Section 3 Bundle branch block

Right bundle branch block (RBBB)

Incomplete right bundle branch block

Left bundle branch block (LBBB)

Incomplete left bundle branch block

Left anterior hemiblock

Left posterior hemiblock

Right bundle branch block with left anterior hemiblock and long PR interval (‘trifascicular’ block)

Right bundle branch block with left anterior hemiblock (bifascicular block)

Phasic aberrant ventricular conduction

Case 35 A 75-year-old lady with pneumonia

Right bundle branch block (RBBB)

• QRS duration of 120 ms (3 small squares) or more.

• Secondary R wave (R′) in lead V1.

• Other features:

– slurring of S wave in the lateral leads V4-6, I and aVL

– the T wave tends to be opposite to the terminal QRS component, i.e. T wave inversion in the septal leads (V1-3) may be seen.

Features of this ECG

• Sinus tachycardia, 114 b.p.m., normal QRS axis

• Diagnostic features of RBBB (Fig. 35.1):

– broad QRS, 145 ms

– secondary R wave in V1, rSR′ pattern

• Other features of RBBB:

– T wave inversion (Fig. 35.1)

– slurred S wave (Fig. 35.2)

• Terminal negative component of P wave in lead V1 (Fig. 35.1):

– possible left atrial abnormality

Fig. 35.1 Lead V1.

Fig. 35.2 Lead I.

Causes of right bundle branch block

→ May occur in the absence of heart disease

→ Fibrotic degeneration

→ Ischaemic heart disease

→ Hypertension

→ Cardiomyopathy

→ Congenital heart disease:

– atrial septal defect

– Fallot’s tetralogy

→ Acute, massive, pulmonary embolus

Case 36 A healthy 29-year-old man

Incomplete right bundle branch block

• QRS duration of less than 120 ms (3 small squares)

• With greater degrees of RBBB the following features appear in leads V1-2:

– decrease in depth of S wave

– notch in upstroke of S wave

– small r′ wave develops from this notch

– rSr′ complex appears.

Features of this ECG

• Sinus arrhythmia, 66 b.p.m., leftward but normal QRS axis

• The QRS duration is about 100 ms (2.5 small squares)

• There is notching of the upstroke of the S wave in V1 (Fig. 36.1)

Fig. 36.1 Notched S waves.

Case 37 An 85-year-old man with left ventricular failure

Left bundle branch block (LBBB)

• QRS duration of 120 ms (3 small squares) or more.

• No secondary R wave in lead V1.

• No Q waves in the lateral leads (V5-6, I and aVL).

• Secondary ST-T changes:

– ST segment changes, opposite to the dominant (terminal) QRS component

– T wave changes in the same direction as the ST segments.

These changes can mask the primary changes of acute myocardial infarction.

Features of this ECG

• Sinus rhythm, 66 b.p.m.

• Diagnostic features of LBBB (Fig. 37.1):

– broad QRS, 135 ms

– no secondary R wave in V1

– no Q waves in the lateral leads

• Other features of LBBB:

– ST elevation in leads V1-4 (Fig. 37.2)

– T wave inversion in leads I and aVL (Fig. 37.3)

• Left axis deviation −30°

Fig. 37.1 Lead V1.

Fig. 37.2 Secondary ST elevation.

Fig. 37.3 Secondary T wave inversion.

Causes of LBBB, left anterior or posterior hemiblock

→ Ischaemic heart disease

→ Hypertension

→ Fibrotic degeneration

→ Calcific aortic stenosis

→ Congestive or hypertrophic cardiomyopathy

→ Congenital heart disease

→ Following cardiac surgery

LBBB itself does not cause a change of QRS axis. LBBB with left axis deviation implies more extensive conduction system disease involving the main bundle proximally and the left anterior fascicle distally. It therefore carries a poorer long-term prognosis.

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