In bundle branch block one of the two main branches of the heart's conduction system is slow or blocked, so one ventricle is activated late and the QRS becomes wide. Right bundle branch block can be a normal finding, while new left bundle branch block often points to heart disease and needs a workup.
Key symptoms
- Usually no symptoms; found on a routine ECG
- Symptoms of the cause, such as chest pain or breathlessness
- Fainting if it progresses to a higher-degree block
- Fatigue or swelling if heart failure is present
What you find on exam
- Wide split second heart sound in right bundle branch block
- Paradoxical splitting of the second sound in left bundle branch block
- Look for high blood pressure, murmurs and signs of heart failure
- Signs of lung disease or pulmonary embolism with a new right bundle branch block
Tests
- 12-lead ECG: QRS 120 ms or more; RSR' in V1 for right, broad notched R in V5 to V6 for left
- Echocardiogram, especially for left bundle branch block
- Troponin and urgent review if chest pain with a new left bundle branch block
- Stress testing or coronary imaging when ischemia is suspected
Treatment basics
- No treatment for the block itself when there are no symptoms
- Treat the cause: high blood pressure, ischemia, cardiomyopathy
- Pacemaker if it progresses to high-degree AV block
- Cardiac resynchronization therapy for heart failure with left bundle branch block and low ejection fraction
- Sgarbossa criteria to judge a heart attack with left bundle branch block
Red flags
- Chest pain with a new left bundle branch block
- Fainting
- Alternating right and left bundle branch block
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Related guides
Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.