Structural Causes of Right Bundle Branch Block—Time for a Closer Look?

Right bundle branch block is an electrocardiographic phenomenon with specific criteria. Currently, two specific forms of right bundle branch block are acknowledged, a proximal and a distal variant. A vast array of pathologies can cause proximal, distal or even combined forms of right bundle branch block. In this study it is suggested that a third type of right bundle branch block exist: one caused by a subaortic muscular tendon in the left ventricle, leading to an increased velocity of conduction in the left ventricle, with a resultant “relative” right bundle branch block. It is concluded that it is necessary (and time) to take a closer look at endoventricular structures in the assessment of structural causes of right bundle branch block.