The bundle of His, known as the AV bundle or atrioventricular bundle, is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

 from the AV node (located between the atria and the ventricles

Ventricle (heart)

In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

) to the point of the apex of the fascicular branches. The fascicular branches then lead to the Purkinje fibers

Purkinje fibers

For the nervous cells, see Purkinje cellPurkinje fibers are located in the inner ventricular walls of the heart, just beneath the endocardium...

 which provide electrical conduction to the ventricles, causing the cardiac muscle

Cardiac muscle

Cardiac muscle is a type of involuntary striated muscle found in the walls and histologic foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle...

 of the ventricles to contract at a paced interval.

Etymology

These specialized muscle fibres in the heart were named after the Swiss cardiologist Wilhelm His, Jr.

Wilhelm His, Jr.

Wilhelm His, Jr. was a Swiss-born cardiologist and anatomist.He was born on December 29, 1863 to Wilhelm His, Sr.. In 1893, he discovered the bundle of His, which is a specialized tissue in the heart that transmits the electrical impulses and helps synchronize contraction of the cardiac muscles...

, who discovered them in 1893.

Function

This bundle is an important part of the electrical conduction system of the heart

Electrical conduction system of the heart

The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...

 as it transmits the impulse from the sinoatrial (SA

Sinoatrial node

The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

) node (pacemaker

Cardiac pacemaker

right|thumb|350px|Image showing the cardiac pacemaker which is the SA nodeThe contraction of heart muscle in all animals with hearts is initiated by chemical impulses. The rate at which these impulses fire controls the heart rate...

) located in the right atrium to the rest of the heart. The intrinsic rate of the Bundle of His is between 40 - 60 bpm. The bundle of His branches into the three bundle branches: the right, left anterior and left posterior bundle branches that run along the interventricular septum

Interventricular septum

Interventricular septum , abbreviated IVS, is the stout wall separating the lower chambers of the heart from one another....

. The bundles give rise to thin filaments known as Purkinje fibers

Purkinje fibers

For the nervous cells, see Purkinje cellPurkinje fibers are located in the inner ventricular walls of the heart, just beneath the endocardium...

. These fibers distribute the impulse to the ventricular muscle. Together, the bundle branches and Purkinje network comprise the ventricular conduction system. It takes about 0.03-0.04s for the impulse to travel from the bundle of His to the ventricular muscle.

Pathology

If the Bundle of His is blocked, it will result in dissociation between the activity of the atria and that of the ventricles, otherwise called a third degree heart block

Third degree heart block

-Presentation:Third-degree AV block, also known as complete heart block, is a medical condition in which the impulse generated in the SA node in the atrium does not propagate to the ventricles....

. The other cause of a third degree block would be a block of the right, left anterior, and left posterior bundle branches. A third degree block is a very serious medical condition that will most likely require an artificial pacemaker

Artificial pacemaker

A pacemaker is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart...

.

His Bundle Pacing

Direct His-Bundle pacing has produced synchronous ventricular depolarization and improved cardiac function relative to apical pacing.

In some patients with atrial fibrillation

Atrial fibrillation

Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...

and a fast ventricular rate, as a last ditch effort to control the heart rate, electrophysiologists perform AV node modification / ablation following a pacemaker placement.

External links

- "Right atrioventricular bundle branch, anterior view"

• http://www.healthyheart.nhs.uk/heart_works/heart03.shtml