Corpus: Bundle of His

The Bundle of His is an essential part of the cardiac conduction system.

The Bundle of His is approximately 4 mm thick and 20 mm long. It originates at the atrioventricular (AV) node, travels beneath the endocardium in the atrium, passes through the right fibrous trigone of the heart's fibrous skeleton, and then divides into the Tawara branches within the membranous portion of the ventricular septum. Like the ventricular branches, the Bundle of His is insulated from the surrounding heart muscle by connective tissue sheaths.

Normal electrical activation of the heart begins in the sinoatrial (SA) node, the heart’s primary pacemaker, which produces 60 to 80 impulses per minute. These signals propagate through the right atrium to the AV node. If the SA node fails or there is an AV block (a disruption in signal transmission), the AV node can serve as a backup pacemaker, generating 40 to 50 impulses per minute.

The Bundle of His conveys electrical signals from the AV node and splits into the Tawara branches, which further extend into the ventricles as Purkinje fibers. This system ensures a synchronized and complete contraction of the ventricles.

If both the SA and AV nodes fail, the Bundle of His can produce its own rhythm, known as a ventricular escape beat. However, this rhythm is very slow, at only 20 to 30 beats per minute, which is inadequate to sustain proper blood circulation. In such cases, an immediate pacemaker implantation is usually required to maintain sufficient cardiac output.

Conditions affecting the Bundle of His include bundle branch blocks and, more rarely, congenital Bundle of His tachycardia or junctional ectopic tachycardia, which can occur in newborns and infants under 6 months old.

These conduction disorders can be identified on a standard electrocardiogram (ECG) and further investigated using a Bundle of His ECG for more detailed analysis.