The in vivo measurement of the contractile response caused by electrical excitation has been studied to detect myocardial ischemia in its early stages. In the present study, we used our previously proposed local velocity estimator to measure the two-dimensional distribution of the strain rate using high-density beam scanning to obtain propagation of the local and minute contractile response in the heart walls of healthy humans. Alternate layers of contraction and relaxation were observed around the time phase representing the onset of the conduction of electrical excitation. The contraction propagated along the direction of the myocardial fiber in the myocardial layer. These results indicated that the electrical excitation conducted in each myocardial layer and the transmural shearing deformation occurred at the boundary between alternate layers of contraction and relaxation. The measurement of the propagation of the local and minute contractile response can reveal the effective contraction with the transmural shearing deformation.
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