High temporal resolution measurement of propagation pattern of myocardial stretching in left ventricle

Abstract

Purpose: The objective of the present study is to visualize propagation of myocardial stretching in the left ventricle by measuring the axial strain rate on the ultrasound beam (aSR). Subjects and Methods: Twenty healthy volunteers and six additional cases with informed consent were enrolled in the study. The RF signal was obtained by sparse scan in which high-frame-rate imaging was realized by reduction of scanning line density. Phase differential tracking was applied to the RF signal to obtain high temporal aSR. The aSR of each scanning line was obtained in the left ventricular (LV) long-axis view and multiple LV short-axis views with different scan angles. Results and Discussion: The LV long-axis view showed the propagation of the myocardial contraction from the LV apex to the base from the late diastole to isovolumic contraction phase. Thus, both contraction and relaxation were observed in the same cardiac phase. The multiple LV short-axis views showed that clockwise rotation occurred in the systole and anticlockwise rotation occurred in the diastole at the basal and mid portions. The LV short-axis views at the apex showed that contraction first occurred in the endocardium and propagated to the epicardium with strong contraction toward the endocardium. Anticlockwise rotation was observed in the systole and clockwise rotation was observed in the diastole. These results suggested that the contraction of the myocardium was non-uniform, and that the method had potential to show propagation of myocardial stretching in the cardiac conduction system and ordinary myocardium. Conclusion: Measurement of high temporal resolution aSR from multiple angles visualized not only local myocardial contraction but also spatial and temporal inhomogeneity of myocardial stretching in the whole heart. Evaluation of cardiac contraction with aSR measurement may provide important information for understanding cardiac pump function.