Comparative effectiveness of NOAC vs VKA in patients representing common clinical challenges: results from the GARFIELD-AF registry

Introduction

Large phase III trials of non-valvular atrial fibrillation (AF) patients have shown a favourable risk-to-benefit ratio with Non-Vitamin K antagonist oral anticoagulants (NOAC) compared to Vitamin K antagonists (VKA). Although the results of these trials are directly applicable to many AF patients, important subsets of patients were under-represented. Thus, there remains uncertainty about the safety and effectiveness of NOAC therapy in common challenging scenarios.

Purpose

The main purpose of this study is to quantify and compare the impact of NOAC vs VKA in settings where clinical uncertainty still exists and represents a considerable proportion of AF patients in clinical practice.

Methods

The analysis was conducted in patients enrolled in the largest AF multinational prospective registry (the Global Anticoagulant Registry in the FIELD–Atrial Fibrillation, GARFIELD-AF). We evaluated the effectiveness and safety of NOAC compared to VKA in three groups of patients representing common clinical challenges (CCC): 1) elderly patients (i.e. age ≥75), 2) increased bleeding risk (i.e. HAS-BLED ≥3 or prior bleeding), and 3) renal impairment (i.e. CKD stages II to IV).

We applied a propensity score using an overlap weighting scheme to obtain unbiased estimates of the treatment effect within each CCC group. Weights were applied to Cox proportional hazards models to estimate the effects of the NOAC vs VKA comparison on the occurrence of death, non-haemorrhagic stroke/SE and major bleeding within 2 years of enrolment.

Results

Comparative effectiveness of NOAC vs VKA was assessed in 8607 elderly patients, 1711 with increased bleeding risk, and 4460 with renal impairment.

The proportion of anticoagulated patients was low in patients with increased bleeding risk (59%), while in the other two CCC groups the corresponding proportion was close to the one in the overall population (72%).

Among anticoagulated patients, NOAC were prescribed to 50–55% of patients in the CCC groups. Patients with a high risk of bleeding and impaired kidney function were less likely to be prescribed NOAC instead of VKA compared with the overall anticoagulated population (−5.4% and −4.7%, respectively).

Propensity-weighted hazard ratios for all-cause mortality favored NOAC (vs VKA) in all three CCC groups: 0.86 (95% CI: 0.74–0.99) for elderly patients, 0.73 (0.53–1.00) for patients with increased bleeding risk, and 0.80 (0.65–0.98) for patients with renal impairment (Figure).

Conclusion

In the selected common challenging scenarios of AF patients, there were significant mortality reductions in favor of NOACs compared to VKAs. These observations suggest that NOACs are safe and effective in patients who are elderly, at increased bleeding risk, or renally impaired.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): This study was supported by an unrestricted research grant from Bayer AG, Berlin, Germany, to TRI, London, UK, which sponsors the GARFIELD-AF registry. The work is supported by KANTOR CHARITABLE FOUNDATION for the Kantor-Kakkar Global Centre for Thrombosis Science.

Safety and efficacy of apixaban and rivaroxaban versus warfarin in real-world atrial fibrillation patients are similar to their randomized trials: insights from GARFIELD-AF registry

Introduction

Generalisability of patient selection in the landmark trials for the approval of apixaban (ARISTOTLE) and rivaroxaban (ROCKET AF) for use in non-valvular atrial fibrillation (AF) is limited. Although observational data have confirmed the safety and efficacy of these non-vitamin K oral anticoagulants (NOACs) in unselected AF populations, robust replication of randomized trials in observational studies is warranted.

Purpose

To investigate the proportion of real-world AF patients who would have been eligible for the landmark trials for ARISTOTLE and ROCKET AF, and to assess reproducibility of these landmark trials in the largest, worldwide, prospective registry of newly diagnosed AF patients.

Methods

We analysed data from the Global Anticoagulant Registry in the FIELD–Atrial Fibrillation (GARFIELD-AF) registry. We assessed the eligibility of AF patients treated with apixaban or vitamin K antagonist (VKA) for ARISTOTLE, and those treated with rivaroxaban or VKA for ROCKET AF, using the selection criteria of the original trials. We replicated the inclusion and exclusion criteria of ARISTOTLE and ROCKET AF by deriving the set of patients eligible for each trial and calculating the adjusted hazard ratios (HRs) for stroke or systemic embolism, major bleeding, and all-cause mortality within 2 years of enrolment, using a propensity score overlap weighted Cox model. We compared the results from observational data with those reported in the original ARISTOTLE and ROCKET AF publications.

Results

Among all patients enrolled in GARFIELD-AF, 67% were eligible for recruitment in ARISTOTLE and 37% in ROCKET AF. The corresponding proportions among anticoagulated patients were 70% and 39%, respectively. Among patients on apixaban and VKA, 2570/3615 (71%) and 8005/11718 (68%), respectively, were eligible for ARISTOTLE. Of patients using rivaroxaban and VKA, 2005/4914 (41%) and 4368/11721 (37%), respectively, were eligible for ROCKET AF. Annual eligibility rates among real-world NOAC users were stable over time (Figure 1). Registry participants on rivaroxaban or VKA eligible for ROCKET AF had a higher burden of cardiovascular co-morbidity than those on apixaban or VKA eligible for ARISTOTLE. The adjusted HRs in observational data were compatible with results of the original trials in all selected outcomes (Figure 2).

Conclusion

Representativeness of ARISTOTLE and ROCKET AF for real-world AF populations was limited, with ROCKET AF's criteria being more restrictive. Despite inclusion of only incident AF cases in GARFIELD-AF versus mostly prevalent AF cases in the original trials, the results were similar. Our work indicates that the results from ARISTOTLE and ROCKET AF appear robust and reproducible in real-world patients with newly diagnosed AF.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): This work was supported by an unrestricted research grant from Bayer AG, Berlin, Germany, to TRI, London, UK, which sponsors the GARFIELD-AF registry. This work is supported by KANTOR CHARITABLE FOUNDATION for the Kantor-Kakkar Global Centre for Thrombosis Science.

Comparing rivaroxaban and apixaban in GARFIELD-AF according to ROCKET AF and ARISTOTLE trial selection criteria

Introduction

There is debate on the extent to which differences in selection criteria and outcome definitions used for ARISTOTLE and ROCKET AF – the trials for the approval of apixaban and rivaroxaban, respectively, for non-valvular atrial fibrillation – influenced their differences in outcomes relative to vitamin K antagonists (VKAs). In absence of randomized trials comparing the two non-vitamin K oral antagonists (NOACs) directly, this question can be addressed using data from the Global Anticoagulant Registry in the FIELD–Atrial Fibrillation (GARFIELD-AF) registry, a large, high-quality prospective observational study of newly diagnosed AF patients.

Purpose

To assess the influence of the ARISTOTLE and ROCKET AF inclusion and exclusion criteria on results for safety and efficacy of apixaban and rivaroxaban versus VKA using uniform endpoints in GARFIELD-AF.

Methods

We selected patients treated with apixaban, rivaroxaban or VKA from GARFIELD-AF who were eligible for ARISTOTLE or ROCKET AF as per the original trial criteria. We replicated the inclusion criteria in the GARFIELD-AF population and derived those eligible for each trial. We calculated the adjusted hazard ratios (HRs) for stroke or systemic embolism, major bleeding and all-cause mortality within 2 years of enrolment for apixaban as well as rivaroxaban versus VKA (reference) in those eligible for each trial. We used a propensity score overlap weighted Cox model to emulate trial randomization between NOAC and VKA.

Results

Among patients on apixaban, rivaroxaban and VKA, 2570/3615 (71%), 3560/4914 (72%) and 8005/11734 (71%) were eligible for ARISTOTLE, respectively, and 1612/3615 (45%), 2005/4914 (41%) and 4368/11734 (37%), respectively, were eligible for ROCKET AF. Cardiovascular co-morbidity was greater in those eligible for ROCKET AF than in those eligible for ARISTOTLE. In patients selected using the more restrictive ROCKET AF criteria, apixaban and rivaroxaban users showed similar results when compared with VKA (see Figure). The two sets of comparisons remained non-significant in difference when applying the less restrictive ARISTOTLE criteria, but there were trends for less similarity.

Conclusion

Apixaban showed similar results to rivaroxaban when selecting for higher-risk patients using the ROCKET AF criteria. In patients selected using ARISTOTLE criteria the similarity was less pronounced. Our results underline the problems faced in comparing treatments across rather than within clinical trials. For instance, co-morbidities were substantially different for patients recruited into the original ARISTOTLE and ROCKET AF trials. The current work points to the need for high-quality observational data for assessment of relative drug performance in absence of direct drug comparisons through randomized trials.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): This work was supported by an unrestricted research grant from Bayer AG, Berlin, Germany, to TRI, London, UK, which sponsors the GARFIELD-AF registry. This work is supported by KANTOR CHARITABLE FOUNDATION for the Kantor-Kakkar Global Centre for Thrombosis Science.

The effect of body mass index on clinical outcomes in patients with newly diagnosed atrial fibrillation in the GARFIELD-AF registry

Introduction

Higher body mass index (BMI) is associated with a higher risk of atrial fibrillation (AF). However, previous evidence has suggested an inverse association between BMI and risk of AF outcomes.

Purpose

To explore the association between BMI and outcomes in those with newly diagnosed AF in the GARFIELD-AF registry.

Methods

GARFIELD-AF is an international registry of consecutively recruited patients aged ≥18 years with newly diagnosed AF and ≥1 stroke risk factor. Data were collected prospectively on 52,080 patients. Participants with missing or extreme BMI values and those without two-year follow-up were excluded. Cox proportional hazard models were used to estimate the effect of BMI on the risk of outcomes. Models were adjusted for age, sex, ethnicity, smoking, alcohol, and ≥moderate chronic kidney disease. Where appropriate participants were divided into groups based on BMI. Restricted cubic splines were used to assess non-linear relationships.

Results

BMI and outcome data were available for 40,495 patients. Those with higher BMI were generally younger, and more likely to have pre-existing hypertension, diabetes, or vascular disease (Table). Underweight patients received anticoagulation less often than those in other groups (60.3% vs 67.9%, respectively). During follow-up, 2,801 participants (6.9%) died and 603 (1.5%) had new/worsening heart failure. Following adjustment for potential confounders, a U-shaped relationship was seen between BMI and all-cause mortality and new/worsening heart failure (Figure). For all-cause mortality, the lowest risk was at 30kg/m2. Below this level, there was an 8% higher risk of mortality (95% confidence interval (CI) 6 to 9%) per 1kg/m2 lower BMI. Above 30kg/m2, there was a 5% higher risk of mortality per 1kg/m2 higher BMI (95% CI 4 to 7%). For new/worsening heart failure, the lowest risk was at 25kg/m2. Above this level, 1kg/m2 higher BMI was associated with an 5% higher risk (95% CI 13 to 6%).

Conclusions

BMI was an important risk factor for both all-cause mortality and new/worsening heart failure in AF. Those at both extremes of BMI are at higher risk.

BMI and selected outcomes

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): The GARFIELD-AF registry is funded by an unrestricted research grant from Bayer AG.

Permanent discontinuation of different anticoagulants in patients with atrial fibrillation and the impact on clinical outcome: data from the GARFIELD-AF registry

Background

Non-Vitamin K Antagonists (NOAC) are replacing vitamin K Antagonists (VKA) as first line oral anticoagulant therapy (OAC) in patients with non-valvular atrial fibrillation (NVAF). Discontinuation of OAC might put patients at increased risk. It was anticipated that patients who were on NOAC would discontinue OAC less.

Purpose

We compare the rates and impact on outcome of the discontinuation of NOAC and VKA using data from the GARFIELD-AF registry.

Methods

Patients included in GARFIELD-AF, had a new diagnosis of NVAF and at least 1 stroke risk factor. In this analysis 26,299 patients (VKA: 13,012; NOAC: 13,287) that received OAC were included. Permanent discontinuation was defined as stopping OAC for at least 7 consecutive days (whether or not restarted during follow-up). Marginal structural Cox proportional hazards models estimated the effect of discontinuation on death, cardiovascular (CV) death, non-haemorrhagic stroke + systemic embolism (NHS+SE), myocardial infarction (MI), or combined endpoints. Adjustments were made for both baseline factors and time dependent variables.

Results

Of all patients, 15.6% discontinued OAC (VKA: 15.4%; NOAC: 15.8%) over a median follow-up of 181 days (IQR: 359). Most discontinued early (67.0% of patients on VKA and 47.1% of patients on NOAC ≤4 months). Significantly higher discontinuation risk was seen with worsening kidney function, coronary artery disease, history of bleeding (baseline factors), as well as with all types of bleeding (time dependent factors). Lower discontinuation rates were seen with history of stroke/TIA, hypertension, increasing age, permanent AF (all p<0.01).

Mean CHA2DS2-VASc score was 3 in all groups. Patients in both treatment arms who discontinued were at increased risk for death, NHS+SE, MI as well as combined endpoints of death/NHS+SE/MI, death/NHS+SE and a trend towards higher CV death (Figure 1). All interaction tests for the interaction of treatment and discontinuation had a p value >0.4. The association between discontinuation and outcomes did not change when a 30 day discontinuation window was used.

Conclusion

The rate of discontinuation in this study was 15.8% and comparable for VKA and NOAC over a 2-year follow-up. Discontinuation rates were the highest soon after the initiation of treatment. When VKA or NOAC was stopped for ≥7 consecutive days, the risk of NHS+SE, death, MI or any combined endpoints were significantly worse in both treatment arms. These data suggest that discontinuation of anticoagulant treatment with VKA or NOAC should be discouraged.

HR of patients who discontinued OAC

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): The GARFIELD-AF registry is funded by an unrestricted research grant from Bayer AG.

Clinical outcomes of patients with newly diagnosed atrial fibrillation who refused anticoagulation: findings from the global GARFIELD-AF registry

Introduction

Atrial fibrillation (AF) remains a common cause of stroke and anticoagulation (AC) treatment reduces the risk of stroke. Reasons for patients with AF not receiving anticoagulation are generally attributed to the clinician decision, however in reality a proportion of patients refuse anticoagulation. The aim of our study was to investigate the clinical outcomes of patients with AF who refused anticoagulation.

Methods

The Global Anticoagulant Registry in the FIELD (GARFIELD-AF) was an international prospective observational study of patients ≥18 years with newly diagnosed AF and ≥1 investigator determined risk factor for stroke. We analysed two-year outcomes (unadjusted) of non-haemorrhagic stroke/systemic embolism (stroke/SE), major bleeding and all-cause mortality in patients at high risk of stroke (men with CHA2DS2VASc≥2 and women with CHA2DS2VASc≥3) who did not received anticoagulation due to patient refusal, patients at high risk of stroke who received anticoagulation, and patients who were not on anticoagulation due to reasons other than patient refusal.

Results

Out of 43,154 patients, 13,283 (30.8%) are at the higher risk of stroke and did not received anticoagulation at baseline. The reason for not receiving anticoagulation was unavailable for 38.7% (5146/13283); of the patients with a known reason for not receiving anticoagulation, 12.5% (1014/8137) refused anticoagulation. Overall the study participants had a mean (SD) age of 72.2 (9.9) years and 50% were female. The median (Q1; Q3) CHA2DS2VASc score was 3.0 (3.0; 5.0) in patients who refused anticoagulation and 4.0 (3.0; 4.0) in patients who received anticoagulation. The median (Q1; Q3) HAS-BLED score was 1.0 (1.0; 2.0) in both groups. Of the patients who received anticoagulants, 59.7% received VKA and 40.3% received non-VKA oral anticoagulants. 79.4% of patients who refused anticoagulation were on antiplatelets. At two-year follow up the rate of events per 100 person-years (AC refused vs AC received) were: stroke/SE 1.42 vs 0.95 (p=0.04), major bleeding 0.62 vs 1.20 (p=0.02), and all-cause mortality 2.28 vs 3.90 (p=0.0004) (Figure). The event rates in patients who were not on anticoagulation for reasons other than patient refusal were stroke/SE 1.56, major bleeding 0.91, and all-cause mortality 5.49.

Conclusion

In this global real-world prospective study of patients with newly diagnosed AF, patients who refused anticoagulation had a higher rate of stroke/SE but lower rates of all-cause mortality and major bleeding than patients who received anticoagulation. While patient refusal of anticoagulation is an acceptable outcome of shared decision-making, clinically it is a missed opportunity to prevent AF related stroke. Patients' beliefs about AF related stroke and anticoagulation need to be explored. The difference in all-cause mortality warrants further investigation; further analysis will include adjusted results.

Event rates at two years of follow-up

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): The GARFIELD-AF registry is funded by an unrestricted research grant from Bayer AG.

Guideline-directed medical therapies for comorbidities among patients with atrial fibrillation: results from GARFIELD-AF

Introduction

The GARFIELD-AF registry is a prospective, multicentre, observational study of adults with recently diagnosed non-valvular atrial fibrillation (AF) and at least one risk factor for stroke. In GARFIELD-AF the absolute risk reduction of mortality associated with anticoagulation is far greater than the apparent absolute risk reduction in (ischemic) stroke. One potential explanation is improved treatment, with the use of comprehensive guideline-directed medical therapies (GDMT), in patients with AF receiving oral anticoagulant (OAC) therapy. The objectives were to identify the potential relationships between anticoagulation status, GDMT use and clinical outcomes.

Methods

Use of GDMT was determined on the basis of published European Society for Cardiology guidelines operative between 2010 and 2016. We explored the use of GDMT in patients enrolled in GARFIELD-AF (March 2010-Aug 2016) with CHA2DS2-VASc ≥2 and with one or more of five comorbidities–coronary artery disease, diabetes mellitus, heart failure, hypertension and peripheral vascular disease. Association between GDMT use and clinical outcomes events was evaluated with Cox-proportional hazards models. The models included stratification by all possible combinations of the five comorbidities used to define GDMT eligibility.

Results

The study population comprised of 39,946 patients who had one or more comorbidities (3238 [8.1%] received none of the GDMT, 17,398 [43.6%] received some, and 19,310 [48.3%] received all of the GDMT for which they were eligible). Patients on OAC tended to receive all the GDMTs more frequently compared to patients on no OAC (50.2% vs 44.8%, respectively).

Comprehensive GDMT was associated with a lower risk of all-cause mortality (HR: 0.89 [0.80–0.99]) and non-cardiovascular mortality (0.80 [0.68–0.95]) compared to inadequate or no GDMT but was not associated with a lower risk of stroke (HR: 1.04 (0.88–1.24)] (Figure). The effect of OAC was beneficial for mortality and stroke risk whether receiving comprehensive GDMT or not.

Conclusion

OAC therapy is associated with a lower risk of all-cause mortality, non-cardiovascular mortality and stroke/SE in comparison with no OAC, irrespective of GDMT use in patients with CHA2DS2-VASc ≥2. Although the use of GDMT is associated with a significant reduction in mortality, there is little evidence that this explains the decrease in mortality with the use of OAC.

GDMT use at two years of follow-up

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): The GARFIELD-AF registry is funded by an unrestricted research grant from Bayer AG.

Rivaroxaban

Rivaroxaban (Xarelto®), ein neuartiger oraler, direkter Faktor-Xa-Hemmer, ist in klinischer Entwicklung zur Prävention und Behandlung thromboembolischer Erkrankungen. Rivaroxaban hemmt die Clot-assoziierte und die freie Faktor-Xa-Aktivität, die Prothrombinase, und die Thrombinbildung. In Tiermodellen verhinderte Rivaroxaban die Bildung und das Wachstum venöser und arterieller Thromben. Rivaroxaban hat eine hohe orale Bioverfügbarkeit, schnellen Wirkeintritt und vorhersagbare Pharmakokinetik. In Phase-II-Studien zur Prävention venöser Thromboembolien (VTE) nach großen orthopädischen Operationen und zur Behandlung tiefer Venenthrombosen war Rivaroxaban wirksam und gut verträglich. In einer Phase-III-Studie zeigte Rivaroxaban höhere Wirksamkeit als Enoxaparin zur Vorbeugung von VTEs bei Kniegelenkersatzoperationen bei vergleichbar niedrigen Blutungsraten. Rivaroxaban wird zudem zur Therapie und Sekundärprävention von VTEs, zur Schlaganfallprophylaxe bei Vorhofflimmern und zur Sekundärprävention bei Patienten mit akutem Koronarsyndrom geprüft. Rivaroxaban ist eine vielversprechende Alternative zur aktuellen Therapie mit Antikoagulanzien bei thromboembolischen Erkrankungen.

Peri-procedural use of rivaroxaban in elective percutaneous coronary intervention to treat stable coronary artery disease. The X-PLORER trial

Patients on rivaroxaban requiring percutaneous coronary intervention (PCI) represent a clinical conundrum. We aimed to investigate whether rivaroxaban, with or without an additional bolus of unfractionated heparin (UFH), effectively inhibits coagulation activation during PCI. Stable patients (n=108) undergoing elective PCI and on stable dual antiplatelet therapy were randomised (2:2:2:1) to a short treatment course of rivaroxaban 10 mg (n=30), rivaroxaban 20 mg (n=32), rivaroxaban 10 mg plus UFH (n=30) or standard peri-procedural UFH (n=16). Blood samples for markers of thrombin generation and coagulation activation were drawn prior to and at 0, 0.5, 2, 6-8 and 48 hours (h) after start of PCI. In patients treated with rivaroxaban (10 or 20 mg) and patients treated with rivaroxaban plus heparin, the levels of prothrombin fragment 1 + 2 at 2 h post-PCI were 0.16 [0.1] nmol/l (median) [interquartile range, IQR] and 0.17 [0.2] nmol/l, respectively. Thrombin-antithrombin complex values at 2 h post-PCI were 3.90 [6.8]µg/l and 3.90 [10.1] µg/l, respectively, remaining below the upper reference limit (URL) after PCI and stenting. This was comparable to the control group of UFH treatment alone. However, median values for thrombin-antithrombin complex passed above the URL with increasing tendency, starting at 2 h post-PCI in the UFH-alone arm but not in rivaroxaban-treated patients. In this exploratory trial, rivaroxaban effectively suppressed coagulation activation after elective PCI and stenting.

Rivaroxaban versus placebo in patients with acute coronary syndromes (ATLAS ACS-TIMI 46): a randomised, double-blind, phase II trial

BACKGROUND

Rivaroxaban is an oral direct factor Xa inhibitor that has been effective in prevention of venous thromboembolism in patients undergoing elective orthopaedic surgery. However, its use after acute coronary syndromes has not been investigated. In this setting, we assessed the safety and efficacy of rivaroxaban and aimed to select the most favourable dose and dosing regimen.

METHODS

In this double-blind, dose-escalation, phase II study, undertaken at 297 sites in 27 countries, 3491 patients stabilised after an acute coronary syndrome were stratified on the basis of investigator decision to use aspirin only (stratum 1, n=761) or aspirin plus a thienopyridine (stratum 2, n=2730). Participants were randomised within each strata and dose tier with a block randomisation method at 1:1:1 to receive either placebo or rivaroxaban (at doses 5-20 mg) given once daily or the same total daily dose given twice daily. The primary safety endpoint was clinically significant bleeding (TIMI major, TIMI minor, or requiring medical attention); the primary efficacy endpoint was death, myocardial infarction, stroke, or severe recurrent ischaemia requiring revascularisation during 6 months. Safety analyses included all participants who received at least one dose of study drug; efficacy analyses were by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00402597.

FINDINGS

Three patients in stratum 1 and 26 in stratum 2 never received the study drug. The risk of clinically significant bleeding with rivaroxaban versus placebo increased in a dose-dependent manner (hazard ratios [HRs] 2.21 [95% CI 1.25-3.91] for 5 mg, 3.35 [2.31-4.87] for 10 mg, 3.60 [2.32-5.58] for 15 mg, and 5.06 [3.45-7.42] for 20 mg doses; p<0.0001). Rates of the primary efficacy endpoint were 5.6% (126/2331) for rivaroxaban versus 7.0% (79/1160) for placebo (HR 0.79 [0.60-1.05], p=0.10). Rivaroxaban reduced the main secondary efficacy endpoint of death, myocardial infarction, or stroke compared with placebo (87/2331 [3.9%] vs 62/1160 [5.5%]; HR 0.69, [95% CI 0.50-0.96], p=0.0270). The most common adverse event in both groups was chest pain (248/2309 [10.7%] vs 118/1153 [10.2%]).

INTERPRETATION

The use of an oral factor Xa inhibitor in patients stabilised after an acute coronary syndrome increases bleeding in a dose-dependent manner and might reduce major ischaemic outcomes. On the basis of these observations, a phase III study of low-dose rivaroxaban as adjunctive therapy in these patients is underway.

FUNDING

Johnson & Johnson Pharmaceutical Research & Development and Bayer Healthcare AG.

Oral rivaroxaban for the prevention of symptomatic venous thromboembolism after elective hip and knee replacement

A once-daily dose of rivaroxaban 10 mg, an oral, direct Factor Xa inhibitor, was compared with enoxaparin 40 mg subcutaneously once daily for prevention of venous thromboembolism in three studies of patients undergoing elective hip and knee replacement (RECORD programme). A pooled analysis of data from these studies (n = 9581) showed that rivaroxaban was more effective than enoxaparin in reducing the incidence of the composite of symptomatic venous thromboembolism and all-cause mortality at two weeks (0.4% vs 0.8%, respectively, odds ratio 0.44; 95% confidence interval 0.23 to 0.79; p = 0.005), and at the end of the planned medication period (0.5% vs 1.3%, respectively; odds ratio 0.38; 95% confidence interval 0.22 to 0.62; p < 0.001). The rate of major bleeding was similar at two weeks (0.2% for both) and at the end of the planned medication period (0.3% vs 0.2%). Rivaroxaban started six to eight hours after surgery was more effective than enoxaparin started the previous evening in preventing symptomatic venous thromboembolism and all-cause mortality, without increasing major bleeding.

Differences in urinary prothrombin fragment 1 + 2 levels after total hip replacement in relation to venous thromboembolism and bleeding events

BACKGROUND

Prothrombin fragment 1 + 2 is excreted in urine (uF1 + 2) as a result of thrombin generation and, therefore, may be a useful marker of coagulation status.

OBJECTIVES

To assess uF1 + 2 levels after total hip replacement (THR) in patients with venous thromboembolism (VTE) and bleeding events.

PATIENTS/METHODS

This study was conducted in parallel with a prospective, dose-finding study evaluating the efficacy and safety of different doses of rivaroxaban (Xarelto, Bayer HealthCare AG, Wuppertal, Germany) for thromboprophylaxis, relative to enoxaparin. Deep vein thrombosis was diagnosed by mandatory venography performed 5-9 days after THR, or earlier if symptomatic. Symptomatic pulmonary embolism was diagnosed by objective testing. Bleeding complications were registered and stratified into major bleeding, clinically relevant, non-major bleeding, and minor bleeding, using predefined criteria.

RESULTS

Eighty-four patients had a VTE and 57 patients had a bleeding event (n = 722). Significantly higher median uF1 + 2 levels were observed in the VTE group on day 3 after THR (P = 0.03), compared with control. Median uF1 + 2 levels were lower in the bleeding group on day 3 after THR (P = 0.005) and on the day of venography (P = 0.36), compared with control. Comparisons between the VTE and bleeding groups showed significantly lower median uF1 + 2 levels in the bleeding group on day 3 after THR and on the day of venography (P < 0.0001 and P = 0.006, respectively).

CONCLUSIONS

Measurement of uF1 + 2 could provide a simple clinical test to evaluate non-invasively the intensity of coagulation activation after THR. However, further studies are required to confirm these encouraging preliminary results.

Rivaroxaban. A novel, oral, direct factor Xa inhibitor in clinical development for the prevention and treatment of thromboembolic disorders

Rivaroxaban (Xarelto) is a novel, oral, direct Factor Xa (FXa) inhibitor in late-stage development for the prevention and treatment of thromboembolic disorders. Rivaroxaban inhibits clot-associated and free FXa activity, and prothrombinase activity, and reduces thrombin generation. In animal models, rivaroxaban prevented venous and arterial thrombosis, and was effective at treating venous thrombosis. Rivaroxaban has high oral bioavailability, a rapid onset of action and predictable pharmacokinetics. In phase II studies, rivaroxaban was effective and well tolerated for the prevention of venous thromboembolism (VTE) after major orthopaedic surgery, and for the treatment of deep vein thrombosis. In a phase III study, rivaroxaban demonstrated significantly superior efficacy to enoxaparin for thromboprophylaxis after total knee arthroplasty, with similar low bleeding. Rivaroxaban is also being assessed for the treatment and secondary prevention of VTE, prevention of stroke in patients with atrial fibrillation and secondary prevention in patients with acute coronary syndrome. Rivaroxaban is a promising alternative to current pharmacological agents for thromboembolic disorders.

Ultrasound screening for asymptomatic deep vein thrombosis after major orthopaedic surgery: the VENUS study

BACKGROUND

Venography is currently used to assess the incidence of deep vein thrombosis (DVT) in dose-finding and confirmatory trials of new antithrombotic agents. Centrally adjudicated, complete compression ultrasound (CCUS) could be a non-invasive alternative to venography.

OBJECTIVES

A substudy of two, similarly designed, phase IIb trials of a novel, oral anticoagulant for the prevention of venous thromboembolism after elective hip or knee arthroplasty was undertaken to validate CCUS against venography.

PATIENTS/METHODS

Patients received study drugs until mandatory, bilateral venography was performed 7 +/- 2 days after surgery. CCUS was performed within 24 h after venography by sonographers blinded to the venography result. Sonographers were trained and certified for the standardized examination and documentation procedure. Venograms and sonograms were adjudicated centrally at different sites by two independent readers; discrepancies between readers were resolved by consensus.

RESULTS

A total of 1104 matching pairs of evaluable venograms and sonograms were obtained from the participants of the two trials (n = 1435): 19% of venograms and 20% of sonograms were not evaluable. The observed frequency of any DVT was 18.9% with venography and 11.5% with CCUS. Sensitivity of CCUS compared with venography was 31.1% for any DVT (95% confidence interval 23.4, 38.9), 21.0% (2.7, 39.4) for proximal DVT, and 30.8% (23.1, 38.6) for distal DVT. The figures for specificity were 93.0% (91.0, 95.1), 98.7% (98.0, 99.5), and 93.3% (91.5, 95.3), respectively.

CONCLUSIONS

Based on these results, centrally adjudicated CCUS will be unable to replace venography for DVT screening early after major orthopaedic surgery in studies evaluating anticoagulant drugs.

Prevention of major venous thromboembolism following total hip or knee replacement: a randomized comparison of low-molecular-weight heparin with unfractionated heparin (ECHOS Trial)

AIM

Venous thromboembolism remains a frequent complication after total hip or knee replacement surgery despite routine prophylaxis. However, the ability of pharmacologic thromboprophylaxis to prevent major venous thromboembolism, defined as proximal deep vein thrombosis, and/or pulmonary embolism, and/or death, has not been previously validated.

METHODS

In a double-blind randomized study, 2018 patients, undergoing either total hip or knee replacement surgery, were allocated to receive subcutaneous preoperative reviparin (4,200 anti Xa IU) once daily or 7,500 IU unfractionated heparin twice daily, for a minimum of 11 days. The primary efficacy outcome was major venous thromboembolism, defined as the composite of venographically confirmed proximal deep vein thrombosis, and/or symptomatic pulmonary embolism and death, recorded up to day 14.

RESULTS

The primary efficacy outcome was assessed in 1,628 patients and demonstrated a significant reduction in the reviparin group (3.4% [28 of 813 patients] compared with unfractionated heparin (5.5% [45 of 815]) (odds ratio, 0.61; 95% confidence interval, 0.38 to 0.99, P=0.04) by day 11 to 14. A significant reduction in venous thromboembolism was maintained up to 6-8 weeks (3.4% [28 of 813 reviparin patients] versus 5.6% [46 of 815 unfractionated heparin patients]) (odds ratio, 0.6; 95% confidence interval, 0.37 to 0.97, P=0.03). Major bleeding events occurred in 9 reviparin-treated patients (0.9%) and in 12 unfractionated heparin-treated patients (1.2%).

CONCLUSIONS

Prophylaxis with reviparin significantly reduces the risk of major venous thromboembolism compared with unfractionated heparin in patients undergoing elective hip or knee replacement without increasing the risk of bleeding.

Oral, direct Factor Xa inhibition with BAY 59-7939 for the prevention of venous thromboembolism after total hip replacement

BACKGROUND

Joint replacement surgery is an appropriate model for dose-ranging studies investigating new anticoagulants.

OBJECTIVES

To assess the efficacy and safety of a novel, oral, direct factor Xa (FXa) inhibitor--BAY 59-7939--relative to enoxaparin in patients undergoing elective total hip replacement.

METHODS

In this double-blind, double-dummy, dose-ranging study, patients were randomized to oral BAY 59-7939 (2.5, 5, 10, 20, or 30 mg b.i.d.), starting 6-8 h after surgery, or s.c. enoxaparin 40 mg once daily, starting on the evening before surgery. Treatment was continued until mandatory bilateral venography was performed 5-9 days after surgery.

RESULTS

Of 706 patients treated, 548 were eligible for the primary efficacy analysis. The primary efficacy endpoint was the incidence of any deep vein thrombosis, non-fatal pulmonary embolism, and all-cause mortality; rates were 15%, 14%, 12%, 18%, and 7% for BAY 59-7939 2.5, 5, 10, 20, and 30 mg b.i.d., respectively, compared with 17% for enoxaparin. The primary efficacy analysis did not demonstrate any significant trend in dose-response relationship for BAY 59-7939. The primary safety endpoint was major, postoperative bleeding; there was a significant increase in the frequency of events with increasing doses of BAY 59-7939 (P = 0.045), but no significant differences between individual BAY 59-7939 doses and enoxaparin.

CONCLUSIONS

When efficacy and safety were considered together, the oral, direct FXa inhibitor BAY 59-7939, at 2.5-10 mg b.i.d., compared favorably with enoxaparin for the prevention of venous thromboembolism in patients undergoing elective total hip replacement.

BAY 59-7939: an oral, direct factor Xa inhibitor for the prevention of venous thromboembolism in patients after total knee replacement. A phase II dose-ranging study

BACKGROUND

BAY 59-7939, a novel, oral, direct factor Xa inhibitor, is in clinical development for the prevention of venous thromboembolism (VTE), a frequent complication following orthopaedic surgery.

METHODS

In a multicenter, parallel-group, double-blind, double-dummy study, 621 patients undergoing elective total knee replacement were randomly assigned to oral BAY 59-7939 (2.5, 5, 10, 20, and 30 mg b.i.d., initiated 6-8 h postsurgery), or subcutaneous enoxaparin (30 mg b.i.d., initiated 12-24 h postsurgery). Treatment was continued until mandatory bilateral venography 5-9 days after surgery. The primary efficacy endpoint was a composite of any deep vein thrombosis (proximal and/or distal), confirmed non-fatal pulmonary embolism and all-cause mortality during treatment. The primary safety endpoint was major, postoperative bleeding during treatment.

RESULTS

Of the 613 patients treated, 366 (59.7%) were evaluable for the primary efficacy analysis. The primary efficacy endpoint occurred in 31.7%, 40.4%, 23.3%, 35.1%, and 25.4% of patients receiving 2.5, 5, 10, 20 and 30 mg b.i.d. doses of BAY 59-7939, respectively (test for trend, P = 0.29), compared with 44.3% in the enoxaparin group. The frequency of major, postoperative bleeding increased with increasing doses of BAY 59-7939 (test for trend, P = 0.0007), with no significant difference between any dose group compared with enoxaparin. Bleeding endpoints were lower for the 2.5-10 mg b.i.d. doses compared with higher doses of BAY 59-7939.

CONCLUSIONS

Oral administration of 2.5-10 mg b.i.d. of BAY 59-7939, early in the postoperative period, showed potential efficacy and an acceptable safety profile, similar to enoxaparin, for the prevention of VTE in patients undergoing elective total knee replacement.

Prevention of venous thromboembolism after knee arthroscopy with low-molecular weight heparin (reviparin): Results of a randomized controlled trial

PURPOSE

Deep venous thrombosis (DVT) is a common, important complication of major orthopaedic surgery, particularly knee arthroplasty. Knee arthroscopy is increasingly performed on an outpatient basis. Few reports have elucidated the incidence of venous thromboembolism (VTE) in patients undergoing arthroscopic surgery receiving no prophylaxis. The objective of the present trial was to evaluate the risk of VTE in those patients and to determine efficacy and safety of a low-molecular weight heparin (LMWH) in preventing VTE.

TYPE OF STUDY

This is the first controlled randomized trial using objective diagnostic methods with blinded outcome assessment to reveal the incidence of VTE in outpatient arthroscopy and determine efficacy and safety of a LMWH (reviparin sodium) in preventing VTE in these patients.

METHODS

There were 262 patients undergoing elective knee arthroscopy prospectively randomized to receive either no treatment or reviparin once daily subcutaneously for 7 to 10 days. The blindly assessed primary outcome measure was the incidence of DVT detected by compression color-coded sonography. Both groups were comparable with regard to demographics and baseline characteristics.

RESULTS

239 patients were evaluable (122 no treatment, 117 receiving LMWH). 6 DVT were detected - 5 in the control group (5/117 - 4.1%) and only one in the active treatment group (1/116 - 0.85%). This particular patient had a low level of protein C and a subnormal level of protein S. The odds ratio of 4.95 approximates a relative risk reduction of about 80%. Treatment with reviparin was safe and well tolerated. There was no major bleeding, four patients with minor bleedings. One patient had a transitory fall in platelet count below 100 giga-particles/L without any clinical symptoms.

CONCLUSIONS

Patients undergoing knee arthroscopy have a moderate risk of VTE and effective prophylaxis can be achieved with LMWH (reviparin).

[Prevention of thromboembolism with low-molecular-weight heparin in ambulatory surgery and unoperated surgical and orthopedic patients]

Prophylaxis of thromboembolism is now well established in orthopaedic outpatients with plaster cast and after elective hip surgery. The present study was undertaken to evaluate the safety of out-of-hospital prevention of venous thromboembolism and to determine the incidence of thromboembolic complications in orthopaedic and surgical patients with or without surgical intervention on an out-patient basis during prophylaxis of thromboembolism with low-molecular-weight heparin and to study the feasibility of this treatment regimen. The treatment period was 1-4 weeks (mean 17 days). Main indications for prophylaxis of thromboembolism were arthroscopy and surgical or non-surgical intervention of bone fractures of the lower leg. The incidence of clinically diagnosed venous thromboembolism was 11/1604 (0.7%) in operated and 8/1017 (0.8%) in non-operated patients. Pulmonary embolism occurred twice in operated patients (0.1%) and in none of the non-operated patients. Minor bleeding complications were rare and major bleeding complications did not occur. Haematomas at the injection site occurred in only 4% of patients. Thrombocytopenia did not occur in any patient. The present study demonstrates the feasibility and safety to prophylaxis of thromboembolism with low-molecular-weight heparin in orthopaedic operated and non-operated out-patients with various orthopaedic or surgical diseases leading to immobilization. The incidence of clinically apparent thromboembolic complications is low and similar to medical bedridden inpatients.

[Prevention of thromboembolism in minimal invasive interventions and brief inpatient treatment. Results of a multicenter, prospective, randomized, controlled study with a low molecular weight heparin]

A prospective, randomised, controlled clinical trial was carried out in order to elucidate the incidence of venous thromboembolism in selected patients undergoing laparoscopic cholecystectomy and other types of minimally invasive surgery, as well as to show safety and efficacy of a low-molecular-weight heparin (LMWH) in the prevention of post-operative venous thromboembolism. Seven hundred and eighteen patients were randomly allocated to one of two groups: One group received physical measures for prevention of deep-vein thrombosis, i.e. graduated elastic stockings (n = 359). The second group also received graduated elastic stockings and, additionally, a LMWH (reviparin sodium, Clivarin) s.c. once daily (n = 359). For safety reasons, with respect to the untreated control group, patients with three or more risk factors for venous thromboembolism were not included into the trial. Diagnosis for DVT was systematically done by duplex scan. In this, rather artificial low-risk selection the overall incidence of thromboembolic events was surprisingly low: five cases of suspected pulmonary embolism, confirmed by scintigraphy in one case only, and one patient with phlebographically confirmed calf vein thrombosis. The use of reviparin for prevention of venous thromboembolism was safe and convenient--the rate of post-operative bleeding complications was 2.3% in the LMWH group, even lower than in the control group (3.2%). The real incidence of venous thromboembolism in patients undergoing laparoscopic cholecystectomy remains unclear. Further trials with unselected patients are needed.

The role of platelet prostanoids and dense granule compounds in initial attachment, spreading and aggregation of platelets on collagen substrates

The role of platelet prostanoids, ADP and 5HT in initial attachment, spreading and aggregation of platelets on collagen substrates (CI, CIII, CIV, CV, CC) was studied. A positive linear correlation was found between thrombi-like aggregate formation on collagen substrates and production of platelet prostanoids. No correlation was established between platelet aggregation and 14C-5HT release. Thrombi-like aggregate formation was completely inhibited by indomethacin and TXA2/PGH2 antagonists (13-APA and BM 13.177). Both 13-APA and BM 13.177 had no effect on platelet spreading, while indomethacin inhibited this process by 25%. The ADP-scavenger system (CP/CPK) inhibited platelet aggregation and spreading by 25-30%. Initial attachment was not influenced by aspirin, indomethacin and CP/CPK. The data obtained indicate that platelet aggregation on collagen substrates is mediated by PGH2 and TXA2 production. These compounds slightly affect the platelet spreading. Both platelet spreading and aggregation on collagen substrates are only partially mediated by ADP and 5HT release. Initial attachment of platelets does not depend on the release reaction and PGH2/TXA2 synthesis.

Phorbol ester stimulates platelet spreading and thrombi-like aggregate formation on the surface of immobilized type V collagen

We have studied the effect of the tumor-promoting phorbol ester, 4 beta-phorbol-12 beta-myristate-13 a-acetate (PMA), and of the stable prostaglandin endoperoxide analogue U46619 on the interaction of human blood platelets with surfaces coated with monomeric human type V collagen (CV) and on free calcium concentration in platelet cytoplasm. It was shown by scanning electron microscopy that native resting platelets sparingly attach to CV and fail to spread or aggregate on the collagenous substrate in the absence of PMA and U46619. Addition of 0.15-1.5 nM PMA or 1.5 microM U46619 stimulates platelet spreading and formation of multilayer (thrombi-like) platelet aggregates on the per se non-thrombogenic type V collagen substrate. It was further demonstrated using the fluorescent indicator quin2 that U46619 (0.1 microM) increases cytoplasmic free calcium concentration from basal level (100-120 nM) up to 600 nM, whereas PMA (0.75-15 nM) exerts only a minor effect, increasing free calcium level by 30-40 nM. These results indicate that the tumor-promoting phorbol ester PMA induces massive platelet spreading and aggregation on surfaces coated with non-thrombogenic type V collagen via activation of protein kinase C with little or no apparent change in free cytoplasmic calcium.

Individually controlled aspirin in the long-term treatment of patients with chronic arterial diseases

A simple method of measuring the biological effect of acetylsalicylic acid (ASA), based on the determination of the disaggregation rate (DR) of platelet aggregation induced by adenosine diphosphate (ADP), is described. The DR was found to correlate with the inhibition of the production of malondialdehyde (MDA) by platelets (r = 0.66, P less than 0.001). Therefore, the DR was used for laboratory monitoring of the ASA effect. The study included 63 arteriosclerotic patients--patients with ischemic heart disease (IHD), peripheral arterial disease (PAD), or cerebrovascular insufficiency (CVI) -- who were analyzed before treatment and after receiving ASA in an individually controlled dosage. Before treatment the authors found an increased level of MDA and a longer euglobulin clot lysis time in patients when compared with healthy volunteers (n = 16). Extremely different doses of ASA were required to normalize initially elevated MDA levels in patients. Normalization of the MDA level corresponds to a DR of at least 50% (in comparison with 0-13% without treatment). When judging the ASA dose individually from the 50% DR, the authors demonstrated that there were no differences in the levels of cyclooxygenase- and lipoxygenase-derived eicosanoids between healthy volunteers (n = 16) and arteriosclerotic patients receiving 100-250 mg (n = 18), 500 mg (n = 17), or 750-1500 mg ASA per day (n = 6). Thus, their results support the idea of using individually controlled ASA as the most promising way of resolving the "aspirin dilemma" and provide a simple and reproducible method of measuring the biological effect of ASA.

Substances that polymerize or depolymerize cytoskeletal proteins affect platelet spreading and thrombus-formation on surfaces coated with human collagen isotypes I, IV, and V

The effect of substances that affect platelet cytoskeleton on the interaction of gel-filtered platelets with surfaces coated with human monomeric type I, IV, and V collagen was studied. The sulfhydryl group oxidizing agent azodicarboxylic acid-bis-dimethylamide (diamide) which causes disulfide-linked polymer formation of certain cytoskeletal proteins, the actin-polymerization inhibitor, cytochalasin B, and 2-mercaptopropionylglycine (2-MPG), a cell-permeable SH-reagent, completely abolish adhesion-induced platelet spreading and mural platelet aggregate formation on collagen-coated surfaces. Extrusion of pseudopods was inhibited by cytochalasin B and 2-MPG as well as by diamide, but only the latter caused spherulation of platelets, whereas cytochalasin B and 2-MPG left the discoid shape of resting platelets intact. These effects are dose-dependent and are not accounted for by a chemical modification of the collagenous substrates by the cytoskeletal perturbing substances. The present data indicate that (i) cytoskeletal rearrangements are essential in adhesion-induced platelet spreading and aggregate formation on surfaces coated with collagen, but not in supporting the initial attachment of native platelets to the substrate; (ii) both, polymerization and depolymerization of actin filaments affect platelet activation; (iii) the sulfhydryl-disulfide status of the platelet seems to be a possible target for anti-platelet drugs, since chemical modification of platelets by the GSH-GSSG-active substances, diamide and 2-MPG, leads to a reversible inhibition of adhesion-induced platelet activation.

Effects of prostacyclin analogue (carbacyclin) on the interaction of platelets with different collagen substrates. Inhibition of cAMP increase by collagens type I, III, and IV

We investigated the effects of a stable prostacyclin analogue, carbacyclin, on the interaction of platelets with collagen substrates differing in their ability to activate platelets: human collagens type I, III, IV and V (CI, CIII, CIV and CV), and commercial calf skin collagen type I (CSC). The total adhesion was measured using 51Cr-labelled platelets, and quantitative morphometry of adherent platelets was performed by scanning electron microscopy (SEM). Carbacyclin in the concentrations inducing a 10-fold rise in platelet cAMP did not affect the adhesion of platelets to weak substrates, CV and CSC, but reduced the adhesion to strong substrates, CIV (by 49%) and CI/CIII (by 78%), which stimulated massive spreading and formation of surface-bound aggregates respectively. Carbacyclin inhibited all morphological manifestations of platelet activation associated with adhesion: conversion of native discoid platelets to spherical ones on CSC; massive spreading on CIV; and aggregate formation on CI/CIII. Massive spreading and aggregation on a weak substrate (CSC) stimulated by arachidonic acid and thrombin was also inhibited by carbacyclin. Under the same concentration of agonists aggregation of platelets was more sensitive to the action of carbacyclin, than spreading. Strong collagen substrates CI, CIII and CIV, but not CV and gelatin, inhibited the carbacyclin-induced rise in platelet cAMP.

Effect of metabolic inhibitors on platelet attachment, spreading and aggregation on collagen-coated surfaces

The interaction of human gel-filtered platelets (GFP) with surfaces coated with fibrillar calf skin collagen (CSC) or monomeric human type I, III, IV, and V collagen (CI, CIII, CIV, CV) includes both energy dependent and independent stages. Incubation of platelets with a collagen-coated surface at 4 degrees C versus 37 degrees C reduces only shape change and the spreading response of adhering platelets, but does not affect the initial attachment. Additionally, the energy dependence was evident from the reduction of platelet spreading and platelet aggregate formation in the presence of 2-Deoxy-D-glucose (2DG). Antimycin A (AMA), Oligomycin (OM), or 2,4-Dinitrophenol (DNP) did not abolish the adhesion-induced platelet activation, indicating that the energy is supplied by glycolysis rather than by oxydative phosphorylation. In contrast, neither inhibition of glycolysis, nor inhibition of the respiratory chain did affect the initial attachment of nonactivated platelets to the collagen-coated surface. The present data suggest (i) that during the interaction of platelets with collagenous substrates there exists an initial energy independent attachment stage, and (ii) that the following stages of adhesion-induced platelet activation require metabolic energy supported mainly by anaerobic glycolysis.

Binding of human monomeric type I collagen to platelets

Interaction of platelets with subendothelial collagen is important in primary hemostasis and thrombosis. Although activation of platelets by collagen polymers has been widely investigated, only insufficient data are available concerning the binding of genetically distinct collagen types in their triple helical (monomeric) form to platelets. We report on the binding of 125I-labeled human type I collagen to platelets. The binding assay was performed at 20 degrees C in the presence of arginine in order to prevent polymerization of the collagen monomers. The binding of monomeric 125I-labeled human type I collagen is dose- and time-dependent, saturable and specific, since it is competitively inhibited by unlabeled type I collagen, but not by unlabeled human type V collagen. Scatchard analysis reveals a class of specific high affinity binding sites with a Kd of 2.5 X 10(-8) M. These results suggest that platelets interact with type I collagen through specific binding sites, and that there are various different binding sites on the platelet membrane for the genetically distinct collagen types.

[Thrombocyte adhesion and aggregation on surfaces coated with human type-I, -III, -IV and -V collagens]

Human collagens of type I, III, IV, and V (CI, CIII, CIV, and CV) can be localized in different anatomic structures of the vessel wall. To investigate the role of vascular collagenous components in mural thrombus formation, the authors studied platelet adhesion to the wells of Falcon culture plates coated with: a) monomeric CI, CIII, CIV, and CV; b) fibrillar CI and CIII, and c) amorphous CIV and CV. On monomeric and amorphous CV, only initial attachment takes place, i.e. platelets bind to the surface without subsequent spreading. Platelet adhesion on monomeric and amorphous CIV proceeds more actively: the total level of adhesion is substantially higher than on CV, with up to 75% of adherent platelets spread out and single unspread platelets from suspension attached to the upper surface of spread platelets. On monomeric and fibrillar CI/CIII, formation of large multi-layer (thrombi-like) aggregates, with spread platelets at the basis, takes place along with processes characteristic for adhesion on CIV/CV. On the contrary, only fibrillar but not monomeric CI and CIII induce platelet aggregation in suspension. The data suggest that the ability of CI and CIII to induce platelet aggregation is fully conditioned by the genetic type of collagen and requires a simultaneous multivalent platelet-collagen interaction, which can be achieved by surface immobilization of collagen or formation of fibrillar structures in suspension.

Step-by-step analysis of adhesion of human platelets to a collagen-coated surface defect in initial attachment and spreading of platelets in von Willebrand's disease

Adhesion of platelets from the platelet-rich plasma (PRP) of patients with von Willebrand's disease (vWD) and healthy donors has been studied in a simple model system - wells of multiwell tissue culture plates coated with fibrillar calf skin collagen (CSC). This model is characterized by: (i) the presence of only one constituent of the vessel wall connective tissue matrix (collagen), (ii) the absence of surface-bound aggregates and thrombi, (iii) absence of overlapping of neighbouring spread platelets. A morphometric quantitation of adhesion by scanning electron microscopy (SEM) has been carried out. It allows to subdivide this process into three stages: 1) initial attachment of unspread platelets to the substrate, 2) platelet spreading on the substrate, and 3) attachment of unspread platelets to the upper surface of spread platelets. It was established that the PRP of vWD patients, compared to that of healthy donors, is characterized by a decreased total adhesion of platelets to a CSC-coated surface, which is manifested in the impairment of both the initial attachment and subsequent spreading of platelets. Addition of platelet-free plasma from healthy donors to the vWD PRP completely restores platelet spreading on collagen but little affects the initial attachment. These experiments performed on isolated collagen preparations provide further evidence for the initial attachment and spreading of platelets on collagenous constituents of the subendothelium being factor VIII/von Willebrand factor (FVIII/vWF)-dependent. In contrast to the adhesion on the collagen substrate, the adhesion of platelets from vWD PRP to a foreign surface, polystyrene plastic of uncoated wells, is the same as that of the normal PRP and, thus, FVIII/vWF-independent.