Plasmin-alpha2-antiplasmin complex in patients with atrial fibrillation. Stroke Prevention in Atrial Fibrillation Investigators.

Plasmin-alpha2-antiplasmin complex (PAP) is an index of recent fibrinolytic activity. We examined PAP levels in patients with atrial fibrillation (AF) to determine whether these levels are correlated with clinical characteristics associated with stroke risk. We obtained blood for measurement of PAP in a non-random sample of 586 patients with AF on entering the Stroke Prevention in Atrial Fibrillation III Study. PAP levels were measured with an ELISA assay. PAP values were transformed with a natural logarithm (PAPln) prior to all analyses. Older age, female gender, recent congestive heart failure, decreasing fractional shortening, recent onset of AF, and coronary artery disease were each univariately associated with higher levels of PAP (all p<0.05, two-sample t-test, simple linear regression). Older age, recent congestive heart failure, decreasing fractional shortening, and recent onset of AF were independently associated with higher PAP levels by multivariate analysis (linear regression). Among patients receiving warfarin, PAP levels were not correlated with INR levels (linear regression, p=0.60). Patients classified as high-risk for thromboembolism by our risk stratification criteria (systolic blood pressure > 160 mm Hg, prior thromboembolism, recent congestive heart failure, poor left ventricular function, and women over age 75) had higher PAP levels than low-risk patients (antilog mean PAPln 5.6 vs 4.9. p<0.001, two-sample t-test). PAP levels in patients with AF are associated with clinical characteristics predictive of thromboembolism. Elevated PAP levels are particularly associated with poor left ventricular function and are not affected by anticoagulation. PAP levels may be a marker of stroke risk in patients with AF.

The reliability of medication inventory methods compared to serum levels of cardiovascular drugs in the elderly.

Medication inventory is more reliable than self-report in assessing prescription drug use in elderly populations. It is not known how strongly medication inventory reflects actual medication use as measured by serum drug levels. In the Cardiovascular Health Study, medication data were collected annually by study interviewers from medication containers brought to the clinic visit. At the fourth clinic visit, venipuncture was performed under 12-hour fasting conditions. Participants were told to take medications as usual. Based on medication inventory results, we randomly selected 55 users and 55 non-users of four cardiovascular drugs: aspirin, propranolol, hydrochlorothiazide, and digoxin. All 110 blood samples for each of the four drugs were analyzed; cut points were based on detectable levels given laboratory limitations. Kappa statistics (K) tested degree of agreement between medication inventory findings and serum detection. Assays were completed on 400 samples (91%). Agreement for aspirin (n=102) was poor: K=0.16 (95% CI: 0.0-0.32). Agreement for propranolol (n = 98) was fair: K=0.43 (95% CI: 0.27-0.59). Agreement for hydrochlorothiazide (n=100) was good: K=0.62 (95% CI: 0.53-0.91). Agreement for digoxin (n=100) was excellent: K=0.94 (95% CI: 0.74-1.0). For four all drugs, lack of agreement was confined primarily to participants who reported use but did not have detectable levels. Excluding aspirin users, only one non-user (0.7%) had drug detected in serum. The medication inventory is a reasonably sensitive and a fairly reliable method for ascertaining non-aspirin cardiovascular drug use in the elderly even though this method may overestimate use as assessed by serum level.

The measurement of fibrinogen in population-based research. Studies on instrumentation and methodology.

Plasma fibrinogen concentration is a risk factor for cardiovascular disease and has become a common component of epidemiologic studies. Also, fibrinogen analysis has become an important component of clinical trials of thrombolytic therapy and anticoagulation. We studied fibrinogen values from plasma containing three different anticoagulants and compared two different instruments. Clot-rate assays were performed on plasma containing sodium citrate (the recommended specimen) as well as ethylenediamine-tetraacetic acid (EDTA) and EDTA plus D-Phe-Pro-Arg chloromethyl ketone (PPACK) and aprotinin (special anticoagulant), specimens often obtained in multicenter studies. We compared a fibrometer (the BBL) with an analyzer (the Diagnostica Stago ST4), which offers improved throughput, ease of use, and precision. The correlation of citrate and EDTA fibrinogen values (fibrometer) was r = .9718; for citrate and special anticoagulant plasma, r = .9717. Correlations of fibrinogen values from the fibrometer and the analyzer were r = .9558 and r = .9857 for citrate samples and special anticoagulant samples, respectively. We conclude that (1) fibrinogen may be measured by clot-rate assay in EDTA-containing samples and that values may be compared with values obtained from citrate plasma with a correction; (2) samples containing PPACK may be used with only slight modification of the method; and (3) values obtained on the analyzer are directly comparable with those obtained on the fibrometer, facilitating large studies.

Laboratory methods and quality assurance in the Cardiovascular Health Study.

The Cardiovascular Health Study is an observational cohort study of risk factors for cardiovascular disease in 5201 participants, ages > or = 65 years. We report the methods and quality-assurance results for blood procurement, processing, shipping, storage, and sample analysis used during the first examination period (May 1989-June 1990). The most frequent difficulty in phlebotomy and processing was the requirement of more than one venipuncture (in 2.6% of the participants). The CVs for control materials ranged from 0.93% for glucose to 10.7% for insulin; most were < 4%. In addition to standard quality-assurance methods, we applied two other methods: technical error calculation for replicates, and weighted linear regression to assess time trend in results of control materials. After outliers were excluded, technical error values ranged from 1.7 for uric acid to 18.8 for insulin. Factor VII and factor VIII had slight trends over the 12-month analysis period. Results of quality-assurance analyses used to resolve problems were successful, thereby improving the second laboratory examination.

Relationship between prothrombin activation fragment F1.2 and international normalized ratio in patients with atrial fibrillation. Stroke Prevention in Atrial Fibrillation Investigators.

BACKGROUND AND PURPOSE: The prothrombin time (expressed as the international normalized ratio [INR]) is the standard method of monitoring warfarin therapy in patients with atrial fibrillation. Prothrombin activation fragment F1.2 provides an index of in vivo thrombin generation and might provide a better index of the effective intensity of anticoagulation. We examined the relationship between F1.2 and INR in patients with atrial fibrillation. METHODS: We measured INR and F1.2 levels in 846 patients with atrial fibrillation participating in the Stroke Prevention in Atrial Fibrillation III study. Two hundred nineteen (26%) were taking aspirin alone, 326 (39%) were taking adjusted-dose warfarin, and 301 (36%) were taking a low fixed dose of warfarin (1 to 3 mg) plus aspirin (combination therapy). F1.2 levels were measured with an enzyme-linked immunosorbent assay. RESULTS: Patients receiving adjusted-dose warfarin or combination therapy had significantly higher INR and significantly lower F1.2 values than those on aspirin alone (P < or = .0001 for each of the four comparisons). F1.2 values (nanomolar) were inversely correlated with INR (F1.2 = -0.1 + 2.3[1/INR]; R2 = .37; P < .0001; simple linear regression). However, significant variability remained. Among patients receiving warfarin, older patients had higher F1.2 values than younger patients after adjustment for INR intensity (P < .001) in the model. There was no difference in the relationship between F1.2 and INR between men and women. CONCLUSIONS: Increasing intensity of anticoagulation, as measured by the INR, is associated with decreasing thrombin generation as measured by the F1.2 level, but significant variability exists in this relationship. Older anticoagulated patients have higher F1.2 values than younger patients at equivalent INR values. The clinical significance of these differences is not clear. F1.2 measurement might provide information regarding anticoagulation intensity in addition to that reflected by the INR.

Markers of thrombin and platelet activity in patients with atrial fibrillation: correlation with stroke among 1531 participants in the stroke prevention in atrial fibrillation III study.

BACKGROUND AND PURPOSE: Markers of thrombin generation and platelet activation are often elevated in patients with nonvalvular atrial fibrillation, but it is unclear whether such markers usefully predict stroke. Therefore, we undertook the present study to assess the relationship between prothrombin fragment F1.2 (F1.2), beta-thromboglobulin (BTG), fibrinogen, and the factor V Leiden mutation with stroke in atrial fibrillation. METHODS: Specimens were obtained from 1531 participants in the Stroke Prevention in Atrial Fibrillation III study. The results were correlated with patient features, antithrombotic therapy, and subsequent thromboembolism (ischemic stroke and systemic embolism) by multivariate analysis. RESULTS: Increased F1.2 levels were associated with age (P<0.001), female sex (P<0.001), systolic blood pressure (P=0.006), and heart failure (P=0.001). F1.2 were not affected by aspirin use and were not associated with thromboembolism after adjustment for age (P=0. 18). BTG levels were higher with advanced age (P=0.006), coronary artery disease (P=0.05), carotid disease (P=0.005), and heart failure (P<0.001), lower in regular alcohol users (P=0.05), and not significantly associated with thromboembolism. Fibrinogen levels were not significantly related to thromboembolism but were associated with elevated BTG levels (P<0.001). The factor V Leiden mutation was not associated with thromboembolism (relative risk 0.5, 95% CI 0.1 to 3.8). CONCLUSIONS: Elevated F1.2 levels were associated with clinical risk factors for stroke in atrial fibrillation, whereas increased BTG levels were linked to manifestations of atherosclerosis. In this large cohort of patients with atrial fibrillation who were receiving aspirin, F1.2, BTG, fibrinogen, and factor V Leiden were not independent, clinically useful predictors of stroke.

Analytical and biologic variability in measures of hemostasis, fibrinolysis, and inflammation: assessment and implications for epidemiology.

An increasing number of cardiovascular epidemiologic studies are measuring non-traditional risk markers of disease, most of which do not have established biovariability characteristics. When biovariability data have been reported, they usually represent a short time period, and, in any case, there is little consensus on how the information should be used. The authors performed a long-term (6-month) repeated measures study on 26 healthy individuals, and, using a nested analysis of variance (ANOVA) approach, report on the analytical (CVA), intraindividual (CVI), and between individual (CVG) variability of 12 procoagulant, fibrinolysis, and inflammation assays, including total cholesterol for comparison. The results suggest acceptable analytical variability (CVA < or = 1/2 CVI) for all assays. However, there was a large range of intraindividual variation as a proportion of total variance (2-78%), and adjusting for intraindividual and between individual variation in bivariate correlations increased the observed correlation by more than 30 percent for three of these assays. Overall, the assays showed a significant increase in intraindividual variation over 6 months (p < 0.05). While these findings suggest that most of these assays have biovariability characteristics similar to cholesterol, there is variation among assays. Some assays may be better suited to epidemiologic studies, and knowledge of an assay's biovariability data may be useful in interpreting simple statistics, and in designing multivariate models.

Correlates of thrombin markers in an elderly cohort free of clinical cardiovascular disease.

Studies suggest that thrombosis is important in the progression of atherosclerotic lesions. The biochemical markers prothrombin fragment 1-2 and fibrinopeptide A reflect in vivo thrombin generation and activity, respectively. As such, they are markers that might be associated with cardiovascular risk. From the Cardiovascular Health Study, a cohort study of 5201 persons over 65 years of age, 399 persons free of clinical cardiovascular disease (CVD) at the baseline examination were selected for study of specialized markers of hemostasis. We report the cross-sectional relationships of the thrombin markers to CVD risk factors and measures of subclinical CVD. The range of fragment 1-2 2 was 0.12 to 0.85 nmol/L. The range of fibrinopeptide A was 0.9 to 44.1 micrograms/L. High levels of fragment 1-2 and fibrinopeptide A were associated with age, with levels higher in women than men. Fragment 1-2 was associated with smoking; high levels of triglyceride, creatinine, and C-reactive protein; and low levels of glucose. Fibrinopeptide A was associated with high C-reactive protein and apolipoprotein(a) and lower ankle-brachial index. There were no significant associations of the thrombin markers with race, fibrinogen, alcohol consumption, diabetes, or most measures of subclinical CVD. Study findings support a hypothesis that there are physiological interrelationships between cardiac risk factors, hemostasis, inflammation, and progression of atherosclerosis.

Lifetime smoking exposure affects the association of C-reactive protein with cardiovascular disease risk factors and subclinical disease in healthy elderly subjects.

Blood levels of C-reactive protein (CRP), a marker of inflammation, are related to cardiovascular disease risk. To determine cross-sectional correlates in the elderly, we measured CRP in 400 men and women older than 65 years and free of clinical cardiovascular disease at baseline as part of the Cardiovascular Health Study. Only 2% of the values were greater than 10 mg/L, the cut-point usually used to identify inflammation. CRP levels appeared tightly regulated, since there were strong bivariate correlations between CRP and the following: inflammation-sensitive proteins such as fibrinogen (r = .52); measures of fibrinolysis such as plasmin-antiplasmin complex (r = .23); pack-years of smoking (r = .30); and body mass index (r = .24; all P values < or = .001). The association with pack-years was independent of the length of time since cessation of smoking. CRP levels were also associated with coagulation factors VIIc, IXc, and Xc; HDL cholesterol (negative) and triglyceride; diabetes status; diuretic use; ECG abnormalities; and level of exercise. Because of effect modification, two multiple linear regression prediction models were developed for CRP, one each for never smokers and ever smokers. An a priori physiologic model was used to guide these analyses, which disallowed the use of other inflammation-sensitive variables such as fibrinogen. In never smokers, the independent predictors were body mass index (+), diabetes status (+), plasmin-antiplasmin complex (+), and the presence of ECG abnormalities (+); this model predicted 15% of the CRP population variance. In ever smokers, the predictors were body mass index (+), plasmin-antiplasmin complex (+), pack-years of smoking (+), HDL cholesterol (-), and ankle-arm blood pressure index (-); this model predicted 42% of the population variance. We conclude that levels of CRP in the healthy elderly are tightly regulated and reflect lifetime exposure to smoking as well as level of obesity, ongoing level of fibrinolysis, diabetes status, and level of subclinical atherothrombotic disease. Moreover, exposure to smoking affects the relation of CRP to these other factors.