Right Bundle Branch Block
QRS 120 ms or more
Right Bundle Branch Block
cautionThe right ventricle is activated last and slowly, adding a late R′ in V1 and a broad terminal S in I and V6 to an otherwise normal QRS.
On the trace
Read the tracing above in this order; it shows the complete block (the Variant control beside the title switches to incomplete). Tap any lead to see its own measurements. In the box that opens, the QRS view colours each part of the complex by the part of the heart that drew it, with the late right ventricle in orange-red, and the Normal button draws the same lead without the block in grey behind it. The Normal switch under the tracing does the same for the whole ECG: the grey shows only where the block changed something.
- Measure the QRS.
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143 ms across the twelve leads. Anything at 120 ms or more is a wide complex, and the next two steps decide which kind. - Look at V1.
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Three deflections: a small r, an S, then a taller R′ at the end. rSR′. The R′ is the late right ventricle, seen from the front. - Look at I and V6.
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An ordinary qR, then a terminal s that is shallow but broad: 71 ms, longer than the R before it. It is the same late right ventricle, seen from the left, so it points away. - Look at aVR.
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A small r at the very end of the complex, 2.7 mm. aVR looks from the right shoulder and sees the late forces coming towards it. - Check where the delay falls.
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The R-peak time in V1 is 104 ms, far over the 50 ms limit. In V6 it is 47 ms, which is normal. The delay is on the right; the left ventricle was activated on time. - Look at the T waves.
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Inverted in V1 and V2, flat in V3, upright in I and V4 to V6. They are inverted only where the QRS ends in an R′, which is what a secondary change looks like. - Check the axis.
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+80°, normal. A block of the right bundle alone does not move the axis far. A marked left or right axis means a fascicle is involved too.
How to recognise it
| Feature | Value | Notes |
|---|---|---|
| QRS duration | 120 ms or more | 143 ms here. 110 to 119 ms with the same shape is incomplete RBBB. |
| V1 (or V2) | rsr′, rsR′ or rSR′ | rSR′ here: r 3.3 mm, S 8.9 mm, R′ 7.5 mm. The R′ is usually wider than the first r. |
| I and V6 | Terminal S longer than the R, or over 40 ms | 71 ms in both, against an R of about 52 ms. Broad and slurred rather than deep. |
| R-peak time | Over 50 ms in V1, normal in V5 and V6 | 104 ms in V1, 47 ms in V6. |
| aVR | Terminal R | 2.7 mm here. |
| ST and T | Opposite the R′ in V1 to V3 | T inverted in V1 and V2, flat in V3; upright where the QRS ends in an S. |
| Axis | Normal | +80° here. |
These are the criteria of the 2009 AHA/ACCF/HRS recommendations on intraventricular conduction.
Mechanism
Ventricular activation normally runs in phases. The left bundle reaches the septum first, which depolarises from left to right: the small r in V1 and the small q in I and V6. Then both ventricles depolarise together, and the left, being far larger, dominates: the deep S in V1 and the tall R in V6.
In right bundle branch block the first two phases are unchanged, because both depend on the left bundle. What is lost is the fast route into the right ventricle. The right ventricle is still activated, but from the left, cell to cell through ordinary muscle, which conducts far more slowly than the bundle does. It therefore finishes last, alone, after the left ventricle is done.
That late, slow, unopposed right-ventricular activation is a third phase, pointing to the right and forward. V1 sits in front of the right ventricle and reads it as the R′. I and V6 sit to the left and read the same forces going away, as the broad terminal S. The two findings are one event seen from opposite sides, which is why they appear together.
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Why the T wave turns over in V1
Tissue that depolarises late also repolarises late, so repolarisation of the right ventricle lags too. The ST segment and the T wave therefore point away from the late forces: down in the leads that show the R′. This is a secondary change, caused by the altered activation rather than by any disease of repolarisation, and it is expected. A T inversion in a lead that ends in an S, such as V5 or V6, is not explained by the block and should be read as a primary change: ischaemia, a drug, an electrolyte disturbance.
Variants of V1
The classic rSR′ is not the only form. The S may never cross the baseline, leaving a wide, notched R with its tallest point at the end. The complex may be multiphasic, rSR′S′. What stays constant is the late positive deflection in V1 and the broad terminal S on the left.
Incomplete RBBB, and the normal rSr′
The same shape with a QRS of 110 to 119 ms is incomplete RBBB: the right bundle conducts, only slowly. Choose Incomplete beside the title for its tracing and how to tell it apart.
A narrow QRS with a tiny terminal r′ in V1 or V2, of 2 mm or less, is a common normal variant, especially in the young, and should not be reported as a bundle branch block at all.
RBBB with a fascicular block
The right bundle and the left anterior fascicle share a blood supply and often fail together. RBBB with left anterior fascicular block adds a marked left axis (rS in II, III and aVF) to the RBBB pattern: bifascicular block, with only the left posterior fascicle left conducting. A PR that is also long does not prove disease of the third fascicle, but it is the combination that earns the closest follow-up. See the tracings: RBBB with left anterior fascicular block and RBBB with left posterior fascicular block.
Rate-related RBBB
Some people conduct normally at rest and develop RBBB only above a certain heart rate, when the right bundle has too little time to recover between beats. The block comes and goes with the rate.
Clinical impact
The block itself causes no symptoms and does not slow the heart. Its importance lies in what it can point to. It becomes more common with age, through degenerative disease of the conduction system, and it goes with anything that strains the right heart: pulmonary embolism, pulmonary hypertension, chronic lung disease, an atrial septal defect, repaired congenital heart disease. It can follow cardiac surgery or a right heart catheter, and it occurs in cardiomyopathies, myocarditis and Chagas disease.
In acute myocardial infarction, a new RBBB usually means a large anterior infarct from a proximal left anterior descending occlusion, and it carries a worse outcome and a higher risk of complete heart block. Unlike left bundle branch block, RBBB leaves the ST segments readable: ST elevation still means what it means, and the usual STEMI criteria apply.
Management
Read it in context
An isolated RBBB in someone well, found incidentally, needs no treatment. A new one needs a reason: compare with old tracings, and look for right heart strain and ischaemia.
Treat chest pain as a possible infarct
RBBB with ongoing ischaemic symptoms warrants the same urgency as a STEMI, and European guidance advises considering immediate coronary angiography.
Look for the rest of the conduction system
A fascicular block, a long PR or syncope raises the question of intermittent complete heart block. Ambulatory monitoring, and sometimes an electrophysiology study, answer it.
Pace for alternating bundle branch block
RBBB alternating with LBBB means both bundles are failing, and is an indication for a permanent pacemaker. Pacing is otherwise reserved for proven high-grade block or symptoms explained by it.
Differential
Also wide, but the delay is on the left: a broad, notched R in I and V6 with no q, and a QS or rS in V1. There is no R′ in V1, and no terminal S in V6.
A wide-complex tachycardia can have an RBBB-like shape. A monophasic R or an R taller than the R′ in V1, and an axis far outside normal, point to VT. In a rhythm, look for AV dissociation.
Mimics RBBB in V1 and V2, with an R′-like wave, but the ST segment is coved and elevated and runs into an inverted T. There is no broad terminal S in I and V6, which a true RBBB has.
A tiny terminal r′ of 2 mm or less in V1 with a narrow QRS, under 110 ms, and no broad S on the left. A normal finding, common in young people.
References
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, Part III: Intraventricular Conduction Disturbances — Circulation, 2009
- 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay — Circulation, 2019
- 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy — European Heart Journal, 2021
- 2023 ESC Guidelines for the management of acute coronary syndromes — European Heart Journal, 2023