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.