In this observational study, we consecutively collected young patients (18-35 years of age), diagnosed with CAD and underwent coronary angiography (CAG) at Anzhen Hospital between January 2013 and May 2020. The exclusion criteria were as follows: repeated hospitalization, missing homocysteine data, and smoking cessation for more than1 year. Patients with severe renal insufficiency, hypothyroidism, psoriasis, multiple arteritis, Kawasaki disease, rheumatic heart disease, myocarditis, infective endocarditis, congenital heart disease, cardiomyopathy, valvular heart disease, or having vitamin or folate supplementation within three months were also excluded. This study was approved by the Institutional Ethics Committee of Beijing Anzhen Hospital. The demographic and clinical data we used were retrospectively obtained from electronic medical records.
Definitions and Grouping
Serum levels of Hcy >15umol/L was defined as HHcy . Occasional or regular smoking≥1cig/day was defined as smoking status, which also included former smokers with cessation period ≤ 1 year . Pack-years of smoking was defined as the average number of packs of cigarettes smoked per day multiplying the number of years of smoking. Hypertension was defined as a systolic blood pressure (SBP) ≥140mmHg and/or diastolic blood pressure (DBP) ≥ 90mmHg, or using antihypertensive medications currently . Diabetic mellitus (DM) was defined as fasting blood glucose (FBG) ≥7.0 mmol/L and/or random glucose level ≥11.1mmol/L, or previously diagnosed DM with the treatment of diet, oral agents, or insulin . Hypertriglyceridemia was defined as triglycerides (TG)≥1.7mmol/L, hypercholesterolemia was defined as total cholesterol (TC) ≥5.2mmol/L, a high low-density lipoprotein cholesterol (LDL-C) level was defined as LDL-C≥3.4mmol/L, and a low high-density lipoprotein cholesterol (HDL-C) level was defined as HDL-C<1.0mmol/L . Serum uric acid (UA) level ≥420mmol/L in males and ≥357mmol/L in females was considered to be hyperuricemia . Someone with average alcohol intake ≥50g/day was considered to be drinker.
The study population was divided into four groups according to presence or absence of HHcy and smoking status, which were as follows: HHcy-Smoker- group, HHcy+Smoker- group, HHcy-Smoker+ group and HHcy+Smoker+ group.
All patients received coronary angiography using a standard technique. A luminal diameter stenosis ≥ 50% in any of the major coronary arteries, including the left main, left circumflex, left anterior descending, right coronary artery, and main branches with a diameter of more than 2.0mm, was defined as CAD. In addition, patients who diagnosed as acute myocardial infraction were also considered to have CAD. Left main stenosis≥50% was considered as a double-vessel disease. Multivessel disease was defined as ≥ 50% stenosis in more than one major coronary vessels. Gensini Score was used to quantify the severity of CAD . Based on the results of CAG, the score of each lesion was calculated by severity score, which reflected the stenosis degree of luminal narrowing and modified by the collateral adjustment factor, multiplying region factor, which reflected the geographic importance of the lesion location in the coronary tree. The final Gensini Score was expressed as the sum of all the lesion scores.
Baseline venous blood samples were taken from all participants after an overnight fast within the first 24h of hospitalization. The following biochemical parameters were analyzed: TG, TC, LDL-C, HDL-C, UA, blood urea nitrogen (BUN), creatinine (CR), glycated hemoglobin (HbA1c) and high-sensitivity C- reactive protein (hs-CRP). Hcy commercial kit (enzymatic cycling method) was used to test serum Hcy levels by a Beckman Coulter AU5400 automatic biochemical analyzer.
The clinical data of participants, including age, gender, body mass index (BMI), history of hypertension and DM, family history of CAD as well as smoking and drinking status, were retrospectively obtained from electronic medical records.
All the analysis was conducted by the statistical software SPSS 22.0 (IBM-SPSS Inc., Chicago, USA). Kolmogorov-Smirnov test was used to evaluate the normality of continuous data. Accordingly, normally distributed continuous variables were presented as mean ± standard deviation, and non-normally distributed data as median [interquartile (25th–75th percentiles) range]. Where indicated, one-way analysis of variance and Kruskal–Wallis H test were applied to evaluate statistical differences among groups with different Hcy levels and smoking status. Then, pairwise comparison was performed among groups using S-N-K test or Mann-Whitney U test. Categorical variables were expressed as counts and percentages (%), and differences among these groups were examined by Chi-square test. The relationship between serum Hcy levels and pack-years of smoking was evaluated using Spearman analysis. Multivariate liner regression analysis was performed to determine the effect of variables on the severity of CAD, which was calculated by Beta with 95% confidence intervals (95% CI). Moreover, the relationship of Hcy, pack-years of smoking and the severity of CAD was also assessed by multivariate linear regression analysis. P values of <0.05 in a two-sided test was considered statistically significant.