Increasing pressure in the pulmonary artery lead to subsequent increased pressures and dilation in the right ventricle and atria. This shifts the position of the heart (RAD). This will also lead to increased stretch on the mycoytes which can lead to other electrical abnormalities like complete or incomplete RBBB. Sinus tach is by far the most common ecg finding on any PE followed by RBBB and RAD. RBBB is a sign of markedly increased risk of mortality.