When a cardiac patient is diagnosed with an infra-Hisian block, it signals a conduction problem specifically in the bundle of His, a key component of the heart’s electrical system. Understanding the bundle of His is essential for grasping how heart rhythm disorders occur and are managed.

The Bundle of His: Structure and Function

The bundle of His, also known as the atrioventricular bundle, is a collection of specialized heart muscle cells designed for electrical conduction. It transmits electrical impulses from the atrioventricular (AV) node, located between the atria and ventricles, down to the bundle branches in the ventricular septum. This electrical signal then spreads through the Purkinje fibers to the ventricular walls, causing coordinated ventricular contraction necessary for pumping blood.wikipedia+2

The bundle of His is composed of muscle cells, pacemaker cells, and conductive fibers, but it is not a nerve fiber. Its primary function is conducting the electrical impulses that control heartbeat rhythm, not innervating muscles like nerves do.study+1

Intrinsic Rate of the Bundle of His

The bundle of His acts as a backup pacemaker if higher pacemakers like the sinoatrial (SA) node and AV node fail. Its intrinsic pacing rate is about 20 to 40 beats per minute, depending on sources, generally slower than the SA node’s typical 60-100 bpm. This rate is sufficiently slow and not meant for normal heart rhythm maintenance but serves as a safety mechanism.ncbi.nlm.nih+1

Location of the Bundle of His

It is located between the atria and ventricles, extending from the AV node into the interventricular septum, where it bifurcates into the left and right bundle branches. These branches continue down the septum and propagate signals to the Purkinje fibers in the ventricular myocardium, enabling synchronous contraction of the heart’s ventricles.clevelandclinic+2

It is not located only in the ventricles, nor is it related to blood vessels or pulmonary oxygen transport.byjus+1

Evaluating the Statements

1. “The bundle of His is a collection of specialized nerve fibres which help in electrical conduction.”

   • This is incorrect because the bundle of His is composed of specialized muscle fibers, not nerve fibers, although it functions similarly by conducting electrical impulses.wikipedia+1

2. “The intrinsic rate of the bundle of His is 20 or less beats per minute.”

   • This is partially true, but the commonly accepted intrinsic rate is around 20 to 40 beats per minute, making “20 or less” slightly understated.study+1

3. “The bundle is located only in the ventricles to allow for contraction.”

   • This is incorrect; the bundle of His begins at the AV node (between atria and ventricles) and then branches into the ventricles, but it is not exclusive to the ventricles.hobartcardiology+1

4. “The bundle arises in blood vessels that are connected to the lung and bring O2 to the heart.”

   • This is false. The bundle of His is unrelated to blood vessels or oxygen transport. It is part of the electrical conduction system.clevelandclinic+1

Summary

The most accurate statement from the options is:

• The bundle of His is a collection of specialized muscle fibers (not nerve fibers) that conduct electrical impulses from the AV node to ventricles.

• Its intrinsic rate is approximately 20 to 40 beats per minute, acting as a backup pacemaker.

• It is located between the atria and ventricles and branches within the interventricular septum.

• It has no relation to blood vessels or oxygen transport.

Thus, none of the given statements are fully correct verbatim, but statement (2), with a minor adjustment regarding intrinsic rate, is the closest to true.

Importance in Infra-Hisian Block

An infra-Hisian block disrupts conduction in or below the bundle of His, significantly affecting ventricular rhythm. This can cause bradycardia or heart block, sometimes necessitating pacemaker implantation to maintain normal heart rhythms.

Understanding the biology and function of the bundle of His is critical for diagnosing and treating arrhythmias and conduction abnormalities effectively.

Would a detailed explanation of types of heart blocks and their treatments be helpful next?Slug: bundle-of-his-heart-block-facts

Title: Bundle of His Explained: True Facts About Heart’s Electrical Conduction and Infra-Hisian Block

Meta Description: Learn the true role of the bundle of His in the heart’s electrical system, its location, intrinsic rate, and why it’s vital in infra-Hisian heart block diagnosis and treatment.

When a cardiac patient is diagnosed with an infra-Hisian block, it means there is a conduction problem specifically in the bundle of His, a critical part of the heart’s electrical conduction system. Understanding the bundle of His helps clarify how heart rhythms are controlled and what happens when this system malfunctions.

What is the Bundle of His?

The bundle of His, also called the atrioventricular bundle, is a collection of specialized heart muscle cells responsible for transmitting electrical impulses from the atrioventricular (AV) node to the ventricles. It is not a collection of nerve fibers but cardiac muscle fibers specialized for conduction.

Located in the heart’s interventricular septum, it divides into right and left bundle branches which further transmit impulses via Purkinje fibers, causing synchronized contraction of the ventricles to pump blood.hobartcardiology+2

Intrinsic Rate of the Bundle of His

The bundle of His can act as a backup pacemaker if the primary pacemakers (SA and AV nodes) fail. Its intrinsic pacing rate is about 20 to 40 beats per minute, which is slower than the sinoatrial (SA) node’s normal rate of 60-100 beats per minute. This slower rate is a safety feature to sustain heartbeat in emergencies.ncbi.nlm.nih+1

Location and Role

The bundle of His arises from the AV node, situated between the atria and ventricles, and passes into the interventricular septum. It is not located only in the ventricles; rather, it conveys impulses from the AV node down into the ventricles for contraction coordination.

It is also unrelated to blood vessels or oxygen transport functions, disproving any notion that it arises from pulmonary blood vessels.wikipedia+1

Evaluating the Statements

1. “The bundle of His is a collection of specialized nerve fibres which help in electrical conduction.”
   Incorrect. The bundle is made of specialized cardiac muscle fibers, not nerve fibers.

2. “The intrinsic rate of the bundle of His is 20 or less beats per minute.”
   Partially correct. The typical intrinsic rate is about 20 to 40 beats per minute—slightly higher than 20 bpm.

3. “The bundle is located only in the ventricles to allow for contraction.”
   Incorrect. The bundle begins at the AV node (between atria and ventricles) and then branches into ventricles.

4. “The bundle arises in blood vessels that are connected to the lung and bring O2 to the heart.”
   False. The bundle of His has no connection to blood vessels or oxygen transport.

Conclusion

The bundle of His is a specialized cardiac muscle fiber bundle critical for transmitting electrical impulses from the AV node to ventricles at a rate of approximately 20-40 beats per minute. It is located between the atria and ventricles (not only in ventricles) and is unrelated to blood vessels.

Therefore, the nearest correct statement regarding the bundle of His is statement (2), acknowledging the intrinsic rate aspect with a slight refinement. Understanding this helps explain the nature of infra-Hisian heart blocks and their impact on cardiac rhythm and function.