Restoring Forces And Lengthening Load Are Independent And Important Determinants Of Peak Early-Diastolic Mitral Annulus Velocity

Background: Mechanisms of early-diastolic mitral annulus velocity (E′) are poorly understood. We investigated if restoring forces, generated by contraction below unstressed length, and lengthening load , the expanding effect of LV pressure during early filling, may be determinants of E′ in addition to LV relaxation ( tau ). Methods: In 15 anesthetized dogs we evaluated LV transmural pressure-diameter loops to define unstressed LV long-axis diameter (L 0 ). As a reflection of restoring forces we used the difference between minimum LV long-axis diameter and L 0 (L min −L 0 ). As a measure of LV lengthening load we used LV pressure at the time of mitral valve opening (LVP MVO ). E′ was measured by sonomicrometry and tissue Doppler imaging (TDI) at baseline, during volume loading, dobutamine infusion (n=9), and after 15 minutes and 3 hours (n=8) of LAD-occlusion. Results: Changes in E′ during dobutamine and ischemia correlated inversely with changes in tau (R=−0.58), confirming a relationship between E′ and relaxation. Furthermore, E′ showed an even stronger correlation with L min −L 0 (R=−0.79, Fig 1 ), suggesting a close relationship between E′ and restoring forces. During increased LVP MVO , however, there was a marked increase in E′ which could not be attributed to changes in tau or in L min −L 0 , but E′ correlated well with LVPMVO (R =0.78, Fig 2 ). Conclusion: The present study indicates that in the non-failing ventricle restoring forces and lengthening load are important determinants of E′. Furthermore, the apparent preload-dependency of E′ is explained by the effect of lengthening load. Fig 1 Fig 2