Fig. 1.

M-mode echocardiogram in LBBB and RBBB/LPFB. In LBBB (left panel) the ‘septal flash’ of early inward septal motion is seen prior to posterolateral wall motion (septo-lateral delay). In RBBB/LPFB (right panel) there is evident hypokinesis, with a contractile sequence that is the reverse of LBBB. Posterolateral wall contraction occurs first, prior to septal motion, and relaxation is underway when septal contraction occurs (latero-septal delay/dyssynchrony). (Left panel adapted from Di Salvo et al. International Journal of Cardiovascular Research [7]. Used with permission).