Right Bundle Branch Block and Impaired Left Ventricular Function as Evidence of a Left Ventricular Conduction Delay

BACKGROUND: The indications and efficacy of cardiac resynchronization therapy (CRT) have not been sufficiently clarified in patients with right bundle branch block (RBBB). METHODS AND RESULTS: This study included 55 patients with normal QRS morphology and duration (Control-Gr) and 49 patients with complete RBBB (CRBBB-Gr). Using tissue Doppler imaging, the time difference (TD) between the electromechanical delay of the septal wall, left ventricular (LV) lateral wall, and right ventricular free wall were measured. Using tissue tracking imaging, the coefficient of the time variation from the beginning of the QRS to the peak displacement time of 6 regions of the LV (CV-PMDLV) was calculated. The TD between the septal wall and that of the LV lateral wall (TDSEPT-LAT) did not differ between the Control-Gr and RBBB-Gr. However, a significant difference was found in the TDSEPT-LAT between the CRBBB patients with LV systolic dysfunction (ejection fraction (EF) < or =50%) and those with normal LV function (EF >50%; p<0.001). The CV-PMDLV was greater in the CRBBB patients with LV systolic dysfunction than in those with a normal LV function (p<0.05). The RBBB-Gr patients with LV dysfunction and a great TDSEPT-LAT, improved clinically after the CRT. CONCLUSIONS: The presence of RBBB and LV dysfunction may indicate LV dyssynchrony and a heterogeneous mechanical dysfunction.