This study was approved by the ethic committee of our hospital. The patients with peripheral arterial occlusive disease in lower extremities who were admitted to our hospital between October 2013 and October 2015 were retrospectively reviewed. The inclusion criteria were patients with symptoms of intermittent claudication, rest pain and/or gangrene; peripheral arterial occlusive disease confirmed by duplex sonography, magnetic resonance angiography or digital subtraction angiography during the admission; patients with carotid artery stenosis confirmed by color doppler imaging during the admission. The exclusion criteria were patients with ischemic stroke history, patients with a history of carotid artery disease, patients allergic to contrast agent, patients with combined heart, liver and/or kidney disease, patients with artery stenosis caused by non-arteriosclerosis, and patients with blood coagulation disorder. For diagnosis of lower limb PAOD, all patients underwent duplex sonography, magnetic resonance angiography or digital subtraction angiography. Color doppler imaging was performed to diagnose ACAS and evaluate the plaque characteristics. For the asymptomatic carotid stenosis patients with mild or moderate stenosis, they were firstly managed medically with drug including high-intensity statin, antithrombotic agents and blood pressure control, and lifestyle changes including smoking cessation and low-fat diet.
Detailed baseline data and medical history were retrospectively collected from the medical records, including sex, age and potential risk factors  including coronal heart disease, hypertension, diabetes, hyperlipidaemia, hyperfibrinogenemia, cigarette-smoking and alcohol-beverage drinking history. Risk factors were defined as the following. Coronary heart disease was defined as patients with a relevant medical history and who are receiving relevant/appropriate treatment for this. Hypertension was defined as systolic pressure > 140 mmHg and diastolic pressure > 90 mmHg. The diabetes was defined as plasma glucose level ≥ 7.0 mmol/l (126 mg/dl); plasma glucose ≥11.1 mmol/l (200 mg/dl) 2 h after a 75 g oral glucose load as in a glucose tolerance test; symptoms of high blood sugar and casual plasma glucose ≥11.1 mmol/l (200 mg/dl); glycated hemoglobin (HbA1C) ≥48 mmol/mol. The hyperlipidemia was defined as the total cholesterol > 6.2 mmol/L after 12-14 h fasting. Hyperfibrinogenemia was defined as fibrinogen > 4.0 g/L. Cigarette-smoking was defined as a history of having at least one cigarette a day. Alcohol-beverage drinking was defined as a history of having at least 50 ml alcohol beverage a day.
Lower limb PAOD was classified into stage I-IV according to Fontaine R . Stage I: asymptomatic and incomplete blood vessel obstruction. Stage II: mild claudication pain in limb. Stage IIA: claudication when walking a distance of greater than 200 m. Stage IIB: claudication when walking a distance of less than 200 m. Stage III: rest pain, mostly in the feet. Stage IV: necrosis and/or gangrene of the limb. The patients in stage IIB, III and IV were treated with arterial angioplasty or artificial artery transplantation; the patients in stage IIA were treated with drugs rather than surgery.
The carotid artery stenosis was classified according to Mannheim intima-media thickness consensus . It was considered as arteriosclerotic plaque if the thickness between the media-adventitia interface and the intima-lumen interface was above 1.5 mm. Plaques were further classified as soft plaque, hard plaque, flat plaque and ulcerated plaque, with the first two considered as stable and the last two as unstable plaque according to previous reports [11, 12]. The severity of carotid artery stenosis was classified as mild (stenosis ≤50%) with peak systolic velocities (PSV) =125 cm/s and PSVICA/ PSVCCA ratio < 2.0, moderate (50% < stenosis < 70%) with PSV between 125 and 230 cm/s and PSVICA/ PSVCCA ratio between 2.0 and 4.0, serious (70% ≤ stenosis < 99%) with PSV > 230 cm/s and PSVICA/ PSVCCA ratio > 4.0, and complete occlusion . In this study, the patients with stenosis ≥70% were classified as significant ACAS and patients with stenosis < 70% as non-significant ACAS.
Statistical analysis was performed using SPSS 19.0 (SPSS Inc., Chicago, IL, USA). Data were presented as mean ± SD for continuous variables, and frequencies with percentages for categorical variables. Pearson χ2 test was used for categorical variables in the two cohorts and independent t-test for continuous variables. A binary logistic regression further estimated the odds ratio of the risk factors. P value < 0.05 indicated statistically significant.