Non-uniform distribution of the contraction/extension (C-E) in the left ventricular myocardium related to the myocardial function.

ABSTRACT

OBJECTIVE: We attempted to disclose the microscopic characteristics of the non-uniform distribution of the contraction and extension (C-E) of the left ventricular (LV) myocardium using a new methodology (echo-dynamography). METHODS: The distributions of the "axial strain rate" (aSR) and the intra-mural velocity in the local areas of the free wall including the posterior wall (PW) and interventricular septum (IVS) were microscopically obtained using echo-dynamography with a high accuracy of 821 µm in the spatial resolution. The results were shown by the color M-mode echocardiogram or curvilinear graph. Subjects were 10 presumably normal volunteers. RESULTS: (1) Both the C-E in the pulsating LV wall showed non-uniformity spatially and time-sequentially. (2) The C-E property was better evaluated by the aSR distribution method rather than the intra-mural velocity distribution method. (3) Two types of non-uniformity of the aSR distribution were observed i.e. (i) the difference of its (+)SR (contraction C) or (−)SR (extension E) was solely the "magnitude"; (ii) the coexistence of both the (+) SR and (−)SR at the same time. (4) The aSR distribution during systole was either "spotted," or "multi-layered," or "toned" distribution, whereas "stratified," "toned," or "alternating" distributions were observed during diastole. (5) The aSR distribution in the longitudinal section plane was varied in the individual areas of the wall even during the same timing. (6) To the mechanical function of the LV, there was a different behavior between the IVS and PW. . CONCLUSIONS: The aSR and its distribution were the major determinants of the C-E property of the LV myocardium. Spatial as well as time-sequential uniformity of either contraction or extension did not exist. The myocardial function changed depending on the assemblage of the aSR distribution, and by the synergistic effect of (+)SR and (-)SR, the non-uniformity itself potentially served to hold the smooth LV mechanical function.