Left Atrium Research Paper

Mechanical Function of Left Atrium The mechanical function of LA has been traditionally described in three phases within the cardiac cycle: the ‘reservoir’, the ‘conduit’ and the ‘contractile’ machinery. During ventricular systole and isovolumic relaxa-tion, the LA functions as a ‘reservoir’ receiving blood from pulmonary veins. The early phase of ventricular diastole sets the stage for LA operating as a ‘conduit’ for blood passing from the pulmonary veins into the LV. This is followed by atrial ‘contraction’ during which the LV stroke volume is augmented by approximatly twenty percent (Mitchell et al., 1969).

Various LA volumes have been used to describe LA phasic function : 1. Reservoir volume, is calculated as the difference between maximal and minimum LA volumes. Maximal LA volume occurs at ventricular end-systole just before the opening mitral valve; while minimum LA volume oc-curs at end diastole, just before closure of mitral valve. 2. Conduit volume, is calculated as the difference between maximum and pre-atrial contraction LA volume. 3. Contractile volume, is calculated as the difference between mini-mum and pre-atrial contraction LA volume.

The relative contribution of LA phasic function to LV filling is de-pendent upon the diastolic

The length is measured from posterior wall to the middle of the plane of mi-tral annulus. Left atrial volume is estimated on the basis of the algorithm (0.85 × A1 × A2)/L where A1 and A2 are the areas of LA in two and four chamber views and L is the shortest of the lengths gained from the orthogo-nal views (Note: the smaller of the two lengths has been applied for L, it is accepted if the difference between the two is no more than 5 mm otherwise, foreshortening should be considered) and indexed to body surface area (Lang et al.,