Left atrial Frank-Starling law assessed by real-time, three-dimensional echocardiographic left atrial volume changes

Background: The Frank-Starling law describes the relation between left ventricular volume and function. However, only a few studies have described the relation between left atrial volume (LAV) and function. Objective: To describe an LA Frank-Starling law by studying changes in LAV measured by real-time, three-dimensional echocardiography (RT3DE). Methods: LAV was calculated by RT3DE in 70 patients at end-systole (LAVmax), end-diastole (LAV min) and pre-atrial contraction (LAVpre-A). According to LAVmax, patients were classified into three groups: LAVmax <50 ml (group I), LAVmax 50-70 ml (group II) and LAV max >70 ml (group III). Calculated indices of LA pump function were active atrial stroke volume (SV), defined as LAVpre-A - LAV min, and active atrial emptying fraction (EF), defined as active atrial SV/LAVpre-A x100% Results: Active atrial SV was significantly higher in group II than in group I (mean (SD) 19.0 (9.2) vs 8.2 (4.9) ml, p<0.0001), in group III it was non-significantly lower than in group II (16.7 (12.5) vs 19.0 (9.2) ml). Active atrial SV correlated well with LAV pre-A (r = 0.56, p<0.001), but decreased with larger LAV pre-A. Active atrial EF tended to be higher in group II than in group I (43.1 (18.2) vs 33.2 (17.5), p<0.10), in group III it was significantly lower than in group II (26.2 (18.5) vs 43.1 (18.2), p<0.01). Conclusion: A Frank-Starling mechanism in the left atrium could be described by RT3DE, shown by an increase in LA contractility in response to an increase in LA preload up to a point, beyond which LA contractility decreased.