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Figure 1 An example of typical velocity, strain rate, and strain curves from the mid-septum in left bundle branch block. Each curve represents an average from three consecutive cardiac cycles. Dotted vertical lines separate the isovolumic intervals from the ejection period, as identified by mitral and aortic valvular opening (AVO) and closure (AVC). In this patient, longitudinal septal shortening (indicated by negative strain rate and negative strain) starts early in the cardiac cycle, and peak negative strain occurs briefly after AVO (open arrow), whereas the peak systolic velocity is identified in late systole (solid arrow). Only a small part of septal shortening contributes effectively to ejection, as indicated by the hatched area in the strain curve. ECG = electrocardiogram; IVCT = isovolumic contraction time; IVRT = isovolumic relaxation time.