Consistent regional heterogeneity of passive diastolic stretch: a mechanism for normal systolic function

Purpose: Frank-Starling (FS) law states that increased LV preload induces an increase in LV performance. It also holds true on the regional level, where differences of preload measured as diastolic stretch (preS) across the LV result in regional differences in systolic strain (SS). We aimed to investigate the consistency of the normal spatial intraventricular preS distribution pattern and to compare it to that of SS. Methods: TDI (FR ∼200 Hz) of 6 LV walls were acquired in 54 subjects (42±15y) without cardiac pathology. In each wall 3 samples distributed from base to apex were tracked through cardiac cycle with custom software. The reference point for strain estimation was set at the onset of atrial activation (P wave on ECG). PreS was measured as peak positive strain after the P wave and SS as total shortening during systole. Obtained segmental values were compared between LV walls and levels. For each subject linear regression line was estimated through 18 segmental preS and SS values. Results: Segmental preS and SS correlated significantly in all study subjects (mean r2=0.68). As for regional distribution, both PreS and SS were significantly higher in the septal and inferior walls than in the lateral and anterior walls (Fig. 1a). Apical segments had lower regional preS and SS values than mid or basal ones (Fig. 1b). ![Figure][1] Figure 1. preS and SS differences between LV walls Conclusion: In a normal LV, a consistent regional distribution of preS is observed. Wall segments known to be flatter and/or later activated (related to a higher wall stress at the onset of contraction) are stretched more than spherical and/or early activated segments. A similar distribution pattern of LV SS show, that a major part of intraventricular systolic strain variability can be explained by regional differences in diastolic stretch as a direct consequence of FS mechanism. [1]: pending:yes