Conduction disease
Right bundle branch block
rSR′ in V1 with a broad terminal S in the lateral leads — often benign, occasionally the clue to something else.
What you see
- QRS ≥ 120 ms.
- rSR′ ('M' pattern) in V1–V2.
- Broad, slurred S wave in I, aVL and V6.
- T wave inversion in V1–V3 — expected, and not evidence of ischaemia.
Why it looks like that
The right bundle blocks, so the right ventricle is depolarised late through myocardium after the left ventricle has finished. That delayed rightward vector produces the terminal R′ in V1 and the slurred S in the left-sided leads.
What to do
- Isolated RBBB in an asymptomatic person needs no treatment and no restriction.
- New RBBB with chest pain, hypoxia and tachycardia should prompt thought about pulmonary embolism.
- RBBB with left axis deviation is bifascicular block; add a long PR and it is often labelled trifascicular.
The trap
Unlike LBBB, RBBB does not prevent you reading the ECG for ischaemia in the left-sided leads. Dismissing anterior ST elevation because 'there is a bundle branch block' loses an anterior STEMI.
More in conduction disease
First degree AV block
A PR interval over 200 ms with every P wave still conducted.
Mobitz I (Wenckebach)
The PR interval lengthens beat by beat until one P wave fails to conduct.
Mobitz II AV block
P waves drop without warning while the PR interval stays fixed — infranodal disease, and a pacemaker indication.
Complete (third degree) heart block
P waves and QRS complexes marching independently, with a slow escape rhythm keeping the patient alive.