In right bundle branch block (RBBB), the His-Purkinje conduction system cannot conduct normally into the right ventricle (RV). Therefore, the RV is depolarized across the interventricular septum AFTER the left ventricle (LV) is depolarized. This delay creates several key EKG findings.
In the right-sided pre-cordial leads (V1-V3), we can see the classic rSR’ finding. I call the two ‘R’ waves “bunny ears” and they represent the electrical superimposition of the LV and RV during systole. Additionally, one can note ST depression and T wave inversion in these leads. In the lateral leads (V5-6, I, and aVL), a deep, slurred S wave can be noted.
Anything that creates right heart strain can create a RBBB: right ventricular hypertrophy, pulmonary embolism, pulmonary hypertension, cardiomyopathy, intrinsic conduction abnormalities, ischemia, and rheumatic heart disease to name a few etiologies. Some patients with depressed ejection fractions in the context of RBBB also qualify for the placement of a biventricular implantable cardioverter defibrillator (BiV-ICD). To make things even more confusing, keep in mind that RBBB can be a finding in healthy adults too!
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