IJCS | Volume 32, Nº2, March/April 2019

165 Lei & Bin Differences of risk factors in young AMI patients Int J Cardiovasc Sci. 2019;32(2)163-176 Review Article Results We retrieved 781 citations from the initial search and excluded 525 studies that did not meet the inclusion criteria; subsequently, we excluded 200 articles based on the initial abstract review. Afterwards, we excluded 46 articles through full-text review, and finally 8 eligible studies 10-17 were selected for the meta-analysis (figure 1). The assessed 13,358 patients included 1,122 young AMI patients and 4,766 older AMI patients. Table 1 shows the general characteristics of these selected studies. Bias risk assessment According to the Cochrane Risk of Bias Tool for Randomized Controlled Trials, 8 selected studies had different bias risks. All eight studies referred to “randomized controlled trial”, but no detailed description was mentioned in these studies. All 8 studies reported the outcome completelywithout selective reporting. None of the studies reported blinding and allocation concealment. One study 13 had a selection bias, and two studies 12,15 might have other bias. According to bias risk graph (figure 2) and bias risk summary (figure3), Yunyun et al. 12 , Chua et al. 15 and Anderson et al. 13 had high risk, while the other studies 10,11,14,16,17 had a relatively low risk. Meta-analysis outcome Risk factors Eight studies10-17 compared smoking (figure 4) in young and older AMI patients. The studies showed high heterogeneity (p < 0.001, I 2 =85%), thus the random- effect model was used to perform the statistical analysis. Significant differences were observed in the outcome (OR = 2.71, 95%CI: 1.87 to 3.92). The rate of smoking in young AMI patients was much higher than that in older AMI patients (71.51% vs 40.43%). Six studies 10-12,14,16,17 compared a family history of CAD in young and older AMI patients (figure 4), and the studies showed high heterogeneity (p < 0.001, I 2 = 89%), and thus the random- effect model was used to perform the analysis. Significant differences were observed between the two groups (OR = 2.36, 95%CI: 1.22 to 4.59) and young AMI patients had a higher rate of family history of CAD than older AMI patients (43.48% vs 28.27%). Five studies 10,13-15,17 compared obesity (figure 4) between young and older AMI patients. The studies showed heterogeneity (p = 0.0002, I 2 = 82%), and so the random-effect model was used to perform the analysis. There were significant differences in the outcome (OR = 1.76, 95% CI: 1.13 to 2.74), and the rate of obesity in young AMI patients was higher than that in older AMI patients (36.21%vs 31.95%). Only three studies 11,12,16 compared alcohol consumption in young and older AMI patients (figure 4). The studies showed heterogeneity (p = 0.10, I 2 = 56%), and thus random-effect model was used to perform the analysis. Significant differences were observed in the outcome (OR = 1.76, 95% CI: 1.04 to 2.97); young AMI patients showed a much higher rate of alcohol consumption than older AMI patients (34.16% vs 24.97%). Eight studies10-17 compared hypertension in the two groups (figure 4). The studies showed heterogeneity (p < 0.001, I 2 = 83%), and thus random-effect model we was used to perform the analysis. Significant differences were observed in the outcome (OR = 0.52, 95%CI: 0.37 to 0.73), the rate of hypertension in young AMI patients was lower than that in older AMI patients (34.48% vs 51.2%). Eight studies 10-17 compared diabetes mellitus between the two groups; low heterogeneity was observed in the studies (p = 0.52, I 2 = 0%), and thus the fixed-effect model was used to perform the statistical analysis. Significant differences were observed between the two groups (OR = 0.58, 95%CI: 0.50 to 0.67), and young AMI patients had a lower diabetes mellitus incidence than older AMI patients (17.02% vs. 24.9%). Four studies 11,13-15 compared hyperlipidemia (figure 4) between young and older AMI patients. The studies showed high heterogeneity (p < 0.001, I 2 = 94%) and, therefore, the random-effect model was used to perform the analysis. The outcome showed no significant differences between the two groups (p = 0.45). Then, we performed a subgroup data analysis (figure 5), comparing serum levels of TC, LDL, TG and HDL between the two groups. The random-effect model was used to perform the analysis. We found that young AMI patients had comparatively higher levels of serum TG (p = 0.01), LDL (p = 0.001), TC (p = 0.002) and lower levels of serumHDL (p = 0.008) than older AMI patients. Clinical characteristics Three studies 13,14,17 compared LVEF values in young and older AMI patients (figure 6) and low heterogeneity was observed regarding the outcome (p = 0.43, I 2 = 0%) and thus, the fixed-effect model was used to perform the