Statistical Analysis
Statistical analysis was performed using SPSS Statistics 25.0 (IBM SPSS
Statistics for Windows, Version 25.0, Armonk, NY).
Since both surgical procedures were performed consecutively over time
yielding only a limited time overlap during the learning phase of MIVT,
this study is inherently biased. Therefore, a propensity-score matched
analysis with a tolerance of 0.05 and without replacement was executed
for the patient characteristics having a baseline significant
difference. Adjustment was performed for differences in preoperative
NYHA class and previous cardiac surgery to match both study groups.
Data distribution is verified for normality by the Shapiro-Wilk test.
Categorical variables are expressed by number and percentage. Continuous
variables are noted as mean and standard deviation or as median and
interquartile range, depending on the distribution normality of the
data. Categorical variables were compared between groups by Chi-square
or Fisher’s exact test. Comparison of continuous data was done by the
unpaired t-test or Mann-Whitney U-test.
To examine significant between-group differences in biomarker evolution
over time points, an repeated ANOVA-analysis was used. Significance was
based on Wilk’s-Lambda or Greenfeld-Houser testing depending on
Mauchly’s sphericity preservation of the data. Survival analysis was
performed by the Kaplan–Meier estimation method with log-rank testing
of the difference between both procedures. All tests were performed
2-tailed and considered as statistically significant for a p-value
< 0.05.