Statistical analysis
The continuous variables are expressed as mean values ± SD. The intra-
and inter-observer reproducibility of the LA strain measures were
evaluated in 20 patients by two operators (M.I., N.D.) by means of the
intraclass correlation coefficient (ICC), which measures the strength of
the association between the two baseline recordings. The data were
considered reproducible if the ICC was >0.60, and the
reproducibility was considered almost perfect if the ICC was between
0.81 and 1.00 [10].
Pearson’s linear correlations were used to assess the relationship
between atrial strain measures and the other variables studied. Cox’s
proportional hazard model was used to verify the associations between
the variables and the endpoints. Hazard ratios (HRs) are given with
their 95% confidence intervals (CIs) and refer to a unit increase in
the variable. The variables used in the forward stepwise multivariable
models were selected based on their statistical significance during
univariate analysis and the most relevant risk parameters for HF
patients. Discrimination of the univariate and multivariate models was
determined using a modified concordance statistic (C-index) for censored
data.
Receiver operating characteristic (ROC) curves and the area under the
curve (AUC) of the ROC were calculated to determine the associations
between the studied variables and 1-year events. The best cut-off values
for the analysed events were defined based on the highest sum of
sensitivity and specificity. The event-free curves were based on
Kaplan–Meier analysis stratified by the best cut-offs of LASr and
LASr/Ees and were compared using a log-rank test. The proportional
hazards assumption was formally assessed. Statistical analyses were
performed using STATA, version 12 (StataCorp, College Station, Texas,
USA), or Statistica 6.1 (StatSoft Inc., Tulsa, Oklahoma, USA).P -values <0.05 were considered statistically
significant.