Statistical analysis
Statistical analyses were performed using statistical software
STATISTICA(TIBCO Software Inc.2017,version-13.Palo Alto-USA). Continuous
variables were expressed as means±SD, while categorical variables as
numbers and percentages. For continuous data Student’s t-test was used
for in between groups comparisons, while categorical variables were
compared with Pearson-χ2-test. Cox regression models were used to find
the univariable and multivariable predictors of late all-cause
mortality. Multivariable model for the whole cohort was built using
preoperative variables presented in Table-1 in addition to type of
surgery: On-pump-CABG(ONCAB) or off-pump-CABG(OPCAB) and completeness of
revascularization. The multivariable model considered all univariate
significant variables(p <0.1) with using the stepwise
method(backward and forward methods resulted in the same model).
To further confirm the results and to reduce the risk of selection bias
inherent to a retrospective, observational studies, a propensity
score(PS) matching was used to match patients between the
groups(SITA+Vein group vs 2nd-arterial group)and(RITA
group vs RA group). Propensity scores were generated from a
multivariable logistic regression model based on 18-preoperative
variables as mentioned in Table-1. Patients were then matched in 1:1
fashion using a caliper matching method without replacement with a
caliper width of 0.2-standard deviation of the logit of the
PS18-20. The balance of the covariates was tested
using standardized mean difference(SMD). Statistical guidelines suggest
a meaningful covariate balance of the variables used to generate the PS
between the two groups to be between -0.1≤SMD≤
0.118.Matched data were analyzed using procedures for
matched analyses. McNemar’s test was used for binary outcomes.
Survival in the unadjusted and PS adjusted populations were estimated
using the Kaplan-Meier method and were expressed as percentages.
Log-rank test was used to compare the data. Statistical significance was
defined as p- value of<0.05.