Bundle Branch Block: Left

Question 1

What diagnostic criteria can be observed on an ECG for LBBB?

Answer 1

• QRS > 0.12s
• ‘M’ pattern in V₅
• Dominant s in V₁
• Inverted T waves in I, aVL and V₅-V₆

Question 2

Briefly describe what can be seen from this ECG of LBB

Answer 2

V₁: dominant S wave

V₆: broad, notches ‘M’ shape R wave

Question 3

Briefly describe the electrophysiology of LBBB

Answer 3

• In LBBB, conduction delay means that impulses travel first via the right bundle branch to the RV, and then to the LV via the septum
• Septal activation is thus reversed eliminating lateral Q waves
• The overall depolarisation vector from the right to left ventricle produces tall R waves in lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3). The delay between activation of the RV and LV produces the characteristic “M-shaped” R wave seen in lateral leads
• Delayed overall conduction time to the LV extends the QRS duration to > 120 ms

Question 4

Give examples of causes of LBBB

Answer 4

• Aortic stenosis
• Ischaemic heart disease
• Hypertension
• Dilated cardiomyopathy
• Anterior MI
• Lenègre-Lev disease: primary degenerative disease (fibrosis) of the conducting system
• Hyperkalaemia
• Digoxin toxicity

Question 5

What is the pneumonic to remember LBBB?

Answer 5

WiLLiaM MaRRoW

• WiLLiaM- in LBBB there is a ‘W’ in lead V1 and an ‘M’ wave in lead V6
• MaRRoW- in RBBB there is an ‘M’ wave in lead V1 and a ‘W’ wave in lead V6