Factors Associated with Intima-Media Complex Thickness of the Common Carotid Artery in Japanese Noncardioembolic Stroke Patients with Hyperlipidemia: The J-STARS Echo Study

There may be ethnic differences in carotid atherosclerosis and its contributing factors between Asian and other populations. The purpose of this study was to examine intima-media complex thickness (IMT) of the carotid artery and associated clinical factors in Japanese stroke patients with hyperlipidemia from a cohort of the Japan Statin Treatment Against Recurrent Stroke Echo Study.Patients with hyperlipidemia, not on statins, who developed noncardioembolic ischemic stroke were included in this study. Mean IMT and maximum IMT of the distal wall of the common carotid artery were centrally measured using carotid ultrasonography. Significant factors related to mean IMT and maximum IMT were examined using multivariable analysis.In 793 studied patients, mean IMT was 0.89±0.15 mm and maximum IMT was 1.19±0.32 mm.Age (per 10 years, parameter estimate=0.044, p＜0.001), smoking (0.022, p=0.004), category of blood pressure (0.022, p=0.006), HDL cholesterol (per 10 mg/dl, －0.009, p=0.008), and diabetes mellitus (0.033, p=0.010) were independently associated with mean IMT. Age (per 10 years, 0.076, p＜0.001), smoking (0.053, p=0.001), HDL cholesterol (－0.016, p=0.036), and diabetes mellitus (0.084, p=0.002) were independently associated with maximum IMT.Baseline mean and maximum values of carotid IMT in Japanese noncardioembolic stroke patients with hyperlipidemia were 0.89±0.15 mm and 1.19±0.32 mm, respectively, which were similar to those previously reported from Western countries. Age, smoking, hypertension, HDL cholesterol, and diabetes mellitus were associated with mean IMT, and those, except for hypertension, were associated with maximum IMT.

section_content: Carotid ultrasound is used to measure intimamedia complex thickness (IMT) as a marker of atherosclerosis, as well as a risk factor for cardiovascular events [1] [2] [3] [4]. I Western countries, IMT has been reported to be attenuated by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) that can decrease cholesterol biosynthesis in the liver [5] [6] [7] [8] [9]. However, the effect of HMG-CoA reductase inhibitors on IMT has not been well established in Japan. The Japan Statin Treatment Against Recurrent Stroke (J-STARS) trial is a multicenter, prospective, randomized, open-label, parallel group trial of secondary stroke prevention using pravastatin 10 mg/ day (usual dose in Japan) in the stroke patients with hyperlipidemia. The aim of this trial is to examine whether pravastatin prevents stroke recurrence in Japanese patients with noncardioembolic ischemic stroke. The J-STARS Echo Study is a substudy of the J-STARS study that aims to explore the pleiotropic effects of regular statin therapy on the changes of carotid atherosclerosis assessed by ultrasonography. Base ine characteristics, baseline mean and maximum IMTs, and the atherosclerosis factors correlated with the baseline mean and maximum IMTs were examined.
section_name: Background and Purpose

section_name: Patients and Methods

section_content: The study design methods of the J-STARS Echo Study were described elsewhere 10, 11) ; thus, the methods are stated briefly here. The protocol and informed consent form of the present substudy were approved by the institutional review board of each center, and written informed consent was obtained from each patient together with the main trial. The J-STARS Echo Study is registered with ClinicalTrials. gov (NCT00361530) and the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (C000000212) separately from J-STARS (NCT00221104, UMIN C000000207).
section_name: Study Design

section_content: Patients from 61 hospitals with certified sonographers in the J-STARS Echo Study were enrolled in this substudy. The inclusion criteria for the main trial were as follows: (1) age between 45 and 80 years; (2) clinical diagnosis of noncardioembolic ischemic stroke developing within the preceding month to 3 years; and (3) history of hyperlipidemia with serum total cholesterol levels maintained between 4. 65 and 6. 21 mmol/L (180 and 240 mg/dL), without the use of statins. Additional exclusion criteria for the main trial have been described in elsewhere 10, 11).
section_name: Patient Population

section_content: The patients were enrolled through a web-based registration and follow-up system for the main trial. Patients assigned to the pravastatin group received pravastatin 10 mg/day, and those in the control group received no statin treatment, although other drugs were administered when necessary.
section_name: Randomization and Treatment

section_content: Carotid ultrasonography was performed in each participating institute by well-trained physicians or laboratory technicians who were certified as expert examiners for this study. Baseline examinations were performed at the time of enrollment in the study. The examination methods have been described in elsewhere 11).
section_name: Carotid Ultrasonography

section_content: Videotapes or CD-Rs of the ultrasonography were sent to the J-STARS ECHO office for assessment, including kinetic measurements. All measurements were performed by a well-trained technician who was blinded to all clinical information. 

Carotid IMT measurement methods have been described in elsewhere 11). Still images (640×480 pixels) were imported from the videotapes or CD-Rs via a video port with a resolution of 1 pixel corresponding to 0. 1 mm (Fig. 1 ). All still images were then imported into an IMT measurement software (IntimaScope; Mediacross, Tokyo, Japan), and IMT was measured on the distal wall in a continuous 2-cm section on the central side of the common carotid artery (CCA) bifurcation 12). This software was programmed to automatically draw 2 lines at the junctions of the intimamedia complex with the blood and the adventitia, and it was capable of measuring distances down to 0. 01 mm 13). Mean and maximum values of IMT in a 2-cm continuous section of the distal CCA were calculated automatically, and plaque thickness was similarly measured at the site of each plaque. Pivotal parameters for analysis were mean IMT (right, left, and mean of right and left) and maximum IMT (right, left, and thicker value of right and left) of the distal wall of the CCA in the above-mentioned 2-cm section.
section_name: Carotid IMT Measurements

section_content: Baseline characteristics between the pravastatin and control groups and between the patients included in the J-STARS Echo Study and those not included in the J-STARS Echo Study were compared using the chi-square test, t-test, and Wilcoxon rank-sum test, as appropriate. The mean and maximum IMTs stratified by baseline characteristics were compared using nonpaired t-test. Multivariable analyses to assess factors associated with mean and maximum IMTs were performed using stepwise multiple linear regression analysis with age, sex, weight, body mass index, diabetes mellitus (DM), smoking habit, total cholesterol, HDL cholesterol, LDL cholesterol, triglyceride, categories of blood pressure, glomerular filtration, creatinine clearance, urinary protein, chronic kidney disease, subtype of stroke, size of responsible infarction, location of infarction vessel, carotid bruit, and atrial flutter/fibrillation as independent variables. In the stepwise multiple linear regression analysis, independent variables were selected by the method of predicted residual error sum of squares statistic. The factors used as variables for the stepwise multiple linear regression analysis are described in Table 1. 

All analyses were performed using SAS software (Cary, NC, USA), and the level of significance was set at p＜0. 05 (two-tailed).
section_name: Statistical Analysis

section_content: Among the 123 participating sites in the main J-STARS study, 61 centers had certified sonographers available. From these 61 centers, 941 patients were enrolled in the main J-STARS study, and 864 patients agreed to participate in the J-STARS Echo Study between March 2004 and February 2009 (Fig. 2 ). Among the 864 patients, 71 patients did not undergo ultrasound evaluation. Thus, 793 patients were included in this study [530 men (66. 8%), 66. 4±8. 3 years old]. Of these 793 patients, 388 patients (49%) were assigned to receive pravastatin (pravastatin group), and 405 (51%) did not receive any statins (control group). 

The baseline characteristics of the patients in this substudy and the remaining 796 patients in the J-STARS study were generally similar (Supplementary Table 1 ). Table 1 shows the baseline characteristics of the patients in the pravastatin and control groups enrolled in the J-STARS Echo Study. There were no significant differences between the two groups, except for the baseline National Institutes of Health Stroke Scale (NIHSS) scores: median, 0 (IQR 0-2) vs. 1 (IQR 0-2), respectively (p = 0. 02). 

Overall mean IMT was 0. 89±0. 15 mm: 0. 89± 0. 15 mm in the pravastatin group and 0. 89±0. 15 IMT is automatically calculated using a computer-assisted measurement system (IntimaScope; Mediacross, Tokyo, Japan). T-chol: total cholesterol; HDL-chol: high density lipoprotein cholesterol; LDL-chol: low density lipoprotein cholesterol; TG: triglyceride; FBS: fasting blood sugar § Size of infarction: small was defined as lesion within a diameter of 1. 5 cm, large was defined as a lesion more than half of the cerebral lobe. Medium was defined as between small and large. 2 ). 

Table 3 shows relationships between baseline IMT and potentially associated factors in univariate analysis. Women, patients aged 65 years or older, category of blood pressure, hypertension, DM, smoking habit, HDL cholesterol less than 50 mg/ml, chronic kidney disease, and carotid bruit were positively associated with mean IMT. Stepwise multiple linear regression analysis included those factors that had differences in the univariate analysis. Age (per 10 years) (p＜0. 001), smoking habit (p = 0. 004), category of blood pressure (p = 0. 006), HDL cholesterol (per 10 mg/dl) (p = 0. 008), and DM (p = 0. 010) were selected and significantly associated with mean IMT (Table 4 ). 

Similarly, women, patients aged 65 years or older, hypertension, DM, smoking habit, and HDL cholesterol less than 50 mg/ml were positively associated with maximum IMT in the univariate analysis. Age (per 10 years) (p＜0. 001), smoking habit (p = Size of infarction: Small was defined as a lesion within a diameter of 1. 5 cm, large was defined as a lesion more than half of a cerebral lobe. Medium was defined between small and large. § ACA, anterior cerebral artery; MCA, middle cerebral artery; PCA, posterior cerebral artery; VB, vertebrobasilar artery 0. 001), DM (p = 0. 002), and HDL cholesterol (p = 0. 036) were selected and significantly associated with maximum IMT in the stepwise multiple linear regression analysis (Table 5 ).
section_name: Results

section_content: The J-STARS Echo Study enrolled the largest sample size in Asia to assess the relationship between IMT progression and statin use, comparable to previous trials from Western countries. Baseline characteristics and contributing factors to the baseline mean and maximum IMTs were assessed in Japanese noncardioembolic stroke patients. Age, smoking habit, category of blood pressure, DM, and HDL cholesterol were independently related to the baseline mean IMT, and they were also related to the baseline maximum IMT, except for category of blood pressure. 

Carotid IMT has been used to define atherosclerosis in a number of recent clinical trials for cardiovascular diseases and stroke. The relationship between IMT and statin use has been assessed in many studies and trials from Western countries, but there are few trials, with a small number of patients, from Asian countries. The Stroke Prevention by Aggressive Reduc-tion in Cholesterol Levels (SPARCL) trial is the largest study, including 4731 patients who had a stroke or transient ischemic attack, which showed the effect of statin use on reduction in the risk of stroke. However, the SPARCL trial did not include carotid IMT as a clinical outcome 14). The present study included the largest sample size of noncardioembolic stroke patients, examining the effect of statin on the progression of carotid IMT. 

The Japanese population has been reported to have thinner carotid IMTs than Western populations, probably due to the differences in the lifetime period levels of obesity through adipocytokines or certain levels of inflammation through lipoprotein distribution, rather than differences in genetic factors [15] [16] [17] [18] [19]. K reans and Japanese Americans have been found to have thicker IMTs than native Japanese, and this might explain such risk factors, rather than genetic factors, contributing to carotid IMT 15, 20). Supplementary Tables 2 and 3 show previous trials that reported the association between IM and statin use 6, 7, [21] [22] [23] [24] [25] [26]. Interestingly, the baseline mean and maximum IMTs in the present study were similar to those from previous trials that examined the effects of statin therapy in Western and Asian countries (Supplementary Table 2 ). Because this study focused on patients with a history of ischemic stroke and they had a high prevalence of atherosclerotic risk factors, such as aging, high blood pressure, and DM (Supplementary Table 3 ), carotid IMT assessed in the present study may be higher than that in other non-stroke-related Japanese populations 20, 27). 

Age, smoking habit, category of blood pressure, DM, and HDL cholesterol were independently associated with mean IMT. These factors have been previously reported as atherosclerotic risk factors and have been strongly related to carotid IMT and atherothrombotic ischemic stroke [28] [29] [30] [31] [32] [33] [34]. H wever, the factors related to maximum IMT were somewhat different from those related to mean IMT in the present study; category of blood pressure was not significantly related to maximum IMT. This result may be due to different phenotypes of the atherosclerotic process between mean and maximum IMTs 35). Mean IMT reflects the hypertensive hypertrophic response of the medial cells, which seems to be related to changes in local shear stress, and represents a part of arterial remodeling that occurs at the early stage of atherosclerosis [36] [37] [38] [39], whereas maximum IMT often reflects plaques that mainly occur in the intima (endothelial cell, basal lamina, and subendothelial matrix), which represent the late stage of arteriosclerotic change related to inflammation, oxidation, endothelial dysfunction, and smooth muscle cell proliferation 40). Given this pathophysiological difference, hypertension may not have a significant influence on maximum IMT. 

LDL cholesterol, a well-known atherosclerotic risk factor 41, 42), was not significantly associated with mean and maximum IMTs in the present study, probably because enrolled patients had a limited range of total cholesterol (4. 65-6. 21 mmol/L) and relatively low LDL cholesterol levels compared with those in other trials (Supplementary Table 3 ). Recently, the ratio of LDL cholesterol/HDL cholesterol was indicated as a risk factor for atherosclerosis 43). Further multivariable analyses with this ratio, instead of LDL cholesterol and HDL cholesterol, showed that this ratio was independently associated with both mean and maximum IMTs in this cohort (Supplementary Tables 4 and 5 ). 

One of the limitations of this trial is that all enrolled patients for the main J-STARS trial were not randomized to the J-STARS Echo Study, because only patients from institutes that had certified sonographers were enrolled. However, baseline characteristics of enrolled patients in the J-STARS Echo Study were almost similar to those of non-enrolled patients (Supplementary Table 1 ). The relatively low statin dosage in this trial, compared with the dosage used world-wide, may also be a limitation. High-dose statin use is known to strongly suppress inflammation-related atherosclerotic factors, but there is still controversy regarding its efficacy and safety because of the small number of randomized, controlled trials involving statins 44). 

Because there are scarce data regarding the relationship between IMT and statin use in patients with prior ischemic stroke, we examined this relationship in a large sample of Japanese noncardioembolic stroke patients. From this baseline data analyses, we showed factors associated with baseline IMTs and the similarity of baseline characteristics and IMTs between the pravastatin and control groups. We will examine the effect of the associated factors, such as age, smoking, category of blood pressure, HDL cholesterol, and DM, on the change in IMTs over 5 years of follow-up. Further observation of the relationship between statin use and sequential changes in IMT over 5 years will be conducted.
section_name: Discussion

section_content: In the Japanese stroke patients recruited for the J-STARS Echo Study, the overall mean and maximum IMTs were 0. 89±0. 15 mm and 1. 19±0. 32 mm, respectively. Age, smoking, hypertension, HDL cholesterol, and DM were associated with mean IMT, and those, except for hypertension, were associated with maximum IMT. GL, Wolfson SK Jr. Carotid-artery intima and media thickness as a risk factor for myocardial infarction and stroke in older adults. N Engl J Med. 1999; 340: 14 T-chol: total cholesterol, HDL-chol: high density lipoprotein cholesterol, LDL-chol: low density lipoprotein cholesterol, TG: triglyceride, FBS: fasting blood sugar ‡ Size of infarction: small was defined as lesion within diameter 1. 5 cm, large was defined as lesion more than half of cerebral lobe. Medium was defined as between small and large.
section_name: Conclusion

section_name: Acknowledgments

section_content: We would like to thank the patients and their families involved in the present study, and we also appreciate the other study participants, physicians, supporting medical staff, and coworkers for their assistance in the preparation and execution of this study. The authors thank Mr. Hideki Kono and Ms. Yoko Nakagawa ( Foundation for Biomedical Research and Innovation Translational Research Informatics Center) for their statistical analysis support, Drs. Tatsuo Kohriyama, Setsuro Ibayashi, and Manabu Inoue for their valuable advice, and Ms. Kie Yamaguchi ( Clinical Research Nurses at the National Cerebral and Cardiovascular Center ) for ultrasound assessments.
section_name: Acknowledgments

section_content: on behalf of the Japan Statin Treatment Against Recurrent Stroke (J-STARS) Echo Study Collaborators

section_name: Sources of Funding

section_content: The present study was supported by a grant from the Ministry of Health, Labour and Welfare of Japan. After the period of governmental support expired, the study was conducted in collaboration with Hiroshima University Medical School and the Foundation of Bio- Beishiuizen, ED 14 METEOR 13 JART 15 Kim, KH 16 Ishigaki, Y
section_name: Sources of Funding