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.