulantly-active heparin from plasma proteins. Although dextran sulfates of varying molecular weights also increased the anti-factor Xa activity, less sulfated heparin-like polysaccharides had no effect. These findings suggest that the ability to displace active heparin from plasma protein binding sites is related to charge and may be independent of molecular size. In contrast to its effect in plasma containing unfractionated heparin, there was little augmentation in anti-factor Xa activity when LAH was added to plasma containing low molecular weight heparin (LMWH), indicating that LMWH binds less to plasma proteins than unfractionated heparin. This concept is supported by studies comparing the anticoagulant activity of unfractionated heparin and LMWH in plasma with that in buffer containing antithrombin III. The anti-factor Xa activity of unfractionated heparin was 2-fold less in plasma than in the purified system. In contrast, LMWH had identical anti-factor Xa activity in both plasma and buffer, respectively. These findings may be clinically relevant because the recovered anti-factor Xa activity of unfractionated heparin was 33% lower in plasma from patients with suspected venous thrombosis than in plasma from healthy volunteers. The reduced heparin recovery in patient plasma reflects increased heparin binding to plasma proteins because the addition of LAH augmented the anti-factor Xa activity. In contrast to unfractionated heparin, there was complete recovery of LMWH added to patient plasma and little increase of anti-factor Xa activity after the addition of LAH. These findings may explain why LMWH gives a more predictable dose response than unfractionated heparin.

The Additive Effect of Low Molecular Weight Heparins on Thrombin Inhibition by Dermatan Sulfate

The aim of this study was to investigate the mechanism by which the anticoagulant activity of dermatan sulfate (DS) is increased by low molecular weight heparin (LMWH). In platelet poor plasma, LMWH enhances the effect of DS on thrombin (IIa) inhibition as determined by thrombin clotting times and with a chromogenic substrate assay. Analysis of the results of the chromogenic assays using either the algebraic fractional or the graphic isobole method suggests that LMWH has an additive effect on the anti-IIa activity of DS. This additive effect was lost when the experiments were repeated in plasma immunodepleted of antithrombin III (ATIII), indicating that the anti-IIa activity of LMWH is ATIII-dependent. To further explore the mechanism of the interaction between LMWH and DS, 125I-labeled IIa was added to plasma in the presence or absence of DS and/or LMWH and the formation of IIa-inhibitor complexes was assessed using SDS-PAGE followed by autoradiography. DS addition selectively increases the formation of heparin cofactor II (HCII)-IIa complexes, whereas LMWH enhances ATIII-IIa complex generation. Compared to plasma containing DS alone, the formation of ATIII-IIa complexes also is increased when the combination of DS and LMWH is added. These findings suggest that the additive effect of LMWH on the anti-IIa activity of DS reflects their different modes of IIa inhibition; DS potentiates IIa inhibition by HCII, while LMWH catalyses ATIII-dependent IIa inactivation. The potential clinical significance of these findings requires further investigation.

Fibrin Clot Lysis by Thrombolytic Agents Is Impaired in Newborns due to a Low Plasminogen Concentration

Although thrombolytic drugs have been extensively used in adults, there is sparse information on their effectiveness in newborns whose fibrinolytic system differs significantly from adults. The purpose of this study was to determine if low plasma levels of plasminogen in cord plasma limited the therapeutic effectiveness of thrombolytic agents. Urokinase (UK), streptokinase (SK) and tissue plasminogen activator (TPA) were compared for their ability to lyse washed 125I-labelled adult or cord fibrin clots suspended in cord or adult plasma. 125I-labelled fibrin clots were prepared by recalcifying cord or adult plasma spiked with labelled fibrinogen and then placed into cord or adult plasma which contained either saline or differing amounts of a specific thrombolytic agent. After a 60 min incubation, the remaining 125I-fibrin in clots released 125I-fibrin fragments, and concentrations of fibrinogen, α2-antiplasmin, and plasminogen in the bathing plasma were measured and compared to starting values. Cord fibrin clots were more resistant than adult fibrin clots to all thrombolytic drugs tested (p <0.001). On average, the cord system retained 27% more 125I-fibrin in clots, and released 32% less 125I-fibrin fragments into plasma. Fibrinogenolysis was also decreased in cord plasmas compared to adult plasmas. The degree of fibrinolysis and fibrinogenolysis in cord plasma increased to adult values when plasminogen concentrations were increased in the bathing plasma. Thus, cord fibrin clots have an impaired response to thrombolytic agents secondary to low levels of plasminogen. We speculate that the clinical response of newborns to thrombolytic agents is also impaired and will not be enhanced by increasing doses of thrombolytic agents but may be enhanced by increasing the concentration of plasminogen.

Optimal Duration of Oral Anticoagulant Therapy: A Randomized Trial Comparing Four Weeks with Three Months of Warfarin in Patients with Proximal Deep Vein Thrombosis

The optimal duration of oral anticoagulant therapy for patients with acute proximal deep vein thrombosis (DVT) is uncertain. Based on the hypothesis that a normal impedance plethysmogram (IPG) following DVT defines a group of patients at low risk of recurrent venous thromboembolism (VTE), a trial was conducted to evaluate the efficacy of only four weeks of warfarin. Patients with venographically confirmed acute proximal DVT who had received four weeks of warfarin after initial heparin and whose four week IPG was normal were allocated to either continue warfarin (targeted International Normalized Ratio 2.0 to 3.0) for a further eight weeks or receive placebo. Patients with an abnormal four week IPG received warfarin for a further eight weeks. Based on clinical characteristics at the time of the qualifying thrombosis, all patients were classified as having either continuing or transient risk factors for recurrent VTE. During the eight weeks following randomization, nine (8.6%) of the 105 placebo patients developed recurrent VTE compared to one (0.9%) of the 109 warfarin patients, P = 0.009. Over the entire 11 months of follow-up, 12 placebo patients developed recurrence compared to seven warfarin patients, P = 0.3. Nineteen of the 192 patients with an abnormal four week IPG experienced recurrence during the nine months after discontinuing warfarin.

In the 301 patients who received three months of warfarin in the randomized trial or in the cohort study, all 26 recurrent events were in the 212 patients with continuing risk factors.

In conclusion, an IPG four weeks after proximal DVT is not a useful predictor for recurrent VTE; whereas the presence of continuing risk factors is a very strong predictor. Four weeks of oral anticoagulants may be all that is required in patients without continuing risk factors. Patients with continuing risk factors may require more than three months of oral anticoagulants.

The Effect of Thrombin Inhibitors on Tissue Plasminogen Activator Induced Thrombolysis in a Rat Model

Successful coronary thrombolysis depends on rapidly restoring blood flow and maintaining patency of the infarct-related artery. Although widely used as an adjunct to lytic therapy, heparin is limited in its ability to produce these effects. Since the limitations of heparin may reflect its inability to inactivate clot-bound thrombin, we developed a rat model of tissue plasminogen activator (t-PA) induced thrombolysis to compare doses of heparin, hirudin, hirulog (a synthetic hirudin-derived peptide), and D-Phe-Pro-ArgCH2Cl (PPACK) that produced a 4-fold prolongation of the baseline activated partial thromboplastin time (APTT) with saline in terms of their ability to accelerate thrombolysis and to prevent reocclusion. A thrombus rich in red cells and fibrin was formed in the distal aorta by applying an external constrictor after denuding the endothelium with a balloon catheter. Thrombolysis was induced with t-PA (1 mg/kg bolus, followed by 1 mg kg–1 h–1 over 30 min) and the rats were then randomized to receive a concomitant 80 min infusion of a thrombin inhibitor or saline. By continuously monitoring blood flow and pre- and post-stenotic blood pressures, the time to clot lysis, and the number of reocclusions were determined. Compared to saline, heparin had no significant effect on these variables. In contrast, hirudin, hirulog, and PPACK significantly (p <0.01) increased the percentage of the time that the vessel remained patent from 63.9 ± 7.7 to 90.7 ± 2.2, 94.0 ± 0.9, and 94.7 ± 1.0%, respectively by significantly (p <0.01) decreasing the number of reocclusions. The superiority of the antithrombin III-independent inhibitors over heparin supports the hypothesis that the limited effectiveness of heparin in this setting reflects its inability to inactivate clot-bound thrombin. Compared to saline, hirulog and PPACK also significantly (p <0.02) accelerated the time to thrombolysis from 10.5 ± 2.3 to 4.4 ± 0.6, and 4.2 ± 0.8 min, respectively, whereas heparin and hirudin did not. The ability of the lower molecular weight inhibitors of thrombin to accelerate lysis may reflect their greater accessibility to clot-bound thrombin. These findings raise the possibility that the antithrombin III-independent inhibitors of thrombin may not be equally effective as adjuncts to thrombolytic therapy with t-PA.

Characterization of Patients with Embolic Strokes of Undetermined Source in the NAVIGATE ESUS Randomized Trial

BACKGROUND

The New Approach Rivaroxaban Inhibition of Factor Xa in a Global Trial vs. ASA to Prevent Embolism in Embolic Stroke of Undetermined Source (NAVIGATE-ESUS) trial is a randomized phase-III trial comparing rivaroxaban versus aspirin in patients with recent ESUS.

AIMS

We aimed to describe the baseline characteristics of this large ESUS cohort to explore relationships among key subgroups.

METHODS

We enrolled 7213 patients at 459 sites in 31 countries. Prespecified subgroups for primary safety and efficacy analyses included age, sex, race, global region, stroke or transient ischemic attack prior to qualifying event, time to randomization, hypertension, and diabetes mellitus.

RESULTS

Mean age was 66.9 ± 9.8 years; 24% were under 60 years. Older patients had more hypertension, coronary disease, and cancer. Strokes in older subjects were more frequently cortical and accompanied by radiographic evidence of prior infarction. Women comprised 38% of participants and were older than men. Patients from East Asia were oldest whereas those from Latin America were youngest. Patients in the Americas more frequently were on aspirin prior to the qualifying stroke. Acute cortical infarction was more common in the United States, Canada, and Western Europe, whereas prior radiographic infarctions were most common in East Asia. Approximately forty-five percent of subjects were enrolled within 30 days of the qualifying stroke, with earliest enrollments in Asia and Eastern Europe.

CONCLUSIONS

NAVIGATE-ESUS is the largest randomized trial comparing antithrombotic strategies for secondary stroke prevention in patients with ESUS. The study population encompasses a broad array of patients across multiple continents and these subgroups provide ample opportunities for future research.

KidsBrainIT: A New Multi-centre, Multi-disciplinary, Multi-national Paediatric Brain Monitoring Collaboration

OBJECTIVES

Validated optimal cerebral perfusion pressure (CPP) treatment thresholds in children do not exist. To improve the intensive care unit (ICU) management of the paediatric traumatic brain injury (TBI) population, we are forming a new paediatric multi-centre collaboration to recruit standardised ICU data for running and reporting upon models for assessing autoregulation and optimal CCP (CPPopt).

MATERIALS AND METHODS

We are adapting the adult BrainIT group's approach to develop a new Paediatric Brain Monitoring and Information Technology Group (KidsBrainIT), which will include a repository to store prospectively collected high-resolution physiological, clinical, and outcome data. In the first phase of this project there are 7 UK Paediatric Intensive Care Units, 1 Spanish, 1 Belgium, and 1 Romanian Centre interested in participating. In subsequent phases, we plan to open recruitment to other centres both within Europe, US and abroad. We are collaborating with the Leuven Group and plan to use their LAx (low-frequency autoregulation index), DATACAR (dynamic adaptive target of active cerebral autoregulation), CPPopt and visualisation methodologies. We also plan to use the continuous diffuse optical monitoring and tomography technology developed in Barcelona as an acute surrogate end-point for optimising brain perfusion. This technology allows non-invasive continuous monitoring of deep tissue perfusion and oxygenation in adults but its clinical application in infants and children with TBI has not been studied previously.

RESULTS

We report on the current status of setting up this new collaboration and also on pilot analyses in two centres which are the basis of our rationale for the need for a prospective validation study of CPPopt in children. Specifically, we demonstrated that CPPopt varied with time for each patient during their paediatric intensive care unit (PICU) stay, and the median overall CPPopt levels for children aged 2-6 years, 7-11 years and 12-16 years were 68.83, 68.09, and 72.17 mmHg respectively. Among survivors and patients with favourable outcome (GOS 4 and 5), there were significantly higher proportions with CPP monitoring time within CPPopt (p = 0.04 and p = 0.01 respectively).

CONCLUSIONS

There is a need and an interest in forming a multi-centre PICU collaboration for acquiring data and performing analyses for determining validated CPPopt thresholds in the paediatric TBI population. KidsBrainIT is being formed to meet that need.

Like Fibrin, (DD)E, the Major Degradation Product of Crosslinked Fibrin, Protects Plasmin from Inhibition by α2-antiplasmin

Plasmin generation is localized to the fibrin surface because tissue-type plasminogen activator (t-PA) and plasminogen bind to fibrin, an interaction that stimulates plasminogen activation over a hundred-fold. To ensure efficient fibrinolysis, plasmin bound to fibrin is protected from inhibition by α2-antiplasmin. (DD)E, a major soluble degradation product of cross-linked fibrin that is a potent stimulator of t-PA, compromises the fibrin-specificity of t-PA by promoting systemic activation of plasminogen. In this study we investigated whether (DD)E also protects plasmin from inhibition by α2-antiplasmin, facilitating degradation of this soluble t-PA effector. (DD)E and fibrin reduce the rate of plasmin inhibition by α2-antiplasmin by 5- and 10-fold, respectively. Kringle-dependent binding of plasmin to (DD)E and fibrin, with Kd values of 52 and 410 nM, respectively, contributes to the protective effect. When (DD)E is extensively degraded by plasmin, yielding uncomplexed fragment E and (DD), protection of plasmin from inhibition by α2-antiplasmin is attenuated. These studies indicate that (DD)E-bound plasmin, whose generation reflects the ability of (DD)E to stimulate plasminogen activation by t-PA, has the capacity to degrade (DD)E by virtue of its resistance to inhibition. This provides a mechanism to limit the concentration of (DD)E and maintain the fibrin-specificity of t-PA.

Spotlight on unmet needs in stroke prevention: The PIONEER AF-PCI, NAVIGATE ESUS and GALILEO trials

Atrial fibrillation (AF) is a major healthcare concern, being associated with an estimated five-fold risk of ischaemic stroke. In patients with AF, anticoagulants reduce stroke risk to a greater extent than acetylsalicylic acid (ASA) or dual antiplatelet therapy (DAPT) with ASA plus clopidogrel. Non-vitamin K antagonist oral anticoagulants (NOACs) are now a widely-accepted therapeutic option for stroke prevention in non-valvular AF (NVAF). There are particular patient types with NVAF for whom treatment challenges remain, owing to sparse clinical data, their high-risk nature or a need to harmonise anticoagulant and antiplatelet regimens if co-administered. This article focuses on three randomised controlled trials (RCTs) that are investigating the utility of rivaroxaban, a direct, oral, factor Xa inhibitor, in additional areas of stroke prevention where data for anticoagulants are lacking: oPenlabel, randomized, controlled, multicentre study explorIng twO treatmeNt stratEgiEs of Rivaroxaban and a dose-adjusted oral vitamin K antagonist treatment (PIONEER AF-PCI); New Approach riVaroxoban Inhibition of factor Xa in a Global trial vs Aspirin to prevenT Embolism in Embolic Stroke of Undetermined Source (NAVIGATE ESUS); and Global study comparing a rivAroxaban-based antithrombotic strategy to an antipLatelet-based strategy after transcatheter aortIc vaLve rEplacement to Optimize clinical outcomes (GALILEO). Data from these studies present collaborative efforts to build upon existing registrational Phase III data for rivaroxaban, driving the need for effective and safe treatment of a wider range of patients for stroke prevention.

Derivation of a Simple Clinical Model to Categorize Patients Probability of Pulmonary Embolism: Increasing the Models Utility with the SimpliRED D-dimer

We have previously demonstrated that a clinical model can be safely used in a management strategy in patients with suspected pulmonary embolism (PE). We sought to simplify the clinical model and determine a scoring system, that when combined with D-dimer results, would safely exclude PE without the need for other tests, in a large proportion of patients. We used a randomly selected sample of 80% of the patients that participated in a prospective cohort study of patients with suspected PE to perform a logistic regression analysis on 40 clinical variables to create a simple clinical prediction rule. Cut points on the new rule were determined to create two scoring systems. In the first scoring system patients were classified as having low, moderate and high probability of PE with the proportions being similar to those determined in our original study. The second system was designed to create two categories, PE likely and unlikely. The goal in the latter was that PE unlikely patients with a negative D-dimer result would have PE in less than 2% of cases. The proportion of patients with PE in each category was determined overall and according to a positive or negative SimpliRED D-dimer result. After these determinations we applied the models to the remaining 20% of patients as a validation of the results. The following seven variables and assigned scores (in brackets) were included in the clinical prediction rule: Clinical symptoms of DVT (3.0), no alternative diagnosis (3.0), heart rate >100 (1.5), immobilization or surgery in the previous four weeks (1.5), previous DVT/PE (1.5), hemoptysis (1.0) and malignancy (1.0). Patients were considered low probability if the score was <2.0, moderate of the score was 2.0 to 6.0 and high if the score was over 6.0. Pulmonary embolism unlikely was assigned to patients with scores <4.0 and PE likely if the score was >4.0. 7.8% of patients with scores of less than or equal to 4 had PE but if the D-dimer was negative in these patients the rate of PE was only 2.2% (95% CI = 1.0% to 4.0%) in the derivation set and 1.7% in the validation set.

Importantly this combination occurred in 46% of our study patients. A score of <2.0 and a negative D-dimer results in a PE rate of 1.5% (95% CI = 0.4% to 3.7%) in the derivation set and 2.7% (95% CI = 0.3% to 9.0%) in the validation set and only occurred in 29% of patients. The combination of a score <4.0 by our simple clinical prediction rule and a negative SimpliRED D-Dimer result may safely exclude PE in a large proportion of patients with suspected PE.

Mechanism of Action of Plasminogen Activators

Acute coronary ischemic syndromes and stroke are usually caused by thrombosis in arteries where obstruction leads to ischemia of the heart or brain, respectively. Likewise, venous thrombosis predisposes to pulmonary emboli that cause infarction of lung tissue by blocking pulmonary arteries. Although antithrombotic drugs form the cornerstone of treatment of established thrombosis, pharmacologic lysis of fibrin thrombi, using plasminogen activators, is a widely used approach for treatment of acute myocardial infarction and selected cases of stroke or venous thromboembolism.

Plasminogen activators cause thrombus dissolution by initiating fibrinolysis (Fig. 1). The fibrinolytic system is comprised of inactive plasminogen, which is converted to plasmin by plasminogen activators.1 Plasmin, a trypsin-like serine protease, degrades fibrin into soluble fibrin degradation products. The fibrinolytic system is regulated to provide efficient localized activation of plasminogen on the fibrin surface, yet prevent systemic plasminogen activation. To localize plasminogen activation to the fibrin surface, both plasminogen and tissue-type plasminogen activator (t-PA), the major initiator of intravascular fibrinolysis, bind to fibrin. Plasminogen activator inhibitors,2 the most important of which is type-1 plasminogen activator inhibitor (PAI-1), prevent excessive plasminogen activation by t-PA and urokinase-type plasminogen activator (u-PA). Systemic plasmin is rapidly inhibited by α2-antiplasmin, whereas plasmin generated on the fibrin surface is relatively protected from inactivation by α2-antiplasmin.3

The beneficial effect of thrombolytic therapy reflects dissolution of fibrin within occlusive thrombi and subsequent restoration of antegrade blood flow. Bleeding, the major side effect of thrombolytic therapy, occurs because plasmin is a relatively nonspecific enzyme that does not distinguish between fibrin in occlusive thrombi and fibrin in hemostatic plugs. In addition, circulating plasmin also degrades fibrinogen and other clotting factors, a phenomenon known as the systemic lytic state. Although the contribution of the systemic lytic state to bleeding remains controversial, much attention has focussed on the development of plasminogen activators that produce thrombolysis without depleting circulating fibrinogen in the hope that agents with greater fibrin-specificity will produce less bleeding.

In addition to causing bleeding, currently available plasminogen activators have other limitations. Despite aggressive dosing regimens and adjunctive antithrombotic drugs, up to 25% of coronary thrombi are resistant to thrombolysis at 60 to 90 minutes. Early thrombotic reocclusion of previously opened coronary arteries further reduces the benefits of thrombolytic therapy.4-6 These problems have triggered the quest for more potent thrombolytic agents that have the potential to overcome factors that render some thrombi resistant to lysis. Furthermore, to simplify administration, plasminogen activators with longer half-lives have been developed so that bolus dosing is possible.

This chapter reviews the mechanism of action of currently available plasminogen activators, including agents with greater fibrin-specificity, longer half-lives, and a potential for increased thrombolytic potency.

The Effects of Standard and Low Molecular Weight Heparin on Bone Nodule Formation In Vitro

Previously, we demonstrated in a rat model of heparin-induced osteoporosis that low molecular weight heparin (LMWH) produces less bone loss than unfractionated heparin, and that only heparin increases osteoclast number and activity. In contrast, both heparin and LMWH were found to decrease osteoblast function to a similar extent, possibly because at the doses tested both agents produced maximal inhibition. To examine the relative effects of heparin and LMWH on osteoblast function more closely we used an in vitro bone nodule assay, together with measurements of alkaline phosphatase (ALP) activity. Both agents inhibited bone nodule formation and ALP activity in a concentration-dependent manner, but 6 to 8-fold higher concentrations of LMWH were required to achieve equivalent effects. The effect of heparin on osteoblast function was both chain-length and negative charge-dependent because the ability of defined heparin fragments to inhibit nodule formation correlated with their molecular weight (r = 0.98), and N-desulfated heparin was less inhibitory than heparin. In contrast, the effect of heparin on osteoblast function was pentasaccharide-independent because heparin with low affinity for antithrombin had similar activity to heparin with high antithrombin activity. These findings help to explain mounting clinical evidence that the risk of osteoporosis is lower with LMWH than with heparin.

Fibrinolytic Variables in Patients with Recurrent Venous Thrombosis: a Prospective Cohort Study

To determine whether fibrinolytic testing predicts recurrent venous thrombosis, we have performed a prospective cohort study in which 303 patients with a first episode of venous thromboembolism underwent comprehensive fibrinolytic testing while receiving oral anticoagulants, and after anticoagulants had been discontinued. They were then followed for up to 3 years for recurrent venous thrombosis. No systematic differences in the levels or activity of type 1 plasminogen activator inhibitor (PAI-1), tissue plasminogen activator (tPA) or euglobulin clot lysis times were detected between patients who did, or did not, suffer recurrent thrombosis. There were also no differences in these variables when patients whose initial thrombosis was idiopathic were compared to patients whose thrombosis occurred in the setting of a known thrombotic risk factor. Based on these results, neither measuring fibrinolytic parameters in patients with venous thromboembolism, nor modification of treatment based on the results of such testing, are justified. Our study also confirms that patients with idiopathic venous thromboembolism have a high risk of recurrence.

Two doses of rivaroxaban versus aspirin for prevention of recurrent venous thromboembolism

Patients with unprovoked venous thromboembolism (VTE) are at high risk for recurrence. Although rivaroxaban is effective for extended VTE treatment at a dose of 20 mg once daily, use of the 10 mg dose may further improve its benefit-to-risk ratio. Low-dose aspirin also reduces rates of recurrent VTE, but has not been compared with anticoagulant therapy. The EINSTEIN CHOICE study is a multicentre, randomised, double-blind, active-controlled, event-driven study comparing the efficacy and safety of two once daily doses of rivaroxaban (20 and 10 mg) with aspirin (100 mg daily) for the prevention of recurrent VTE in patients who completed 6–12 months of anticoagulant therapy for their index acute VTE event. All treatments will be given for 12 months. The primary efficacy objective is to determine whether both doses of rivaroxaban are superior to aspirin for the prevention of symptomatic recurrent VTE, while the principal safety outcome is the incidence of major bleeding. The trial is anticipated to enrol 2,850 patients from 230 sites in 31 countries over a period of 27 months. In conclusion, the EINSTEIN CHOICE study will provide new insights into the optimal antithrombotic strategy for extended VTE treatment by comparing two doses of rivaroxaban with aspirin (clinicaltrials.gov NCT02064439).

Zinc: An important cofactor in haemostasis and thrombosis

There is mounting evidence that zinc, the second most abundant transition metal in blood, is an important mediator of haemostasis and thrombosis. Prompted by the observation that zinc deficiency is associated with bleeding and clotting abnormalities, there now is evidence that zinc serves as an effector of coagulation, anticoagulation and fibrinolysis. Zinc binds numerous plasma proteins and modulates their structure and function. Because activated platelets secrete zinc into the local microenvironment, the concentration of zinc increases in the vicinity of a thrombus. Consequently, the role of zinc varies depending on the microenvironment; a feature that endows zinc with the capacity to spatially and temporally regulate haemostasis and thrombosis. This paper reviews the mechanisms by which zinc regulates coagulation, platelet aggregation, anticoagulation and fibrinolysis and outlines how zinc serves as a ubiquitous modulator of haemostasis and thrombosis.