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The main function of the left atrium is to connect the pulmonary circulation with the corresponding ventricle, acting as a reservoir, during atrial filling, when the mitral valve is closed, as a booster, when the atrial contraction ensues, but especially acting as a conduit, during diastasis. Accordingly, the atrial cavity has, in the past, been assigned the minimalistic role of a ‘transit chamber’, devoted exclusively to collecting and redirecting the reflux blood from the pulmonary district towards the systemic circulation. It would be wrong, however, to deduce from this ‘pipeline’ function that the left atrium is a passive player in the complex scenario of the cardiac activity.
Left atrial cavity, in fact, is intimately related to ventricular function throughout the whole cardiac cycle.1 During ventricular systole, longitudinal fibre shortening forces the descent of the cardiac base, contributing to atrial filling from the pulmonary veins2 while, during diastole, the atrium passively and actively contributes to ventricular filling. Since the cavity, during early and mid-diastole, is directly exposed to the ventricular pressure through the open mitral valve, the atrial emptying pattern is obviously strongly influenced by the left heart diastolic properties.3
Atrial function can be best described by the relation between pressure and volume.4 Gathering this information, however, implies the use of a high-fidelity pressure catheter in the atrial chamber, a manoeuvre that is not performed routinely nowadays in clinical practice. A more simplistic way to describe atrial function is to rely on the atrial volume curve, which can easily be obtained nowdays using three-dimensional (3D) echocardiography.5
It must be emphasised, however, that the atrial volume curve does not provide an exact measure of the amount of blood entering the left ventricle from the atrium during diastole. In the phase of passive atrial emptying and atrial diastasis, …
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