LA Phasic function and size
40%of LV filling - During ventricular systole, LA acts as a reservoir, stores energy under the form of pressure.
35% of LV filling - During early ventricular diastole, LA operates as a conduit via pressure gradient (passive during ventricular diastasis)
25% of LV filling - During late ventricular diastole, LA contracts to augment LV SV by ~ 20%. The relative contribution of this booster pump
becomes more important in the setting of LV dysfunction.
Maximal LA volume occurs right before MV opening
LA size measurement by Simpson's or area-length method
Maximal LA volume 22 +/- 6 ml/m2
Pressure Overload: MS, LV dysfunction, LA fibrosis/Calcification (Stiff LA) => reduction of LA compliance, increased LA nad pulmonary
pressures and right heart failure => abnormal myocyte relaxation
Volume Overload:MR, AVF, high output states (chronic anemia, athletic heart, hyperthyroidism , beri-beri, Paget disease) => normal myocyte
In the basence of LA disease and mitral disease, LA volume reflects an average effect of LV pressures over time (similar to hba1c)
LA and AF
The relationship between LA volume and AF is complex:
LA Electrical remodeling occurs within hours and is caused by shortening of atrial myocyte Action Potentials
LA Mechanical remodeling occurs after weeks and results rearrangement and replacement of atrial myocytes by fibrotic tissue
A few studies have assessed the impact of sustained AF on atrial structure.
In the Framingham study, a 5 mm increase in the AP diameter was associated with a 39% increased risk for subsequent development of AF.
In the Cardiovascular Health Study, subjects in sinus rhythm with an AP LA diameter > 5.0 cm had approximately 4x the risk of developing AF.
The relationship between LA volume and LA dimension is non linear and it has been confirmed that LA volume represented a superior measure
over LA diameter for predicting outcomes including AF, and provided information that was incremental to clinical risk factors.
LA and CVA
85% of strokes occur in individuals who are in apparent sinus rhythm. in the general population LA size has been determined to be a a predictor of
CVA and death. Increased LA volume has also been shown to predict th onset of first stroke in clinic based elderly patients who were in sinus
LA and CHF
LA volume is a barometer of LV filling pressures and reflects the degree of LV diastolic dysfunction. In a large prospective study subjects with
incident CHF during follow-up had a higher baseline LA linear diameters (39 in women and 41 in men).
LA and DEATH
LA diameter independently predicts death in the general population. However in other population-based studies, the relationship between LA size
and death has been attenuated when LV mass, LV hypertrophy, or diastolic function has been considered.
LA size is potentially modifiable with medical therapy, but whether LA size reduction translates to
improced outcomes remains to be established.