Associations Between Carotid Atherosclerosis and High Factor VIII Activity, Dyslipidemia, and Hypertension
Background and Purpose A subsample of 147 Chinese subjects from a population-based study of cardiovascular diseases (Cardiovascular Disease Risk Factor Two-Township Study) participated in an ancillary study on extracranial carotid color duplex ultrasonography that aimed to assess the relations of coagulation factors to stroke and carotid atherosclerosis.
Methods Logistic models were used to study the associations between cardiovascular disease risk factors and stroke/carotid atherosclerosis, controlling for the effects of age and sex.
Results Stroke was significantly associated with hypertension and high values of plasma glucose but not with fibrinogen, factor VIIc, or factor VIIIc. Carotid plaques identified in this study were mostly mild and moderate. The presence of these mild and moderate carotid plaques was significantly associated with high values of factor VIII activity, hypercholesterolemia, hypertriglyceridemia, and hypertension. The highest tertile of factor VIIIc (>1.53) was associated with an odds ratio of 3.35 for carotid atherosclerosis when compared with the lowest tertile (<1.20). A multiple logistic regression including all significant risk factors showed that the degree of association between factor VIIIc and atherosclerosis was attenuated to an odds ratio of 2.65 (P=.061).
Conclusions In the present study, the roles of hypertension, hypercholesterolemia, and hypertriglyceridemia have been implicated in the pathogenesis of carotid atherosclerosis, and roles for hypertension and hyperglycemia in stroke were indicated. A positive association between factor VIIIc and carotid atherosclerosis in this Chinese population was found. Whether this association is independent of the effect of other cardiovascular risk factors awaits further study.
The role of coagulation factors in the pathogenesis of CVD has gained much attention recently. Particularly, plasma levels of fibrinogen and factor VIIc were independently associated with risk of cardiovascular diseases in several prospective studies.1 2 3 4 5 In the Northwick Heart Study, the highest tertile group of factor VIII levels was associated with a 44% increase in risk of coronary artery disease in the 5-year follow-up study.2 The association was not statistically significant (P=.2). In the recent 16.1-year follow-up study,6 an increase of 1 SD of factor VIIIc significantly raised the incidence of fatal coronary artery disease by 28%.
It is generally believed that acute thrombosis formation on an atherosclerotic plaque triggers the cardiovascular events.7 8 However, whether coagulation parameters are involved in the process of atherosclerosis is a subject of great interest. This study used high-resolution color duplex ultrasonography to detect the presence of plaque and the degree of stenosis at the maximal stenotic position of the carotid artery as an indicator of atherosclerosis. Studies have indicated that the degree of stenosis in the major arteries of Chinese subjects is not as severe as that found in whites.9 10 Although there are several studies on the relationship between hemostatic factors and carotid atherosclerosis11 12 13 14 15 16 17 18 in whites, primarily implicating a role of fibrinogen in the development of atherosclerosis, there are very few such studies in Chinese. Therefore, the purpose of this study was to elucidate the relationship of some hemostatic parameters and traditional CVD risk factors to stroke and to carotid atherosclerosis in Chinese subjects.
Subjects and Methods
The present study is ancillary to an ongoing longitudinal study, CVDFACTS.19 From November 1990 through December 1993, 4410 men and women aged 30 years and above participated in our study; they were residents of the Chu-Dung and Pu-Tzu townships located in western and southwestern Taiwan. The study was approved by the Department of Health during the review process. All subjects gave their informed consent before the examinations.
Two neurologists reviewed the answers to a TIA questionnaire administered at baseline to identify potential stroke/TIA patients. TIA was defined as a temporary focal neurological deficit presumably related to ischemia, lasting less than 24 hours. Cerebral strokes were defined as a focal neurological deficit attributed to a vascular origin, lasting more than 24 hours. Fifty-two potential stroke/TIA patients and 95 neighborhood control subjects (77 men and 70 women aged 30 years and above) randomly selected from the Chu-Dung cohort participated in an ancillary study on extracranial carotid color duplex ultrasonography in December 1993. Among the 52 patients, 24 (19 men and 5 women) were confirmed as real stroke/TIA cases after an interview with a neurologist (J.-R.C.) before the ultrasonography. Of these 24 patients, 4 had TIA and 20 had mild stroke. We will use the term “stroke” instead of stroke/TIA throughout this report.
Assessment of Carotid Atherosclerosis
Color flow imaging of the carotid arteries was performed (J.-R.C.) with a Hewlett-Packard Sono 1000 equipped with a linear-array probe with a transducer frequency of 7.5 MHz in B-mode and 5.6 MHz in pulsed Doppler and color examination. For imaging, the subjects were lying in a supine position with the head slightly extended and rotated 45° away from the side being scanned. Transverse and longitudinal scans were performed to image the common carotid artery, carotid bifurcation, and internal and external carotid arteries. The B-mode images of these arteries of both sides were measured during systole. Maximal diameter stenosis was carefully determined by examining the course of the bilateral common carotid, bifurcation, and internal and external carotid arteries from both transverse and longitudinal scans. When there was plaque visible, two paired cursors were used to mark the original outer diameter of the vessel and the inner residual luminal diameter. Maximal intima-media thickness was measured. The percentage of stenosis was defined as ([original lumen diameter−residual lumen diameter]/original lumen diameter×100%). The presence of plaque was defined as irregular intimal surface, lumen encroachment, wall thickness exceeding 50% thickness of adjacent intima-media thickness, and/or image characteristics reflective of structure heterogeneity of the arterial wall, such as acoustic shadowing. A second reading of the ultrasonography tapes was made (J.-R.C.), blind to the results of the first reading. The agreement between the first and second grading was 94% for plaque presence.
Data Collection and Laboratory Measurements
Data collection was carried out in the main study from November 1990 through December 1993, before the ultrasonography study. For each subject, background data (age, sex, etc) were obtained from questionnaires. Blood pressure was measured three times with a standard mercury sphygmomanometer after 5 minutes of rest. The last two readings were averaged for this analysis.
Fasting venous blood samples were also collected to measure clinical chemistry profiles and hemostatic parameters. To minimize trauma, a small butterfly needle (No. 21, Nissho Corp) was used for puncture. No more than one puncture was considered a successful collection. The first 10 mL of blood was collected into a tube containing sodium heparin (Sherwood Medical). After the tourniquet was released, 4.5 mL of blood was collected into each of two precooled tubes containing sodium citrate (Becton Dickinson) within 30 seconds. All samples were inverted and maintained at 4°C. Within an average of 27 minutes after blood drawing, samples were spun for 15 minutes at 3000g at 4°C. After separation, plasma samples were immediately stored at −70°C until chemical analysis was performed.
Clinical chemistry parameters included in this study were levels of cholesterol, triglyceride, glucose, and uric acid. These measurements were made for heparinized blood using a Monarch 2000 (Instrumental Laboratory). Hemostatic parameters included in this study were levels of fibrinogen, factor VIIc, factor VIIIc, and antithrombin III. All hemostatic measurements were performed within 1 month of drawing blood on an ACL 300 Plus (Automated Clotting and Fibrinolysing Analysis System), using reagents provided by Instrumentation Laboratory. The coefficients of variation for fibrinogen, factor VIIc, factor VIIIc, and antithrombin III were 2.8%, 6.5%, 8.2%, and 7.6%, respectively. The coefficients of variation for all clinical chemistry results were <5%.
Data analysis was carried out using SAS (Statistical Analysis System), version 6.06. Logistic regression was used to associate various CVD risk factors to stroke and to the presence of plaque. The effects of age and sex were controlled for, using a multiple logistic regression approach. All continuous variables were grouped into tertiles. Clinical cutoff points for borderline, high, and very high cholesterol (<5.20, 5.20 to 6.21, and >6.21 mmol/L), triglyceride (<1.13, 1.13 to 2.26, and >2.26 mmol/L), and glucose (<5.55, 5.55 to 7.77, and >7.77 mmol/L, respectively) levels were alternatively used to group patients.20 The coefficients of the logistic regression were converted into ORs representing the risk ratio between subgroups.
The status of stroke and carotid atherosclerosis in the studied population is presented first; cardiovascular risk factors will then be compared among subjects by stroke status and by carotid atherosclerosis status.
Status of Carotid Stenosis and Stroke in the Studied Subjects
Among the 147 subjects examined, 103 (70.1%) had no sign of carotid plaques. Nineteen subjects (12.9%) had stenosis of <30%, another 19 subjects had 30% to 49% stenosis, and 6 had 50% to 79% stenosis. No one had stenosis >80%. In 24 stroke subjects, 12 had no evidence of plaque. The OR corresponding to the association between stroke and carotid atherosclerosis was 2.94 (95% CI, 2.04 to 3.84) (Table 1⇓).
Relationship Between Risk Factors and Stroke Status
Comparison was made between those with stroke (24 subjects) and those without stroke (Table 2⇓). Those with stroke were older and had higher values of waist-hip ratio, systolic blood pressure, and uric acid. There were more hypertensive patients in the stroke group than in the nonstroke group.
Logistic regression analysis (Table 3⇓) was used to compute age- and sex-adjusted ORs for stroke. No clear relationships were shown between stroke and plasma cholesterol, triglyceride, fibrinogen, factor VIIc, factor VIIIc, antithrombin III, and smoking status. Hypertension was significantly associated with a 6.05-fold risk of having stroke. High levels of plasma glucose were also associated with a significantly higher risk of stroke. Risk prediction trends for stroke were also shown for waist-hip ratio and uric acid, which were not statistically significant.
In multivariate logistic regression analysis (Table 4⇓), hypertension and high plasma glucose levels were independently associated with stroke in the multivariate logistic regression models.
Relationship Between Risk Factors and Carotid Atherosclerosis
Comparison was made between those with plaque (44 subjects) and those without plaque (Table 5⇓). Those with plaque were older and had higher values of systolic blood pressure, triglyceride, glucose, uric acid, waist-hip ratio, and factor VIIIc. There were more hypertensive patients in the plaque group than in the control group.
Logistic regression analysis (Table 6⇓) was used to compute age- and sex-adjusted ORs for the presence of carotid plaque. Hypertension was significantly associated with a 3.13-fold risk of having carotid plaque. Both hypercholesterolemia (serum cholesterol, 6.21 mmol/L; OR, 4.26) and hypertriglyceridemia (serum triglyceride, ≥1.19 mmol/L; OR, 5.72) were associated with significantly increased risk of carotid plaque. Alternatively, ORs for being in the highest tertile of serum cholesterol and triglyceride were 2.08 and 2.46, respectively. These effects were not statistically significant. On the other hand, being in the highest tertile of factor VIIIc was significantly associated with a 3.35-fold risk of carotid plaque. Variables not significantly associated with risk of carotid atherosclerosis but showing a risk prediction trend included high levels of glucose, uric acid, fibrinogen, and factor VIIc and low values for antithrombin III and body mass index. No clear relationships were evident between carotid atherosclerosis and waist-hip ratio or smoking habits.
In multivariate logistic regression analysis (Table 7⇓), hypertension, cholesterol, triglyceride, and factor VIIIc were included in the multivariate logistic regression models. Two models were fitted. When cholesterol, triglyceride, and factor VIIIc were grouped as tertiles in the multiple logistic regression model, hypertension status was significantly associated with presence of plaque. Level of factor VIIIc in the highest tertile was associated with the presence of plaque at a borderline significant level (P=.061). However, when cholesterol and triglyceride were grouped with clinical definitions (see “Subjects and Methods”), hypercholesterolemia and hypertension were both significantly associated with the presence of plaque. In this model, hypertriglyceridemia and the highest tertile of factor VIIIc were no longer significantly associated with carotid plaque as in the case of univariate analysis. However, the OR for the highest tertile of factor VIIIc compared with the lowest tertile was as high as 2.16.
Levels of serum cholesterol, triglyceride, and factor VIIIc were interrelated (Table 8⇓). All correlation coefficients (0.2 to 0.3) were statistically significant. Diastolic blood pressure correlated with triglyceride levels (0.26) but not those of cholesterol and factor VIIIc.
In this sample of the Chinese population, 44 subjects had signs of carotid plaques that were mostly mild and moderate. The presence of these mild and moderate carotid plaques was significantly associated with a high level of factor VIIIc, hypertension status, hypercholesterolemia, and hypertriglyceridemia, respectively, after age and sex factors were controlled for in the univariate analysis. On the other hand, no relationship was found between stroke and blood lipids, smoking, and coagulation factors (fibrinogen, factor VIIc, and factor VIIIc). Stroke was associated with hypertension and high levels of fasting glucose, independent of age and sex.
There have been several studies examining the relationship between hemostatic factors and carotid atherosclerosis for various white populations. Among them,11 12 13 14 plasminogen activator inhibitor-1,13 tissue plasminogen activator,13 d-dimer,13 and fibrinogen14 15 16 17 were associated with carotid atherosclerosis. We demonstrated in the age- and sex-adjusted logistic regression analysis that the highest tertile of factor VIIIc value corresponded to the highest OR value (3.35) among all variables grouped into tertiles, including cholesterol and triglyceride. Although studies have shown that coronary artery disease mortality was reduced in hemophilic patients with very low levels of either factor VIII or factor IX,21 both the 5-year and 16.1-year follow-up studies of the Northwick Park Heart Study demonstrated a weak association between factor VIIIc and coronary artery disease mortality. Statistical significance was demonstrated only in the 16.1-year study. Our finding of a positive association between factor VIIIc and carotid atherosclerosis suggests that factor VIII may play a role in the process of atherosclerosis. It is also possible that this phenomenon is associated with other atherosclerosis-related phenomena. There has been interest in factor VIII and von Willebrand factor as potential markers of endothelial cell injury.22 23 24 Our data also showed that factor VIIIc was significantly correlated with blood cholesterol (r=.21) and triglyceride (r=.31). In the Northwick Park Heart study, no correlation between factor VIIIc and cholesterol level was found (r=.01).
When multivariate logistic regression analysis was carried out including age, sex, cholesterol, triglyceride, hypertension, and factor VIIIc in the model, the degree of association between factor VIII activity and carotid atherosclerosis was attenuated, and the significance level decreased to a borderline value (P=.061). When hypercholesterolemia and hypertriglyceridemia, rather than tertiled cholesterol and triglyceride, were alternatively included in the model, the attenuation was even greater, suggesting that the role of factor VIIIc may be in part associated with very high cholesterol or triglyceride values. Because significant correlations have been found among levels of cholesterol, triglyceride, and factor VIIIc, caution should be used when interpreting the results of this multiple logistic regression. Lack of independent effects in multiple regression analysis does not necessarily negate the biological significance of a given variable that is statistically associated with a disease in univariate analysis. Other experimental evidence is required to interpret the present findings. Nevertheless, the risk of having carotid plaque for persons with the highest tertile of factor VIIIc was more than twice that of those with the lowest tertile in the multiple regression model.
Studies have shown that individuals with non-O blood groups had a higher risk of coronary heart disease.25 26 Higher values of von Willebrand factor and factor VIII antigen in non-O blood typed individuals have also been reported.6 21 Because von Willebrand factor is the carrier protein for factor VIII, further studies are needed to elucidate the roles of both proteins in relation to factor VIII activity and carotid atherosclerosis.
On the other hand, fibrinogen and factor VIIc have been associated with increased risk of coronary artery disease in many prospective studies.1 2 3 4 5 A recent study also indicated that levels of fibrinogen, von Willebrand antigen, and tissue plasminogen activator antigen were independent predictors of subsequent acute coronary syndromes.27 Several recent reports showed significant associations between fibrinogen and carotid artery stenosis.14 15 16 17 However, no association was found between factor VIIc and fibrinogen and carotid artery intima-media thickness in young and middle-aged volunteers in a recent study.11 This was also not found in the present study.
In the present study, the roles of hypertension, hypercholesterolemia, and hypertriglyceridemia have been implicated in the pathogenesis of carotid atherosclerosis, and hypertension and hyperglycemia were indicated as playing a role in stroke. The positive association between factor VIIIc and carotid atherosclerosis in this Chinese population is an interesting finding. Whether this association is independent of the effect of other cardiovascular risk factors awaits further study.
Selected Abbreviations and Acronyms
|CVDFACTS||=||Cardiovascular Disease Risk Factor Two-Township Study|
|TIA||=||transient ischemic attack|
This project was supported by grants from the Department of Health (DOH80-27, DOH81-021, DOH8202-1027, DOH83-TD-015, and DOH84-TD-006) and Shin Kong Wu Ho-Su Memorial Hospital (SKMH8302-84-2103-01) in Taiwan.
Reprint requests to Dr Wen-Harn Pan, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan 11529, ROC. E-mail email@example.com.
- Received June 14, 1996.
- Revision received September 24, 1996.
- Accepted October 8, 1996.
- Copyright © 1997 by American Heart Association
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