Ventricular dyssynchrony of idiopathic versus pacing-induced left bundle branch block and its prognostic effect in patients with preserved left ventricular systolic function

The extent of left ventricular (LV) dyssynchrony might not be comparable between right ventricular pacing-induced left bundle branch block (RV-LBBB) and idiopathic LBBB (iLBBB), despite the morphologic analogy on the electrocardiogram. The objectives of the present study were to elucidate the differences in the LV dyssynchrony index (LVdys) between RV-LBBB and iLBBB, and to assess the prognostic implication of LV dyssynchrony. The conventional echocardiographic parameters, LVdys, and LV end-systolic wall stress were evaluated in 20 healthy volunteers and 21 patients with iLBBB and 20 with RV-LBBB with preserved LV systolic function. Three types of LVdys were evaluated: LVdys-6, LVdys-2, and LVdys-standard deviation. The patients were clinically followed up for about 3 years. The prevalence of LV dyssynchrony was not rare in those with either iLBBB or RV-LBBB, but it was more prevalent in the patients with iLBBB than in those with RV-LBBB. The patients with iLBBB had greater LVdys than those with RV-LBBB (84 ± 55 vs 55 ± 50 for LVdys-6, 51 ± 49 vs 31 ± 40 for LVdys-2, 37 ± 24 vs 24 ± 22 for LVdys-standard deviation in iLBBB vs RV-LBBB). LVdys displayed significant correlations with QRS duration, LV volumes, LV ejection fraction, LV end-systolic wall stress, and mitral inflow E/mitral annular E' velocity ratio. Multivariate logistic regression analysis showed that the LV end-diastolic volume and LV end-systolic wall stress were independent determinants of the presence of LV dyssynchrony. During follow-up, no cardiovascular death or hospitalization for heart failure was reported in either group. In conclusion, despite similarities in electrocardiographic morphology, the extent of LV dyssynchrony were greater in patients with iLBBB, with LV preload and afterload the main determinants. No association was found between the presence of LV dyssynchrony and prognosis.