True complete left bundle branch block reveals dyssynchrony evaluated by semiconductor single‐photon emission computed tomography

Background Conventional complete left bundle branch block ( CLBBB ) criteria sometimes result in a false‐positive diagnosis that does not represent dyssynchrony. Recently, true CLBBB criteria have been proposed to detect responders to cardiac resynchronization therapy ( CRT ), although their correlation with severity of dyssynchrony or natural prognosis is unclear. Methods Ninety‐four consecutive patients (74 ± 9 years, 63 men) with conventional CLBBB during sinus rhythm underwent semiconductor SPECT . They were divided into two groups: patients with true CLBBB and others. True CLBBB was characterized by the mid‐ QRS notching/slurring and wide QRS duration (male, ≥140 milliseconds; female, ≥130 milliseconds). Multivariate analysis was performed to detect left ventricular dyssynchrony ( LVD ), defined as bandwidth ≥145° and/or phase standard deviation ( SD ) ≥43°. Primary endpoints (hospitalization for heart failure or cardiac death) were evaluated. Results True CLBBB had wider bandwidth (145 ± 83° vs 110 ± 64°, P  = 0.024) and higher phase SD (48 ± 26° vs 35 ± 19°, P  = 0.007). Ejection fraction ( EF ), end‐diastolic volume ( EDV ), summed rest score ( SRS ), and the presence of ischemic heart disease ( IHD ) showed no differences between groups ( P  = 0.401, 0.591, 0.165, and 0.212, respectively). Multivariate analysis revealed that true CLBBB , EF , and EDV were significant predictors of LVD (odds ratio, 12.6, 0.90, 1.03; P  = 0.003, 0.002, 0.022, respectively). At 3‐year follow‐up (median 667 days), primary endpoints were comparable in both groups (log‐rank, P  = 0.92). Conclusions Patients with true CLBBB had more severe dyssynchrony on single‐photon emission computed tomography than patients with nontrue CLBBB . On the other hand, the two groups showed no differences in EF , EDV , the presence of IHD , hospitalization for heart failure, and cardiac death.