Echocardiographic Evaluation of Ventricular Dyssynchrony in patients with LBBB.

INTRODUCTION : Left bundle branch block (LBBB) generally associated with structural heart disease is a frequent conduction disorder. In patients with LBBB and structural heart disease, overall mortality is significantly increased. Moreover, it is also known that the incidence of cardiovascular disorders and subsequent mortality is increased in isolated LBBB. In the presence of LBBB, due to delay of left ventricular (LV) mechanical activity, interventricular dyssynchrony and abnormal interventricular septal movement occurs. As a result of abnormal septal movement, stroke volume, ejection fraction (EF), and LV filling are decreased. Recently, cardiac resynchronization therapy (CRT) is advocated in heart failure in patients with NYHA class III, IV on maximum antifailure medication with wide QRS complex (≥ 130 msec) and decreased EF (≤ 35 %). AIM OF THE STUDY: To evaluate Tissue Doppler as a tool in detecting dyssynchrony in patients with LBBB. METHODS: From an initial cohort of patients with LBBB, 38 patients with low ejection fraction £ 50 and 31 with normal LV systolic function, all comparable in age and sex underwent standard Doppler echo, ECG and Tissue Doppler Imaging. The precontraction time [PCTm from the beginning of Q wave of ECG to the onset of Sm] was calculated as an index of myocardial systolic activation in five different basal myocardial segments (LV anterior, inferior, septal, lateral walls –RV lateral wall). Intraventricular systolic dyssynchrony was analyzed by difference of PCTm in different LV myocardial segments. Interventricular activation delay was calculated by the difference of PCTm between the most delayed LV segment and RV lateral wall. RESULTS: Patients with low LV ejection fraction showed increased qrs duration and LV end diastolic diameter. By DMI these patients showed increased intraventricular delay [p=0.03] in activation of the LV lateral wall. They also showed increased interventricular dyssynchrony [p=0.006]. By receiving operating characteristic [ROC] curve analysis, a cut off value of 48.5msec of interventricular delay showed 71% sensitivity and 65% specificity in identifying patients with impaired ejection fraction. In the overall population by use of stepwise forward multivariate linear regression analyses, LV end diastolic diameter, ejection fraction and qrs duration were the only determinants of interventricular activation delay. CONCLUSION : Pulsed DMI is an effective noninvasive technique for assessing the severity of regional delay in activation of ventricular walls in patients with LBBB. The impairment of interventricular systolic synchronicity is strongly related to LV dilatation and systolic dysfunction. By knowing the exact delay in contraction of the various myocardial segments patients with dilated cardiomyopathy suitable for cardiac resynchronization therapy may be better selected