Left atrial function: pathophysiology, echocardiographic assessment, and clinical applications

Abstract

This article describes the pathophysiology of left atrial mechanical function and discusses both conventional and new echocardiographic parameters used to evaluate left atrial function. The evidence regarding the clinical usefulness of left atrial function assessment is also presented. PATHOPHYSIOLOGY OF LEFT ATRIAL MECHANICAL FUNCTIONAtrial function, in a close interdependence with left ventricular (LV) function, plays a key role in maintaining an optimal cardiac performance. The left atrium (LA) modulates LV filling through its reservoir, conduit, and booster pump function, whereas LV function influences LA function throughout the cardiac cycle. The LA can act to increase LA pressure (in significant atrial disease) and can react to increased LV filling pressure (in significant ventricular disease). LA remodelling is related to LV remodelling w1 and LA function has a central role in maintaining optimal cardiac output despite impaired LV relaxation and reduced LV compliance.1 Understanding how each component of LA function is influenced by LV performance, and how each LA phasic function contributes to maintain an optimal stroke volume in normal and diseased hearts, is important for interpreting data derived from quantification of LA function.During LV systole and isovolumic relaxation, the LA functions as a reservoir, receiving blood from the pulmonary veins and storing energy in the form of pressure. This atrial function is modulated by LV contraction, through the descent of the LV base during systole, by right ventricular systolic pressure transmitted through the pulmonary circulation, and by LA properties (ie, relaxation and chamber stiffness).w2 During early LV diastole and diastasis, the LA functions as a conduit. Blood is transferred into the LV through the LA via a small pressure gradient during early diastole and flows passively from the pulmonary veins into the LV during diastasis. The conduit function is modulated especially by LV diastolic properties (LV relaxation and early diastolic pressures). During late LV diastole, the LA functions as a pump, the LA contraction augmenting LV stroke volume by approximately 20e30% in normal subjects and substantially more in the presence of impaired LV relaxation. LA booster pump function is modulated by LV compliance, LV end-diastolic pressure, and LA intrinsic contractility.

Assessment of Left Atrial Deformation and Function by 2‐Dimensional Speckle Tracking Echocardiography in Healthy Dogs and Dogs With Myxomatous Mitral Valve Disease

“…Only 1 study evaluated the prognostic relevance of LA function in dogs with MMVD, showing a worse prognosis in those animals with a poorer LA systolic function 2. However, most of the studied echocardiographic parameters of LA function are highly preload dependent and they are influenced by changes in hemodynamic load associated with mitral regurgitation (MR), thus raising the need for more sophisticated echocardiographic techniques 10. Assessment of atrial deformation profiles obtained by tissue Doppler imaging (TDI) and its derived variables, strain and strain rate, has been recently proposed as an alternative method of exploring LA mechanics in both humans3, 4, 10 and dogs 11.…”

“…However, most of the studied echocardiographic parameters of LA function are highly preload dependent and they are influenced by changes in hemodynamic load associated with mitral regurgitation (MR), thus raising the need for more sophisticated echocardiographic techniques 10. Assessment of atrial deformation profiles obtained by tissue Doppler imaging (TDI) and its derived variables, strain and strain rate, has been recently proposed as an alternative method of exploring LA mechanics in both humans3, 4, 10 and dogs 11. Nevertheless, a number of potential drawbacks of this approach should be considered, including suboptimal reproducibility, angle dependence, and the confounding effect of noise artifacts 3, 4, 10, 11.…”

“…Assessment of atrial deformation profiles obtained by tissue Doppler imaging (TDI) and its derived variables, strain and strain rate, has been recently proposed as an alternative method of exploring LA mechanics in both humans3, 4, 10 and dogs 11. Nevertheless, a number of potential drawbacks of this approach should be considered, including suboptimal reproducibility, angle dependence, and the confounding effect of noise artifacts 3, 4, 10, 11. Many of these limitations might be overcome by 2D speckle tracking echocardiography (STE), the most recent and promising ultrasound technology for the direct evaluation of LA function from standard grayscale echocardiographic images 3, 4, 10.…”

“…Nevertheless, a number of potential drawbacks of this approach should be considered, including suboptimal reproducibility, angle dependence, and the confounding effect of noise artifacts 3, 4, 10, 11. Many of these limitations might be overcome by 2D speckle tracking echocardiography (STE), the most recent and promising ultrasound technology for the direct evaluation of LA function from standard grayscale echocardiographic images 3, 4, 10. Specifically, regional myocardial deformation can be calculated from continuous frame‐by‐frame tracking of the tiny echo‐dense speckles created by the interference between the ultrasound beam and myocardium.…”

“…The movement of the speckle during the cardiac cycle follows myocardial movement, and a change between speckles is assumed to represent myocardial deformation. In this manner, STE allows for the assessment of myocardial function independent of cardiac translation and angle of insonation 3, 4, 10. In people, reference range values, feasibility, and reproducibility of STE for the study of LA mechanics have been extensively documented 12, 13, 14, 15.…”