DOI: 10.6084/m9.figshare.7409606.v1
title: A score to predict the occurrence of very late stent thrombosis in patients treated by percutaneous coronary intervention for acute coronary syndrome

description: <b>Study population</b> From January 1, 2014 to June 1, 2015, a total of 6,038 consecutive ACS patients who were admitted to Jilin University 1<sup>st</sup> hospital for PCI treatment and met the basic inclusion and exclusion criteria were enrolled . The primary endpoint was definite stent thrombosis. We exclude patients who died prior to discharge (n=236), did not agree to take part in the follow-up interview (n=413), or were lost to follow-up after discharge (n=204). The median length of follow-up was 1,502 days. The external validation cohort included 2,438 consecutive patients admitted to the first affiliated hospital of Shantou University for PCI from January 1, 2014 to January 1, 2015 with the same inclusion and exclusion criteria. We exclude patients who died prior to discharge (n=88), did not agree to take part in the follow-up interview (n=186), or were lost to follow-up after discharge (n=106). The median length of follow-up was 1422 days. Ethics committee approval was obtained for all investigational sites, and the study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. All patients gave written informed consent. <b>Definition of VLST</b> VLST was defined according to the 2007 definition of Academic Research Consortium (ARC) stent thrombosis criteria: stent thrombosis that occured more than one year after coronary stent implantation and was clearly confirmed by coronary angiography (CAG). <b>Statistical Analysis</b> Data are summarized as number (percentages) for categorical variables. Continuous variables are expressed as mean±SD. Categorical data were compared using the Chi-square test or Fisher exact tests while quantitative data were compared using the Mann–Whitney U test. All tests were 2-sided at the 0.05 significance level. The derivation cohort was used to identify predictors of occurrence of VLST and to establish a risk-scoring system which was verified in the validation cohort. The significant variables (p&lt;0.05) in univariable cox regression analysis and independent risk factors reported in previous literature were included in the multivariate cox regression analysis, and the optimal predictive variables of VLST were obtained by backward stepwise method. Some variables, such as leukocyte count (there is no sufficient evidence to completely exclude the possibility of infection and other factors that leading to its increase) are not included in the final model. Procedural variables such as stent diameter, length, type, and post-dilation were based on the operator's consideration during PCI. Multicollinearity between the variables in the final model was assessed by calculation of the variance inflation factor. These corrected coefficients of significant predictors in the final model were then divided by the lowest coefficient value and rounded to the nearest integer to assign a weight to each predictor. Total score of each patient was calculated by adding these weights together. An objective assessment of calibration was obtained by performing the Hosmer–Lemeshow goodness-of-fit test and by plotting observed vs. predicted incidence rate across deciles of risk score. The predictive performance of the risk model was assessed by the c-statistic and was cross-validated (leave one out method) in the development cohort. Clinical usefulness was evaluated using decision curve analysis. Statistical analysis was performed with the use of Statistical Package for Social Sciences version 23 (SPSS, Chicago, IL, USA) and R version 3.5.0 (R Foundation for Statistical Computing, Vienna, Austria) using the packages rms.