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.