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1. A single heartbeat originates from an area of tissue in the heart called the sinoatrial node (SA node). The SA node is in the right upper chamber of the heart or the right atrium. Usually the SA node creates electrical impulses around 60 to 100 times per minute. The two upper heart chambers are stimulated first followed by the two lower large ventricle chambers.

2. Electrical impulses originating from the SA node use electrical circuits to stimulate areas of the heart in a well-regulated manner and are made up of specialized tissue – these are anatomically composed of a number of conduction circuits exist in the right atrium – and are called:

a. The anterior internodal tract

b. The middle internodal tract

c. The posterior internodal tract

d. A fourth electrical tissue bundle projects from the right atrium to the left atrium and is called Bachman’s bundle.

4. From the AV node two large electrical circuits propagate into the lower chambers and are called the left and right bundles and these provide pathways for electrical stimulation of the two large lower ventricles of the heart.

5. These tracts of tissue can be thought of as electrical wiring within the heart, but this is a simplistic analogy as the circuits are often not cleanly defined as would a piece of electrical wiring in a machine.

6. Initial triggering of the electrical stimulations comes from the SA node, the AV node can be thought of a regulating the electrical stimulation of the two lower large ventricles by creating a delay cycle – thus the upper two chambers are triggered, and the AV node creates a delay to the lower chambers are triggered appropriately to keep the total heartbeat cycle synchronized.

A number of disease states relating to defects in the electrical circuitry described can occur.

The function of the AV node has further complexity and in conditions such as Paroxysmal supraventricular tachycardia - a type of arrhythmia that originates in the atrioventricular (AV) junction. The most common underlying anatomical cause of PSVT is atrioventricular nodal reentry, which accounts for more than half of the cases.