S/SR analysis
For LA and LV S/SR, a single reader (M.K.) analyzed the 2D apical four-
and two-chamber and apical long-axis (APLAX) views with speckle tracking
using the Q-analysis function of EchoPAC (v.203, GE-Vingmed AS, Horten,
Norway). The LV S/SR from APLAX views was analyzed in 176 Tromsø7
participants and the global S/SR was derived from the four- and two-
chamber views only.
Cycles for LV strain analysis were set to start at peak R, whereas the
cycle for atrial contraction was defined as the end of the P-wave. In
AF, peak R was defined as the onset of the cardiac cycle. Aortic valve
closure was defined by using a transaortic CW Doppler signal. For atrial
and ventricular measurements, the region of interest (ROI) was manually
traced at the subendocardial border, with consecutive adjustments in the
ROI width. Automated tracking was visually controlled and suboptimal
tracking results were repeated a maximum of three times. For LV and LA
strains, segmental values were extracted from longitudinal
mid-myocardial strain curves averaged over the number of segments. The
LV strain was measured at the time of ES. As shown in Figure 2, the LA
S/SR was measured from the global strain curves derived from the strain
and SR curves of all six segments of the four-chamber view. As the
Q-analysis function did not provide all peak atrial S/SR measurements
for the defined time periods, the results were automatically extracted
from the strain curves using customized software. Although atrial
strains reflect longitudinal shortening and should be expressed as
negative values, there appears to be a general consensus on reporting
atrial longitudinal strain values as positive numbers. LA strain was
measured in three defined time periods: peak atrial contraction strain
(PACS) between the onset of atrial contraction and peak negative strain;
ATS, defined as the difference between the negative and positive peaks;
and ACS, defined as the difference between the positive peak and the
onset of atrial contraction. In the LA and LV, diastolic SR E was
measured at peak SR after AVC and before the onset of the atrial
contraction, SR during atrial contraction (A) was the SR peak after the
onset of the atrial contraction, and systolic SR during systole (S) was
the peak in the opposite direction between the start of the cycle and
AVC. Tissue Doppler velocities from the septum and lateral wall were
derived from basal segmental speckle tracking analyses, which were
chosen to overcome the differences between the two study populations in
terms of tissue Doppler acquisitions with different ultrasound systems
and machine settings. Mitral E/e´ was calculated from the MV E and the
average basal and lateral four-chamber e’ was calculated from the basal
speckle tracking-derived velocities. LASI was calculated as the ratio of
the E/e´ and ATS, where e´ was derived from the basal velocities of the
septum and lateral wall in the four-chamber view.
Statistical analyses
Statistical analyses were performed using IBM SPSS version 28.0. (IBM
Corp: Armonk, NY, US). The two groups were compared using either the
t-test or χ2 test for continuous and categorical variables,
respectively. Unless otherwise stated, continuous variables are
presented as means ± standard deviations (SD). Variables with skewed
distributions are presented as medians with quartiles (Q1/Q3).
Categorical characteristics are presented as absolute numbers and
proportions (%). For comparison between the three groups with EF more
than or equal to 50% (EF≥50%), EF less than 50% (EF<50%),
and AF, group differences in continuous variables were tested using
one-way analysis of variance (ANOVA) with Bonferroni post-hoc tests.
For the independent and dependent correlations of echocardiographic
indices with the presence of elevated NT-proBNP levels, univariate and
multivariate logistic regression analyses were performed. Variables with
a p-value of less than or equal to 0.20 in the univariate analysis were
selected and tested by forward and backward multivariate logistic
regression analysis. For final inclusion in the multiple regression
model, a p-value of less than or equal to 0.05 was considered
statistically significant. Independent predictors of the multivariate
analysis were combined as weighted predictors and a receiver operating
characteristic (ROC) curve analysis was performed.
Intra- and interobserver variability
For intra-and inter-observer variability in atrial S/SR measurements,
the same observer repeatedly analyzed 45 randomly selected
echocardiographic records. The same data was reanalyzed by a second
experienced observer. Intra- and inter-observer values were calculated
as intraclass correlations and 95% confidence intervals (CIs).