Bundle Branches: Structure and Function in Cardiac Conduction

The bundle branches consist of specialized cardiac muscle cells called Purkinje fibers. They are larger in diameter with fewer myofibrils than regular myocardial cells. Purkinje fibers rapidly conduct electrical impulses from the atrioventricular node to the ventricles, ensuring coordinated heart chamber contraction each beat.

Anatomy

• Bundle of His: Penetrates fibrous trigone → divides into right and left bundle branches.
• Right bundle branch (RBB): Courses along right ventricular septum → moderator band → Purkinje network.
• Left bundle branch (LBB): Divides into anterior and posterior fascicles → Purkinje network.

Clinical Significance

• Bundle branch block (BBB): Delay in one branch → widened QRS (>120 ms). RBBB: rsR' in V1; LBBB: broad R in I, V5–V6.
• Hemiblock: Fascicular block → axis deviation (LAHB: left axis; LPHB: right axis).
• Purkinje system: Also involved in ventricular arrhythmias (PVCs, VT).