Conduit Flow Compensates for Impaired Left Atrial Passive and Booster Functions in Advanced Diastolic Dysfunction

Abstract

BACKGROUND: Quantification of left atrial (LA) conduit function and its contribution to left ventricular (LV) filling is challenging because it requires simultaneous measurements of both LA and LV volumes. The functional relationship between LA conduit function and the severity of diastolic dysfunction remains controversial. We studied the role of LA conduit function in maintaining LV filling in advanced diastolic dysfunction. METHODS: We performed volumetric and flow analyses of LA function across the spectrum of LV diastolic dysfunction, derived from a set of consecutive patients undergoing multiphasic cardiac computed tomography scanning (n=489). From LA and LV time-volume curves, we calculated 3 volumetric components: (1) early passive emptying volume; (2) late active (booster) volume; and (3) conduit volume. Results were prospectively validated on a group of patients with severe aortic stenosis (n=110). RESULTS: The early passive filling progressively decreased with worsening diastolic function ( P <0.001). The atrial booster contribution to stroke volume modestly increases with impaired relaxation ( P =0.021) and declines with more advanced diastolic function ( P <0.001), thus failing to compensate for the reduction in early filling. The conduit volume increased progressively ( P <0.001), accounting for 75% of stroke volume (interquartile range, 63–81%) with a restrictive filling pattern, compensating for the reduction in both early and booster functions. Similar results were obtained in patients with severe aortic stenosis. The pulmonary artery systolic pressure increased in a near-linear fashion when the conduit contribution to stroke volume increased above 60%. Maximal conduit flow rate strongly correlated with mitral E-wave velocity (r=0.71; P <0.0001), indicating that the increase in mitral E wave in diastolic dysfunction represents the increased conduit flow. CONCLUSIONS: An increase in conduit volume contribution to stroke volume represents a compensatory mechanism to maintain LV filling in advanced diastolic dysfunction. The increase in conduit volume despite increasing LV diastolic pressures is accomplished by an increase in pulmonary venous pressure.

Left Atrial Conduit Volume Provides Insights Into Left Ventricular Diastolic Function

“…LA conduit volume is a welcome addition to the existing variables used to estimate LV filling pressures and to grade LV diastolic dysfunction. It can be used as an absolute value, or as done by Aronson et al, 3 it can be utilized using its ratio to LV stroke volume. Invasive studies are needed to determine the cutoff value of LA conduit volume (as well as its index to body surface area and its ratio to LV stroke volume) that best identifies patients with increased LV filling pressures.…”

“…Grading LV diastolic function was achieved only with echocardiographic imaging without invasive measurements, and the clinical relevance with respect to the outcome events of heart failure hospitalizations was not addressed with the cross-sectional design of the study. There are important questions to answer after the study by Aronson et al 3…”