Right atrium
The right atrium (RA) is located on the upper right-hand side of the heart and has relatively thin walls. From an anatomical point of view, the RA comprises three basic parts, the appendage, the vestibule of the tricuspid valve, and the venous component (superior and inferior vena cava, and the coronary sinus) receiving the deoxygenated blood. The RA is a dynamic structure dedicated to receive blood and to assist right ventricular (RV) filling. The three components of atrial function are the reservoir function during ventricular systole, the conduit function which consists in passive blood transfer from veins to the RV in diastole, and the booster pump function in relation to atrial contraction in late diastole to complete ventricular filling. Right atrial function depends on cardiac rhythm (sinus or atrial fibrillation), pericardial integrity, RV load and function, and tricuspid function. Right atrial dimension assessment is limited in two-dimensional (2D) echocardiography. Right atrial planimetry in the apical four-chamber view is commonly used with an upper normal value of 18-20 cm2. Minor and major diameters can also be measured. Three-dimensional (3D) echocardiography could overcome the limitation of conventional echocardiography in assessing RA size. Right atrial function has been poorly explored by echocardiography both in physiological and pathological contexts. Although tricuspid inflow and tissue Doppler imaging of tricuspid annulus can be used in the exploration of RA function, 2D speckle tracking and 3D echocardiography appear promising tools to dissect RA function and to overcome the limitations of standard echocardiography.