Statistical analysis
The data are expressed as median (interquartile range). Survival
probabilities were evaluated using the Kaplan-Meier method. The
Mann–Whitney U-test was used to compare continuous variables between
the PVO and non-PVO groups; an effect size greater than 0.50 was
considered a large difference. The χ2 test was used to compare the
categorical data between the two groups. The overall accuracy of the
potential variables in predicting postoperative PVO was summarized using
the area under the receiver operating characteristic (AUROC) curves. The
optimal cut-off values of the postoperative V-A angle and ratio to
predict postoperative PVO were determined by the Youden index.
Differences were considered statistically significant if the P-value was
<0.05. All data were analyzed using IBM SPSS Statistics,
Version 24.0 (IBM Corp, Armonk, NY).