Left Ventricular Work and Power are Constant Despite Varying Cardiac Cycle Length—Implications for Patients with Atrial Fibrillation

Atrial fibrillation (AF) is associated with stroke and heart failure, and poses a significant global health burden. Consequently, efforts remain ongoing in better characterising and understanding AF and its underlying mechanisms. This study explores cardiac energetics associated with AF by testing the hypothesis that left ventricular stroke work and systolic power are conserved despite changes in cardiac cycle duration. By combining invasive haemodynamic data and 3D echocardiography, we generated two in vivo pressure-volume loops (corresponding to a short and long cardiac cycle within the same subject) in a sample of 20 patients exhibiting sinus arrhythmia. Subsequently, we found no statistically significant differences in work (0.10 ± 0.22 J) or power (0.03 ± 0.56 W), despite significant differences in stroke volume (7 ± 13 ml) and cardiac output (1.08 ± 0.98 L/min) between short and long cycles (differing by 274 ± 145 ms). Given the repeatability in work and power despite substantial R-R variability, left ventricular energetics may provide more reliable metrics for cardiac function in the presence of AF to better guide patient management.