Statistical Analysis
Data were collected and analyzed using SPSS® (version 24) and R (version
3.5.1). Continuous variables were expressed as mean ± standard
deviation, and categorical variables were expressed as frequency and
percentages. Differences among continuous variables for two groups
(patients with RAVI/LAVI above or below the median) was assessed using a
two-sample t-test, and analysis of variance was used to assess
differences in continuous variables among more than two groups (patients
in different quartiles of RAVI/LAVI). Chi-squared tests were used to
assess differences among categorical variables. A p-value
<0.05 was considered statistically significant.
Kaplan Meier curves were used to assess the differences in time to
survival with stratification based on either the median value of
RAVI/LAVI or quartiles of RAVI/LAVI. The proportional hazards assumption
was confirmed by visual inspection of the survival curves, and the log
rank test was utilized to test whether there was a significant
difference between groups with the proportional hazards assumption met.
The Breslow-Wilcoxon method was considered as an alternative if the
proportional hazards assumption had not been confirmed.
A multivariable Cox proportional hazards model was used to examine the
association of RAVI/LAVI with death or implantation of LVAD. An alpha
value of less than 0.05 was used for statistical significance.
Intraobserver variability among measurements was assessed in 113
patients using the intraclass correlation coefficient. Bland-Altman
plots were constructed for both RAVI and LAVI.