Untangling the effects of flow transport and chamber function on left ventricular stasis*

Flow inside the left ventricle (LV) harbors complex swirling patterns connecting the diastolic inflow jet with the systolic outflow jet. These flow patterns wash out the chamber preventing blood stasis. LV flow patterns partition the chamber into four Lagrangian volumes with distinct transport dynamics (direct flow, retained inflow, delayed ejection, and residual volume). These regions are altered in heart failure (HF). Most notably, the direct flow volume entering and exiting the LV within the same cardiac cycle decreases, and the residual volume with residence time (RT) longer than two cycles increases. Based on this evidence, the general wisdom is that direct flow (DF) facilitates LV washout. However, this view neglects the effect of LV ejection fraction (EF), which decreases with cardiomyopathy. Applying queueing theory to LV transport, we predict how mean LV blood residence time (RT) depends on EF and DF, showing that, in fact, DF is deleterious to efficient blood transport. We validate our theory using RT measurements on ~300 volunteers and patients with acute and chronic LV dysfunction. Our results suggest that DF decrease in HF could be an evolutionary adaptation to compensate for decreased EF.