Left Ventricular Mechanical Discoordination in Nonischemic Hearts: Relationship with Left Ventricular Function, Geometry, and Electrical Dyssynchrony

BACKGROUND: Mechanical discoordination (MD) is known as a myocardial deformation of opposite strain during ejection, reflecting dyssynchronous electrical activation. We used speckle tracking echocardiography to examine the relationship between MD, left ventricular (LV) function and geometry, as well as electrical dyssynchrony in various nonischemic hearts. METHODS AND RESULTS: We examined 131 subjects (left bundle branch block [LBBB] 27; dilated cardiomyopathy [DCM] without LBBB 33; LV hypertrophy 28; and normal heart 43) using circumferential strain rate analysis. Integration of positive (stretch) and negative (shortening) components during the ejection time was obtained in the mid-ventricular level for 6 myocardial segments, and MD was quantified as the stretch to shortening ratio (SSR). The SSR in the septal region (anteroseptal and septal segments) was markedly elevated in the LBBB and DCM groups compared with the other groups. With univariate analysis, SSR over the septal region was found to be correlated with QRS duration, LV end-diastolic dimension, and LV ejection fraction. Multivariate analysis revealed that QRS duration and LV ejection fraction were significant independent determinants of SSR for the septal region. CONCLUSIONS: In nonischemic hearts, electrical dyssynchrony and LV dysfunction may contribute synergistically to MD in the septal region. The finding that non-LBBB DCM patients exhibited a certain amount of SSR may provide new insight into therapeutic strategies for cardiac resynchronization therapy.