Right Bundle Branch Block
caution
Variant
The same pattern, QRS 110 to 119 ms
Right Bundle Branch Block
cautionHR75bpm
RR800msQT377ms
RR800msPR186msQRS118msQT377msQTcF406ms
Pause, then click any lead to inspect itDraws the normal ECG in grey behind every lead. Shortcut: N.Incomplete right bundle branch block
The same late right-ventricular phase as the complete block, shorter: the right bundle still conducts, only slowly, so the rSR′ pattern appears in a QRS of 110 to 119 ms.
On the trace
Try each step, then check it.
- Measure the QRS.
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118 ms: wide for a normal heart, short of the 120 ms that makes a complete block. - Look at V1 and V2.
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Still rSR′: a small r, an S, then an R′, 5.2 mm in V1. The late right-ventricular forces are there, only briefer. - Look at I and V6.
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A narrow terminal s, 2.4 mm in I and 3.0 mm in V6, where the complete block has a broad one. - Check the R-peak time in V1.
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90 ms, still over 50 ms: the right ventricle is reached late. - Look at the T waves.
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Inverted in V1 and V2, upright on the left, as in the complete block but shallower.
Telling it apart
| Incomplete RBBB | Complete RBBB | |
|---|---|---|
| QRS | 110 to 119 ms (118 here) | 120 ms or more (143) |
| V1 | rSR′, smaller R′ | rSR′, broad R′ |
| Terminal S in I and V6 | Narrow | Broad, 40 ms or more |
| Normal rSr′ variant | A tiny r′ of 2 mm or less with a narrow QRS is normal, not incomplete RBBB |
What it means
On its own, incomplete RBBB is common and usually harmless, particularly in the young and in athletes. It is also the pattern of a stretched right ventricle, and in an atrial septal defect it can be the first clue on the ECG, so a new one, or one with a murmur or breathlessness, deserves an echocardiogram.
Full articleRight Bundle Branch BlockHow to recognise it, why it happens, what it means and what to do.