Left Bundle Branch Block (LBBB)

Question 1

What is the key QRS feature of LBBB?

Answer 1

QRS duration ≥ 0.12 seconds (wide QRS).

Question 2

Which leads show broad/notched QRS complexes in LBBB?

Answer 2

Leads I, V5, and V6.

Question 3

In LBBB, what do you see in lead V1?

Answer 3

Deep, broad S waves (sometimes “W” shape).

Question 4

What is the “M” pattern in LBBB and where is it found?

Answer 4

Broad notched R wave (M-shaped) in leads I, V5, V6.

Question 5

How is R wave peak time used to detect LBBB?

Answer 5

R-wave peak time in V5–V6 > 0.06s.

Question 6

List three common causes of LBBB.

Answer 6

Ischaemic heart disease, dilated cardiomyopathy, aortic stenosis.

Question 7

What drug toxicity can cause LBBB?

Answer 7

Digoxin.

Question 8

How can an acute MI cause LBBB?

Answer 8

Infarct involving the left anterior descending artery (LAD).

Question 9

What happens to T waves in LBBB?

Answer 9

Discordant T-wave changes (opposite to main QRS direction).

Question 10

If patient is asymptomatic with normal LV function, how is LBBB managed?

Answer 10

No specific treatment; just monitoring.

Question 11

What treatment is considered if patient has LBBB + heart failure + reduced EF?

Answer 11

Cardiac Resynchronisation Therapy (CRT).

Question 12

When is a permanent pacemaker indicated in LBBB?

Answer 12

If symptomatic with advanced conduction disease or severe LV dysfunction.

Question 13

What NICE guidance exists for CRT/LBBB patients?

Answer 13

CRT considered in HF with QRS ≥ 0.15s + symptoms despite optimal therapy.

Question 14

What underlying diseases are managed if patient has LBBB?

Answer 14

Heart failure, hypertension, coronary artery disease.

Question 15

What medications may be given if patient has LBBB with structural heart disease?

Answer 15

ACE inhibitors, ARBs, beta-blockers, SGLT2 inhibitors.