2.4 | Statistical Analysis
Categorical variables were expressed as absolute numbers and percentages and continuous variables were expressed as mean (standard deviation (SD)) or median ( (IQR) depending on the distribution. Kolmogorov-Smirnov test was used to access the normal distribution.
The pre-operative variables were selected a priori (not a stepwise method): age, gender, obesity, hypertension, Diabetes Mellitus (DM), smoking (included ex-smokers), New York Heart Association (NYHA) III/IV, Left ventricular ejection fraction (LVEF) <40%, peripheral vascular disease, creatinine clearance (CreatCl), respiratory disease, gastrointestinal disease, previous valvular surgery, sPAP and atrial fibrillation. Categorical variables were compared using χ2 test. Normal distributed continuous variables were compared with Student’s T-test and Levene’s test for variance equality assessment. Mann–Whitney U-test was used for independent samples not normally distributed.
Variables with a univariate p <0.05 were included in the Multivariable Cox Proportional Hazards Regression and Logistic Regression models to identify risk factors for in-hospital mortality, in-hospital morbidity and follow-up mortality. Long-term survival was estimated using the Kaplan-Meier method. A probability value of p<0.05 was considered statistically significant. All analyses were performed using IBM SPSS Statistics for Windows, Version 22.0. (IBM Corp. Armonk, NY)