Relatively common and generally carries little prognostic significance.¹
- Most younger patients with RBBB have no underlying heart disease
- In fact, prognosis has little to do with the RBBB itself and more to do with the underlying process that causes the RBBB
With a functional Left bundle, i.e. isolated RBBB, then these patients do not appear to suffer from clinically significant ventricular dyssynchrony → LV contractions remain coordinated and efficient.
Incidence ↑ with age ¹
- <1% in 50 yo → 10% in 80 yo
Common in conditions that affect the right ventricle, e.g. Pulmonary Hypertension, right ventricular hypertrophy, RV inflammation or infarction. Can also appear abruptly with sudden ↑ in R-sided filling pressures, e.g. Pulmonary Embolism.

Masquerading Bundle Branch Block (MBBB)

Suggested by presence of QRS morphology resembling RBBB conduction in the precordial leads but resembling LBBB conduction in the limb leads ²
Special type of IVCD that although uncommon, is important to recognize because it identifies a group of patients with:
- Very severe underlying heart disease
- A much higher predisposition for developing complete AV block (and needing a pacemaker)
- An extremely poor long-term prognosis

ECG Features

Widened, R-R’ appearance detected in leads V1 and V2
- Most commonly will have a rsR’ appearance in V1 with (appropriate) discordant T wave changes, i.e. inverted T wave
Wide, slurred S wave in lateral leads (I, aVL, V5-6)
In RBBB, the ST segment should be depressed up to 1 mm in V1-V3, i.e. discordant to the R’-wave (or >1 mm in the case of a high voltage R’-wave, such as in RVH) ²
- ∴ ANY STE in V1-V3 in a patient with RBBB is OMI until proven otherwise

Fogoros, R. N., & Mandrola, J. M. (2017). Fogoros’ electrophysiologic testing. John Wiley & Sons. ↩ ↩²
https://hqmeded-ecg.blogspot.com/2025/04/never-send-chest-pain-patient-home.html ↩ ↩²