Abstract 551: Left Ventricular Lengthening Load and Shear Strain Are Important and Independent Determinants of Rate of Diastolic Untwist
Background: Previous studies suggest that peak rate of LV untwist (UTR) is determined by rate of LV relaxation. We tested the hypothesis that circumferential-longitudinal shear strain (SCL) representing restoring forces and LV lengthening load, defined as LV pressure at onset of filling, are two other independent determinants of UTR.
Methods: In 8 anesthetized dogs we measured LV lengthening load as LV pressure at mitral valve opening (LVPMVO). End-systolic SCL and peak diastolic UTR were measured by sonomicrometry and UTR also by speckle tracking echocardiography (STE) at different levels of contractility induced by dobutamine and LAD-occlusion, and different lengthening loads induced by volume loading and caval constriction.
Results: Changes in UTR during dobutamine and ischemia correlated well with changes in tau (R = 0.81; P<0.01), and with SCL (Fig 1⇓), confirming a strong relationship between UTR and relaxation and restoring forces, respectively. Elevation of LVPMVO by 5.4 ± 3.1 mmHg (mean ± SD, P<0.01) was associated with an increase in UTR from 59±10 to 82±27 °/s (P<0.05) and reduction of LVPMVO by 6.4±1.3 mmHg (P<0.01) with a decrease in UTR to 45±12 °/s (P<0.05). Changes in UTR during loading interventions were associated with minor changes in tau and SCL. Therefore, neither relaxation nor restoring forces could account for these changes in UTR, whereas LVPMVO correlated well with UTR (Fig 2⇓), suggesting a causal relationship. Similar changes in UTR were found using STE.
Conclusion: The present findings indicate that in the non-failing ventricle shear strain and lengthening load are important determinants of UTR, in addition to LV relaxation.