STATISTICAL ANALYSIS.
Continuous variables were expressed as mean ± SD. Categoric variables were described as number and percentage. For comparison 2 normally distributed variables, Student t test for continuous variables and chi-squared test for categorical variables were used. The analysis was adjusted for age and sex.
In order to evaluate diastolic parameters that could serve as early markers of cardiovascular outcome, several statistical analyses were performed. The following Cox regression models were constructed: a) a univariate model with all the variables of interest collected; b) a multivariate model including parameters currently used to indicate surgery (LVEDV, LVESV and LVEF) and the most relevant conventional diastolic function parameters that were statistically associated with the composite endpoint in the univariate analysis (E, E/e´ ratio and LA volume; SPAP was excluded in the analysis because its echocardiographic evaluation was only possible in 39 patients). The backward elimination method was used for selection of covariates; c) for the subgroup of patients with TTE performed in a Philips station, a second multivariate model, including the significant variables in the previous model and LA strain, was constructed. LASr was the LA strain parameter used for the analysis for being the strongest LA strain parameter available with more reliable scientific evidence.
Area under the receiver-operating characteristic curve (AUC) was used to evaluate LASr accuracy to predict cardiovascular events. The Kaplan-Meier survival curves for patients above and below the median value of LASr were performed to summarize the follow-up experience of the study population. Interaction was studied. This was a hypothesis-generating and exploratory study; therefore, no formal sample size calculation was performed in advance.
The statistical analyses were performed using SPSS software version 26.0 (SPSS Inc, Chicago, Illinois, United States) and R version 3.3.2.