Statistical Analysis
Statistical analysis was performed using SPSS version 23 (IBM Corp.,
USA). Quantitative variables were expressed as means ± standard
deviation (SD) or medians and Interquartile Range [IQR, (25th
percentile, 75th percentile)]. Categorical variables were reported as
numbers and percentages. Preoperative, intraoperative and postoperative
patients’ characteristics were analyzed descriptively and compared among
cohorts with between-cohort differences assess using chi-squared tests
or Fisher’s exact test for categorical variables and Wilcoxon rank-sum
tests for the continuous variables both before and after matching.
Propensity score matching was then used to mitigate underlying
differences in covariates between the cohorts, and a multivariable
logistic regression was used to build the propensity score model. Module
of Propensity score matching for SPSS (Version 3.0.4) was used. All
variables were retained in formulating the propensity score regardless
of statistical significance because they were believed to be clinically
relevant. Upon the estimation of propensity score, a greedy matching
algorithm matched the LVD cohort to NLVF cohort 1:2. To ensure pairs
were precisely matched on important covariates, the following variables
were exact-matched: age groups (<60 years vs ≥60 years) and
gender. Only patients with complete data sets were used in the creation
of the propensity score.
Kaplan-Meier analysis was then used to estimate time to all cause death
and cardio-death in LVD cohort versus NLVF cohort. To account for
pairing, between-cohort differences were assed using partial likelihood
ratio tests. Next, the number and proportion of patients who experienced
major cardiovascular disease within the follow up period was estimated,
and between-cohort differences were calculated using McNemar’s test.
Multivariable Cox proportional hazard regression analysis was used to
quantify the relative risk of mid-term mortality in the LVD cohort
versus the NLVF cohort, controlling for covariates and stratified by
matched pairs. Statistical significance was accepted as a two-sided test
with an alpha level of 0.05.