INTRODUCTION
The left atrium (LA) used to be regarded as a simple conduit chamber;
however, LA structure and function are directly related to left
ventricular (LV) filling pressure. Speckle-tracking echocardiography
provides measurements of the deformation of all cardiac chambers over
time and has been used for over a decade to measure LA strain and strain
rate (S/SR) (1). LA strain has been shown to reflect different stages of
atrial function which can be described as LA peak longitudinal
shortening during atrial contraction (PACS), atrial conduit strain
(ACS), and total strain (ATS) (or reservoir strain) reflecting the sum
of the passive (ACS) and active (PACS) shortening of the atrial wall
during the cardiac cycle (2). Atrial strain has been associated with
elevated filling pressures (3-5) possibly indicating diastolic
dysfunction (6, 7), heart failure with preserved ejection fraction
(HFpEF) (8, 9), the clinical prognosis of different cardiovascular
diseases (10, 11), and the prediction of new-onset atrial fibrillation
(AF) (3, 4, 12). Normal LA S/SR values have been established in previous
meta-analyses (13) and large population-based studies (14, 15).
NT-proBNP is a well-established marker of LV filling pressure (16).
Noninvasive assessment of diastolic dysfunction, especially in HFpEF, is
challenging; therefore, NT-proBNP and echocardiography are the only
available screening methods for assessing increased diastolic pressure
parameters in heart failure diagnostics.
There are multiple parameters from different echocardiographic
modalities indicating elevated filling pressures, where all single
measures seem to be suboptimal and only the combination of several
parameters is an acceptable indicator. Some studies have shown promising
results using LA S/SR for the detection of high filling pressures and
NT-proBNP (5, 10).
The 2016 guidelines for the assessment of LV diastolic function have not
yet mentioned LA S/SR; however, although they recommend combining
different echocardiographic parameters, the sensitivity and specificity
were rather low, especially in inconclusive cases. The first artificial
intelligence (AI)- based studies on echocardiographic strain-based
parameters (17, 18) supported the inclusion of LA S/SR in a combined
approach for the assessment of cardiovascular risk and showed
significant improvement by including these parameters.
This study aimed to to determine the normal ranges for speckle-tracking
imaging-derived atrial S/SR and LA stiffness index (LASI) based on two
population studies from Norway and Russia and investigate whether LA
S/SR parameters, including LASI, render incremental values in addition
to conventional echocardiographic parameters to detect elevated
NT-proBNP in the general population. According to the 2016
recommendations (19), the study population was divided into normal,
reduced, and AF groups.