CYP2C19 genotyping

CYP2C19 genotype was measured in all study patients. A peripheral venous blood sample was obtained before the operation. Genomic DNA was extracted from whole blood using the DNA Extractor kit (Tiangen, Beijing, China). Polymerase chain reaction-restriction fragment length polymorphisms for CYP2C19*2 (681G>A) and CYP2C19*3 (636G>A) were performed as previously described. CYP2C19 genotypes were classified into three phenotypes: (I) extensive metabolizer (EM) carrying normal function alleles (CYP2C19*1/*1); (II) intermediate metabolizer (IM) carrying one loss-of-function allele (*1/*2, *1/*3); (III) poor metabolizer (PM) carrying two loss-of-function alleles (*2/*2, *2/*3, *3/*3).

Sample size: according to previous studies, aspirin plus Ticagrelor has a venous graft occlusion rate of 13% one year after surgery. As for aspirin plus Clopidogrel, the rate is 3.7%. We found that a 5% difference between 2 arms can be reliably detected under a power of 80%, if we have 170 venous grafts in each arm (significance level =0.05).