Background: The extent of left ventricular (LV) dyssynchrony may not be comparable between right ventricular pacing-induced (RV-LBBB) and idiopathic left bundle branch block (iLBBB), despite morphologic analogy in electrocardiogram. The objectives of this study were; 1) to elucidate differences in LV dyssynchrony index (LVdys) between RV-LBBB and iLBBB, and 2) to assess the prognostic implication of LV dyssynchrony.
Methods: A total of 61 patients with preserved LV systolic function were included (20 healthy volunteers, 21 iLBBB, and 20 RV-LBBB). Conventional echocardiographic parameters, LVdys and LV end-systolic wall stress (LV-ESWS) were calculated. Three types of LVdys were evaluated; LVdys-6, LVdys-2, and LVdys-SD. Patients were clinically followed for about 3 years.
Results: The prevalence of LV dyssynchrony was not rare in both iLBBB and RV-LBBB, that is, at least 10% depending on the LVdys used, but it was more prevalent in iLBBB than in RV-LBBB. Patients with iLBBB had higher LVdys (84짹55 for LVdys-6, 51짹49 for LVdys-2, 37짹24 for LVdys-SD) than those with RV-LBBB (55짹50 for LVdys-6, 31짹40 for LVdys-2, 24짹22 for LVdys-SD). LVdys displayed significant correlations with QRS duration, LV volumes, LV ejection fraction, LV-ESWS, and mitral inflow E/mitral annular E��� velocity ratio. Multivariate logistic regression analysis using the above variables and the group factor showed that LV end-diastolic volume and LV-ESWS were independent determinants of the presence of LV dyssynchrony. During follow-up, neither cardiovascular death nor hospitalization for heart failure was observed in either patient group.
Conclusion: Despite similarities in electrocardiographic morphology, extents of LV dyssynchrony were greater in iLBBB patients, with LV preload and afterload being the main determinants. There was no association between the presence of LV dyssynchrony and prognosis.