Left ventricular systolic function is sensitive to cycle-length irregularity in patients with atrial fibrillation and systolic dysfunction

Background: Left ventricular (LV) systolic function during atrial fibrillation (AF) is positively correlated with an index of ventricular cycle-length irregularity, the ratio of preceding R-R interval to pre-preceding R-R interval (RR _p/RR _pp). This study was designed to elucidate the relationship between the RR _p/RR _pp ratio and LV function, and to identify factors which influence the relationship. Methods: Beat-to-beat variation of LVfunction was determined by biplane Simpson's ejection fraction (EF) over 20 beats in 120 patients with chronic AF. The relationship of normalized EF (y) versus the RR _p/RR _pp ratio (x) were analyzed by the regression equation y = a + bx. The relation-slope b describes the steepness of the relationship and is a measure of the sensitivity of LV function to ventricular cycle-length irregularity. Results: Mean EF and mean heart rate were factors affecting the relation slope. Negative correlations between mean EF and the relation slope were similarly present at faster heart rates (≥ 80/min, r = -0.81, p < 0.001) and slower heart rates (< 80/min, r = -0.85, p < 0.001). A steeper relationship with faster heart rates was present in patients with normal LV function (r = 0.67, p < 0.001) but not in patients with LV dysfunction (r = 0.23, p = 0.09). Conclusion: Beat-to-beat variation of LV systolic function (LV EF) is more sensitive to ventricular cycle-length irregularity during AF in patients with lower EF or higher heart rate.