Bundle Branch Blocks
Cardiology (12%) Core Clinical Conditions
1B: Able to identify the condition as a possible diagnosis: may not have the knowledge or resources to confirm the diagnosis or to manage the condition safely, but can take measures to avoid immediate deterioration and refer appropriately
Jump to content
Definition Aetiology Pathophysiology Risk factor Sign and Symptoms Investigations Diagnosis Management
Definition
A bundle branch block (BBB) occurs when there is an obstruction or a blockage in the electrical impulse travelling through the ventricles (the bottom chambers of the heart). Therefore the signal moves more slowly than it should.
There are two types of BBB:
Left bundle branch block (LBBB)
Right bundle branch block (RBBB)
Aetiology
Electrical impulses cause the heart to contract. Impulses start from the sinoatrial node or sinus node and spread out into the two branches of the heart called bundle branch (see image 1). If either of these branches sustains injury, as could occur after a myocardial infarction (MI). The heart's signalling mechanism can be damaged
Image 1
Illustration of heart signal. Starting from the SA node.
Below are example of common causes for LBBB or RBBB:
Left bundle branch block
● Cardiomyopathy
● Hypertension
● Myocarditis
● Myocardial infarction
Right bundle branch block
● Myocarditis
● Myocardial infarction (MI)
● Congenital heart defects
● Pulmonary hypertension
● Pulmonary embolism (PE)
Pathophysiology
A bundle branch may stop conducting electrical impulses properly if it is damaged (by underlying heart disease, myocardial infarction, or heart surgery). As a result, the mechanisms for ventricular depolarization are changed. The electrical movement may be slowed down and the direction of the impulses may be altered because the electrical impulse can no longer travel along the bundle branch's predetermined pathway.
Risk factors
Age
Underlying health conditions: hypertension or heart disease
Sign and symptoms
Bundle branch block rarely show any symptoms. Some are unaware that they have a bundle branch block.In rare cases, the symptoms may include syncope or feeling as though you're going to pass out (presyncope).
Common symptoms are:
● Breathlessness
● Bradycardia
● Abnormal heartbeat
Investigations
● ECG
● Echocardiogram
● Blood test
Diagnosis
Right bundle branch block (RBBB)
When the QRS complex on the ECG is longer than 120 ms, a bundle branch block can be identified. Typically, a right bundle branch block lengthens the final portion of the QRS complex and may slightly tilt the electrical axis of the heart to the right. The terminal R wave in lead V1 and the slurred S wave in lead I will both be seen on the ECG.
The MarRoW mnemonic can be used to recognise a RBBB.
Complexes in V1 resemble the letter MaRroW's initial "M," while those in V6 resemble a "W." (the sixth letter of MaRroW) (see image 2).
Image 2
ECG features of Right Bundle Branch block
Left bundle branch block (LBBB)
Typically, a right bundle branch block the QRS complex is >120ms. There is a dominant S wave in V1. A broad, monophasic R wave can be observed in leads I, aVL and V5-V6. The Q waves in lateral leads are absent. Finally, the R wave in V5-V6 are prolonged.
The WiLliaM mnemonic can be used to recognise a LBBB.
The letter WiLliaM's first letter, W, is resembled by complexes in V1, and the letter M is resembled by complexes in V6 (the sixth letter of WiLliaM) (see image 3)
Image 3
ECG features of Left Bundle Branch block
Management
Treatment is determined by symptoms. If a patient is asymptomatic no treatment is needed. A pacemaker is an efficient method of treating heart block because it frequently transmits electrical pulses to keep your heart pumping effectively.
Check out our youtube channel
