Left Bundle Branch Block (LBBB) and Right Bundle Branch Block (RBBB) are conditions where electrical impulses in the heart are not conducted normally through the left or right bundle branches, respectively. This disruption affects how the ventricles contract.
Understanding Bundle Branch Blocks
The heart's electrical system ensures coordinated contractions, pumping blood efficiently. The electrical signal originates in the sinoatrial (SA) node, travels through the atria, and then passes to the ventricles via the atrioventricular (AV) node and the bundle of His. The bundle of His then divides into the left and right bundle branches, which carry the electrical signal down to the left and right ventricles.
When one of these bundle branches is blocked, the electrical signal is forced to take an alternate route, leading to a delay in ventricular activation and characteristic changes on an electrocardiogram (ECG).
Right Bundle Branch Block (RBBB)
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Definition: RBBB occurs when there's a blockage or delay in the right bundle branch. This means the right ventricle is activated later than the left ventricle.
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Cause: RBBB can be caused by a variety of factors, including:
- Heart disease (e.g., pulmonary embolism, congenital heart defects, coronary artery disease).
- Lung disease (e.g., chronic obstructive pulmonary disease - COPD).
- Sometimes, it can be present in healthy individuals without any underlying heart condition.
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ECG Findings: The ECG typically shows a widened QRS complex (greater than 0.12 seconds) and a characteristic "rabbit ear" appearance in the right precordial leads (V1 and V2).
Left Bundle Branch Block (LBBB)
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Definition: LBBB occurs when there's a blockage or delay in the left bundle branch. This means the left ventricle is activated later than the right ventricle.
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Cause: LBBB is more often associated with significant underlying heart disease. Common causes include:
- Coronary artery disease.
- Hypertension (high blood pressure).
- Cardiomyopathy (disease of the heart muscle).
- Aortic stenosis.
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ECG Findings: Similar to RBBB, LBBB also shows a widened QRS complex (greater than 0.12 seconds). However, the ECG patterns differ, with broad, notched R waves in the lateral leads (I, aVL, V5, and V6) and absent Q waves in these leads.
Key Differences Summarized
| Feature | Right Bundle Branch Block (RBBB) | Left Bundle Branch Block (LBBB) |
|---|---|---|
| Affected Branch | Right Bundle Branch | Left Bundle Branch |
| Common Causes | Heart disease, lung disease, sometimes normal variant | Coronary artery disease, hypertension, cardiomyopathy, aortic stenosis |
| QRS Duration | > 0.12 seconds | > 0.12 seconds |
| ECG Appearance | "Rabbit ear" appearance in right precordial leads (V1, V2) | Broad, notched R waves in lateral leads (I, aVL, V5, V6); Absent Q waves in these leads |
| Significance | May be normal or associated with heart/lung disease; Prognosis generally better than LBBB if no underlying disease. | Usually indicates underlying heart disease; often associated with a worse prognosis compared to RBBB if present. |
Clinical Significance
While RBBB can sometimes be a normal finding, LBBB often indicates underlying heart disease and warrants further investigation. Both RBBB and LBBB can affect the interpretation of other ECG findings, making diagnosis of conditions like myocardial infarction (heart attack) more challenging. Depending on the underlying cause and severity, treatment might include managing the underlying heart condition, lifestyle modifications, or in some cases, a pacemaker.
In summary, LBBB and RBBB are disruptions in the heart's electrical conduction system, detectable via ECG, with LBBB generally indicating a higher likelihood of underlying heart disease compared to RBBB.
