Mechanical dyssynchrony is similar in different patterns of left bundle-branch block.

Background: Left bundle-branch block (LBBB) and the presence of systolic dysfunction are the major indications for cardiac resynchronization therapy (CRT). Mechanical ventricular dyssynchrony on echocardiography can help identify patients responsive to CRT. Left bundle-branch block can have different morphologic patterns.

Objective: To compare the prevalence of mechanical dyssynchrony in different patterns of LBBB in patients with left systolic dysfunction.

Methods: This study assessed 48 patients with ejection fraction (EF) < 40% and LBBB consecutively referred for dyssynchrony analysis. Conventional echocardiography and mechanical dyssynchrony analysis were performed, interventricular and intraventricular, with ten known methods, using M mode, Doppler and tissue Doppler imaging, isolated or combined. The LBBB morphology was categorized according to left electrical axis deviation in the frontal plane and QRS duration > 150 ms.

Results: The patients' mean age was 60 ± 11 years, 24 were males, and mean EF was 29% ± 7%. Thirty-two had QRS > 150 ms, and22, an electrical axis between -30º and +90º. Interventricular dyssynchrony was identified in 73% of the patients, while intraventricular dyssynchrony, in 37%-98%. Patients with QRS > 150 ms had larger left atrium and ventricle, and lower EF (p < 0.05). Left electrical axis deviation associated with worse diastolic function and greater atrial diameter. Interventricular and intraventricular mechanical dyssynchrony (ten methods) was similar in the different LBBB patterns (p = ns).

Conclusion: In the two different electrocardiographic patterns of LBBB analyzed, no difference regarding the presence of mechanical dyssynchrony was observed.