Electrical structure of the heart

Electrical structure of the heart

In the normal heart, the electrical impulse begins in the sino-atrial (SA) node. The SA node is located high in the right atrium, next to the vena cava.

After leaving the SA node, the impulse travels through specialised conduction tissue in the atria to the atrial muscle cells, causing them to contract. The atrioventricular (AV) node is located in the posterior of the right atrium, close to the septal leaflet of the tricuspid valve. The AV node and the surrounding conduction tissue, including the Bundle of His is commonly referred to as the AV junction. The hearts electrical impulse slows briefly at the AV junction tissue, allowing atrial contraction to precede ventricular contraction and maintain cardiac output. Ventricular conduction structures consist of the bundle branches and the Purkinje fibres. Two major bundle branches emerge from below the His bundle the right bundle branch (RBB), which carries the electrical impulse to the right ventricle and the left bundle branch (LBB), which carries the electrical impulses to the left ventricle. The main left bundle branch divides into two subdivisions the antero-superior and posterior- inferior divisions. The Purkinje fibres emerge from the ends of the bundle branches and carry the impulse through each ventricle to the ventricular muscle cells.

Coronary arteries

Like other organs in the body, the heart has its own rich blood supply. The heart receives blood for its own maintenance from two coronary arteries. The right and left coronary arteries originate from the aorta, close to the aortic valve and provide oxygenated blood for both electrical and mechanical structures of the heart.

Right coronary artery (RCA)

The right coronary artery branches off the aorta and proceeds to the heart’s anterior surface, winding around between the right atrium and right ventricle before reaching the surface of the heart. A small branch from the RCA supplies the SA node. The RCA then winds around the back of the heart and descends posteriorly, this branch is known as the Posterior Descending branch (PDA). The RCA supplies a branch to the AV node at approximately the same level as the origin of the PDA.

Right Coronary Artery supplies the

· SA node (55%)

· AV node (90%)

· Bundle of His (portion)

· posterior inferior division of LBB (portion)

· posterior third of septum

· right atrial; and ventricular muscle

· posterior wall of left ventricle

The left coronary artery

The left coronary artery supplies a larger portion of the left ventricle than the RCA. The left coronary artery emerges from the aorta. The initial portion of this artery is known as the left main artery. The left main artery then divides into two main branches as it reaches the surface of the heart. One of these branches descends anteriorly and is known as the left anterior descending artery (LAD). The LAD supplies most of the RBB and the antero- superior division LBB. The second branch-known as the left Circumflex branch (L.Cx.) winds to the left side and the back of the heart and may descend posteriorly.

Left Anterior Descending Artery supplies

· anterior two thirds of septum

· right bundle branch (RBB)

· antero superior division of left bundle

· anterior wall of left ventricle

Circumflex supplies the

· SA node (45%)

· posterior inferior division of left bundle (Portion)

· lateral wall of left ventricle