Theoretical validity of predicting right ventricular systolic pressure by a quantitative index of interventricular septal displacement in acute right ventricular pressure overload.

A leftward shift of the interventricular septum (IVS) of the heart is observed in patients with right ventricular pressure overload (RVPO). We simulated the leftward displacement of IVS in a modified ellipsoidal model on the assumption that the IVS generates the same tension as the left ventricular (LV) free-wall in acute RVPO, and derived the relational equations between ventricular pressures (RVP, LVP) and eccentricity index (EI = LVAPD/LVSLD, LVAPD: left ventricular anterior-posterior diameter, LVSLD: left ventricular septal-lateral diameter). The equations indicate that RVP/LVP correlates with simultaneous EI, independent of the absolute LV wall tensions and the LV size. To confirm this result, we undertook recurrent pulmonary embolizations in anesthetized open-chest dogs, and analyzed the relationship between RVP/LVP and EI at four phases in systole through the course of RVPO and shock. The advance of RVPO shifted the peak of RVP toward late-systole and made the values of RVP/LVP and EI significantly greater at late-systole than at early-systole. There were significant linear relationships between instantaneous EI and RVP/LVP at each phase, expect for the early systole in the shock stage, and the regression lines on all phases were similar to one another. These results are consistent with our theoretical ones. Therefore we conclude that it is reasonable to predict RVP by using EI, theoretically and experimentally.