Modulation of left atrial function by ventricular filling impairment.

Left atrial function is an important determinant of ventricular filling. Assessment of the complex role that the atrial cavity exerts in the ventricular filling process can be made noninvasively. Computing the net instantaneous difference between mitral and pulmonary venous flow is an approach which permits the construction of the left atrial volume curve throughout the cardiac cycle (as well as the left ventricular volume curve during diastole), and to quantify the 3 different functions that the cavity performs. In particular, increasing degrees of ventricular filling impairment are met by mechanical left atrial adaptations which basically rely on the Starling mechanism, with the reservoir/pump complex activated to the limit of the preload reserve of the cavity. At end-stage left ventricular dysfunction, however, the atrial reservoir and the booster pump function decline and conduit takes precedence, suggesting afterload mismatch, impaired atrial compliance and, perhaps, depressed atrial contractility. Increased wall stiffening and reduced elastic recoil induced by chronic atrial distension might explain the additional power of atrial size in stratifying prognostically patients with left ventricular dysfunction.