Bundle Branch Block (BBB)
Bundle Branch Block (BBB) is a condition in which there’s a delay or obstruction along the pathway that electrical impulses travel to make your heart beat. It can occur in the right bundle branch (Right Bundle Branch Block – RBBB) or the left bundle branch (Left Bundle Branch Block – LBBB).
Right Bundle Branch Block (RBBB): The electrical impulse is blocked within the right bundle branch. This is the most common type of BBB and often has no significant symptoms.
Left Bundle Branch Block (LBBB): The blockage occurs within the left bundle branch or its fascicles. This type is more concerning as it can affect the efficiency of the left ventricle’s contraction.
Bi-fascicular Block: Involves a block in two of the three conduction pathways: left anterior fascicle, left posterior fascicle, or right bundle branch.
Identifiable Markers in ECG
- Right Bundle Branch Block (RBBB):
- QRS Duration: Prolonged > 120 ms
- V1 & V2: rSR’ pattern (R’ taller than initial R wave)
- Leads I, V5, V6: Wide S wave
- ST Segment and T Wave: Usually show discordance (T wave in opposite direction to QRS complex)
- Left Bundle Branch Block (LBBB):
- QRS Duration: Prolonged > 120 ms
- V1 & V2: Broad, deep S waves (may show a QS or rS pattern)
- Leads I, V5, V6: Broad, notched (‘M’-shaped) R waves
- ST Segment and T Wave: Usually show discordance (T wave in opposite direction to QRS complex)
Causes of Bundle Branch Block
Several factors can cause a bundle branch block:
- Scarring: Heart attack, heart surgery, or certain heart muscle diseases can leave scar tissue that disrupts the electrical conduction pathway.
- Congenital Heart Defects: Structural abnormalities present from birth can affect the conduction system.
- Electrolyte Imbalances: Abnormal levels of electrolytes like potassium, calcium, or magnesium can disrupt electrical signals.
- Myocarditis: Inflammation of the heart muscle can damage the conduction system.
- Cardiomyopathies: Diseases affecting the heart muscle itself can impair conduction.