Quite often one encounters a wide QRS in the dominant rhythm of the electrocardiogram which may have features of either or both bundle branch blocks but is typical of neither. It is often referred to as nonspecific intraventricular conduction delay (IVCD). If the condition is chronic and stable (that is, not due to external factors such as drug effects or hyperkalemia) it generally represents diffuse myocardial scarring and it's a sure bet the patient's ejection fraction will be reduced.
One such pattern, recently described in this paper which caught my eye, is characterized by the RBBB pattern in the precordial leads but with the LBBB pattern in the limb leads and has been termed masquerading BBB. It has been conceptualized in various ways but represents bilateral conduction system disease as a reflection of multifocal myocardial scarring, reflecting extensive damage. It tends to be a poor prognostic sign.
One of the early papers on this topic, back in the days of physician-scientists when autopsies were done and doctors were actually interested in clinicopathological correlations, is here and it is a fascinating read.