RESULTS
The characteristics of the participants are presented in Table 1.
Participants were divided into two groups based on their NT-proBNP
levels being above or below 250 pg/ml with high NT-proBNP levels being
observed in 4.6% of patients in the selected cohort. High NT-proBNP
levels were more prevalent in men and in a high proportion of the
Russian population. Participants with high NT-proBNP levels were
significantly older and had larger weights, body mass indexes, higher
glycosylated hemoglobin levels, creatinine levels, and high-sensitive
C-reactive protein levels. Furthermore, participants with higher
NTproBNP levels displayed a higher percentage of cardiac pathology (by
Hx, echocardiogram, or ECG), whereas the majority (85.3%) of
participants in this group had no cardiac diagnosis; however, 71% were
taking antihypertensive drugs, indicating a high prevalence of
hypertension. Low-density lipoprotein (LDL) and total cholesterol levels
were lower, probably because of the higher prescription rate of
lipid-lowering drugs in this group.
Table 2 presents age- and sex-related normal ranges for atrial strain
and SR values in a selection of 1069 healthy individuals (619 females
and 450 males). ACS, ATS, atrial SR E were significantly dependent on
age and sex, being higher with age and reduced in males. LASI increased
with age and male sex, while PACS SR S and SR A showed no significant
age- and sex-related changes.
Systolic and diastolic conventional and strain derived atrial and
ventricular parameters are listed in Table 3 grouped by EF≥50%,
EF<50% and AF. In each group, we aimed to identify the
indicators of high and low NT-proBNP levels.
In all groups, NT-proBNP was highly correlated with lower atrial S/SR,
higher LASI, some indicators of impaired relaxation such as lower basal
E velocity and LV PL, SR, and E, and indicators of higher filling
pressures such as higher E/e´. The E/A ratio was higher only in the AF
group, and systolic parameters were significantly lower only in the
EF<50% group. In the EF≥50% group, EDV and ESV were
slightly, but insignificantly, reduced, and the LV mass was higher,
indicating the presence of LV hypertrophy in subclinical heart failure
with normal EF.
The mean values and differences between the three groups are shown in
Table S1. Compared with the EF≥50% group, the EF<50% and AF
groups displayed lower atrial and ventricular diastolic S/SR and
velocities. LASI increased with reduced EF and AF, whereas the
Doppler-derived diastolic functional parameters in AF were not
significantly different. However, parameters with one-sided changes
during diastolic dysfunction, like tricuspid regurgitation peak
gradient, E/e´, and LA volume, indicated significant diastolic
dysfunction of the low EF ventricles with AF.
Tables 4, 5, and 6 display univariate and multiple binary logistic
regression analyses for systolic and diastolic echocardiographic
parameters in relation to normal and high NT-proBNP levels for the
EF≥50% (Table 4), EF<50% (Table 5), and AF (Table 6) groups.
In participants with EFs more than or equal to 50% (Table 4),
univariate regression showed a large number of diastolic and systolic
parameters as indicators for the presence of high NT-proBNP levels.
Multiple regression analysis revealed that ATS and MV-DT were the
strongest independent indicators of a normal EF. In the
EF<50% group (Table 5), the results of the univariate
analysis were similar, whereas PACS, LV, and LVESV were independent
indicators of the presence of high NT-proBNP by multiple binary
regression. In the smallest group with AF (Table 6), only univariate
regression was performed because the number of positive cases was too
low for a reliable result in the multiple regression analysis. Similar
to hearts without AF, all atrial S/R parameters and many systolic and
diastolic parameters indicated the presence of high NT-proBNP levels.
Figure 3 shows the ROC curves for both groups with low and normal EF for
the combination of parameters of the multiple regression analyses
discriminating the presence of high NT-proBNP levels. For normal EF, the
combination of parameters did not significantly increase the area under
the curve (AUC), whereas adding PACS to MV DT and ESV significantly
increased the AUC from 0.719 to 0.805. The intra- and interobserver
variability by intra-class correlation shown in Table S2 shows
acceptable to good reproducibility for all atrial S/SR parameters.