A case of coexisting tachycardia- and bradycardia-dependent bilateral bundle branch block

Electrocardiograms and His bundle electrograms were presented from a patient with a rare combination of intermittent bilateral bundle branch block. Critical analyses of R-R intervals and evolution of bundle branch block patterns revealed both tachycardia dependent right bundle branch block and bradycardia dependent left bundle branch block. Evaluation of HV intervals on His bundle electrograms suggested an additional possibility of bradycardia dependent conduction delay in the right bundle branch system.