Approximately 50% of left bundle branch blocks are associated with structural heart disease, while the other half are idiopathic or due to fibrosis of the cardiac conduction system which occurs ...

However, unlike in the presence of a left bundle branch block, myocardial ischemia and infarction can easily be detected on ECG when a RBBB is present (see anterior and inferior wall MI examples).

Overnight, the patient remained hemodynamically stable, but was noted to have continued intermittent heart block with alternating left and right bundle branch block QRS morphology (Fig.