The Role of Left Atrium

Abstract

Left atrium (LA) contributes 20-30% of cardiac output. LA volume and function measured by 2D biplane area length and real-time 3D echocardiography have been well-validated and widely used. LA function consists of 3 components, including reservoir, conduit, and active contractile phases. The most frequently used echocardiographic method for evaluation of phasic function of LA is volumetric method. LA volume measured by biplane area-length method and corrected by body surface area is a useful index for studying LA remodeling, and early LA remodeling has been proven to have prognostic significance in heart failure after myocardial infarction. Phasic changes of LA volume can be measured in different phases of cardiac cycle. Volumetric measurements are useful in evaluation of LA, however, volumetric changes can not reflect changes of the LA wall itself. Tissue Doppler imaging has been applied for the assessment of cardiac function, including atrial function. Atrial deformation evaluated by tissue Doppler derived strain or strain rate imaging can be used for assessment of LA wall directly. Newly developed speckle tracking echocardiography is useful in assessment of left ventricular strain and strain rate. This non-Doppler two-dimensional strain imaging avoids effects of Doppler angle and ventricular tethering. Speckle tracking echocardiography was recently used for assessment of LA function after resynchronization therapy. The feasibility of LA longitudinal strain and strain rate measured by speckle tracking echocardiography has been verified in healthy subjects, and adequate tracking can be performed in 94% of subjects or in 97% of segments. Early changes of LA function can be documented by speckle tracking echocardiography. We have found the phasic LA function changed in untreated hypertension subjects and correlated with left ventricular diastolic function. LA strain also has prognostic implications such in primary mitral regurgitation or in atrial fibrillation.