ECG rhythms Conduction, ST and QT
Right bundle branch block ECG
Right bundle branch block. Wide QRS (≥120 ms) with an rSR′ in V1 and a broad terminal S wave in I and V6.
A 30-second recording of the heart model, played in real time. Run live starts the engine itself with this rhythm.
Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.
Measured on this recording
| Ventricular rate | 72/min |
|---|---|
| PR | 159 ms |
| QRS | 151 ms |
| QT | 427 ms |
| QTc (Bazett) | 468 ms |
| QTc (Fridericia) | 454 ms |
What it is
The right bundle branch does not conduct, so the left ventricle activates first and the right ventricle late. The QRS widens to 120 ms or more, with an rSR′ in V1 and a broad terminal S wave in I and V6.
How to read this strip
| Rate | 60–100/min. |
|---|---|
| Rhythm | Regular sinus. |
| P waves | Normal. |
| PR | Normal. |
| QRS | Wide (≥120 ms); rSR′ in V1, broad S in I and V6. |
| ST–T | Secondary changes may follow the terminal delay, opposite in direction to it. |
Causes
- Can be a normal finding.
- Right heart strain: pulmonary embolism, pulmonary hypertension, chronic lung disease.
- Congenital heart disease (atrial septal defect).
- Coronary artery disease.
- Degenerative conduction disease; after cardiac surgery.
What to consider
- Isolated RBBB in a person without symptoms is usually benign.
- New RBBB with chest pain or shortness of breath: consider pulmonary embolism or ischemia. RBBB does not usually mask ST elevation, so standard STEMI criteria still apply; new RBBB with ongoing ischemic symptoms may need emergency reperfusion assessment.
- A Brugada pattern (coved ST elevation in V1–V2) can mimic RBBB.
- RBBB with a fascicular block (a block in one division of the left bundle: bifascicular block) or with a long PR suggests more extensive conduction disease.
- The wide QRS lengthens the QT, so the QTc overstates repolarization time in bundle branch block.
Key point
Look at V1 first in any wide QRS: a terminal R′ points to right bundle branch block.
Not to be confused with
- Left bundle branch block — In LBBB, V1 is mainly negative and lateral leads have broad R waves without a terminal S. Here V1 ends in a tall R wave.
- Normal 12-lead ECG — The QRS is wide, and V1 has a terminal R′ wave.
- Wolff–Parkinson–White pattern — WPW has a short PR and a slurred delta-wave upstroke. Here the PR is normal and the delay is at the end of the QRS.