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(Circulation. 1996;94:2057-2063.)
© 1996 American Heart Association, Inc.

Articles

Fibrinolytic Factors and the Risk of Myocardial Infarction or Sudden Death in Patients With Angina Pectoris

Irene Juhan-Vague, MD, PhD; Stephen D.M. Pyke, MSc; Marie Christine Alessi, MD, PhD; Jorgen Jespersen, MD, DSc; Frits Haverkate, PhD; Simon G. Thompson, MA; on behalf of the ECAT Study Group*

the Hematology Laboratory, CHU Timone, Marseille, France (I.J.-V., M.C.A.); the Medical Statistics Unit, London (UK) School of Hygiene and Tropical Medicine (S.D.M.P., S.G.T.); Centralsygehuset, Esbjerg, Denmark (J.J.); and Gaubius Laboratory, TNO-PG, Leiden, Netherlands (F.H.).

Correspondence to Irene Juhan-Vague, Hematology Laboratory, CHU Timone, 13385 Marseille Cedex 5, France.

	Abstract

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Background Disturbances of the fibrinolytic system that lead to decreased removal of fibrin deposits may be important risk factors for coronary thrombosis. There is as yet no consensus on the prognostic value of fibrinolytic parameters, which may be attributed in part to the choice of confounding variables controlled for.

Methods and Results The ECAT study is a prospective multicenter study of 3043 patients with angina pectoris followed for 2 years. Baseline measurements included 10 fibrinolytic variables. The results were analyzed in relation to the subsequent incidence of myocardial infarction or sudden coronary death. They are presented before and after adjustment for clusters of confounding variables that are markers of different mechanisms: insulin resistance (body mass index, triglyceride, and HDL cholesterol), inflammation (fibrinogen and C-reactive protein), and endothelial cell damage (von Willebrand factor). An increased incidence of events was associated with higher baseline concentrations of tissue plasminogen activator (TPA) antigen (P=.0002), plasminogen activator inhibitor-1 (PAI-1) activity (P=.02), and PAI-1 antigen (P=.001). The associations of PAI-1 activity and PAI-1 antigen with risk of events disappeared after adjustment for parameters reflecting insulin resistance but were not affected by other adjustments. TPA antigen was affected to a similar extent by adjustment for parameters reflecting insulin resistance, inflammation, or endothelial cell damage, but the risk association disappeared only after combined adjustments.

Conclusions The prognostic role of PAI-1 in predicting coronary events is related principally to insulin resistance, whereas that of TPA antigen could be explained only by its relationship with different mechanisms, including insulin resistance, inflammation, and endothelial cell damage.

Key Words: risk factors • fibrinolysis • plasminogen activators • angina • myocardial infarction

	Introduction

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Coronary thrombosis is now generally recognized as the precipitating event in acute ischemic heart disease, manifested by acute MI and sudden death of coronary causes.^{1 2 3} In addition to local stimuli such as disruption of plaques, systemic thrombogenic factors may contribute to the occurrence, extent, and persistence of coronary thrombosis and its clinical sequelae.⁴ Among the thrombogenic mechanisms, disturbances of the fibrinolytic system, which lead to decreased removal of fibrin deposits,^{5 6} may be important.

Intravascular fibrinolytic activity is regulated by a balance between plasminogen activators, the main one being TPA, and inhibitors, such as PAI-1 and ₂-antiplasmin. The key event in the system is the conversion of the inactive plasminogen into the proteolytically active plasmin, which degrades fibrin. Plasmin formation in the circulating blood is strongly dependent on PAI-1 levels.⁷ PAI-1 inhibits, by complex formation, TPA released by the vascular endothelium. Decreased fibrinolytic activity, demonstrated by a prolonged lysis time, is accompanied by elevated PAI-1 and TPA antigen levels,^{7 8 9 10 11} the latter reflecting predominantly TPA/PAI-1 complex.¹²

There is not yet a consensus on the prognostic value of all these fibrinolytic variables.¹³ Although clot lysis time¹⁴ and TPA antigen^{15 16 17 18 19 20} have been shown to be predictive of cardiovascular events and mortality, TPA activity and PAI-1 activity are prognostic in some studies^{21 22 23} but not in others.^{15 16 24} The lack of uniformity of analysis in these studies, in particular in the choice of confounding variables controlled for, has clouded the issue. Indeed, hypofibrinolysis, increased PAI-1 levels, and increased TPA antigen levels belong to a common metabolic disorder called the insulin resistance syndrome,^{25 26 27 28} which includes a cluster of abnormalities, such as obesity, predominantly in the upper part of the body; glucose intolerance; hypertension; hyperinsulinemia; and lipid disorders with elevated TGs and decreased HDL cholesterol. This syndrome corresponds to a prediabetic stage with increased risk of the development of atherothrombosis.^{29 30} Fibrinolysis dysregulation has also been related to inflammation,^{9 31} and a link with endothelial cell damage has been proposed.^{16 17}

In the ECAT prospective study of 3000 patients with angina pectoris, it was shown that, after adjustment for all other known nonhemostatic coronary risk factors and the drugs used at the time of blood sampling, an increased risk of coronary events during a two-year follow-up period was associated with higher baseline concentrations of fibrinogen, von Willebrand factor, and TPA antigen.¹⁷ Our purpose here is to examine in detail the prognostic relationship of a full range of fibrinolytic variables and to gain insights into their pathophysiology by considering specific adjustments for clusters of variables that represent potential markers of biological mechanisms. These analyses may also help to explain the discrepant results previously reported in the literature. The ECAT study is unusually well placed to do this, having prospectively measured 10 fibrinolytic variables^{32 33} in a large study population.

	Methods

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Patients
Men and women who underwent coronary angiography because of suspected coronary artery disease were eligible for the study. Patients who had had an MI within the preceding 2 months or who had severe right heart failure or noncardiac diseases likely to cause death within 1 year were excluded. A total of 3043 patients (2597 men and 446 women) from 18 European centers (listed in the "Appendix") were recruited between October 1984 and June 1987.

A detailed analysis of baseline clinical and laboratory data at entry has been presented earlier,³⁴ as well as the interrelationships between the fibrinolytic variables and their association with conventional risk factors.^{26 31}

Blood Sampling and Measurements of Fibrinolytic Variables
The conditions of blood sampling and storage and the measurement of hemostatic factors have been described in detail elsewhere.³³ The technicians were trained at a central laboratory, and an external quality-assessment scheme was used to monitor their performance throughout the study.^{32 35}

The fibrinolytic system was assessed as follows: Plasminogen, TPA, and ₂-antiplasmin activity assays were performed with reagents and kits from KabiVitrum Diagnostica. For PAI-1 activity and antigen and for TPA antigen, assay kits from Biopool were used. The ECLT was measured both before and after 10 minutes of venous occlusion, as were TPA antigen and activity. Some of the variables were analyzed centrally: PAI-1 activity and antigen (J. Jespersen) and TPA antigen (I. Juhan-Vague). Other hemostatic factors and cardiovascular risk factors were measured as previously described.^{17 32 33 34}

Follow-up and Ascertainment of End Points
Patients were followed up annually for 2 years, and information on deaths, coronary events, and hospital admissions was obtained. Reported clinical events were reviewed independently by an end-point committee whose members were blinded to the results of the hemostatic tests. The primary end points of the study were fatal or nonfatal MI, defined according to standard diagnostic criteria,³⁶ and sudden death of coronary causes, defined as death within 1 hour of the onset of cardiac symptoms. Events occurring within 72 hours of surgery (usually coronary artery bypass surgery) or angioplasty were considered primarily related to the intervention. Patients with such events were excluded from the analyses, as were patients with possible but unconfirmed MI or death of other cardiac causes, other causes, or uncertain causes.

Of the 3043 patients enrolled in the study, 2960 (97%) were followed for 2 years. During the period, 837 patients underwent coronary artery bypass surgery, 233 underwent coronary angioplasty, and 49 underwent both interventions. A total of 106 definite coronary events occurred (95 in men and 11 in women), including 31 sudden coronary deaths, 9 fatal MIs, and 66 nonfatal MIs. An additional 154 major events did not fulfill the criteria for study end points.

Statistical Analysis
Fibrinolytic variables were analyzed on the logarithmic scale when this gave a more symmetrical (gaussian) distribution. Observation of the ECLT was limited to 300 minutes for practical reasons. Also, a substantial proportion of samples had zero or undetectable levels of TPA activity. Hence, the statistical analysis of these two measurements was based on the proportion of lysis time 300 minutes and of zero TPA values. Most of the hemostatic test results for patients in two centers were unavailable because of technical problems with storage and transportation of the samples.

To investigate the association between the concentrations of fibrinolytic variables and the incidence of definite coronary events, multiple regression analysis was used, with the fibrinolytic factor as the dependent variable. Mean differences between the patients who had events and those who were event free were calculated after adjustment for the medical center and the patient's age and sex. In addition, analyses were done of the association between the fibrinolytic parameters and the risk of coronary events after adjustment for groups of coronary risk factors, including variables related to insulin resistance syndrome (BMI, TG, HDL cholesterol, SBP, history of diabetes), variables related to inflammation (fibrinogen and CRP), and one variable related to endothelial cell damage (von Willebrand factor³⁷ ). Relative risks were calculated either directly from logistic regressions or from the relationship between mean differences and risk gradients for quantitative variables.³⁸

	Results

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Fibrinolytic Parameters in Relation to Coronary Events in the Follow-up
Mean levels of fibrinolytic variables in the group of patients with subsequent coronary events and in the event-free group are presented in Table 1.

View this table: [in this window] [in a new window]   Table 1. Levels of Fibrinolytic Variables According to Coronary Events in the Follow-up

TPA antigen was significantly higher in the event group (P=.0002). PAI-1 antigen, and to a lesser extent PAI-1 activity levels, were also higher in patients with coronary events (P=.001 and P=.02, respectively). The proportion of patients with measurable TPA activity after venous occlusion, reflecting the release of TPA that was not complexed by PAI-1 and remained active, was lower in the event group than in the event-free group (P=.01). The remaining fibrinolytic variables were not significantly different (P>.05) between the coronary event and event-free groups.

The relative risks of coronary events according to quintiles of the distribution of TPA antigen, PAI-1 antigen, and PAI-1 activity are presented in the Figure. The risk increased by almost fivefold from the bottom to the top quintile of TPA antigen, threefold for PAI-1 antigen, and twofold for PAI-1 activity. The risk was almost twofold higher in subjects with zero TPA activity after venous occlusion than in those with nonzero levels. These results suggest a reduced fibrinolytic potential in patients prone to new coronary events. Similar results were obtained, and the conclusions were unaltered, when analyses were restricted to men alone, when allowance was made for the effects of drugs used at the time of blood sampling, or when adjustments were made for total cholesterol levels and reported smoking habit.

View larger version (35K): [in this window] [in a new window]   Figure 1. Relative risk of a coronary event (after adjustment for center, age, and sex) according to fifths of the distributions of fibrinolytic variables. Numbers above bars indicate numbers of patients with events among those patients in the corresponding group.

Correlations Between Fibrinolytic Parameters and Markers of Pathophysiological Mechanisms
The correlations between the four fibrinolytic assays shown to be associated with future coronary risk are given in Table 2. All the measures are strongly related to one another. Other coronary risk factors are also associated with fibrinolytic parameters. Table 3 gives the correlation coefficients between fibrinolytic parameters and those variables related to insulin resistance syndrome (BMI, TG, HDL cholesterol, SBP, history of diabetes), to inflammation (fibrinogen, CRP), and to endothelial cell damage (von Willebrand factor). It can be noticed that PAI-1 activity and PAI-1 antigen are most strongly correlated with the variables included in the insulin resistance syndrome (except SBP) and to a lesser extent with inflammation or endothelial cell damage markers, whereas TPA antigen is associated with the variables relating to all three pathophysiological mechanisms.

View this table: [in this window] [in a new window]   Table 2. Correlations Among Fibrinolytic Parameters*

View this table: [in this window] [in a new window]   Table 3. Correlations Between Fibrinolytic Parameters and Other Coronary Risk Factors*

Within the cluster of variables related to insulin resistance, moderate or strong associations were found between HDL cholesterol and TG (r=-.46), between HDL cholesterol and BMI (r=-.24), and between TG and BMI (r=.22). Likewise, fibrinogen and CRP were strongly related (r=.49), with each of these also related to von Willebrand factor (r=.24 and r=.18, respectively).

Fibrinolytic Parameters in Relation to Coronary Events in the Follow-up After Control for Markers of Pathophysiological Mechanisms
The evaluation of the impact of insulin resistance, inflammation, and endothelial cell damage on the predictive capacity of fibrinolytic variables is presented in Table 4. Differences in means between fibrinolytic variables in the group with coronary events and the event-free group are presented according to different adjustments for other risk factors.

View this table: [in this window] [in a new window]   Table 4. Percentage Difference in Means Between Levels of Fibrinolytic Variables in the Group With Events and the Event-Free Group*

The average increase in TPA antigen in the event group, which was 18.7% (P=.0002) before risk factor adjustments, remained statistically significant but was less pronounced after adjustment for variables related to insulin resistance (10.8%, P=.02), inflammation (12.3%, P=.01), or endothelial cell damage (12.3%, P=.01). However, evidence for mean differences between the groups largely disappeared (5.4%, P=.21) if all three adjustments were made together.

In contrast, for PAI-1 activity and PAI-1 antigen, the mean differences between event and event-free groups were no longer significant after adjustment for variables related to insulin resistance, whereas adjustment for inflammation or endothelial cell damage markers had little effect. The results for TPA activity after venous occlusion were similar to those observed with PAI-1, although less marked, especially when the analysis was restricted to men.

The effects of the same adjustments on the other hemostatic risk markers previously described in the ECAT study,¹⁷ as well as in other studies,^{23 39 40} have been evaluated. The mean difference of fibrinogen values between groups with and without events before adjustment (9.2%, P=.0004) decreased slightly with adjustment for insulin resistance (7.9%, P=.003) or endothelial cell damage (7.8%, P=.002); the combined effect, however, was unable to suppress the difference between groups (5.0%, P=.03). The risk represented by von Willebrand factor before adjustment (mean difference between groups, 10.4%; P=.02) disappeared after adjustment for variables related to inflammation, whereas adjustment for insulin resistance markers had no effect at all.

	Discussion

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In the ECAT study, an extensive assessment of the fibrinolytic system was performed, with 10 assays evaluating the activity or concentration of the main fibrinolytic components. We have shown that in patients with angina, high levels of PAI-1 activity, PAI-1 antigen, and TPA antigen and low levels of TPA activity after venous occlusion are associated with an increased risk of subsequent coronary events. The confidence intervals for the relative risks (Table 1), however, were quite wide, reflecting the follow-up period of 2 years and the consequently relatively limited number of definite coronary events accruing. Yet, a relative risk of 1.4 per SD increase, as estimated for PAI-1 antigen, is substantial: it reflects a relative risk of 2.6 when the top and bottom quintiles of the distribution (which are an average of 2.8 SDs apart; 2.6 equals 1.4 to the power of 2.8) are compared. This is not dissimilar to other major risk factors such as fibrinogen.¹⁷ Because of the short time recording for ECLT (limited to 300 minutes), >50% of the samples presented no lysis at the end of the experiment. Moreover, TPA activity was evaluated in nonacidified plasma; in these conditions, TPA activity is unstable and was not detected in the majority of samples before venous occlusion. Thus, our ECLT and TPA activity results may have lacked some sensitivity.

Interrelationships between all the fibrinolytic parameters measured in the ECAT study have been described previously.³¹ The ECLT and TPA activities, before and after venous occlusion, were strongly related to one another and to PAI-1 levels; PAI-1 activity and PAI-1 antigen were strongly correlated with each other, and a strong positive correlation of PAI-1 values (stronger for PAI-1 antigen) with TPA antigen was observed (Table 2). These results concur with those obtained with healthy subjects^{8 10 41 42 43} or angina patients,⁹ with correlation coefficients between PAI-1 and TPA antigen varying from .36 to .86. The reason for the association between PAI-1 and TPA antigen is not fully understood. TPA antigen detects inactive TPA/PAI-1 complex.^{12 44} PAI-1 activity evaluates free active PAI-1, whereas PAI-1 antigen assays evaluate not only free active PAI-1 but also inactive PAI-1 complexed with TPA,⁴⁵ as well as latent PAI-1, which could have been released by platelets in vitro.^{33 46 47}

A good example of the parallelism between TPA antigen and PAI levels is found in the circadian variation of these parameters.^{48 49} TPA is produced mainly by endothelial cells, whereas many cell types, such as endothelial cells, hepatocytes, smooth muscle cells, fibroblasts, and adipocytes, are able to produce PAI-1; but the principal source of plasma PAI-1 remains unknown. A variety of agents have been shown to increase the synthesis of TPA by cultured endothelial cells and the synthesis of PAI-1 by different cells in culture.⁵⁰ It has been proposed that PAI-1 and TPA production could be triggered simultaneously⁵¹ ; TPA and PAI-1 could also be triggered separately, but TPA/PAI-1 complexes could have a delayed clearance,^{52 53} inducing their accumulation in plasma. Whatever the cause of the interrelation between TPA antigen and PAI-1 levels,^{50 51 52 53} it is recognized that PAI-1 is the dominating factor in the cluster of fibrinolytic assays^{7 11 31} ; therefore, it was surprising that TPA antigen alone remained predictive of coronary event, whereas PAI-1 did not, in the first analysis of the ECAT study.^{17 18} It had been proposed that a smaller intraindividual variability for TPA antigen compared with PAI-1 assay might explain such results.^{15 16 54 55} We have hypothesized that adjustments performed in this first analysis¹⁷ could have affected the predictive capacities of PAI-1 and TPA antigen differently.

Our study contains information of potential pathophysiological importance. If we consider the predictive capacity of fibrinolytic parameters after adjustment for only center, age, and sex, TPA antigen was the strongest predictor of subsequent coronary event, followed by PAI-1 antigen and then by PAI-1 activity. The effect of the different adjustments suggests that TPA antigen values may be related to insulin resistance, to inflammation, and to endothelial cell damage. TPA antigen concentration may therefore be related to a combination of pathological pathways. It should be emphasized that inflammation and endothelial cell damage, as evaluated, could be a reflection of low-grade inflammatory response in patients with atherosclerosis. By contrast, PAI-1 concentration was apparently related to insulin resistance alone. PAI-1 antigen, which in part evaluates TPA/PAI-1 complexes, was also very slightly related to the inflammation state. With adjustment for only age, sex, and center, the hemostatic variables were predictive in the following order (relative risk per SD increase in parentheses): TPA antigen (1.50), fibrinogen (1.45), PAI-1 antigen (1.41), CRP (1.39), PAI-1 activity (1.29), von Willebrand factor (1.28). In the analysis performed previously,¹⁷ the adjustments included mainly parameters belonging to the insulin resistance syndrome (BMI, TG, SBP, history of diabetes); therefore, PAI-1 antigen and PAI-1 activity were no longer considered to be risk factors after these adjustments, and TPA antigen was only moderately affected.

Our results show that adjustment for markers of inflammation or endothelial cell damage also affects the prognostic value of TPA antigen but has no effect on PAI-1. On the basis of these results, we could speculate that the positive correlations observed between TPA and PAI-1 antigen values were triggered by insulin resistance, whereas inflammation and endothelial cell damage affected predominantly TPA antigen values. It is interesting to note that after adjustment for markers of inflammation, von Willebrand factor, a marker of endothelial cell damage,³⁷ was no longer predictive of a subsequent coronary event, whereas it was not at all affected by insulin resistance adjustments. This is in agreement with results of population-based cross-sectional studies.^{8 31 56} The clinical implications of these results may be important from a mechanistic point of view. However, it cannot be inferred from our data that fibrinolytic measures have independent clinical value for screening or prevention in cardiological practice.

The reasons for the current lack of consensus withregard to the relative importance of the fibrinolytic parameters are clear if we review the type of adjustments used in other prospective studies that have evaluated the prognostic value of fibrinolytic parameters. In the Northwick Park Heart Study,¹⁴ the whole-blood clot lysis time (which was recorded during 24 hours) was a strong predictor of ischemic heart disease in subjects 40 to 54 years old even after adjustment for fibrinogen. No adjustments were made for metabolic variables, although fibrinolytic activity was strongly negatively correlated with skinfold thickness (a marker of obesity) and TG. In the Physicians' Health Study,¹⁹ TPA antigen levels were compared in apparently healthy men who later developed MI and in an equal number of control subjects matched for age and smoking habit who remained free of cardiovascular disease. In a crude matched-pair analysis, TPA antigen was a strong predictor of cardiac events, but after adjustments for BMI, HDL cholesterol, blood pressure, physical exercise, history of diabetes (all part of the insulin resistance syndrome), and history of MI, TPA antigen was no longer predictive of subsequent cardiac events. In the ECAT study, which included not a healthy population but rather patients with angina, the predictive effect of TPA antigen was reduced but not suppressed after adjustments for variables related to insulin resistance.¹⁷ It largely disappeared after additional adjustments for markers of inflammation or endothelial cell damage were made, as shown here. The results of studies by Jansson et al^{15 16} are somewhat contradictory. In a 4-year prospective study of 47 cardiovascular events among 213 angina patients, TPA antigen was predictive in univariate (P<.01) but not in multivariate analysis (adjusted for BMI, TG, previous MI, hypertension, and ejection fraction). However, in a 7-year follow-up of the same patients investigating 33 deaths of any cause, TPA antigen was predictive (P<.05) in both univariate and multivariate analyses. Here, it is difficult to disentangle the effects of the different outcomes considered, of the play of chance induced by the relatively small numbers of events, and of adjustment for the risk factors.

Atherothrombosis is a multifactorial disease, and several pathological mechanisms are involved in its development, including lipid disorders, such as abnormal cholesterol transport; metabolic abnormalities, such as insulin resistance; and inflammation. The etiological interpretation of epidemiological predictive studies that evaluate hemostatic risk factors has to take into account the cluster of coronary risk variables used for the adjustments. From our results, we propose that, although the etiological role of PAI-1 is related primarily to insulin resistance, TPA antigen is more widely influenced by a variety of pathophysiological pathways, including insulin resistance, inflammation, and endothelial cell damage.

	Selected Abbreviations and Acronyms

 

BMI = body mass index CRP = C-reactive protein ECLT = euglobulin clot lysis time MI = myocardial infarction PAI-1 = plasminogen activator inhibitor-1 SBP = systolic blood pressure TG = triglyceride TPA = tissue plasminogen activator

	Footnotes

 
*The investigators and institutions participating in the European Concerted Action on Thrombosis and Disabilities (ECAT) Angina Pectoris Study are listed in the "Appendix."

This work was carried out within the framework of the European Concerted Action on Thrombosis and Disabilities (ECAT) of the Commission of the European Communities.

Participating Centers (in Order of Number of Patients Recruited; Numbers in Parentheses)
Bordeaux, France: Hopital Cardiologique, Clinique Medicale Cardiologique and Laboratoire d'Hemobiologie (341). Lyon, France: Hopital Cardiovasculaire et Pneumologique Louis Pradel and Faculte de Medicine Alexis Carrel, Laboratoire d'Hemobiologie (325). Munster, Germany: University Departments of Cardiology and Hematology (319). Bad Rothenfelde, Germany: Schuchtermann-Klinik, Department of Cardiology (288). Basel, Switzerland: Kantonsspital, University Department of Cardiology and Hemostasis Laboratory (235). Vienna, Austria: First University Department of Medicine (208). Athens, Greece: Nimts Hospital, Department of Cardiology, Alexandra Hospital, Department of Clinical Therapeutics, and Laikon General Hospital, Blood Transfusion Center (162). Frankfurt, Germany: University Center for Internal Medicine, Departments of Cardiology and Angiology (156). Giessen, Germany: University Department for Internal Medicine (144). Paris, France: Hopital Broussais, Clinique Cardiologique and Hotel-Dieu, Laboratoire Centrale d'Hematologie (132). Bern, Switzerland: Inselspital, University Department of Medicine (128). Pisa, Italy: CNR Institute of Clinical Physiology (118). Brussels, Belgium: Clinique Universitaire St Luc, Department of Cardiology, and University of Louvain, Laboratory for Hemostasis and Thrombosis Research (114). Leeds, UK: General Infirmary, Departments of Cardiology and Medicine (84). Bad Nauheim, Germany: Max Planck Institut fur physiologische und klinische Forschung, Kerckhoff Klinik (82). Mannheim, Germany: First University Department of Medicine (80). Marseille, France: CHU Timone, Department of Cardiology and Laboratoire d'Hematologie (67). Eindhoven, Netherlands: Catharina Hospital, Departments of Cardiology and Hematology (60).

Responsible Investigators (C, Cardiologists; H, Hematologists)
Athens: C.D. Michalopoulos (C), S.D. Moulopoulos (C), T. Mandalaki (H). Bad Rothenfelde: R. Buchwalsky (C), J. Kienast (H; Munster). Basel: F. Burkart (C), F. Duckert (H). Bern: H.P. Gurtner (C), P.W. Straub (H). Bordeaux: H. Bricaud (C), M.R. Boisseau (H). Brussels: F. Lavenne (C), R. Masure (H). Eindhoven: J.J.R.M. Bonnier (C), H.R. Michels (C), J.J.M.L. Hoffmann (H). Frankfurt: W.D. Bussmann (C), K. Breddin (H). Giessen: B. Wusten (C), F.R. Matthias (H). Bad Nauheim: M. Schlepper (C), G. Muller-Berghaus (H). Leeds: D.R. Smith (C), C.R.M. Prentice (H). Lyon: J.B. Delahaye (C), M. Dechavanne (H). Mannheim: B. Stegaru (C), W. Kirschstein (H). Marseille: A. Serradimigni (C), I. Juhan-Vague (H). Munster: U.S. Muller (C), U. Schmitz-Hubner (H). Paris: L. Guize (C), M.M. Samama (H). Pisa: A. L'Abbate (C), R. de Caterina (H). Vienna: G. Kronik (C), H. Niessner (H).

Reference Laboratories
F. Duckert, Basel, Switzerland (vWF, fibrinogen); P.J. Gaffney, London, UK (plasminogen); L. Petersen, Hvidovre, Denmark (₂-antiplasmin); F.E. Preston, Sheffield, UK (ECLT); J. Verheijen, Leiden, Netherlands (TPA activity); I. Juhan-Vague, Marseille, France (TPA antigen); E. Kruithof, Lausanne, Switzerland (PAI-1).

Laboratory Assay Committee
F. Duckert, Basel, Switzerland; J.J. Sixma, Utrecht, Netherlands; J. Jespersen, Esbjerg, Denmark; R.M. Bertina, Leiden, Netherlands; D.S. Pepper, Edinburgh, UK; L. Poller, Manchester, UK; D.C. Rijken, Leiden, Netherlands.

Central Analysis of Assays
J. Jespersen, Esbjerg, Denmark (PAI-1 activity and antigen); I. Juhan-Vague, Marseille, France (TPA antigen, CRP).

ECAT Advisory Board
E.F. Luscher, Bern (chairman); P. Brakman, Leiden; D. Juilian, London; J. Lubsen, Rotterdam, Netherlands; C.R.M. Prentice, Leeds; M. Verstraete, Leuven, Belgium.

Statistical Center
S.G. Thompson, S. Pyke, London.

End-Point Committee
G. Breithardt, Munster; M. Brochier, Tours, France; H. Tunstall-Pedoe, Dundee, UK.

Executive Committee
F. Duckert, Basel; F. Haverkate, Leiden; J van de Loo, Munster; S.G. Thompson, London.

Study Coordinator
J. van de Loo, Munster.

ECAT Project Leader
F. Haverkate, Leiden.

Received March 25, 1996; revision received August 1, 1996; accepted August 7, 1996.

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