Abstract 21317: Spatial Heterogeneity of Fiber Relengthening Underlies Impaired LV Filling in the Dyssynchronous Left Ventricle
Introduction: Intraventricular electrical dyssynchrony (EDys), as indicated by a wide QRS, generally gives rise to mechanical heterogeneity and reduced left ventricular (LV) systolic function. While impaired global LV relaxation and filling have also been attributed to EDys, the role of spatial and temporal heterogeneity of fiber mechanics remains unclear.
Hypothesis: Impaired filling in the dyssynchronous LV may result from an increase in spatial heterogeneity of fiber relengthening.
Methods: In open-chest, anesthetized dogs (n=10), EDys was produced with atrioventricular (AV) sequential pacing at the posterior LV wall near the interventricular septum. Regional deformation was assessed with high-speed (125 fps) biplane cineradiography of implanted markers in the anterolateral LV midwall. The time-course of fiber strain was determined, on average, at 48 ± 10 sites. Fiber relengthening strain was measured from end-systole to end-diastole, with a reference configuration at aortic valve opening (i.e. negative strains at end-systole). Internal stretch fraction, an index of spatial heterogeneity of systolic shortening, was modified (mISF) to quantify heterogeneity of relengthening. mISF was defined as the ratio of shortening to stretch during diastole (i.e. mISF of 0 represents uniform relengthening). Significant differences (P < 0.05) between atrial and AV pacing were determined by a paired Student's t-test.
Results: In all animals (n=10, mean ± std), AV pacing increased QRS width (118 ± 13.3 ms vs. 64.7 ± 7.56 ms) compared with atrial pacing. Values of mISF (n=5) were 0.185 ± 0.104 and 0.265 ± 0.124 for atrial and AV pacing, respectively. A percent increase of 57.3 ± 33.6 % in mISF during AV pacing was significantly different from zero. Early LV filling rate, from LV volume catheters (n=5), was reduced by 33.9 ± 12.8 %, and stroke volume decreased from 26.4 ± 4.18 mL to 19.1 ± 3.50 mL during AV pacing.
Conclusions: Electrical dyssynchrony increased the spatial heterogeneity of fiber relengthening in the anterolateral LV midwall. This finding was associated with marked reductions in early LV filling rate and stroke volume, suggesting that spatial heterogeneity of fiber relengthening is an important determinant of LV filling in the dyssynchronous heart.
- © 2010 by American Heart Association, Inc.