| Bundle branches | |
|---|---|
 The left bundle branch (4) and the right bundle branch (10) | |
| Anatomical terminology |
Thebundle branches, orTawara branches,[1] transmitcardiac action potentials (electrical signals) from thebundle of His toPurkinje fibers inheart ventricles. They are offshoots of the bundle of His and are important to theelectrical conduction system of the heart.[2]
There are two branches of the bundle of His: theleft bundle branch and theright bundle branch, both of which are located along theinterventricular septum. The left bundle branch further divides into theleft anterior fascicle and theleft posterior fascicle. These structures lead to a network of thin filaments known as Purkinje fibers. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials to the Purkinje fibers.[2]
When a bundle branch or their fascicles becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately, resulting in altered pathways for ventricular depolarization. This condition is known as abundle branch block.[3]
The bundle branches were separately described by Retzer and Braeunig as early as 1904, but their physiological function remained unclear and their role in the electrical conduction system of the heart remained unknown untilSunao Tawara published his monograph onDas Reizleitungssystem des Säugetierherzens (English:The Conduction System of the Mammalian Heart) in 1906.[4] Although Tawara's monograph had demonstrated that the branches of the bundle of His may transmit cardiac action potentials to the ventricles, the functional proof for his observation was not provided until 1910, whenHans Eppinger andCarl Julius Rothberger showed that cutting off both branches to induce a bilateral bundle branch block results in a completeheart block.[5]